Recommended Techniques for Effective Maintainability

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W..e_: NASA Technical Memorandum 4628

A Continuous Improvement Initiative of the NASA Reliability and Maintainability Steering Committee

December 1994

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(NASA-TM-4628) RECOMMENOEO N95-31530 TECHNIQUES FOR EFFECTIVE MAINTAINABILITY. A CONTINUOUS IMPROVEMENT INITIATIVE OF THE NASA Unclas RELIABILITY AND MAINTAINABILITY STEERING COMMITTEE (NASA) 105 p H1/38 0060399

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h_ PREFACE

Current and future NASA programs face the challenge of achieving a high degree of mission success with a minimum degree of technical risk. Although technical risk has several . , w elements, such as safety, reliability, and performance, a proven track record of overall system effectiveness ultimately will be the NASA benchmark. This will foster the accomplishment of

r mission objectives within cost and schedule expectations without compromising safety or w program risk. A key CharaCteristic of systems effeci_veness is the impiementation of appropriate levels of maintainability throughout the program life cycle.

Maintainability is a process for assuring the ease by which a system can be restored to operation following a failure. It is an essential consideration for any program requiring ground n and/or on-orbit maintenance. TheiOffice of S_._ty"and Mission Assurance (OSMA) has undertaken a continuous improvement initiative to develop a technical roadmap that will provide a path toward achieving the desired degree of maintainability while realizing cost and schedule benefits. Although early life cycle costs are a characteristic of any assurance program, operational cost savings and improved system availability almost always result from

__° a properlY administered maintainability assurance program. Past experience on NASA w programs has demonstrated the value of an effective maintainability program initiated early in the program life cycle.

This memorandum provides guidance towards continuous improvement of the life cycle development process within NASA. It has been developed from NASA, Department of Defense, and industry experience. The degree to which these proven techniques should be w imposed resides with the project/program, and will require an objective evaluation of the applicability of each technique. However, each applicable suggestion not implemented may represent an increase in program risk. Also, the information presented is consistent with w OSMA policy, which advocates an Integrated Product Team (IPT) approach for NASA systems acquisition. Therefore, this memorandum should be used to communicate technical knowledge that will promote proven maintainability design and implementation methods resulting in the highest possible degree of mission success while balancing cost effectiveness and programmatic risk. w

Frederick D. Gregory Associate Administrator for Safety and Mission Assurance

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DEVELOPING ACTIVITY

U The development of this technical memorandum has been overseen by the NASA Reliability and Maintainability (R&M) Steering Committee, which consists of senior technical representatives from NASA Headquarters and participating NASA field installations. This Committee exists to m provide recommendations for the continuous improvement of the R&M discipline within the NASA community, and this manual represents the best technical "advice" on designing and m operating maintainable systems from the participating Centers and the Committee. Each J technique presented in this memorandum has been reviewed and approved by the Committee.

CENTER CONTACTS m

Appreciation is expressed for the dedication, time, and technical contributions of the following M individuals in the preparation of thismanual. Without the support of their individual Centers, U and their enthusiastic personal support and willingness to serve on the NASA R&M Steering c-bmmittee, the capture oftlie m_inffinab_tytechniques _ofi/a_ned in this manual would not be possible. -" R

All of the NASA Centers are invited to participate in this activity and contribute to this manual. The Committee members listed below may be contacted for more information pertaining to these i maintainability techniques.

Mr. Donald Bush Mr. Leon Migdalski George C. Marshall Space Flight Center John F. Kennedy Space Center I CR85 Bldg 4203 RT-SRD-2 KSC HQS 3548 Marshall Space Flight Center, Alabama 35812 Kennedy Space Center, Florida 32899

B Mr. Vincent Lalli Mr. Ronald Lisk Lewis Research Center NASA Headquarters Code QS MS 501-4 Code 0152 200 E Street, SW g 21000 Brookpark Road Washington, DC 20546 Cleveland, Ohio 44135

u Mr. Malcolm Himel Lyndon B. Johnson Space Center

Bldg. 45 RM 618A, Code NB2 m Houston, Texas 77058

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m I . J TABLE OF CONTENTS w SECTION PAGENUMBER

PREFACE ...... i DEVELOPING ACTIVITY ...... ii CENTER CONTACTS ...... ii w I. INTRODUCTION ...... v w A. Purpose ...... v B. Control/Contributions ...... v C. Maintainability Technique Format Summary ...... vi

II. RECOMMENDED TECHNIQUES FOR EFFECTIVE MAINTAINABILITY

Program Management

22 Technique PM-I : The Benefits of Implementing Maqntainability on NASA Programs .... PM-2 w Technique PM-2 : Maintainability Program Management Considerations ...... PM-8 Technique PM-3: Maintenance Concept for Space Systems ...... PM-14

Design Factors and Engineering

Technique DFE-I : Selection of Robotically Compatible Fasteners and Handling Mechanisms ...... DFE-2 Technique DFE-2: False Alarm Mitigation ...... DFE-8

Analysis and Test

Technique A T-l: Neutral Buoyancy Simulation of On-Orbit Maintenance ...... AT-2 Technique A T-2: Mean Time To Repair Predictions ...... AT-7 Technique A T-3: Availability Prediction and Analysis ...... AT-12 Technique A 7-4: Availability, Cost, and Resource Allocation (ACARA) Model to Support Maintenance Requirements ...... AT- 17 Technique AT-5: Rocket Engine Failure Detection Using an Average Signal Power Technique ...... AT-21

Operations and Operational Design Considerations

Technique OPS-I : SRB Maintainability and Refurbishment Practices ...... OPS-2 Technique OPS-2: Electrical Connector Protection ...... OPS-9 Technique OPS-3: Robotic Removal and Application of SRB Thermal Systems ...... OPS- 11 Technique OPS-4: GHe Purging of H 2 Systems ...... OPS- 17 Technique OPS-5: Programmable Logic Controller ...... OPS-20

III TABLE OF CONTENTS (CONT.) m

IBm SECTION: PAGE NUMBER

Operations and Operational Design Considerations (cont.) m

Technique OPS-6: DC Drive - Solid State Controls ...... OPS-24

i Technique OPS-7: AC- Variable Frequency Drive Systems ...... OPS-28 m Technique OPS-8: Fiber Optic Systems ...... OPS-32 Technique OPS-9: Pneumatic Systems-Dome Loaded Pressure Regulator Loading .... OPS-36 Technique OPS-IO: Modular Automatic Power Source Switching Device OPS-39 I Technique OPS-11: Pneumatic System Contamination Protection ...... OPS-42

m m m. APPENDIX A: CANDIDATE TECHNIQUES FOR FUTURE DEVELOPMENT ...... A-1

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I. INTRODUCTION r

A. PURPOSE

w Maintainability is a process for assuring the ease by which a system can be restored to operation following a failure. Designing and operating cost effective, maintainable systems ? f (both on-orbit and on the ground) has become a necessity within NASA. In addition, NASA w cannot afford to lose public support by designing less than successful projects. In this era of shrinking budgets, the temptation to reduce up front costs rather than consider total program life cycle costs should be avoided. In the past, relaxation of R&M requirements to reduce up front costs has resulted in end-items that did not perform as advertised and could not be properly maintained in a cost effective manner. Additional costs result when attempts are

L_ made late in the design phase to correct for the early relaxation of requirements. w The purpose of this manual is to present a series of recommended techniques that can increase overall operational effectiveness of both flight- and ground-based NASA systems. Although each technique contains useful information, none should be interpreted as a requirement. The objective is to provide a set of tools to minimize the risk associated with:

• Restoring failed functions (both ground and flight based) • Conducting complex and highly visible maintenance operations • Sustaining a technical capability to support the NASA mission utilizing aging equipment W or facilities.

This document provides (1) program management considerations - key elements of an effective maintainability effort; (2) design and development considerations; (3) analysis and test considerations - quantitative and qualitative analysis processes and testing techniques; and (4) operations and operational design considerations that address NASA field experience. Updates will include a section applicable to on-orbit maintenance with practical experience from NASA EVA maintenance operations (including ground and on-orbit operations and ground-based simulations). This document is a valuable resource for continuous improvement ideas in executing the systems development process in accordance with the NASA "better, faster, smaller, and cheaper" goal without compromising mission safety. w B. CONTROL/CONTRIBU_ONS

L . This document will be revised periodically to add-new techniques or revisions to the existing techniques as additional technical data becomes available. Contributions from aerospace contractors and NASA Field Installations are encofir_/ged. Any technique based on project/program experience that appears appropriate for inclusionin this manual should be submitted for review. Submissions should be fo _n-nattedid_entical!y to the techniques in this memorandum (Figure 1) and sent to the address below for consideration.

National Aeronautics and Space Administration Code QS 300 E Street S.W. Washington, DC 20546

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Organizations submitting techniques that are selected for inclusion in this manual will be recognized on the lower portion of the first page of the published item. Contacts listed earlier in D this document should be used for assistance. If additional information on any technique is desired, the contacts listed earlier in this document can be utilized for assistance.

D C. MAINTAINABILITY TECHNIQUE FORMAT SUMMARY

The maintainability techniques included in this manual are Center-specific descriptions of I processes that contribute to maintainability design, test, analysis and/or operations. Each technique follows a specific format so users can easily extract necessary information. The first =_ page of each technique is a summary of the information contained, and the rest of the technique g contains the specific detail of the process. Figure 1 shows the baseline format that has been used to develop each technique.

Technique Title, page numbeJ m Technique XXX-._ *_ IB TECHNIQUE FORMAT

Techniaue: A brief statement defining the design technique and how it is used.

Benefits: A concise statement of the technical improvement andor impact on resource expenditure realized from implementing the technique.

Key Words: Any term that captures the theme of the technique or provides insight into the scope. Utilized for document search purposes. m

J Application Experience: Identifiable programs or projects that have applied the technique within NASA and/or industry.

Technical Rationale: A brief technical justification for the use of the technique. BB

Contact Center: Source of additional information, usually sponsoring NASA Center.

Techniaue Description: A technical discussion that is intended to give the details of the process. The U information should be sufficient to understand how the technique should be implemented.

References: Publications that contain additional information about the technique. w

'* Each technique within a section is identified using one of the following acronyms specific to that section 'ollowed by the associated sequential technique number. m • PM: Program Management • DFE: Design Factors and Engineering

• AT: Analysis and Test m • OPS: Operations and Operational Design Considerations

Figure 1: Technique Format Definitions w

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Program Management

A fundamental key to program and mission success is the development of systems that are reliable

and affordable to operate and maintain with today's limited resources. Early definition of both

hardware and software requirements that provide the capability for rapid restoration when failures

occur is essential. While incorporation of a maintainability program may require some additional w early investment, the resulting benefits will include operational cost savings and improved system

availability. The techniques included in this section are intended to provide management personnel

with an understanding of all information necessary to develop, foster, and integrate a successful

maintainability program that will enhance mission success and lower overall costs. Each technique

provides high-level information on a specific subject, and can be tailored or expanded to achieve

optimum application.

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Technique Programmatic provisions for ease of maintenance greatly enhance hardware and software system operational effectiveness for both in- space and ground support systems.

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Benefits Implementation of maintainability principles can reduce risk by increasing operational availability and reducing lifecycle costs. Provisions for system maintainability also yields long term benefits that include decreased maintenance times, less wear and tear on project personnel, and extended useful life of ground and in-space assets.

Key Words System maintainability, program management, lifecycle costs, _ T availability, concept development, human factors

Application International Space Station Program, Hubble Space Telescope, SRB's, Experience Shuttle GSE, Space Acceleration Measurement System, and others.

_5 Technical Maintainability requirements for programs that require ground and/or Rationale in-space maintenance and anomaly resolution have to be established early in the program to be cost effective. Lack of management support to properly fund maintainability activities up-front can result in increased program risk. Including maintainability in the design process will greatly reduce the number of operational problems associated with _z_r r _ system maintenance, improve the availability of the system, and reduce program costs.

Contact Center All NASA Field Installations

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Be_fits of Implementing Maintainability environment under which maintenance is: II on NASA Programs performed. Applying maintainability principles Techniqm _ PM-1 will enhance the systems readiness/availability through factors such as visibility, accessibility, i testability, simplicity, and interchangeability of Over the years, NASA has =successfully the Systems being maintained. Using ill launched manned spacecraft to the moon, sent maintainability prediction techniques and other unmanned probes into the outer reaches_f - = qu_titativ e m_n_tainability analyses can greatly the sc' system, and developed reusable enhance the confidence in operational l I space zems for earth orbitable missions. capabilities of a design. These predictions can NASA alS ° _performs v_uable atmos.pheric - also ai___d!n des!gn dec!sions_an_d [fade studies research and development of ground systems, whe_sex, erfil-design options are being _ i all of which contain complex hardware and considered. Also, cost savings and fewer : ,ftware that must be maintained during all schedule impacts in- tl3e oPerational phase of the program will result due to decreased :_ases of operafior[s an-d-in multiple g environments. However, in this age of maintenance time, minimization of support shrinking budgets, doing more with less is equipment, and increased system availability. becoming the overall programmatic theme. Another benefit is a decrease in management I NASA space flight programs are being driven overhead later on in the life cycle as a result of towards more automated, compact designs in including maintainability planning as a full which fewer support resources will be par-trier in early maintenance/logistics concept I available than in past programs. This planning and development. technique will outline _e _nefits of ...... implementing well-defined and user-friendly PROGRAMMA TIC BENEFITS ii principles of maintainability on all NASA programs, regardless of the operational Maintainability Program Implementation m scenario. Emphasis is placed on how and Project management is responsible for I why a maintainability program can enhance implementing maintainability on a program via the effectiveness of a system and its overall development of specific requirements for cost m operation. It must be noted, however, that effective system maintenance in the early phases maintainability of unmanned deep space of the life cycle. Trade studies of the impacts of systems provides a different set of challenges. maintainability design on life cycle costs are used to evaluate the balance between cost of w Mal tainabilitY is defined inNASAHandbook designing to minim!ze maintenance times and

53(_).4(1E), "Maintainability Program the associated increase m system availability ,= . Requirements for Space Systems," as: "A resulting from the decrease in maintenance measure of the e a_ and rapiditY with which a times. Usually, the up-front cost of designing- = in maintainability is much less than the cost system or equipment can be restored to u operational status following a failure," and is savings realized over the operational portion of consistent with NHB 7120.5, "Management the life cycle. M of Major Systems and Projects." It is a w characteristic of equipment and installation, Several programs have opted to accept the personnel availability inthe_qu_ed s_.kiH .... short-term cost savings by deleting = _ [HI levels, adequacy of maintenance procedures maintainability requirements in the design D and test equipment, and the physical phase, but the associated increase in

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! . maintenance and support costs incurred during operations would have been f significant. An example of this is the Space Station Program, which had deleted requirements for on-orbit automated fault detection, isolation and recovery (FDIR), saving the program up-front money. However, the alternative concept was to L increase the mission control center manpower w during operations for ground based FDIR, but this presented a significant cost increase when averaged over the life cycle. Another positive example is the Hubble Space Telescope Program. Maintainability concepts were included early in the life cycle, where maintenance planning and optimum ORU

a usage in design saved the program significant costs when on-orbit repairs became necessary. Figure 1 accentuates the cost tradeoffs between introducing maintainability w concepts into a program and the time at which they are introduced. These tradeoffs can mean the difference between a successful maintainability program and a costly, less Figure 1: Effect of Implementing effective one. Maintainability Program vs. Phase

The NASA systems engineering process should require that the system be designed for MaintenanceLogistics Concept Development r-- ease of maintenance within it's specified Development of the maintenance and logistics operating environment(s), and should ensure concepts for a program early in the life cycle that the proper personnel (design and must include the maintainability characteristics Z = , operations maintainability experts) and funds of the design. The maintenance concept is a are committed to development of the process plan for maintenance and support of end-items to achieve maximum program benefit. on a program once it is operational. It provides L Program schedule will be affected by lack of the basis for design of the operational support system maintainability because necessary system and also defines the logistics support

L, ground support will increase, maintenance program, which will determine the application times will be higher, necessary maintenance of spares and tools necessary for maintenance. actions will increase, EVA will be at a The use of other logistic resources, such as premium, and system availability will be tools and test equipment, facilities and spare _=_ lower. Table 1 highlights key program parts, will be optimized through including benefits. maintainability planning as a key operational element. Derivation of these plans early on in the life cycle solidifies many operational aspects

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m Table 1: Maintainability Programmatic Testability Benefits Testability is a measure of the ability to detect system faults and to isolate them at the lowest • Enhanced System Readiness/Availability replaceable component(s). The speed with m - Reduced Downtime which faults are diagnosed can greatly influence - Supportable Systems - Ease of Troubleshooting and Repair downtime and maintenance costs. For example, I • System Growth Opportunities deficiencies in Space Shuttle Orbiter testability - Hardware/Software Modifications design have caused launch delays, which - Interchangeability translate to higher program costs. As - Modular Designs i technology advances continue to increase the - Decreased Storage Considerations • Reduced Maintenance Manpower capability and complexity of systems, use of • Reduced Operational Costs automatic diagnostics as a means of FDIR n II • Compatibility with other Programs substantially reduces the need for highly trained • Reduced Management Overhead maintenance personnel and can decrease

maintenance costs by reducing the erroneous I of the program, thus allowing for integrated replacement of non-faulty equipment. FDIR design and support planning development. systems include both internal diagnostic systems, referred to as built-in-test (BIT) or II MAINTAINABILITY DESIGN BENEFITS built-in-test-equipment (BITE), and external diagnostic systems,referred to as automatic test II Visibility equipment (ATE), test sets or off-line test i Visibility is an element of maintainability equipment used as part of a reduced ground design that provides the system maintainer support system, all of which will minimize visual access to a system component for down-time and cost over the operational life i maintenance action(s). Even short duration cycle. tasks such as NASA space shuttle orbiter component inspection can increase downtime Simplicity m if the component is blocked from view. System simplicity relates to the number of Designing for visibility greatly reduces subsystems that are within the system, the maintenance times. number of parts in a system, and whether the I parts are standard or special purpose. System Accessibility simplification reduces spares investment, J Accessibility is the ease of which an item can enhances the effectiveness of maintenance troubleshooting, and reduces the overall cost of be accessed during maintenance and can u greatly impact maintenance times if not the system while increasing the reliability. For B inherent in the design, especially on systems example, the International Space Station Alpha where on-orbit maintenance will be required. program has simplified the design and L_ When accessibility is poor, other failures are potentially increased the on-orbit maintainability g often caused by removal/disconnection and of the space station, thus avoiding many incorrect re-installation of other items that operational problems that might have flown with the Freedom Programl One example is the hamper access, Causing rework. Accessibility J of all replaceable, maintainable items will Command and Data Handling Subsystem, provide key time and energy savings to the which is the data processing backbone for the system maintainer. space station. Formerly, the system consisted m of several different central processing units,

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of several different central processing units, However, early evaluation during concept multiple level architecture, and several development can assure early application of different network standards. The new design anthrop0metriee0nsiderations. Use of these comprises only one network standard, one evaluations results leads to improved designs standard CPU, and a greatly reduced number largely in the areas of system provisions for of orbital replaceable units (ORU's). equipment access, arrangement, assembly, Maintainability design criteria were definite storage, and maintenance task procedures. The factors in the design changes to this space benefits of the evaluation include less time to station subsystem. effect repairs, lower maintenance costs, improved supportability systems, and improved Reduced training costs can also be a direct safety. w result of design simplification. Maintenance requires skilled personnel in quantities and Summary skill levels commensurate with the complexity Implementation of maintainability features in a of the maintenance characteristics of the design can bring about operational cost savings system. An easily maintainable system can be for both manned and unmanned systems. The LJ quickly restored to service by the skills of programmatic benefits of designing system w available maintenance personnel, thus hardware and software for ease and reduction increasing the availability of the system. of maintenance are numerous, and can save a program, as seen with NASA's Hubble Space Interchangeability Telescope. Maintenance in a hostile, micro- Interchangeability refers to a component's gravity environment is a difficult and ability to be replaced with a similar undesirable task for humans. Minimal exposure component without a requirement for time to this environment can be achieved by recalibration. This flexibility in design implementing maintainability features in the reduces the number of maintenance design. The most successful NASA programs w procedures and consequently reduces have been those which included maintainability maintenance costs. Interchangeability also features in all facets of the life cycle. Remote t_ allows for system growth with minimum system restoration by redundancy management associated costs, due to the use of standard or and contingency planning is particularly common end-items. r essential to assuring mission success on projects where manned intervention is either Human Factors undesireable or impractical. Human factors design requirements also should be applied to ensure proper design References consideration. The human factors discipline identifies structure and equipment features 1. NASA Handbook 5300.4(1E) that impede task performance by inhibiting or "Maintainability Program Requirements for prohibiting maintainer body movement, and Space Systems, "March 10, 1987, NASA also identifies requirements necessary to Headquarters. provide an efficient workspace for maintainers. Normally, the system design 2. NASA Handbook 7120.5, "Management of must be well specified and represented in Major Systems and Projects, "November 1993, drawings or sketches before detailed NASA Headquarters anthropometric evaluation can be effective.

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3. Air Force Design Handbook 1-9 I "Maintainability (for Ground Electronic Systems)," Second Edition, Revision 7, Febm_r'y 25, 1988, United States Air FOrce I Aeronautical Systems Division.

m 4. "Maintainability Engineering Design and Cost of Maintainability," Revision II, January 1975, Rome Air Development Center. m

5. Reliability, Maintainability, and

Supportability (RMS) Guidebook, Second aim Edition, 1992, Society of Automotive Engineers G- 11 International RMS Committee. I

6. MIL-STD-470B "Maintainability

Program for Systems and Equipment," May I 30, 1989, Department of Defense

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Technique Identify program management considerations necessary when implementing maintainability principles for NASA spaceflight, T atmospheric, or ground support programs.

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Benefits Early and effective planning and implementation of a maintainability program can significantly lower the risk of reduced system operational effectiveness resulting from maintainability design shortfalls. This reduces maintenance time/support, which directly relates to reduced operating costs and increased system operational time.

KeyWords Maintainability Management, Maintenance Concept, Logistics Support, Quantitative Requirements, Maintainability Planning

Application Hubble Space Telescope, SRB's, Shuttle GSE, and Space Acceleration Experience Measurement System•

Z ; Technical Decisions by program management to establish maintainability Rationale requirements early in the program will provide design impetus towards a system with higher operational availability at lower operational costs• Lower downtime and less complicated maintenance actions will be needed when maintenance is required.

Contact Center NASA Headquarters

__ Page PM-8 Maintainabili_F Program Management Considerations, Page 2 Technique PM-2

Maintainability Program Management D Considerations Technique PM-2 PROGRAM Z g This technique outlines management considerations to observe when applying the principles of maintainability on a program at g NASA. It also provides information on how to realize cost savings and reduced system downtime. This information complements D PM- 1, "Benefits of Implementing Maintainability on NASA Programs," by m providing guidelines for establishing a maintainability program once the benefits have been understood. m PROGRAM CONTROL Program management is responsible for establishing proper integration of m maintainability early in program development and ensuring adequate control of the application of the maintainability discipline Figure 1: Maintainability Program II throughout the development program. Figure Development

1 provides flow diagram for an effective r_

Maintainability program beginning with reflect the function (mission) of the I development of its goals and objectives, system/subsystem and the impact on followed by development of the program/system operational objectives of the program if the maintenance concept and the Mainta[nability system isnon'operational for any length of m Program Plan, and establishment of program time. System availability (the ability of the control and evaluation during design, production system to operate whenever called upon to do

(manufacturing) and operations. The order of so) is very important, _and maximum m these program development elements is availability should be a goal of the program. important, as each affects the next step in the Program maintainability goals and objectives = = process. must be developed with cost and schedule in i ...... mindi hqwever, careful considerationo must (1) ESTABLISH MAINTAINABILITY AS also be given to the technical-and operational w PART OF THE OVERALL SYSTEMS goals of the program. These qualitative goals ENGINEERING AND OPERA TION and objectives are developed by analyzing the J PLANNING PROCESS. system oPerating cycle, the physical and D maintenance support environments, and other Set Goals and Objectives equipment characteristics consistent with One of the missions of the maintainability H mission and cost objectives. J program is to measure the ability of an item to be retained or restored to a specified condition Attention must also be given to existing when maintenance is performed. The degree of support programs to avoid needless w maintainability designed into a system should duplication during development of new

Im Page PM-9

H m Maintainability Program Management Considerations, Page 3 Technique PM-2

support systems. Development of the repair policies, and maintenance resources to maintainability goals and objectives will lead to the desired level of maintainability at derivation of the maintenance concept, acceptable life-cycle costs. The many maintainability plan, and definition of interfaces and feedback paths between maintainability requirements discussed in the maintainability engineering and other product following paragraphs. development and operational disciplines are shown in Figure 2. Establish Interfaces with Other Engineering Disciplines While maintainability personnel must be Maintainability engineering is a system intimately involved in the product engineering discipline that combines system development process and provide inputs to analysis and equipment design with a knowledge design through design techniques and of safety, reliability, human factors, and life-cycle analysis, it is program management's costing to optimize the maintenance responsibility to develop and support the characteristics of system design and to provide relationship between maintainability and the an awareness of interface problems. Its goal is rest of the system engineering disciplines. to optimize the combination of design features, This support is key to establishment of a

TEST AND EVALUATION E REQU|REMENTS DEF|N|'_ON I SYSTEM DESIGN AC'R_PI'r_ES I

Design Feedback

Characteristic:

SYSTEM AVAILABILITY PERFORMANCE

-': 4 Operational SYSTEM Suitability READINESS Analysis PERFORMANCE

SYSTEM Trades II _' I _ PERFORMANCE

I Design d

F_ Operations |1_ [ Test& I Design & Support Feedback

Concepts _' ...... _ Evaluation I

Figure 2: System Reliability, Maintainability and Support Relationships (typical) w Page PM- 10 Maintainability Program Management Considerations, Page 4 Technique PM-2

concurrent engineering process. These These elements are also important _ relationships must be mirrored in the contributors to system maintainability in that Maintainability Program Plan. logistics planning can define how much system down time is required during (2) DEVELOP MAINTENANCE AND maintenance operations. LOGISTICS CONCEPTS EARL Y IN THE CONCEPTUAL PHASE OF THE For example, downtime can be held to a PROGRAM.. minimum if spares are co-located with the system during operations. It is important that The program maintenance concept provides the Program management closely monitor all basis for establishing overall maintainability logistics development to ensure inclusion of design = quirements on the program, and maintenance and logistics concepts early in contains detailed planning on maintenance the program. Both concepts drive the policy. development of lower-level requirements.

It defines overall repair policy, organizational Assess Existing Resources and depot maintenance, system availability, Another important aspect of planning for a repair vs. replacement policy, level of new program is assessment of the existing replacement, skill level requirements, sparing logistic and support infrastructure. As an philosophy, diagnostic/testing principles and example, the infrastructure of the NSTS=: concepts, contractor maintenance system at KSC comprises the launch pad, responsibilities, payload maintenance numerous assembly and support buildings, responsibilities, and crew time allocations for and support personnel and equipment. These maintenance (PM-3 provides details on each of are important factors to consider when these elements). Development of the planning for new programs that will use KSC maintenance concept is based on initial as the central operations base. If some of the maintainability analysis and program inputs such existing structures and equipment can be used as mission profile, system availability and by the new program, then the developmental reliability requirements, system mass properties and operational costs of the program will be constraints, and personnel considerationsl Ttie reduced. During early planning stages, maintenance concept may be developed from the management should also look at how the new ground up, or may come from a similar program can adapt to the existing support successful program, tailored to meet the needs of infrastructure, and what equipment and the new program. New technology may also personnel may be used to eliminate dictate the maintenance concept, :e.g. unnecessary costs. maintainable items may be scrapped instead of repaired because the cost of repair outweighs the Establish a Maintainability Program Plan replacement cost. The maintainability program plan is the master planning and control document for the Definition of logistics and support concepts is a maintainability program. It provides detailed function &the maintenance concept. The activities and resources necessary-to attain the operational environment of the system, the level goals and objectives of the maintainability of support personnel defined by the maintenance program. It must be developed with the _ concept, and cost and schedule are important program contractor(s) if they exist, or if the drivers for the logistics/support programs. program is in-house, all developmental and

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l g Maintainability Program Management Considerations, Page 5 Technique PM-2

operational disciplines must be represented. The These requirements are intended as rules plan must be consistent with the type and system designers follow to meet overall complexity of the system or equipment and must program goals and objectives. They include be integrated with the systems engineering mission, operational environment, and system process. It identifies how the concepts. They must be baselined early and contractor/program office will tailor the not changed unless absolutely necessary. w maintainability program to meet requirements throughout the three major program phases • The requirements can include both Development, Production, and Operations/ quantitative and qualitative values of Support. Typically it contains the following maintainability parameters. Quantitative elements shown in Table 1" maintainability requirements are usually the result of maintainability allocations based on = Table 1. Elements of the Maintainability system availability and operational timing Program Plan requirements, with allocations made at each level down to the replaceable module, Duties of each organizational dement assembly or component level as needed. involved in the accomplishment of the Examples of quantitative requirements are maintainability tasks cited in the product shown in Table 2: specification or statement of work.

Table 2. Examples of Quantitative Interfaces between maintainability and Requirements other project organizations, such as design engineering, software, reliability, safety, • Maintenance manhours per operating maintenance, and logistics. B hour (MMH]OI-I) • Mean-Time-To-Repair (MTTR) Identification of each maintainability task, 7 • Mean-Time-To-Restore-System narrative task descriptions, schedules, and (M'rrgS) supporting documentation of plans for • Fault detection and isolation of sub- task execution and management systems task times w • End item change out time Description of the nature and extent that • Unit removal/installation times the maintainability function participates in • Availability formal and informal design reviews, and authority of maintainability personnel in approval cycle for drawing release.

They may be established at any, or all, levels of maintenance and can help define maintenance criticalities and reduction of (3) PROVIDE UNIFORM QUALITATIVE necessary system components. Qualitative AND QUANTITATIVE MAINTAINABILITY requirements are used to accomplish two REQUIREMENTS. purposes. First, they address maintainability design features which are vital in achieving Maintainability design requirements are the maintainability goals, but cannot be established from the Maintainability Program measured. For example, elimination of Plan and the derived maintenance concept. safetywire/lockwire, standardization of

Page PM- 12 Maintainability Program Management Considerations, Page 6 Technique PM-2

fasteners, use of captive fasteners, and color- and existence of these examples will enhance g coding of electrical wiring are some basic the chance of program success (based on qualitative maintainability requirements used on historical experience). B orbital programs. Second, qualitative IB requirements are used to meet customer/ References program requirements and enhance the m maintainability:characteristics of the system. I. NASA Handbook 5300.4(iE), I Examples include specification of common "Maintainability Program Requirements for Z handtools only for organizational and ! Space Systems, "March 10, 1987, NASA I intermediate levels of maintenance, and Headquarters. 11 designing so that only one skill level is required for all organizational level maintenance 2. Air Force Design Handbook 1-9, I personnel. "Maintainability (for Ground Electronic Systems)," Second Edition, Revision 7, (4) EXERCISE PROGRAM CONTROL AND February 25, 1988, United States Air Force g E VAL UA TI ON. Aeronautical Systems Division.

The maintainability program must be an integral 3. ''Maintainability Engineering Design and J part of the systems engineering process and all Cost of Maintainability, "Revision II, design and development activities. Activities January, 1975, Rome Air Development Center. l include design reviews, development and I implementation of methods for assessing maintainability effectiveness, dissemination of 4. Reliability, Maintainability, and maintainability data, and proper implementation Supportability _S) Guidebook, 'Second I of program test and evaluation. Subcontractor/ Edition, 1992, Society of Automotive supplier control is also a key areas for program Engineers G- 11 International RMS evaluation and monitoring. Committee. J

Summary Related Techniques Program management's participation in the m development and implementation of sound Technique PM- 1, "Benefits of ImPlementing maintainability practices on NASA programs is Maintainability on NASA Programs" m extremely important. Whether the program contains ground based systems, or is orbital and Technique PM-3: "Maintenance Concept for beyond, maintainability plays a key role in Space Systems." J system operations, providing for increased system effectiveness and availability, and lower _m life cycle costs. The steps outlined above are J guidelines towards success, and can be tailored depending on the type of program. However,

the importance of a concurrent engineering g apT.,'oach and the existence of intimate p" _essional relationships between ma:ntainability personnel and other systems i engineering disciplines can not be overstated,

Page PM- 13

g Maintenance Concept for Space Systems, Page 1 Technique PM-3

Technique Develop a maintenance concept early in the program life cycle to provide a basis for full maintainability support. It should be used to influence systems design to ensure that attributes for ease of maintenance, minimization of repair and down time, and logistics support will be present in the final design.

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Benefits Effective development of a maintenance concept can enhance the w effectiveness of maintenance support planning and aid both logistics planning and design of a maintainable system. The maintenance concept can also provide assessments of cost savings for maintenance activities w and resources allowable at each maintenance level. h _

Key Words Maintenance Concept, Spares Requirement, Logistics Support, Maintenance Plan, Maintainability Requirements.

Application Space Acceleration Measurement System (SAMS), Combustion Experience Module- 1 (CM- 1) Shuttle/Station Experiment.

Technical The need to identify quantity, cost, types of spares, and related Rationale servicing techniques required to sustain a space system mission capability is a prime driver in developing maintainability requirements for a space system at the onset of its design. A system maintenance L concept should be developed to define the basis for establishing maintainability requirements and to support design in the system conceptual phase. The maintenance concept provides the practical basis for design, layout, and packaging of the system and its equipment. The number of problems associated with product support and maintenance of space systems can be reduced, if not eliminated, by applying the principles prescribed in the system's maintenance concept.

Contact Center Lewis Research Center (LeRC)

,.., Page PM- 14 Maintenance Concept for Space Systems, Page 2 Technique PM-3

Maintenance Concept for Space Systems orbital space program where on-orbit and Technique PM-3 ground maintenance is planned.

The maintenance concept provides the basis for Repair Policy overall maintainability design requirements for The repair policy should consider the the program, and contains detailed planning of support to be provided at the maintenance maintenance policy for the operational system. echelons (levels) summarized in Table 1. It establishes the scope of maintenance responsibility for each level (echelon) of Table 1. Echelons of Maintenance maintenance and the pers0_el resources _ ...... (maintenance manning and skill levels) required Organizational Depot to maintain a space system. Early development Maintenance Maintenance and application of the maintenance concept in ii structuring the maintainability plan can Where On-orbit NASA Center or Contractor eliafinate or reduce occurrence of problems that Performed m: interrupt system operation. System Flight Crew Center Engineers Maintainer and Technicians The maintenance concept for a new system Basis Repair and retain Repair and return must be systematically formulated during the equipment equipment to early conceptual design phase of a program to stock inventory minimize maintenance problems during the operational phase. This proactive approach is Type of work Inspect equipment Repair at accomplished module, ORU, being used on Space Station-based experiment and component development programs at LeRC to incorporate level current Space Station Program support principles, prescribed Space Acceleration Remove and Repair and replace modules maintain ground Measurement System (SAMS) and Combustion and ORU's support Module One (CM-1) operational and repair equipment policy, and identified sparing requirements. Adjust equipment Calibrate Elements equipment This maintenance concept will aid in logistics planning and will guide design by providing the basis for establishment of maintenance support Organizational Maintenance requirements in terms of tasks to be performed, Organizational maintenance is maintenance frequency of maintenance, preventive and performed by the using organization (e.g., corrective maintenance downtime, personnel flight crew) on its own equipment. This numbers and skill levels, test and support maintenance consists of functions and repairs equipment, tools, repair items, and information. within the capabilities of authorized Inputs to the maintenance concept should personnel, skills, tools, and test equipment. include: a mission profile, system reliability and Organizational level personnel are generally availability requirements, overall size and occupied w_th the operation and use of the weight constraints, and crew considerations. equipment,: and have minimum time available The concept should support the following for detailed maintenance or diagnostic design elements as they apply to a manned checkout; consequently, the maintenance at

Page PM- 15 Maintenance Concept for Space Systems, Page 3 Technique PM-3

this level is restricted to periodic checks of any on-orbit repair actions are planned, they equipment performance. Cleaning of should be clearly identified in the concept. equipment, front panel adjustments, and the At the organizational level, failed items removal and replacement of certain plug-in should be either discarded or sent to the modules and Orbital Replaceable Units (ORUs), NASA Center or contractor for exchange referred to as black boxes, are removed and and repair in accordance with repair/discard forwarded to the Depot Level. policies identified in the system requirements. Corrective maintenance, Depot Maintenance limited to replacement of faulty ORUs and Depot maintenance is maintenance performed at plug-in modules, should be specified to be NASA Centers or contractor facilities for performed during the mission period. Prime completely overhauling and rebuilding the equipment should be designed to have ready equipment as well as to perform highly complex access for maintenance. Quick-opening maintenance actions. The support includes fasteners should also be specified. tasks to repair faulty equipment to the part level, if deemed necessary. This level of Level of Replacement maintenance provides the necessary standards The design for proper level of ORU for equipment calibration purposes, and also definition should consider compatible failure serves as the major supply for spares. rates for hardware parts within the same ORU. Relative ranking of ORLPs through @stem Availability reliability and maintainability considerations Operational Availability (Ao) is defined as the and mission criticality analysis can also probability that at an arbitrary point in time, the contribute toward the proper level of system is operable, i.e., is "up." It is a function replacement definitions. The required level of the frequency of maintenance, active of replacement should be specified at the maintenance time, waiting time, logistics time, plug-in module and ORU levels. administrative time, and the ready time of the Maintenance and support of a system should system, and is expressed as: involve two-tier maintenance echelons. The first level provides for repair of the end-item UPTIME A on-orbit by replacing select faulty or o TOTAL TIME (1) defective plug-in modules and ORUs identified through use of specified diagnostic w procedures. Faulty ORUs should then be Where: evacuated to the second level of the maintenance echelon (depot level), which UPTIME = the total time a system is in an will be at a NASA Center for repair if operable state, and deemed necessary. The particular NASA center/facility should act as the depot for TOTAL TIME = the combination ofuptime repair of faulty items. and downtime, in which downtime is the time in which a system spends in an inoperable state. Skill Level Requirements Hardware should be designed to aid on-orbit Repair v_ Replacement Policy and ground maintenance, inspection, and Normally, on-orbit repair should not be repair. Special skills should not be required performed on any plug-in modules or 0RUs. If to maintain a system. The following design

Page PM- 16 Maintenance Concept for Space Systems, Page 4 Technique PM-3 features should be incorporated: • Custom-made components/parts • Long-lead time items • Plug-in module and 0RU design to minimize installation/removal time and requirements for The quantity of spares required for each hand tools, special tools, and maintenance system and the total quantities to sustain the skills. required operational availability on-orbit should be determined according to the • Plug-in modules and ORUs should be following: designed for corrective maintenance by removal and replacement. • Items that are critical to system operation • Items that have high failure rate • Plug-in module and 0RU designs requiring • Items that have limited life preventive maintenance should be optimized with respect to the access, maintenance hours, In the initial spares provisioning period and and maintenance complexity. to the maximum extent practical, spares should be purchased directly from the actual • Software and its associated hardware should manufacturer; i.e., lowest-tier subcontractor, be designed so that software revisions/ to eliminate the layers of support costs at I corrections can be easily installed on-orbit with each tier. The initial provisioning period minimum skill level requirements. should cover early test and evaluation, plus a

w short period of operation, to gain sufficient l I • Flight crew training for payload flight operational experience with the system. This operation should identify hands-on will provide a basis for fully competitive crewmember training, at the NASA center acquisition of spares. m where the system is built, to familiarize crewmembers with the removal/replacement of Spares with limited shelf life should be hardware. identified and should be acquired periodically U to ensure that adequate quantities of spares Spares Philosophy are available when needed. Spares with

Two basic types of spares should be required to expired shelf lives should be removed and U support a maintainable system: development replaced. spares and operational spares. Development spares are those that must be identified and Procurement of spares should be initiated in u acquired to support planned system test sufficient advance of need to account for activities, integration, assembly, check-out and procurement lead time (administrative and l production. Operational spares are those spares production lead time). that must be acquired to support on-going operations on-orbit. The location of the spares inventory (on- orbit and on-ground) should be a function of The quantity of development spares required the on-orbit stowage allocation capabilities for each system, and the total quantities to and requirements. A volume/weight analysis W sustain the required availability during the should be conducted to determine the planned test activities, integration, assembly, quantity and types of spare items necessary and check'out test should be determined to sustain satisfactoryoperationai m according to the following: availability. The volume/weight analysis shall

Page PM- 17 I

m g Maintenance Concept for Space Systems, Page 5 Technique PM-3

assure available or planned payload volume and to be functionally, mechanically, electrically, weight limits, and planned or available on-board and electronically as independent as practical stowage area. to facilitate maintenance.

Breakout should be addressed during initial The concept should also describe provisioning and throughout the replenishment operating/testing techniques to identify process in accordance with NMI 5900.1, problems and consider the complexity of the Reference 1. Breakout is the spares various types of items in the space system procurement directly from the original and associated maintenance personnel skills equipment manufacturer, prime contractor, or (for all software, firmware, or hardware). other source, whichever proves most cost- The techniques will identify maintenance effective. A spare item requirement list should problems. In all cases of fault simulation, the be maintained by procurement and technical safety of personnel and potential damage to personnel. system/equipment should be evaluated in the concept. The concept should request that a w Diagnostic/7"esting Principles and Concepts safety fault tree analysis be the basis for The system should meet the following failure determining simulation. Also, a Failure detection requirements as a minimum: Modes, Effects, and Criticality Analysis should be used to evaluate and determine • The system should have the capability to fault simulation. Some of the fundamental U detect, isolate and support the display of maintenance actions to be evaluated, failures to the plug-in module level. Crew monitored, and recorded are as follows: observations may be used as a method of failure detection of the following: visual displays, u • Preparation and visual inspection time keyboards/buttons, general lighting, speakers. • Functional check-out time • Diagnostic time: fault locate and fault • System design should provide the capability isolate for monitoring, checkout, fault detection, and • Repair time: gain access, remove and L : isolation to the on-orbit repairable level without replace, adjust, align, calibrate, and close requiring removal of items. access • Clean, lubricate, service time • Manual override and/or inhibit capability for • Functional check-out of the repair action all automatic control functions should be provided for crew safety and to simplify Responsibilities for Contractor [_ checkout and troubleshooting. Maintenance The prime contractor's maintainability • All failures of the system should be program should provide controls for assuring automatically detected and enunciated either to adequate maintenance of purchased the flight crew or the ground crew. hardware. Such assurance is achieved through the following: • Accesses and covers should be devoid of sharp corners/edges and be equipped with grasp • Selection of subcontractors from the areas for safe maintenance activities. standpoint of demonstrated capability to produce a maintainable product. • Systems/subsystems/items should be designed

Page PM- 18 Maintenance Concept for Space Systems, Page 6 i Technique PM-3

• Developmentof adequate design ground processing or maintenance u specifications and test requirements for the operations. The rationale for supporting subcontractor-produced product. these recommendations should include factors such as reduction in ground I • Development of proper maintainability turnaround time and operational support COSTS. requirements to impose on each subcontractor. ml II • Close technical liaison with the subcontractor Allocation of Crew Time for Maintenance (both in design and maintainability areas) to Action: _: _ m II minimize communication problems and to Crew time for maintenance should be facilitate early identification and correction of identified in accordance with system interface or interrelation design problems. complexity, reliability, and criticality of the U items to the system and mission • Continuous review and assessment to assure requirements. Analytical methods exist that each subcontractor is implementing his which can be used to prioritize and allocate I maintainability program effectively. crew time for maintenance actions.

Responsibilities for Payload Maintenance RefeYencg$ L | Director of field installations responsible for launch preparation, maintenance, or repair 1. NASA Management Instruction, Spare activities should be responsible for maintenance Parts Acquisition Policy, NMI 5900.1A, | planning and for providing the resources NASA Responsible Office: HM/Procurement necessary to support the efficient identification Systems Division, Washington, DC, of maintenance related problems in accordance November 6, 1992. II with system requirements. These responsibilities include: 2. NASA Management Instruction, Maintainability and Maintenance Planning m • Implementing a system that will identify, Policy, NMI 5350.1A, NASA Responsible track, and status problems related to routine Office: Q/Office of Safety and Mission maintenance activities attributable to the design Quality, Washington, DC, September 26, I characteristics of flight hardware and sofcware. 1991.

mi • Providing information for use in a data 3. NASA Handbook, Maintainability collection system to improve the accuracy of Program Requirements for Space Systems, quantitative maintainability and availability NHB 5300.4(1E), Reliability, :_...... _=_ w estimates. This information can be used to Maintainability, and Quality Assurance identify failure trends influencing reliability Publication, Washington, DC, March 10, growth characteristics during design and to 19871 m t communicate "lessons learned" from ground maintenance experience. 4. Space Acceleration Measurement System

(SAMS) Experiment, SAMS-SS Product U • Recommending to the Program Manager, Assurance Plan, SAMS-SS-005 (Preliminary), responsible for design and development of flight NASA Lewis Research Center, Ohio. hardware/software, areas for design u improvement to increase the efficiency in 5. Space Acceleration Measurement System

U Page PM-19 m Maintenance Concept for Space Systems, Page 7 Technique PM-3

(SAMS) Experiment, Express Payload Integration Agreement, SAMS-SS PIA, NASA Lewis Research Center, Ohio.

6. Space Station Program, Space Station Program Definition and Requirements, Sections 3 and 4, SSP 30000, NASA Lewis Research Center, Ohio. w 7. Combustion Module One (CM-1) Experiment, Product Assurance Plan, NASA Lewis Research Center, Ohio.

8. Blanchard, Benjamin S., Jr. and Lowery, E. Edward of General Dynamics, Electronics w Division, Maintainability Principles and Practices, McGraw-Hill Inc., N.Y., 1969.

w Page PM-20

w wig

aiD

U |_ Design Factors and |_ Engineering

The objective of the A4aintainabilityfunction is to influence system design such that the end product

can be maintained m a cost effective operational condition with minimum downtime. In order for

the Maintainability discipline to provide maximum influence to a program, design principles to

obtain these objectives must be implemented early in the design phase. Techniques that have proven

to be beneficial on previous programs are presented in this section as design recommendations for

future programs.

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D Selec#on (f Robotically Compatible Faswners" and Handling Mechanisms, Page 1 Technique DFE-1 J

Technique Provide guidelines for the design of maintainable equipment for compatibility with dexterous robots by outlining selection criteria for associated fasteners and handling fixtures. iiiiiiiiiii!iiiiiiiiiiiiiii{iiiiiiiiiiiiiiii!iiiiiiiiiiiiiii!!iiiiiYiiiilliJiiiiiii!iiiiiiiiiiiiiiii!iii!iiiiiiiiiiiii iiiiii i _'_'i'_'_'i'i'_'B'_'j_;ii'i_i'i'i'I_,_i'iJi'i':ii'i'iii'i':':i:i:i:i:iiiii_,i:_:':i:_:i:i:i:i:iS_TEiE_'i'Oi'N'i_i'i_'FI_'R_B_|i_ _L:_i:_:_:_:_;i:_:_i:_:_:i:_:_:_:i:i:i:i:i:_:J:_:_:_: ; 2 r i , i::Miii!iiiifk_l_:_ ::!! ::i_ii!i:2:!i!i::::i::ii::ii::i::i::iii::::i!i ii]iff:ili!i::ii::iii::iiii::::ii::ii!i::::::::_::_i::_::_::_i_::__ i_!: _:_:_:i__:__:_...... _i!i::!_:_i;:!i_;_._i:_::i_i!_:i!i!!_i::!_::_::!i::ii!::i_::i::::ii::i_i_:::_::::_::!::_!!:_::ii::iiii_::i::_i_i_:_!i_!ii_iiiiii::iiii_i_ii::ii:: _ i i _ ii_ _+_#:_i_i::::::::ii!::ii::ii::i_::i_

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Benefits The application of these guidelines to the design process will increase w the effectiveness of dexterous robots by allowing for optimized design of robotics components used during maintenance tasks. In addition, because Extra Vehicular Activity (EVA) tasks performed with robots must be simplified to accommodate robotics dexterity (which is intrinsically inferior to that of a human crew member), robotically compatible designs will facilitate the simplified (less time consuming) EVA tasks. This equates to less system downtime and higher availability for both ground and on-orbit systems.

Key Words Robotically compatible; maintenance: fasteners; handling fixtures 7

Application International Space Station Program Experience w

Technical The following selection guidelines enable design engineers to identify Rationale the criteria required for robotics compatibility and to tailor their specifications to different robotics systems and environments. They provide general concepts for using robotically compatible fasteners and handling fixtures that have been applied on the Space Station program and states the advantages of these concepts.

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Contact Center ,lohnson Space Center (JSC) L_

Page DFE-2 Selection _f Roborically Comparibh, Fasteners and Handling Mechanisms', Page 2 _m Technique DFE- 1

Selection of Robotically Compatible Fa._'teners • Provide for alignment. and Handling Mechanisms • Avoid jamming and binding. Technique DFE-I • Withstand the loads that may be imparted by the robotics systems. m I Before designing an ORU or other component • Provide adequate access. for robotics compatibility, the feasibility of such • Simplify the operation ...... m an effort must first be assessed. Some ;tei-ns • Assist ORUal_gnment and S0_d6ck and [] (e.g., thermal blankets), because &their harddock functions. "Softdock" is defined as flexibility, cannot be manipulated by robotics the initial temporary attachment between two Systemsl The assessment should show (i) if the or more pieces of equipinen(t_ pre_ent [] ORU or component can be manipulated by a inadvertent release prior to permanent robot, (2) if not, whether a major redesign of attachment. m the_tem will be required to make it robot I compatible, and (3) what effect the redesign Reference 2 lists a number of guidelines and will have on weight and cost (a factor that can reqt!!ren2ents that may be applicable t 9 m be d-etermined by simple ana]_yses), designing for-iobotics Compatibility of Space Station hardware. Reference 3 lists a number Reference 1 describes a preliminary analysis of different robotically compatible fasteners that might be used to determine the feasibility and handling fixtures for Space Station use. i of designing for robotics compatibility. Once it The purpose of this technique, however, is to m is determined that the item can be designed to assist designers in applying the stated concepts l be manipulated by a robot, it must then be to their system ORU's and not to list determined how the design relates to and contractual requirements. The six design affects the design of(l) other components in objectives for fastener and handling fixture I the system, (2) the system's layout, and (3) the design requirements are addressed in the robotics system with which it will interface tbllowing section. [] Figure 1, which illustrates the process tbr FASTENER AND HANDLING FIXTURE redesigning for robotics compatibility as I)ESIGN REQUIREMENTS

m detailed in Reference 1, shows the sequence by m which the design of items higher in a process Provide for alignment flow impact the design of the lower items. Alignment provisions may be implemented as

Although the sequence may be altered, the (1) markings, (2) alignment guides, and (3) m alteration may result in increased costs, in design of the robotics system and its control schedule delays, and in less flexibility in system Only the second of these options, applying robotics compatibility. The alignment guides, is addressed in this section. m bidirectional arrows indicate processes that Markings and robotics system designs are should be performed using an integrated described in References I, 2, and 3. approach that considers the impacts the ORU, ! system, and robot design have on each other. Fa,_teners Once the above mentioned analysis is There are more options available for aligning w performed and design of the robotically fasteners than there are for handling fixtures. compatible fasteners or handling fixtures is For example, fasteners are captive and are an F_ begun, the objectives then must be to: integral part of an ORU. Therefore, if the ! ORU contains proper alignment features and is

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I Selection of Robotically Compatible Fasteners and Handling Mechanisms, Page 3 Technique DFE-1

- i

Dr.fine Factors of SalYtv for Loads

Revise Determine/ L_ w Robot's Revise Pa rameters/ System's Capabilities Parameters w

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Define/St'lcct Fastener Type, Dennc/Sek'ct Handling Torque Values, and Fi_llll't_ ._lll(| Lo¢;itiou Location

and Markings Alignmenl Guides t DefiJle/Design Targets I Define/Design ]

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properly aligned and inserted, the fasteners will incorporation of alignrnent features is confined be properly aligned as well. However, since to the fixture and end effector. The ORU handling fixtures are grappled independent of alignment feature design, which is discussed in w the insertion and alignment of the 0RU, the References 2 and 3, is an important

Page DFE-4

_=_ m Selection of Robotically Compatible Fasteners and Handling Mechanisms, Page 4 i Technique DFE-1

m consideration, since it can lessen fastener u microfixture allows positional misalignments of i complexity. The alignment techniques being about 0.3 inch and angular misalignments of used for Space Station fasteners are described about +3 ° =-- below. Cylinder-over-cone Alignment of Tool to Fastener Head The microconical tool slips over and attaches Robotic testing has shown that, provided there collets to the microconical interface, which is is proper visual contrast between the fastener shaped like a cone. The allowable translational

= head and the surrounding structure, a 7/16- inch and angular misalignment tolerances for the Z fastener with a flat head can be easily captured microconical tool are 0.25 inch and +1 °, mu by the robotics end effector (nut driver). respectively Earlier concepts specified or recornmended rounded heads because it was believed the A VOID .lAMMING AND BINDING Ill rounded head would accommodate greater misalignment tolerances. It was found, Fltsteil ers however, that a flat-headed fastener provided Once alignment is accomplished and the the robot with the same misalignment fastener begins to enter the nut, th_e_r¢is still tolerances as the same fastener with a rounded the possibility of cross-threading Cross, _ z top. threading can be avoided by aligning the nut using the unthreaded portion on the bolt, and it ! Alignment of Fastener to Nut can also be avoided by using an expandabie The bolt is aligned to a nut by tapering the end thread diameter nut; i.e., a Zipnut. A Zipnut (pilot) of the bolt and by having a cone or consists of three separate segments within a countersink around the nut. For fasteners that housing that, when assernbled, form the I form an assembly or that are, in Space Station internal threads of a nut. The segments are terminology, "attachment mechanisms," there held against the threads of a bolt or screw by are housings which contain tapered "fingers." springs that force them to a minimal diameter, and a ramp that allows them to separate or come together, depending on the direction in Handling FLvtures i The two alignment techniques for Space Station which the bolt is inserted. When a bolt is g handling fixtures are described below. inserted, the segments are allowed to slide back and away, allowing the b01t to slide V-slot Insertion through without obstruction. This type of nut W The V-slot insertion technique is used with the is described in detail in Reference 2. microfixture and H handle, which interface with the Special Purpose Dextrous Manipulator Handling Fixtures J (SPDM) end effector or the ORU tool When using robotically compatible handling changeout mechanism (OTCM). The OTCM fixtures which apply the slot in the V-groove fits as a V into the grooves of the H handle concept as described above (i.e., the closes its V-shaped grooves around the corners microinterface or X handle), care must be of the microinterface (see reference 2 for a taken that the corners are rounded. This detailed description). The positional precaution must be taken to keep the handle misalignment tolerance allowed for the H from binding to the end effector, as happened fixture is approximately 0.5 inch with angular in t]ie JSC _?obotlcslabora;cories with the firs( ii misalignment tolerance of about +2°. The H handle concept which had sharp corners.

Page DFE-5

U Selection of Rohofically Compatible Fasteners and Handling Mechanisms, Page 5 Technique DFE-I

The corners of the H handle (renamed the X following methods: handle) were rounded, and the binding effect

r was thus eliminated. Use Captive Fasteners Use of captive fasteners is the best method for WITHSTAND LOADS THAT MAY BE simplifying robotics operation. This eliminates IMPARTED BY ROBOTICS" SE._TEMS FOR the need for the robot to carry and insert the FASTENEIL9 AND HANDLING FIXTURES fasteners and thus increases the probability of mission success. SSP 30000, table 3-3, "Factors of Safety," specifies that for metallic flight structures, the Reduce Number of Operations general factor of safety is a yield of 1.25 and an The type of fastener selected can reduce the -2 ultimate of 2.00. number of operations required. For example, using the Zipnut eliminates the need for PRO VIDE ADEQ UA TEA CCESS rotation, since the bolt can be slid through the nut and then tightened with a single rotation. Fasten ers Adequate access for fasteners is provided by Choose Proper Forms of Fastening designing a proper layout of the system as Forms of fastening that require the robot to m described in reference 3. The fastener selection use more than 1 degree of freedom should be (or fastening scheme) can be influenced by the eliminated. Levers, for example, not only will _-7 robotics access if more than 1 degree of increase the access space requirements (as w freedom is required by the robot to engage and described previously), but may also disengage the fastener. A lever, for example, necessitate force moment accommodation and requires more than 1 degree of freedom and more complex control software. w therefore requires significantly more access space to operate than that required to engage a A void Fasteners Requiring Excessive Torque bolt. In addition, the higher the torque value, To engage fasteners that require excessive W the larger the end effector (motor), lessening torque (ie., 50 foot-pounds or over), the robot the allowable robotics access space. For Space must stabilize itself with one arm, constricting

w Station, no levers will be used by robots. the allowable configurations for removing and replacing the ORU. This necessitates Handling FLvtures additional hardware for robot stabilization. In w Certain small Space Station ORU's are being general, care must be taken when using robotic placed so close to each other that inadequate systems for fasteneing due to the reaction access space is provided for the robot to open forces that will be present. its jaws around the interface. The problem was resolved by using the microconical interface Reduce Sizes and T.vpes of Fastener Heads that snaps around the interface in a "stabbing" Using different sizes and types of fastener motion. By using a tool that does not require heads will reduce the number of tools required jaws to open around an interface: i.e, the by the robot. L_2 Z=i microconical tool, the required access space is significantly reduced. Handling Fbctures The grasping of the interface can be simplified a = Simplify the Operation Fasteners by allowing the robot to grasp the interface The robotics operation can be simplified by the fiom a number of different orientations. For

= . Page DFE-6 Selection of Robotically Compatible Fastener_" attd Handling Mechanisms, Page 6 Technique DFE-1

example, the microinterface and the Handling FL,ctures i microconical interface can be grasped from two Alignment and sofldock functions are different orientations of the OTCM relative to described below.

m the handling fixture, while the X handle can I only be grasped from one orientation, There Alignment Functions may be some instances, however, in which it The location of the handling fixture can

would be advisable to limit the allowable significantly impact ORU alignment. The I orientations. For example, if the robot can further the handling fixture is from the ORU's grasp an ORU from only one orientation, there center of gravity, for example, the mote - i is less chance that the ORU will be improperly difficult it is for the robot to maintain a line of I inserted in its base plate. insertion that will be perpendicular to its attachment plate. ASSIST ORU ALIGNMENT AND g SOFTDOCK AND HARDDOCK Other factors to be considered when placing FUNCTIONS handling fixtures are the size of the ORU, the B location and type of alignment guides, and the Fasteners placement of fasteners. These items are When designing robotically compatible ORU's, discussed in Reference 3 because of their i the alignment guides and softdock features may dependence on ORU features. be incorporated as part of the ORU, or fasteners with these features may be designed So.fidock Function l or selected. Sofldock fasteners are thus more Softdock features may be used to prevent an complex and are called "attachment ORU fi'om "floating away" prior to its being m m mechanisms" in the Space Station Program. fastened. This may also be achieved by i I Alignment and sofldock functions are described fastening the ORU without releasing the below. handling fixture. The three above mentioned handling fixtures for Space Station have holes I Alignment Functions in their centers for fasteners, which allows the If alignment features are lacking for the ORU, OTCM to grasp the ORU, insert it, and then

drive the bolt with its nut driver without ever m they can be incorporated via the tapering of m pins, or fingers, located on the housings of the releasing the ORU handle. attachment mechanisms.

Re[erences i Softdock Functions For the Space Station Freedom Program, 1. t?ohoticx System_ htter/'ace Standards, attachment mechanisms achieve sofldock either I ?drone l, Robotics A ccommodation u through the use ofdetents that are housed on Requirements (Draft), SSP 30550. an outer casing of the attachment mechanisms or via the Zipnut method. The Zipnut is 2. Rohotic'x ,S);stems Interlace Standard.', m ramped such that if an attempt is made to }drone 2. Robotics Interface Standards" separate the bolt from the nut, the segments are (Draft), SSP 30550. W pulled together allowing the bolt to be remo\,ed via rotation only. The Zipnut thereby functions 3. 7he [)e.s'i_l Proce.s:sfor AchJevJng as an excellent sofidock attachment. Robotics (;ompatibJlity, Contractor Report u No. .

Page DFE-7 J

R False Alarrn Mitigation Techniques, Page I Technique DFE-2

Technique Minimize the occurrence and effect of Built In Test (BIT) false alarms by applying principles and techniques that are intended to reduce the probability of false alarms and increase the reliability of BIT in avionics and other electronic equipment.

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w Benefits Effectively implementing BIT techniques automatically reduces the number of BIT false alarms. Decreasing the number of BIT false alarms increases a system's availability and decreases the maintenance man- w hours required. The overall result is a reduction of the system's life cycle cost.

Key Words Anomalies, Built-In-Test, False Alarms, Circuit Monitoring

Application International Space Station Program, National Space Transportation _.i Experience System

Technical The reliability of a system's BIT can be determined in part by the Rationale number of false alarms it experiences. If the BIT can not accurately identify and report the occurrence of failures then the test has failed its mission. Testability must be treated with the same level of importance as other design disciplines. BIT reliability must be considered just as critical as any other performance requirement. A system can not perform its mission if its components are constantly being removed for false maintenance.

Contact Center Johnson Space Center

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Page DFE-8 False Alarm Mitigation Techniques, Page 2 Technique DFE-2

m False Alarm Mitigation Techniques the test data reported while only requiring a I Technique DFE-2 single computer or processor.

Continuous Monitoring D In order to mitigate false alarms, a system's Continuous monitoring with BIT filtering can Built In Test (BIT) circuitry must be able to be used in place of the voting scheme. With cope with a limited amount of anomalous this technique, BIT results are based offa I performance. NASA Handbook 5300.4 (1E) integration of successive measurements of a defines a false alarm as "an indicated fault signal over a period of time instead of a single where no fault exists." Based on this definition, check of the signal. The monitoring of the U this technique is concerned only with BIT signal does not have to be continuous but only mu _" _nd]cadons0f system mai_ncdoh-ffhi_'-cause sampled over the time period. -The-fi-lteHng unnecessary maintenance a_ions.The inabiii@ ...... i_olves comparing the current reading of a of a system to detect or report the occurrence signal with past and future readings of the of a failure, a "fails to alarm condition", is not a same signall This filtering aI!ows for the false alarm and is not addressed, disregarding of sporadic out-of-limit measurements. Only when a signal is out-of- BIT should be designed to distinguish between limits for a predefined time limit or a sequence m actual failures and anomalies which must be of tests identify the same failure, should the tolerated due to adverse operating conditions or BIT flag be set.

that are normal anomalies within acceptable D limits. To accomplish this, the following To maximize the effectiveness of continuous

= = principles and techniques must be mandated in monitoring, the BIT data must be recorded. mi m m the system specifications, requirement Once recorded, the data need to be i documents, and design policies and summarized and evaluated so that trends can implemented in the system design. be tracked and weaknesses identified. To help manage all this data, controls should be II Voting Scheme implemented. The number of signals One technique is called the "Voting Scheme." monitored and the maximum sample rate can With the voting scheme, all test data are be limited. The time span over which data are w analyzed by three or more different computers. collected should be set at a reasonable period, A failure is declared only when a majority of the and the type of data accumulated should be computers detect the same failure. An example restricted. Finally, computing techniques can w of this type of architecture is the Space Shuttle be used that do not require the storage of old Orbiter Avionics System. The five General data. Once the information is gathered, a n Purpose Computers (GPCs) are all failure log should be created. interconnected to the same 28 serial data channels. The GPCs perfo_ ai[system-level This failure log is the basis for future i processing and require a majority agreement on modifications to the system's BIT. To improve all test signals. This technique requires an the BIT, every instant of anomalous extensive use of resources but is extremely performance not related to an identified failure effective at mitigating false alarms. A less mode should be analyzed and the root causes complicated version of this is the use of double identified. Some form of corrective action

or triple redundant monitors. Having two or must be taken to avoid recurrence. Ira design D more sensors in series increases the reliability of change cannot be made, then the BIT must be

Page DFE-9

m m False Alarm Mitigation Techniques, Page 3 Technique DFE-2

modified to accommodate the non-failure An excellent technology for combining unit _=_ causing anomaly. level testing with system level testing is boundary scan. Boundary scan is the The need for modification requires BIT to be application of a partitioning scan ring at the flexible. Test parameters and limits must be boundary of integrated circuit (IC) designs to easily changed. The operator should be able to provide controllability and observability access control or even change the test sequence. This via scan operations. In Figure 1, an IC is flexibility allows the necessary changes in the shown with an application logic section, BIT to be made if false alarms start occurring. related input and output, and a boundary scan w For example, the Space Station's Command and path consisting of a series of boundary scan Data Handling System uses programmable cells (BSC), one BSC per IC function pin. Deadman Timers in the multiplexer/ The BSCs are interconnected to form a scan demultiplexer (MDM's) and standard data path between the host IC's Test Data Input processor (SDP's). The response intervals of (TDI) pin and Test Data Output (TDO) pin, the timers can be adjusted by the system for serial access. k=O controller to accommodate changes in system configuration or mode of operation. However, During normal IC operation, input and output L the BIT software must be changed without signals pass freely through each BSC, from the disturbing the system operation. For this to be Normal Data Input (N-DI) to the Normal Data possible, the BIT soi_ware must be independent Output 0qDO). However, when the boundary of the operating software. test mode is entered, the IC's boundary is partitioned in such a way that test stimulus can Decentralized Architecture be shifted in and applied from each BSC Another technique for mitigating false alarms is output (N'DO). The test response can then be the use of a distributed or decentralized BIT captured at each BSC input (NDI) and shifted architecture. With this approach the BIT is out for inspection. Internal testing of the implemented so that a "NO GO" on a given test W application logic is accomplished by applying directly isolates the implied failure to a test stimulus from the input BSCs and replaceable unit. Locating most of the BIT capturing test response at the output BSCs. internal to a unit greatly reduces the possibility External testing of wiring interconnects and of incorrect isolation of a failure. Although the neighboring ICs on a board assembly is decentralized BIT concept consists primarily of accomplished by applying test stimulus from

W unit level tests, some system level testing is still the output BSCs and capturing test response at required. the input BSCs. This application of a scan y

I TDO TDI OUTPUT APPLICATION BSC BSC " _-_ LOGIC

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Figure 1: Built In Test Architecture

Page DFE- 10 False Alarm Mitigation Techniques, Page 4 W Technique DFE-2

path at the boundary of IC designs provides an References I embedded testing capability that can overcome test access problems. The unit level tests can 1. Coppola, Anthony, A Design Guide for l also be combined for a subsystem or system Built-In-Test (BIT), RADC-TR-78-224, April m level verification (Figure 2). More details on 1979. applying these techniques are in IEEE Standards 1149.1 "Boundary Scan" and 1149.5 2. Malcolm, John G., Highland, Richard W., i "System and Maintenance Bus." Analysis of Built-In-Test False Alarm Conditions, RADC-TR-81-220, August 1981. = Finally, high-reliability components should be II used in the design. The reliability of the BIT 3. NASA Handbook 5300.4 (1E), hardware should at least equal or exceed that of Maintainability Program Requirements for m I the hardware it is testing. The BiT software Space Systems, March 10, 1987. also needs to be thoroughly tested and verified to ensure that it will not be a source of false 4. Texas Instruments Inc., TESTABILITE, I alarms. Accordingly, adequate amounts of Test and Emulation Primer, 1989. effort and resources must be allocated during the design phase. The designer should not be I unduly limited by memory size, component count, or any other allocated resource. m ! l I These guidelines are not all inclusive. The false alarm problem is very complex. Each __= lm system is unique and must be approached m differently. The best approach is simply to eliminate each factor as it is identified. m

=== 1

g SYSTEM TEST

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w Analysis -__:_ And w Test

Maintainability analysis is a very important part of the design process in which aspects of the

maintenance concept are quantified and design decisions are made based on results. Hardware and

Software testing not only verifies that the item(s) in question will perform within the specific w environment, but also allows for maintenance items to be identified and verifies maintainability

design features. The techniques containedwithin this section describe a wide range of analysis and

test processes used within the NASA community and should provide a vehicle for education,

communication, and continuous improvement. w

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I Neutral Buoyancy Simulation of On-Orbit Maintenance, Page 1 Technique AT-1

k.a Technique Simulate on-orbit space maintenance activities by using a neutral buoyancy facility to assist in making design decisions that will ensure optimum on-orbit maintainability of space hardware.

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Benefit Neutral buoyancy simulation can provide valuable information for designing-in accessibility, modularity, simplicity, and standardization. It can also provide cost-effective, specific design information on the effectiveness of crew stability aids, crew maneuvering aids, specialized tools, and operational timeliness. Maintainability criteria that can be w established by utilizing this process include: component accessibility; fasteners accessibility, systems installation; and the configuration and operation of crew stability aids and tools.

o , Key Words Neutral Buoyancy Simulation, Maintainability Design Criteria, Space Maintenance Activities, On-Orbit Maintainability, Simulated Weightless Environment, Orbital Maintenance Special Tools, ORU

Application Skylab, Hubble Space Telescope, Space Shuttle Orbiter, International Experience Space Station, Apollo

Technical Equipment and crew interface testing in a simulated weightless Rationale environment at an early development stage in NASA programs is an accurate means of assessing hardware and tool design features and determining crew capabilities and requirements. While other forms of weightlessness simulations (e.g., parabolic flight, motion base, and computer models) have proven effective in specific applications, underwater simulations have proven particularly beneficial in hardware development, crew/hardware interface design, and operations planning, since they can accommodate a large worksite volume and extended test times.

Contact Center Marshall Space Flight Center (MSFC)

.. Page AT-2 Neutral Buoyancy Simulation of On-Orbit Maintenance, Page 2 Technique A T- 1

u Neutral Buoyancy Simulation of On-Orbit T.V. monitors, communications with test Maintenance subjects, audio/video taping capability, Technique A 7'-1 pressure and de, th displays of test subjects, and lightning warning systems.

The neutral buoyancy facility at MSFC has Support of up to four Shuttle space suited mm beenused since 1968to effectlve-ly simulate crew members. mm the weightlessness of space, and has assisted in th-e establishnaentpf rnaint_nabilFty design _ • Umbi!ical'supplied underwater primary IIB criteria, particularly in extravehicular activity life support systems. (EVA). Use of full-scale neutral buoyancy simulations has also allowed for direct • Operational Remote Manipulator Systems m human participation in test operations, as fP.MS). well as for access to the large body mock-up

u hardware _veloped for EVA simulations. • Air-lock for emergency test subject II These methods are a very effective way of evacuation. simulating on-orbit environments for the m purpose of verifying and solidifying =*lae neutral buoyancy tank within the facility D operations :._.d maintenance procedures. is a 1.3 million-gallon water tank that measures 40 ft. deep and 75 ft. in Other neutral buoyancy facilities used for diameter. The water temperature is m NASA hardware development and test and maintained at a range of 88 to 92 degrees crew training are the Weightless Fahrenheit and a pH of 7.50. Cathodic Environment Test Facility (WETF) at protection systems are used to inhibit Johnson Space Center, the Neutral corrosion. The tank accommodates up to Buoyancy Research Facility at-the University four pressure-suited test subjects i of Maryland, College Park, Maryland and the simultaneously. Extravehicular Mobility i neutral buoyancy facility at McDonnell Units are available for four test subjects. Douglas, Huntington Beach, California. The tank can accommodate test durations of Neutral Buoyancy Characteristics up to 6 hours. m The MSFC neutral buoyancy facility has the following overall characteristics: lIST Simulations : Underwater simulations in the neutral m Six-console control room. buoyancy facility strongly influenced the maintainability design criteria for the Hubble i • Three-person, double-lock hyperbaric Space Telescope (I/ST) and its components; chamber. particularly with regard to visibility,

accessibility, and simplicity. Oneofthe m Floating crane for underwater movement primary considerations in maintainability of of hardware (one 2000-pound hoist, one space hardware is the accessibility of

500-pound hoist). components and systems by crew members: I during EVA. To be maintained in space, the • Removable roof section to accommodate components of a hardware item must be seen large hardware. and reached by a pressure-suited astronaut ma or be within range of the appropriate tools.

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II Neutral Buoyancy Simulation of On-Orbit Maintenance, Page 3 Technique AT-1

Altogether, some 70 Orbital Replacement inch double height hex head bolts in three Units (ORUs) on the HST can be replaced types of fittings: J-hooks, captive fasteners, on-orbit. Some of the largest ORUs are and keyhole fasteners. Neutral buoyancy batteries, computers, reaction wheel simulations have proven that the use of assemblies, science instruments, fine standardized bolt heads, clearances, and guidance sensors, and wide field planetary torque limits reduces the complexity of ORU cameras. One of the telephone-booth-sized maintenance in space. To achieve electrical science experiments weighs over 700 connector standardization, neutral buoyancy pounds. These items are mounted in simulation studies have evaluated such equipment bays around the perimeter of the criteria as connector geometry (wing-tab spacecraft. The bays open with large doors presence, length, and diameter) and surface so components can be readily inspected and texture (knurls, ridges, and irregular shapes). handled. Using neutral buoyancy Response variables studied included ease of simulations, design features of these alignment, firmness of grip, and level of components were validated, verified, and torque required to lock the connectors. refined to ensure that the ORU features of Studies of this type led to the development modularity, accessibility, and simplicity were of a standard for blind-mate, scoop-proof, U inherent in the design. Other features low-force, and subminiature connectors. If included a series of crew stability aids; accepted as a standard, these connectors

-= j including handrails, portable handles, tether would be used in the Upper Atmosphere --2 attachments, and foot restraints. Neutral Research Satellite, Explorer Platform, buoyancy simulation studies also determined International Space Station, and in robotic the placement of foot restraints on both the manipulators. HST and the RMS arm for maximum accessibility. These design features give the Human factors studies have been a crew mobility and stability during unstowing, significant part of neutral buoyancy transporting, and stowing ORUs. simulation tests with large space structures. For example, experiments have been Door latch design criteria were also conducted to determine the effect of fatigue addressed in neutral buoyancy simulations on productivity during lengthy EVA involving the HST. All internally stowed structural assembly operations. An ORUs except the Radial Science Instrument experienced test subject assembled a 36 are concealed by doors that must be opened element tetrahedral truss structure repeatedly and closed by a crew member before ORUs for 4 hours, while the subject's heart rate and are installed or removed. general conditions were monitored. These neutral buoyancy simulations demonstrated Simulations and Design Influence EVA productivity to be significantly higher A design criterion that has become in space than in comparable conditions increasingly important in on-orbit simulated in ground tests. Assembly time for maintenance and which has been studied structural assembly tasks was approximately using neutral buoyancy simulation is 20 percent less in actual flight. The standardization of the EVA interface to Experimental Assembly of Structures in ORUs. The practice of standardization EVA (EASE) project, an experiment flown became a key issue in HST development on Space Shuttle mission STS 61-B, with the decision to mount ORUs with 7/16- revealed that a flexible structure can be

r Page AT-4 Neutral Buoyancy Simulation of On-Orbit Maintenance, Page 4 I Technique AT-1

assembledin underwaterconditionswith a m When possible, conduct paper computer U learning curve of 78 percent. It was simulations, and one-g dry run simulations determined that learning rate is independent prior to neutral buoyancy simulations. of the strength, coordination, or size of the I test subject; or the fit of the pressure suit. Principal Limitations The principal limitations of neutral buoyancy Structural configurations have been used at simulations include: (1) the need to design i the MSFC neutral buoyancy simulator to hardware to accommodate the effects of obtain human factors data. In one water corrosion, (2) varying water pressure [] experiment, six-element tetrahedrons were with depth, and (3) frictional resistance of ii used to obtain data on learning and on the the water to body and equipment movement. relative value of a variety of assembly aids. E The structural elements in these tetrahedrons The impact of not taking full advantage of were 11-foot-long tubes of PVC plastic, 4 the neutral buoyancy simulation capabilities inches in diameter. Sleeve-locking at MSFC and other locations could mean B connectors were used to join the beams at entering a space mission without full the nodes of the structure, or "joint cluster." knowledge of the effects of weightlessness

u Much more complex structures were used to on mission tasks, particularly in EVA's. II collect information on fatigue, and on crew Maximum emphasis should be placed on members' ability to deal with complicated conducting simulations with the highest configurations and hardware. A single 3 6- fidelity possible to ensure mission success. 1B element tetrahedral truss served as a baseline Failure to do so results in a greater structure for comparing single-person probability of incurring safety hazards, assembly with two-person assembly, for anomalies, increased maintenance resources II quantifying productivity changes due to the (man-hours), and hardware damage. use of various assembly aids, and for _z evaluating other structural configurations. References lllB

Results of structural assembly experiments Publications that contain additional __= have shown that test subject learning rate is information related to this practice are listed I much higher in the weightless conditions of below: neutral buoyancy than in conditions on dry land. The most time-consuming task during 1. Akin, David L. and Howard, Russell D.: II1 assembly operations is aligning the beams. Neutral Buoyancy Simulation for Space This large time consumption is due to the Telerobotics Operations, In SPIE, m kinematics of water drag. Fatigue is not a Cooperative Intelligence Robotics in Space, significant factorin the assembly process if Vol. II, pp. 414-420, 1991. the subjects pace themselves. None the less, the following considerations must be taken 2. Akin, David L. and Bowden, Mary L.: when running a simulation to avoid "EVA Capabilities for the Assembly of problems: Large Space Structures," IAF-82-393, - Massachusetts Institute of Technology, Assign two safety divers per test subject October 1, 1982. to manage the umbilical and monitor the test subjects performance. 3. Akin, David L." A Design Methodology

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U II Neutral Buoyancy Simulation of On-Orbit Maintenance, Page 5 Technique A 7"-1

for Neutral Buoyancy Simulation of Space 11. Lessons Learned Document from Operations, 88-4628-CP, Massachusetts Neutral Buoyancy Simulation Testing Institute of Technology, September 1988 Activities, MDC H34111, McDonnell ! , Douglas Astronautics Company, Huntington 4. Barnby, Mary E. and Griffin, Thomas J.: Beach, CA, October 1987. Neutral Buoyancy Methodology for Studying 12. Sexton, I.D.: Report for Neutral Satellite Servicing EVA Crewmember Buoyancy Simulations of Transfer Orbit Interfaces, Proceedings of the Human Stage Contingency Extravehicular Activities, Factors Society 33rd Annual Meeting, pp. NASA-TM- 103583, NASA/MSFC, June w 149-153, 1989. 1992.

5. Designing an Observatory for 13. Sexton, J.D.: Test Report for Neutral Maintenance in Orbit: The Hubble Space Buoyancy Simulations of Hubble Space Telescope Experience, NASA/MSFC, April Telescope Maintenance and Refurbishment E 1987. Operations: Simulations of liST w Maintenance and Refurbishment Mission 6. EIA Standard for Connector, Electrical, and New Block H ORU Access Study, Rectangular, Blind-Mate, Scoop-Proof NASA/MSFC, May 1989. = = Low-Force, Subminiature, AN/S/fEIA S- XXX-1991 (drag), American National p_ Standards Institute, Inc., November 18, 1991.

B 7. Griffin, B.N.: Zero-G Simulation Verifies EVA Servicing of Space Station Modules, AIAA-86-2312, AIAA, Space Station in the Twenty-First Century, Reno, Nevada, September 3-5, 1986.

8. Neutral Buoyancy Simulator Test and Checkout Procedures for NBS Test Operations, NBS-TCP-90, NASA/MSFC, =._ April 17, 1992.

9. Sanders, Fred G.: Space Telescope Neutral Buoyancy Simulations - The First Two Years, NASA-TM-82485, NASA/MSFC, June 1982.

2 10. The Design ancl Development of the Hubble Space Telescope Neutral Buoyancy Trainer, Final Report for Contract NAS8-35318, Essex Corporation, December 31, 1990.

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| Mean Time to Repair Prediction, Page 1 Technique AT-2

Technique Predict the mean time to repair (MTTR) of avionics and ground electronics systems at any level of maintenance (on orbit, intermediate or depot level) using analytical methods. This technique assumes a constant failure rate, and should be used accordingly.

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w Benefits The predictions can be used to highlight those areas of a system that

LJ exhibit poor maintainability in order to justify improvement, modification, or a change of design. They also permit the user to make an early assessment of whether the system predicted downtime and logistic requirements are adequate and consistent with the system

w operational requirements and allocations.

w Key Words Maintainability Parameter, Mean Time To Repair (MTTR), Space Prediction, Failure Rate, Maintenance Action

Application International Space Station Program w Experience

Technical This MTTR prediction technique is a fast, simple, accurate and effective Rationale approach for providing a design baseline for repair times. Design and H product assurance engineers can use the MTTR data to effectively define sparing, logistics and maintenance programs for a pending design.

Contact Center Johnson Space Center (JSC)

Page AT-7 Mean Time to Repair Predictions, Page 2 -w Technique A T-2

m Mean Time to Repair Predictions to troubleshoot, remove, repair, and replace a I Technique A T-2 failed system component. An interval estimator for MTTR can be developed from the mean of In general, the MTTR of a system is an estimated the sample data, within a lower and a upper limit I average elapsed time required to perform with a confidence bound. For example, from a corrective maintenance, which consists of fault sample data set, one can find with 90-percent isolation and correction. For analysis purposes, confidence that the range 3.2 to 4.2 will contain I fault correction is divided into disassembly, the population mean. Unfortunately, the exact interchange, reassembly, alignment and checkout MTTR of a system can never be found due to I :tasks. The repatr_ime o-Ta_n-ain_aiffdbl_ti_ ...... dataunce_ainties. generally consists: of both a large number of_ relatively short-time repair periods and a small Log-Nq_rmal D]stn'bution | number of long-time repair periods. The former The distribution most commonly used to would correspond to the more usual case where describe the actual frequencies of occurrence of the failed unit is replaced by a spare at the system repair time is the log normal because it operational site on detection of a failure. The reflects short duration repair-time, a large long downtimes would occur when diagnosis is number of observations closely grouped about difficult or removing a defective part is some modal value, and long repair-time data I complicated due to, for instance, rusted/stripped points. The general shape of log normal mounted nuts. Having a co!lection of such fi_dd distribution is shown in Figure 1. data provides the design engineer an opportunity to assess the Mean Time To Repair (MTTR) of Without getting involved in the derivation of the the current system as it matures, or to predict the distribution equations which can be found in any MTTR of a new system according to its features statistical textbook, the following example will i with the current system. illustrate how MTTR of a replaceable unit may =_ m m MTTR is a useful parameter that should be I used early in planning and designing stages of a system. The parameter is used in assessing the accessibility/locations of system components; iii for example, a component that often fails should be located where it can easily be Frequency removed and replaced. The estimated MTTR may also dictate changes in system designs in order to meet the turn-around time criteria for critical systems, such as communication and life support systems on the Space Station. In addition, the parameter helps in calculating the life cycle cost of a system, which includes cost of the average time technicians spend on a

repair task, or how much Extravehicular w Activity (EVA) time is required for astronauts Timeto Repak (0 to repair a system. Figure 1: Lognorma! Distribution I MTTR is defined as the average time necessary

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g Mean Time to Repair Predictions, Page 3 Technique AT-2

be calculated from a finite observed set of data. How to Implement the MgTR Process Accurately estimating the MTTR of a new Example 1: The repair times t_ for an orbital system is more than applying the derived replaceable unit (ORU) are observed to be 1.3, formulas on field data of any existing systems. 1.5, 1.7, 1.8, 2.2, 2.6, 3.0, 3.1, and 3.9 hours. The designer must know the overall maintenance

r Using log normal distribution to estimate the concept and operating conditions of the new MTTR of the unit. system; for example, how and where the system is going to be operated and how its failed units Solution: will be swapped out. With this background, the designer can proceed to approximate the ti '= in ti (1) maintenance procedure of the new system, then select an existing system that has been exposed w Utilizing statistical methods, the Maximum to similar operating conditions and that has a Likelihood Estimator (MLE), or the best mature set of operating data. After the similarity = = estimated value of the mean is: between the two systems is assessed, the designer then can determine certain conversion (2) factors needed to make the existing system data more applicable to the new system. Once this is done, the predictions for the new system are i Then, t / = 0.79124 more meaningful and accurate.

w The Maximum Likelihood Estimator of the Elements of MTTR variance is: The MTTR prediction of a system begins at the replaceable unit level (RUL) where a defective i s/2_ _1 _ (t/i - t/ / 2 (3) unit is removed and replaced in order to restore n 1_:1 the system to its original condition. Then the F system MTTR predictions are accomplished by Then, s / 2 = 0.1374 integrating the MTTR's of maintainable units. The following defines the elements used in the MTTR prediction of a system:

$/2 (?, -T) _t = MTTR = e Fault Isolation: Time associated with those tasks required to isolate the fault to the item. (4) (0.79124÷ 0.1374) ± e 2 _ w Disassembly: Time associated with gaining Therefore, the mean of the log normal access to the replaceable item or items identified distribution of this example is: during the fault correction process. and its variability of time to repair is: Interchange: Time associated with the removal and replacement of a faulty replaceable item or = MTTR _/(e_'2- 1) suspected faulty item. (s) =2.36 _/(e °'1374- 1) = 0.90 h Reassembly: Time associated with closing up the equipment after interchange is performed. w Page AT-9 Mean Time to Repair Predictions, Page 4 m Technique A T-2

== Alignment: Time associated with aligning the comparable systems and components under t system or replaceable item after a fault has been similar conditions of use and operation. corrected...... m= System Level Prediction i Checkout: Time associated with the verification At the system level, MTTR is calculated by that a fault has been corrected and the system is summing the product of the replaceable items' operational. MTTR's and their corresponding failure rates; the result is then divided into the sum of all Constant failure rates: The rate of failures that replaceable items' failure rates. Mathematically, result l_om strictly random or chance Causes. it can be e_pj_d as: This type of failure occurs predominantly in the llsystem = system

m useful life period of a unit. B n I _ 1 ),iMT K factor: For on-orbit tasks, a conversion factor )u i=1 may be applied to convert elemental task times I performed in 1-g environment to Micro-gravity Where _,i = failure rate of environment. The conversion factor may be to be repair- derived from data of past similar programs or I from the neutral buoyancy testing. (6)

Ground Rules and Assumptions i= 1 J In the prediction, certain ground rules and assumptions apply: and system variance:

• Mean Time To Repair (MTTR.) does not 1 2 n include the maintenance overhead, which is = (-i) x,'-a,' generally non-related task time such as time to i= 1 fill out a requisition, time to go get tools, break- As an example, assume the three OR.Us of a time, time waiting for parts, etc. system have the following MTTR'S, Variance (V), and failure rates (Z,): • Worksite time is the only variable considered. MTTP. V MTTP.*; • All equipment experiences a constant failure ORU 1 4.5 0.5 12.7 57.15 rate. ORU2 2.3 0.7 500.0 1150.00 ORU 3 11.4 0.56 2..2.2 25.08 • All tasks are performed sequentially by one Total: 514.9 1232.23 crew member unless otherwise noted. Apply the above formula to calculate the system • Maintenance is performed in accordance with MTTR: established maintenance procedures and appropriately trained personnel.

• The prediction depends upon the use of recorded reliability and maintainability data and experience that have been obtained from

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and its variance:

(7)

F o 2 _ 1 (0.5x12 system (514.9)2

+ .0 7_><5002 + 0 56x2 The results" o/the above e_/ampl-e indicate that the most otten failed unit will essentially drive the MTTR and variance of a system. w

Overall, the prediction is a straight forward process and is useful in estimating a system's L_ MTTR. Even with a limited set of data, if the prediction is used early in the design phase, the derived value should help in shaping a preliminary w design guideline for the system. In addition, the prediction can also verify logistics and maintainability requirements at some later stage.

References

1. Lamarre, B. G., MathematicalModelling, Reliability and Maintainability &Electronic

w Systems, Edited by: J.E. Arsenault and J.A. Roberts, Computer Science Press, p372 - 373.

2. Miller, Irwin, Probability and Statistics for Engineers, Prentice Hall Inc., Englewood Cliffs, pl16. w

3. MIL-HDBK-338-1 A, Electronic Reliability Design Handbook, Department of Defense.

Page AT- 11 W

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i I Availability Prediction and Analysis, Page I Technique AT-3

Technique Estimate or predict the future availability of a system, function, or unit where availability is defined as the probability that the system, function, or unit will be in an operable state at a random time. Availability may :...; be assessed for a single component, a repairable unit, a replaceable unit, a system of many replaceable units, or a function performed by multiple = systems.

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Benefits Availability prediction and assessment methods can provide quantitative performance measures that may be used in assessing a given design or to compare system alternatives to reduce life cycle costs. This technique increases the probability of mission success by ensuring operational readiness. Analyses based on availability predictions will help assess design options and can lead to definition of maintenance e support concepts that will increase future system availability, anticipate logistics and maintenance resource needs, and provide long term savings in operations and maintenance costs based on optimization of logistics support.

=. = Key Words Availability, Achieved Availability, Inherent Availability, Operational, = = Stochastic Simulation, Maintainability, RMAT, Markov Model

w Application International Space Station Program Experience = :

m Technical Availability estimation is a valuable design aid and assessment tool for Rationale any system whose operating profile allows for repair of failed units or components. These systems include those that operate on earth such as control centers, system test facilities, or flight simulation = . systems/facilities. Applying availability prediction and analysis techniques is also an extremely valuable process for guiding the development of maintenance concepts and requirements.

Contact Center Johnson Space Center (JSC)

wa_

Page AT-12 = Availability Prediction and Analysis, Page 2 m Technique A T-3

Availability Prediction and Analysis calculation does not include such times as Technique ,4 T-3 administrative or logistic delay time, which generally are beyond the control of the designer, and does not include preventive II Availability can be predicted or estimated maintenance time. However, effective trade- m using various methods and measures. offs using the basic times and parameters are Availability is a characteristic of repairable or possible. Trade-off techniques and some m restorable items or systems, and assumes that sample uses are included in Reference 1, Section 5.5.: a failed item can be restoied to operation m m through maintenance,_ec0nIigu_tio_or I reset. It is a function of how often a unit Another measure of availability, achieved fails (reliability) and how fast the unit can be availability or A_, can be expressed as: m g restored after failure (maintainability). A foundation to support both the establishment OT of reliability and maintainability (R&M) l (3) t parameters and trade-offs between these a OT+ TCM+ TP parameters is created by availability prediction and analyses. Availability can be estimated for components, items, or units, where OT is the total time spent in an but overall spacecraft system or ground operating state, TCM is the total corrective ! system availability estimation is based on the maintenance time that does not include III combinations and connectivity of the units before-and-after maintenance checks, supply, within the system that perform the functions, or administrative waiting periods; and TPM m m i.e., the series and redundant operations is the total time spent performing preventive I paths. maintenance. Aa is more specifically directed toward the hardware characteristics than the Availability Measures operational availability measure, which il One basic measure of availability, called considers the operating and logistics policies. inherent availability, is useful during the design process to assess design A third basic measure of availability, g characteristics. The measure involves only operational availability, considers all repair the as-designed reliability and maintainability time: corrective and pi-dveia-tive ma_rttenance characteristics and can be calculated using time, administrative delay time, and logistic u the estimated mean-time-between-failure support time. This is a more realistic (MTBF) and mean-time-to repair (MTTR) definition of availability in terms providing a parameters. The predicted or estimated measure to assess alternative maintenance measure of inherent availability is calculated and logistics support concepts associated _m as: with the operation of a system or fianction. m It is usually defined by the equation:

M'TBF Ai = MTBF + MTTR (1) Uptime _ Upti U (2) Uptime + Downtime Total

! The MTTR time in the inherent availability

I Page AT-13

m l W Availability Prediction and Analysis, Page 3 Technique A 7"-3

where Uptime is the total time a system is in Mean Value Estimation an operable state, and Downtime is the total Mean value estimation of system availability time the system is in an inoperable state. is usually performed by algebraically The sum of Uptime and Downtime, or Total combining component, LRU, and ORU Time, is usually known, specified as a availabilities calculated using equation (1). requisite operating time, or is a given time to When the system is composed of a number perform a critical function. Downtime often of components, LRU's, or ORU's, the failure is broken down into a variety of of any one of which results in the system subcategories such as detection and being down, the system availability is diagnosis time, time waiting for repair parts, calculated from the product of these units' actual unit repair or replacement time, test availability. When the system involves item = . and checkout time, etc. Table 1 shows the redundancy, redundant block availability basic difference between the availability estimates can be calculated using simple measures defined above. Boolean mathematical decomposition procedures similar to reliability block Table 1: Commonly Used Availability diagram solution methods. See Reference 1, Measures Section 10.4.

Availability Function of." Excludes: Measure Computer-Aided Simulation i i i "1.... I Availability prediction using computer-aided i Inherent hardware design ready time, simulation modeling may use either a (A,) preventative stochastic simulation or a Markov model maintenance approach. Stochastic simulation modeling downtime, and administrative uses statistical distributions for the system's downtime reliability, maintainability, and other maintenance and delay time parameters. Achieved hardware design logistics time These distributions are used as mathematical but also includes and

L_ active, administrative models for estimating individual failure and preventative, and downtime restoration times and can include failure w corrective effects and other operational conditions. A rnaintenanee _--i computer program generates random draws downtime from these distributions to simulate when the Operational Product of actual All inclusive system is up and down, maintains tables of t (Ao) operational failures, repairs, failure effects, etc., and environment tracks system or function capability over including ready time, logistics time, time. These data may then be used to = and administrative calculate and output system operational downtime availability estimates using equation (2).

System or Function Availability Estimation Stochastic Simulation Methods w System/function availability estimates may be Discrete event stochastic simulation derived in a limited fashion by algebraically programs are recommended to perform combining mean value estimates of the operational availability predictions and system units, or more rigorously by using analyses for large, repairable systems such as computer-aided simulation methods. the space station or large ground systems and facilities. These methods simulate and

Page AT- 14 m Availability Prediction and Analysis, Page 4 Technique A T-3 monitor the availability status of defined used during a simulation run to dynamically u systems or functions that are composed of a determine queuing priorities based upon collection of Replaceable Units (PUs). The functional criticality and the current level of following process is generally used: remaining redundancy after the simulated failure occurs. l m (i)_ Generate simulated futur_ fa_qUre times m D for each designated RU based on Maintenance is simulated by allocating predicted RU reliability distributions and available maintenance resources and spare m l m parameters. parts to the awaiting maintenance action (or till waiting for resources to become available). (2) Step through simulated operating time, Groups of maintenance actions may also be m and when failure events are encountered, packaged into shiRs of work. If the system evaluate the failure impact or function under consideration is in a space status given the specific failures environment, both external (extravehicular encountered. activity or EVA) or internal (intravehicular I activity or IVA) can be considered. (3) Repair or replace the failed RU using a m maintenance policy and procedure based When the stochastic simulation method is on the availability of required used, each run of the simulation model

maintenance resources, priority or (called an iteration) will yield a single value ! I criticality of the failure, or the current of the availability measure that depends on system or function status. Once an RU is the chance component or unit failures and repaired or replaced, the system or repairs that happened during that iteration. m I function status is reset appropriately, and Therefore, many iterations are required to

a future failure time for the RU is again cover as many potential failure situations as g generated. possible, and to give the analyst a better ! understanding of the variation in the Generation of simulated failures and resulting availability as a function of the maintenance actions for RUs requires as variations in the random failure and repair I input the estimated RU time-to-failure process. The number of iterations required distribution model parameters and factors for accurate availability measure results will that define the frequency of other scheduled depend on the iteration to iteration variation u or unscheduled maintenance. The in the output measure. Experience has maintenance actions can include equipment shown that in system availability simulations failures, preventive maintenance tasks, and with a large iteration-to-iteration variation, environmentally or human-induced failures. 200 to 1000 iterations or more may be required to obtain a statistically accurate To evaluate the effect of a simulated failure estimate of the average system availability. on the function's operational capability at a particular point in time, minimal cut sets of For example, the Reliability and failure events that define the system or Maintainability Asse-: ment Tool (RMAT) is m function failure conditions can be used. a stochastic computer-aided simulation Minimal cut sets of failure events can be method like that described that has been used B generated from reliability block diagrams or at Johnson Space Center for assessing the fault tree analysis of the functions, and then maintainability and availability characteristics

m I Page AT- 15

I Availability Prediction and Analysis, Page 5 Technique A 7"-3

of the Space Station. The output of the cycle costs, availability prediction and RMAT includes the percent of total (or analysis are critical to understanding the specified mission) time each defined space impact of insufficiently defined maintenance station function spends in a "down" state as resources (personnel, spare parts, test well as the percent of time each defined equipment, facilities, etc.), and maintenance function is one failure away from functional concepts on overall system operational outage (is zero failure tolerant). Using availability and mission success probabilities. RMAT, analysts at J'SC have been able to These analyses can therefore greatly reduce perform trade studies that quantify the the life cycle costs associated with deploying differences between alternative Space Station and supporting a space or ground system. configurations in terms of their respective operational availability and maintainability References measure estimates. 1. MIL-HDBK-338; Electronic Reliability The same simulation methods (such as Design Handbook, Reliability Analysis RMAT) that provide for operational Center, Rome, NY, 1989. availability measures will also provide i maintenance resource usage measures such 2. O'Connor, J.T.; PracticalReliability as maintenance manpower needs and spare Engineering, John Wiley & Sons Ltd., part requirements. With this capability, JSC Chichester, 1991. has been able to estimate the maintenance manpower needs, including EVA

_-.-- requirements, of various Space Station alternative configurations.

Markov Model Approach A Markov process, or state-space analysis is a mathematical tool particularly well suited to computer simulation of the availability of w complex systems when the necessary assumptions are valid. This analysis

w technique also is well adapted to use in conjunction with Fault Tree Analysis or Reliability Block Diagram Analysis (RBDA). w Examples of the use of Markov process analysis may be found in Reference 1 or in such standard reliability textbooks as Reference 2.

Failure to use availability predictions and analysis during the design process may lead to costly sub-optimization of the as-designed system reliability and maintainability characteristics. Where operations and support costs are a major portion of the life

Page AT- 16 m

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U Availability, Cost, and Resource Allocation (ACARA) Model to Support Maintenance Requirements, Page 1 Technique A 1"-4

Technique Employ statistical Monte Carlo methods to analyze availability, life cycle cost (LCC), and resource scheduling by using the Availability Cost and Resource Allocation (ACARA) program, which is a soPtware tool developed at Lewis Research Center

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U Benefits The ACARA program is an inexpensive tool for conducting maintainability, reliability and availability simulations to assess a system's maintenance requirements over a prescribed time interval k.d Also, availability parameters such as equivalent availability, state availability (percentage of time at a particular output state capability), and number of state occurrences can be computed.

Key Words Maintainability Modelling, Availability, Computer Simulation

Application International Space Station Program, LeRC Micro-gravity Experiments Experience

= Technical The development of the Space Station and other space systems (i.e., Rationale Space Station payloads and experiments) requiring long-term maintenance support dictates maintenance planning with emphasis on an understanding of the level of support required over a given period of time. The program is written specifically for analyzing availability, LCC, and resource scheduling A combination of exponential and Weibull probability distribution functions are used to model component failures, and ACARA schedules component replacement to achieve optimum system performance. The scheduling will comply with any constraints on component production, resupply vehicle capacity, on-site spares, crew manpower and equipment.

Contact Center Lewis Research Center (LeRC)

_ Page AT- 17 Availabilite, Cost, and Resource Allocation (ACARA) Model to Support Maintenance Requirements, Page 2 I Technique A 1"-4

m Availability, Cost, and Resource Allocation • Frequency of failure and repair. I (A CARA) Model to Support Maintenance Requirements • Lifecycle cost, including hardware, Technique A T-4 transportation, and maintenance. I

The ACARA program models systems • Usage of available resources, including represented by reliability block diagrams maintenance man-hours. I comprising series, parallel, and M-of-N parallel redundan_ blocks. A hierarchical ACARA Inputs - =_ =:_ | description of the system is needed to A RBD must be prepared for ACARA to identify the subsystems and blocks contained simulate a system's availability. The RBD in the system. Given a reliability block depicts a system, and the arrangement of the diagram (RBD) representation of a system, blocks depicts a performed function. the program simulates the behavior of the system over a specified period &time using RBD does not necessarily depict physical • g Monte Carlo techniques to generate block connections in the actual system, but rather failure and repair intervals as a function of shows the role of each block in contributing exponential and/or Weibull distributions. to the system's function. The blocks are [] ACARA interprets the results of a simulation sequentially numbered as B 1, B2, B3, etc. and displays tables and charts for the and subsystems are numbered as S 1, $2, etc, following: =_ which are defined from the inside out. | Figure 1 shows an example of a system with • Performance, i.e., availability and its corresponding blocks and subsystems. reliability of capacity states Beginning with the innermost set of blocks, II each parallel or series set of blocks is

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Page AT- 18

B Availability, Cost, and Resource Allocation (ACARA) Model to Support Maintenance Requirements, Page 3 Technique A T-4

partitioned into a subsystem which in turn parameter is equal to the Mean Time may combined with other blocks or Between Failure (MTBF). subsystems. Wearout failure is also modeled by the The system shown in Figure 1 contains 6 Weibull function. The shape factor must be subsystems: 1 or more. If the block with an initial age (i.e., it is not brand new) is installed, its Subsystems 1 and 2 are both variable M- initial age is subtracted from its first time-to- of-N parallel arrangement of batteries. failure due to wearout. Likewise, if it These subsystems respectively contain undergoes a failure-free period, this period is Blocks 6 through 8 and Blocks 9 through added to its first time-to-failure. 11. m ACARA generates time-to-failure events • Subsystem 3 consists of Subsystems 1 and using one or a combination of these models 2 in parallel. and assigns the minimum resulting time for w each block as its next failure event. The Subsystem 4 is a binary M-of-N parallel early failure model is canceled by assigning arrangement of diodes, Blocks 3 through to the block type an early failure probability w 5. of zero; random failure, by an excessively large MTBF; and wearout failure, by an • Subsystem 5 is a parallel arrangement of excessively large mean life. w two turbines, Blocks 1 and 13. ACARA also simulates redundant pairs of

w Subsystem 6 comprises the entire system active and standby blocks. A standby block and is a series arrangement of Subsystems is installed as dormant and its time-to-failure 3 through 5 and Blocks 2 and 12. is initially modelled by random failure, in = = which the MTBF is multiplied by its Modeling Time-to- Failure characteristic "Dormant MTBF Factor." The ACARA program uses the Weibull Then, the corresponding active time-to- distribution function to model the time-to- failure is modelled by early, random, and failure for the system. The shape and scale wearout failure until the active block is factors are adjusted to modify the form of replaced. the distribution. Uniform random numbers from 0 to 1 are generated and substituted for Modeling Down Time the reliability, R. ACARA uses the early The downtime for a failed block depends in failure(i.e., infant mortality), random failure, part upon the availability of spares and and wearout failure (life-limiting failure) resources. These spares may be local spares, models. These models are adjusted by user- i.e., initially located at the site. Ifa local defined parameters to approximate the spare is available when the block fails, the failure characteristics of each block. block is immediately replaced and downtime will depend only on the mean-time-to-repair w Random failure is modelled by the (MTTR). If no local spares are available, Weibull distribution function where the ACARA will schedule a replacement shape factor is equal to 1 (equivalent to the according to the schedule production exponential distribution) and the scale quantities for that block type, the constraints

Page AT- 19

r • Availability, Cost, and Resource Allocation (ACARA) Model to Support Maintenance Requirements, Page 4 Technique A 7"-4

on mass, volume, and delay associated with mE the manifesting and loading spares to the resupply vehicle. ACARA also checks the constraints on the maintenance agents to determine when the block can be replaced.

Once all the above conditions are met to U allow the block to be replaced, ACARA then estimates the time required to replace it. The [] il time-to-repair depends upon the MTTR's for that block type. MTTR's may be specified for up to three separate maintenance agents. II Examples of maintenance agents are crew, equipment, and robotics. ACARA assumes

that the maintenance actions occur m i simultaneously, so that the block's repair time is determined by the maintenance agent m ! having the maximum MTTR. During the II simulation, the time-to-repair may either be set equal to the maximum defined MTTR or to be determined stochastically. Refer to i Reference 1 for a complete guide on the use

of ACARA and the explanation for entering m data and the output of graphs and [] information. ACARA may be obtained from the Computer Software Management and Information Center (COSMIC) at the I University of Georgia, (706) 542-3265.

References i

1. Stalnaker, Dale K., ACARA User's Manual, NASA-TM- 103751, February 1991.

m 2. Hines, W.W. and Montgomery, D.C., Probability and Statistics m Engineering

and Management Science, 2nd Ed., John w Wiley & Sons, 1980

M Page AT-20

U w Rocket Engine Failure Detection Using an Average Signal Power Technique, Page 1 Technique A 7"-5

Technique Apply a univariate failure prediction algorithm using a signal processing technique to rocket engine test firing data to provide an early failure indication. The predictive maintenance technique involves tracking the variations in the average signal power over time.

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Benefits This technique will therefore reduce unnecessary failures attributed to the traditionally used redline-based system. The average signal power algorithm can be used with engine test firing data to provide significantly earlier failure indication times than the present method of using redline limits. Limit monitoring techniques are not capable of detecting certain modes of failures with sufficient warning to avoid major hardware and facility damage.

_:_

Key Words Rocket Engines, Failure Detection, Detectability

Application Space Transportation System (STS) Experience

Technical Detection of anomalous behavior is critical during the operation of the Rationale E , Space Shuttle Main Engine (SSME). Increasing the detectability of L_ failures during the steady-state operation of the SSME will minimize the likelihood of costly engine damage and maintenance. The average power signal algorithm is superior to the time series algorithm because more parameters contribute to the first simultaneous failure indication times. This increases the agreement between several parameters, thus increasing the likelihood that an engine anomaly has occurred. This method also reduces the number of false failure indications that can prematurely shut down the engine during testing or operation.

Contact Center Lewis Research Center (LeRC)

Page AT-21 w Rocket Engine Failure Detection Using an Average Signal Power Technique, Page 2 Technique A T-5

m Rocket Engine Failure Detection using An average signal power calculations are [] Average Signal Power Technique performed over 2-second, 50-percent

Technique A T-5 overlapping window for nominal test firings m

at both 104- and a 109-percent-rated power I levels. A smaller time increment must be For discrete random processes, probabilistic used to improve the failure detection functions are-used to describe the behavirr capability of the algorithm. g of the rocket engine system. The Power Spectral Density _SD)is computed to The average plUs three standard deviations describe how the variation of the random of/he average signal poWer _e computed process is distributed with frequency. For for all the nominal firings at both engine m stationary=si_ais,- t_e Pg-D is bandi|_nqied to power ievels._ Tiaese Values are combinedto I ±l/(2T), where T is the sampling interval in calculate the thresholds (see Reference 1). seconds. A safety factor ranging from 1.5 to 3.5 is U Average Signal Power Calculations needed to ensure no false failure indications The PSD is defined as the discrete-time are computed for the nominal firings. The Fourier transform of an autocorrelation range of safety factors reflected signal function. (The derivation &the behavior variations that occurred over seven autocorrelation function is shown in nominal A2 firings. When used in the failure

Reference 1.) When the autocorrelation detection mode, failure &the average signal I function is evaluated at zero lag, then an power of a parameter to fall outside its expression for the average signal power threshold results in a failure indication. Also i (ASP) of a random stationary process shown in Table 1 are the thresholds results: calculated from the SSME nominal test firings based on the average signal power +__1 J 2T algorithm along with the associated safety I factors. P = r I0] = f (1) 1 Table 1: Signal Threshold and Safety m 2T Factor for SSME's Average Power P=(f) = discrete- time Parameter Threshold Safety Fourier transfor Factor r=[0] = reverse discret Mixture Ratio 0.00112 1.5 Fourier transfor MCC Coolant Discharge 200 1.5 w MCC Hot Gas Injector Pressure 125 1.5 The average signal power for several SSME para_ _ters is determined by calculating the LPOP Shaft Speed 1598 2.5 J autoc _ elation at zero lag for the LPFP Discharge Pressure 2509 1.5 parak ers provided in Table 1. The assu_, _ion is made that the signal is IqPFP Discharge Pressure 436 1.5 stationary over the computation interval. The Fuel PreburnerChamber Pressure 232 1.5

m Page AT-22

I Rocket Engine Failure Detection Using an Average Signal Power Technique, Page 3 Technique AT-5

one nominal firing were tested using the w PBP Discharge Pressure 911 1.5 thresholds shown in Table 2. An example of HPOP Discharge Pressure 268 1.5 the application of the average signal power w PBP Discharge Temperature 0.04 3.0 algorithm to a SSME anomalous test firing is shown in Figures 1 and 2. Figure 1 MCC Pressure 47 1.5 illustrates the interval over which the average HPFP Inlet Pressure 4 1.5 signal power was computed for a single parameter, HPFP discharge pressure and one HPOP Inlet Pressure 6 1.5 test firing. Figure 2 displays the resulting HPFT Discharge Temperature A 32 2.0 average signal power, as a function of time. As shown, the threshold for the average HPFT Discharge Temperature B 38 2.5 signal power algorithm has been exceeded. I-IPOT Discharge Temperature A 154 3.5

I-IPOT Discharge Temperature B 104 3.5 w I-IPFP Shat_ Speed 550000 3.5

Algorithm Implementation w A system identification and signal processing software package on a RISC workstation provides the average signal power algorithm. Command and Data Simulator (CADS) data from a predetermined number of SSME test firings are used to establish the failure

indication thresholds. 7000 m

G_0 b Several system conditions must be Gg00 i!l considered to ensure that the algorithm does not erroneously indicate an engine fault. 68OO I l a_ W These conditions include sensor failure, I_ !I$1_IIIIIIII_IIIIIIIIRIII propellant tank venting and pressurization, GT_ and propellant transfer. Sensor failure IIIlUlUlIIIIItlll IIIIIllllJlJl IJ! _ $700 : t detection techniques must be exercised I before, or concurrently, with safety , I I I I I l I I monitoring algorithms in order to eliminate w the possibility of a sensor failure being TI_. sic interpreted as an engine problem. Typically, all parameters exhibiting sensor problems are removed prior to the application of the algorithm.

w Failure indication thresholds are established by applying the average signal power m Figure 1: Application of the Average Signal algorithm to a set number of nominal tests. Power Algorithm to the HPFP Discharge For the SSME four anomalous firings and Pressure

Page AT-23 Rocket Engine Failure Detection Using an Average Signal Power Technique, Page 4 I Technique A 7"-5

25OO ...... FAILIII[ I INDIr..ATIGII

_._,,..,,.'_-,_,_.,_,_,_,,_.-i. I o 50 Ioo I._ 2oo zso _ j_ = • m TI_. u¢ I

Figure 2: Average Signal Power for that M Interval with the Failure Indication Threshold i

m Nomenclature: m HPFP high pressure fuel pump HPFT high pressure fuel turbine HPFTP high pressure fuel turbopump HPOP high pressure oxidizer pump H:POT high pressure oxidizer turbine LPFP low pressure fuel pump B MCC main combustion chamber

PID " p-_ameter identification := H I SSME space shuttle main engine

Reference

Meyer, C.M., Zakrajsek, J.F., Rocket Engine =F_lure Detection Using System Identification Techniques, AIAA Paper 90,!993. July 1990.

Page AT-24

m g w

caw Operations And Operational w Design Considerations 7m,_

This section provides a rich source of ideas to any organization that is involved in either spaceflight

operations or design to support those operations. The techniques reflect actual spaceflight

operations experience and related field experience that can be used to achieve continuous

improvement. They can provide a mechanism for feearback from operators of flight hardware to

system designers to make the systems easier, safer, and less costly to operate. Also, they provide

=:= = = the design engineer with valuable information on the latest technology advances in the operations

environment. These techniques also can serve as a communications tool for operations personnel,

Iwl allowing for transfer of knowledge and enhancement of professional development. The techniques

contained herein are the most up-to-date NASA operational processes, process improvements, and

feedback to design engineers, all of which are dedicated to making NASA systems as maintainable

and cost efficient as possible.

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g w SRB Refurbishment Practices, Page 1 Technique OPS-1

Technique Engage in refurbishment activities to rebuild and prepare for reuse of the Solid Rocket Boosters (SRB's) after each Space Shuttle Orbiter launch. These refurbishment activities include: (1) inspection, (2) reworking of anomalies to specification, (3) material review board (MRB) acceptance or scrapping, (4) cleaning, (5) corrosion protection and prevention, (6) scheduled part replacement, (7) test and checkout, and (8) preparation for storage or return to flight buildup. t L-I

LJL__ w

Benefits

Key Words Refurbishment, Maintainability Design Criteria, Salt Water Protection, Galvanic Corrosion, Sealant, Electronic Component Vibration Testing

w Application Space Shuttle Solid Rocket Booster (SRB), Space Shuttle Solid Rocket Experience Motor (SRM). w

Technical Through the past decade of maintaining the SRB by refurbishing the Rationale structures and components; MSFC and its contractors have developed and implemented successful refurbishment specifications and procedures that have proven their effectiveness. For example, failure to adhere to the proven practice of refurbishing recovered hardware from salt water impact can result in unacceptable performance, scrapping of otherwise L usable hardware, expenditure of unnecessary resources, and possible schedule delays.

Contact Center Marshall Space Flight Center (MSFC)

Page OPS-2 SRB Refurbishment Practices, Page 2 m Technique OPS-I

SRB Refurbishment Practices Table 1. SRB Maintainability Factors I Technique OPS-1 . Accessibility 2. Commonality of Fasteners Solid Rocket Booster (SRB) Refurbishment I 3. Electrical Subsystem Installation and encompasses the activities required to return Removal the reusable SRB component to a 4. Thrust Vector Control (TVC) Subsystem I flightworthy condition after SRB ignition, Installation and Removal l_off, and flight; separation from the . Ordnance Installation and Removal 6. external tank; descent (free fall and Markings and Color Coding l 7. Unitization of Subsystems Ii parachute); ocean impact; and retrieval. 8. lrreversibility of Connectors When the decision was made to recover and 9. Tool and Equipment Design reuse the SRB hardware, a design team was 10. Spares Provisioning g organized to formulate the maintainability

criteria for a reus_le booster__The S_K!3_...... t Flow Chart forMaintainability is shown in l Figure 1. The maintainability design team

produced the Solid Rocket Booster Design Process Condderations . i m Maintainab_ilty-Design (_ritei'ia-Document I, ...... Table2Ti]-st-s_]calm_intenanee a_ions that i a document that was used by designers as were considered during the design process. .. they conceived each design feature, The SRB was designed t° withstan__d launch, m performed the necessary tradeoffs of the water impact, and towback environments,- B design parameters, and made other design incorporating the capability of I 0 flights for and product engineering decisions. The the parachutes; 20 flights for design team included maintainability as a electrical/electronic components, Thrust I design goal and incorporated the desired Vector Control (TVC) components, and maintainability features into components of SRM components; and 40 flights for the the end item throughout the design process. structures. SRB structures are typically I Maintainability factors that were considered welded and/or mechanically fastened during the design of the SRB are shown in aluminum except for the external tank attach Table 1. ring, which is mechanically fastened steel. I

Recover Maintainability for and/or Test Dccisionand Reuseto _ DesignEstalishCriteria _ DesignPease ___ ManufactmeAssembly

I (_atio_ Preflight and Rcgovct aad Storage Refurbish Launch

Figure 1. S_ Flow Chart for Maintainability ......

Page OPS-3 SRB Refurbishment Practices, Page 3 Technique OPS-1

Table 2. Maintenance Actions to some components of the TVC system.

1. Inspection 2. The aft skirts of the first few SRB'S 2. Troubleshooting w experienced water impact damage. The 3. Calibration and Adjustment corrective action included the addition of 4. Repair gusset reinforcements to the structural rings. Foam was sprayed on the interior of the aft All aluminum structural assemblies are first skirt to protect the reinforcement rings and painted and then coated with an ablative the TVC components. Impact force with the insulation. The SRM segments are forged water was reduced by increasing the D6AC steel. All structural components are diameter of the main parachutes from 115 z L_ cleaned and/or alodined as appropriate, feet to 136 feet. The larger parachutes w before being primed and top coated with decreased the SRB's water impact velocity paint. The mechanically fastened aluminum from 88 ft/sec to 75.5 _sec (60 mph to 51.5 and steel structural cgmponents are designed mph, respectively). w to be protected from salt water intrusion by applying sealant between adjoining surfaces, 3. During initial teardown and inspection, installing the fasteners with sealant, torquing water and corrosion were found between the w the fasteners, and applying a fillet of sealant mating surfaces of structural members. To along the edge of brackets where they join correct this problem, the sealant application the main structure. The electronic/electrical specifications were modified to require the W components exposed to salt water are sealed, sealant to be applied to both surfaces before and the external surfaces &these joining. components are painted. The TVC hydraulic system is a closed-loop system that does not 4. To eliminate potential water entry into permit the intrusion of sea water. The SRM the forward skirt, the following areas were segments' external surfaces are protected modified or redesigned: with an epoxy paint finish, and the internal surfaces are protected by the propellant a. The aft seal on the forward skirt was w insulator that is bonded to the inside surfaces changed from a rectangular to a "D" of the SRM segments. Areas not protected configuration to allow better contact with paint or bonded-on insulation are between the forward skirt and the forward = : protected with a water-repellent grease. dome of the SRM.

LJ Specific Improvements b. A fillet of sealant was added between B_ Typical areas of the SRB that have been the access door and the surrounding redesigned or modified as a result of trouble structure after final close-out of the r-- areas found during recovery and forward skirt. refurbishment are discussed below: c. Sealant was added to the mating 1. Galvanic corrosion occurred in the aft surfaces and the installation bolts of the skirt of the first few SRB's recovered. To separation nut housing for the main prevent this from recurring the design team parachute attach fittings. added a zinc coating to selected metal components, and bolted anodes (Zinc bars) 5. The following practices improved

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W SRB Refurbishment Practices, Page 4 g Technique OPS-1

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z SRB Flight Configuration U maintainability, parachute deployment, and were being returned to the vendor for parachute inflation: refurbishment. After refurbishment, acceptance test procedures (ATP) were a. To avoid abrasive damage that performed, including vibration and thermal occurred during main parachute testing. The vibration level of these tests 11111 deployment, foam and ablative material caused the remaining life of the component were added to portions &the frustum to be reduced. To prevent the excessive and the main parachute support structure. expenditure of components' lifetime (except for the range safety system components) b. To avoid damage to the parachutes vibration and thermal testing has been during deployment, the parachutes are eliminated during normal turnaround. now packed in a circular pattern rather The constant improvement of electronic than the previous zig-zag pattern. parts by the manufacturer presents a unique problem to the SRB refurbishment effort c. The opening at the top of the main because the improved parts are often not parachute canopy was decreased in interchangeable with their predecessors. diameter to allow quicker inflation of the A sufficient quantity of spare parts must be parachute. procured to meet logistics requirements until the components are redesigned to use the 6. After every flight electronic components improved parts.

Page OPS-5 OI QIN,JJ.., is oF I :)On,"QU ITY

N w SRB Refurbishment Practices, Page 5 Technique OPS-1

Typical Refurbishment Procedures Table 3. Typical Structure Refurbishment Figure 2 depicts the SRB flight Flow configuration. After approximately 125 seconds into the Shuttle flight, the SRB'S 1. Tow SRB from water impact area to dock 2. Remove SRB from ocean, Rinse with potable are jettisoned from the external tank. During water. reentry, the nose cap is jettisoned (it is not 3. Place SRB on transporter. recovered), deploying the drogue parachute. 4. Safe SRB Ordnance and Hydrazine Systems. After the SRB is stabilized in a vertical 5. Assessment Team Inspection position, the frustum is jettisoned and 6. Wash SRB with detergent solution and rinse. descends into the ocean. Its descent is held 7. Remove aft skirt assembly. 8. TVC refurbishment facility. to a safe velocity by the drogue parachute. 9. Remove TVC Components. In the meantime, the jettisoning of the 10. Disassembly area: remove components. frustum deploys the three main parachutes, 11. Critical dimension check. lowering the remaining portion of the SRB 12. Thermal protection system removal, robotic into the ocean. Once in the ocean, the hydrolaser. 13. Inspect, Visual and NDE (XRAY and parachutes (which are jettisoned at water Ultrasonics). impact) and the frustum are removed by the 14. Rework, Touch-up paint (repaint everyftfth

recovery team and positioned onto the use.) recovery vessel. A plug is inserted into the 15. Inspect and identify. SRM nozzle throat and the SRB is 16. Preflight storage. dewatered. Removal of the water from the SRB allows the SRB to be positioned from a vertical position to a horizontal position. The SRB is then towed to the disassembly routed to the refurbishment area where a area dock. prepared refurbishment procedure document is attached to the part. The part is reworked At dockside, the SRB is lifted from the water to conform to the Refurbishment and placed on dollies. The SRB Engineering Specification. This specification pyrotechnics are disarmed, the TVC fuel lists the requirements for refurbishing each vam_ system is depressurized, and an assessment component to flightworthy condition before team inspects and documents anomalies that it is returned to storage. may have occurred during flight. Then the The SRM segments are disassembled in the SRB is washed with a detergent solution in a disassembly facility at dockside, placed on semiautomated wash facility. The aft skirt is rail cars, and transported to the SRM removed and routed to the TVC disassembly contractor located in Utah. At the facility. Table 3 lists a typical flow sequence contractor's plant, the segments are off- for major structure refurbishment. After the loaded and routed to refurbishment areas. aft skirt is removed, the remainder of the All segments that are to be reused must SRB is routed to the disassembly facility. meet the requirements of specification

LI STW7-27443. If segment dimensions fall As the SRB components are removed, they outside the acceptable requirements of this are identified by attaching a metal tag with specification, an individual analysis is their part number and dispositioned per the required to determine the effect on the Predisposition List for SRB Flight structural and sealing capability before Hardware 2 . The SRB component is then reusability is determined. All documented

• .. .- z :

Page OPS-6 SRB Refurbishment Practices, Page 6 Technique OPS-1

on the SRB Excluding the SRM,, g Table4. Types of Hardware That Have 10A00526, NASA/Marshall Space Flight Been Successfully Refurbished Center, AL.

1. Major Structures (Frustrum, Forward Skirt, m

Aft Skirt, External Tank Attach (ETA) Ring, . NASA/MSFC: Sealing of Fasteners Solid Rocket Motor (SRM) Segments, etc. Subject to Sea Water Exposure on the 2. Electronic Components: Integrated Electronic SRB Excluding the SRM, 10A00527, J Assembly (lEA), Integrated receiver Decoder (1RD), etc. NASA/Marshall Space Flight Center, AL. 3. Electrical Cables. I 4. TVC Components Auxiliary Power Unit . NAS_SFC: Protective Finishes for (APU), Hydraulic Pump, Hydraulic Reservoir, Aluminum and Steel Alloys Subject to Fuel Service Module (FSM), etc. Seawater Exposure on the SRB Excluding g the SRM, 10A00528, NASA/Marshall Space Flight Center, AL. nonconformances are reviewed to determine I if the condition of the hardware has changed. 7. NASA/MSFC: Solid Rocket Booster The most critical areas to be reviewed are Flight Hardware Ground Operations case membrane thickness, vent port and leak Plan, SE-019-040-2H, NASA/MarshaU D port threaded areas and sealing surfaces, and Space Flight Center, AL. aft segment stiffener stubs. No surface defects (corrosion, pitting, scratches, 8. NASA/MSFC: Solid Rocket Booster m noncrack-like flaws, etc.) deeper than 0.010 Flight Hardware Refurbishment inch are permitted. All segments are Requirements, SE-019-050-2H, m hydrotested to 1.125 times the Maximum NASA/Marshall Space Flight Center, AL, • III Expected Operating Pressure and magnetic- Systems Analysis and Integration. particle inspected. 9. Thiokol: Space Shuttle SRM,, i References Requirements and Acceptance for Refurbishment Nozzle Metal Components, 1. NASA/MSFC: Soild Rocket Booster STW7-2863, Thiokol Corporation, Maintainability Design Criteria Space Operations, Brigham City, Utah.

Document, SE-019-022-21-1, ...... l NASA/Marshall Space Flight Center, AL. 10. Thiokol: Space Shuttle SRM,, Process Finalization Requirements for Nozzle 2. USBI: Predisposition List for SRB MetalHardware, STW7-3450, Thiokol J Flight Hardware, 10PLN-0027, USBI, Corporation, Space Operations, Brigham United Technologies, Huntsville, AL. City, Utah.

3. Thiokol: Space Shuttle SRM 11. Thiokol: Space Shuttle SRM,, Refurbished Case Acceptance Criteria, Acceptance Criteria, New and Modified

STW7-2744, Thiokol Corporation, Space Case, STW7-3489, Thiokol Corporation, w Operations, Brigham City, Utah. Space Operations, Brigham City, Utah.

4. NASA/MSFC: Sealing of Faying 12. Thiokol: Space Shuttle SRM,, W Surfaces Subject to Sea Water Exposure Acceptance Criteria for Refurbished

l Page OPS-7

g SRB Refurbishment Practices, Page 7 Technique OPS-1

Igniter Chambers and Igniter Adapter, STW7-3861, Thiokol Corporation, Space Operations, Brigham City, Utah.

= •

13, Thiokol: Refurbishment and Acceptance Criteria for Redesigned Barrier-Booster Assembly, STW7-3888, Thiokol Corporation, Space Operations, Brigham City, Utah.

14. Thiokol: Manufacturing Plan for Space Shuttle Redesigned Solid Rocket Motor w (RSRM) Project, TWP,- 10341 (CD), Prepared for NASA by Thiokol Corporation. Brigham City, Utah. w

15. USBI: 10MNL-0028, Solid Rocket Booster Pictorial Representations Handbook, USBI, United Technologies, Huntsville, AL.

w 16. USBI: FrustumAft Skirt Disassembly Requirements, 10REG-0032, USBI, United Technologies, Huntsville, AL. w

17. USBI: Refurbishment Engineering Specifications For Space Shuttle Solid Rocket Booster Assembly Project, 10SPC-0131, USBI, United Technologies, Huntsville, AL.

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qm Electrical Connector Protection, Page 1 Technique OPS-2

Technique Protect the receptacles/plug ends of demated electrical connections with covers provided by manufacturer or with generic plastic caps or if covers are unavailable, leave in downward facing position.

[_i_ii i?."!?:.:ii?.'i!ii ii i:i_.i_iiiii!i_iiiiiiii_ ?.i._iiii i:iiiii_ i:iii _:i_:ii:ii_:i:i:i££:_£i>)i:_:i£_:i:ti:i:i:i:::i_£'£::[i_:i:i_:i£:!:i:!:i:!:ii::::::::::::::::::::::::::::::::::::::::::::::::::::: :i::::: ::::::::i:i: :i::£.<: :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: iliiiiiili!ii/i_iii_ii_ii!i!iii!ili!i_ilil/_/i/ii/fiii ::::::::::::::::::::::::::::::::::::::::::::::::::::.] :_::_ _: _ : ::_::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: : £ :::::::::::::::::::::::::::::::::::::::::::::::::::::::

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: : .5:?.._::..5:_: :::'i".'.".'(' : : ,'," : ::_: :::_£i:'_: : :>.:::::>.;::;.<')_::: :?: : >.::::':':'

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:::::::::::::::::::::::: :,:-:::.:-.,_i:+ :_..:.:.:.:.:.: + :.:, I iiiii_ii_i_i_i_i_i_i_i_i_i_i_i_i_ii_i_i_i_!i_i_is::_i_iiii_::_,`_`_i_i_ii_ii_iii_i_;_`:_i_i_:_iiliIilIillliilii!i?:i.liiiiiiii!ii!iI!l!liiilliillililii?:iiiiii?:_!!_i,:!ilii

[! _.f_!_.':_!_ ::i_.:!ii:!:-1,':!:_:_.!:::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

lilil!lllililiili;iliiiiiiiliii!iii_i _:_I1_iiii_i_ii/_.i/.)_ili..-.'._>_i!i:ifi!-i:il-i! ii_I" .>'_i:::::: i:_.:_..)._i:_:_:_i__£_._ i_!__ i_:!ii:ii!_?..i_:!:::::::::::::::::::::::::::: _: ======::_;:._:_ .,.'::::::i.:_: .::::: !

_:::_::_::_`_.:======

w Benefits Moisture collects in the bag when the double-bag-and-seal method is used. This can lead to corrosion of the connector or possible electrical shock when the connector is reused• The use of plastic caps or manufacturer's covers will prevent moisture buildup, thus alleviating potential hardware damage or injury.

Key Words Connector, Electrical

= = Application Space Transportation System (STS) Experience

Technical If the proper method of protection is not used when connectors are Rationale demated, there is the possibility of electrical shock to personnel

= : connecting receptacles/plug ends, and increased surface corrosion rate due to environmental effects.

E , Contact Center Kennedy Space Center (KSC)

Page OPS-9 Electrical Connector Protection, Page 2 I Technique OPS-2

J Electrical Connector Protection Reference Technique OPS-2

KSC-DE-512-SM, Rev. B, Guide for Design I Engineering of Ground Support Equipment. This practice can be implemented in two ways: D

Provide instructions in operations an__d _ maintenance documents for protecting ' " II the connector after use. (A step should be included to inspect the c_ofs _i:: _:ii_ " _ _i : _ _ for corrosion/debris and provide: " ' I direction for corrosion/debris removal, necess_i) if E-S-D--_-ac-once-rii, do .:._:: not Use generic plastic_cal_"_i_'(he=y can be ESD generators. ESD-approved caps should be used. _ ..... m

Provide placard or tag on or near connector, stating method to leave I connector after use.

m I

L_ w

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IIm Robotic Removal and Application of SRB Thermal Systems, Page 1 Technique OPS-3

Technique When designing robotic systems for removal and application of thermal protection materials, pay close attention to support fixture indexing, precision positioning, optimum sequencing, and protection against robotic cell environmental conditions. By integrating proven hardware and software practices with equipment and facility design and operation, the effectiveness of robotic systems is ensured. =

i_i_i_i_..... #"_i

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w Benefits Adherence to proven robot cell design and operational practices will result in improved consistency, speed, safety, precision, and reliability and increased cost-effectiveness of robotic systems over manual or w semi-automated processes.

= :

Key Words Robot, robotic removal of insulation, robotic application of insulation, robot cell design, and robot operational practices.

w Application Space Shuttle Solid Rocket Booster (SRB) Experience s

Technical SRB refurbishment operations at KSC have resulted in the successful Rationale robotic insulation removal and application of 68 SRB att skirts and other SRB elements. The facility schematic depicted in the description shows the SRB ait skirt in its most environmentally critical operation, insulation removal. This facility has been in operation for 5 years and, under routine maintenance, has been operational since its inception. Similar reliable operation has been experienced in the robotic application of insulation.

Contact Center w Marshall Space Flight Center (MSFC)

Page OPS-11 Robotic Removal and Application of SRB Thermal Systems, Page 2 i Technique OPS-3

Robotic Removal and Application of SRB the SRB structure and the turntable were d Thermal Systems positioned into the spray cell. A technician

Technique OPS-3 (with breathing air and protective equipment) IW1 l was required in the spray cell during actual spraying to take thickness measurements, When the SRB is recovered from the ocean, assist in unplugging the spray gun, and disassembled for refurbishment, and reused remove the wet insulation, if it did not meet gi on subsequent Space Shuttle flights , several specifications. The cured insulation had to N layers of insulating materials and protective meet a flatwire tensile test of 50 to 100 IB coatings must be removed and then re- pounds and _ f01eranced thickness applied. Experience has shown that the use requirement. Adjustments were made to the of robotic systems for insulation removal delivery system and the insulation reapplied I and application will improve productivity in until it met specifications. Preparation of the most operations by a factor in excess of 10 structure for spraying and insulation required

to 1. Originally, the applicationofthe S_ many man-hours. m i insulation was a semi-automatic operation. The nine ingredients (see Table 1) were After automating and robotizing the measured by hand, placed in a large blender application of the insulation, the insulation i and mixer, and mixed to a uniform ingredients are automatically measured, consistency required for spraying. This blended, mixed, pressurized and delivered to

mixture was pressurized and delivered to the the spray gun, which is mounted on a gantry i robot. The gantry robot allows spraying inside the structures without the need to Table 1. Ingredients in the SRB Insulation =__ u rotate the structure for access. The robot is I

1. 2215 Adhesive parts A & B* programmed to automatically attach an end- 2. Ground Cork effector to perform the following operations: 3. Glass Ecco Spheres sanding, cleaning, inspection, masking, i 4. Phenolic Micro Balloons spraying, and thickness measurements. 5. Chopped Glass Fibers 1/4 inch long Automating and robotizing the application of 6. Milled Glass Fibers 1/8 inch long i 7. Bentone 27 insulation eliminated the need for a 8. Ethyl Alcohol technician in the spray cell and eliminated 9. Methylene Chloride/per Chloroethylene many of man-hours of hand work. [] [81

The original adhesive that contained shell At the start of the SRB refurbishment z Catalyst was a carcinogenic program, the insulation was removed manually. This required a technician to manually hold a hydrolaser pressurized to spray gun, which was attached to a pedestal 8,000 to 10,000 psi. This created a mounted robot in the spray cell. The SRB backwash of 72 pounds force that the structures were prepared by hand, i.e., technician had to overcome using two 2-men == sanded, cleaned, inspected, and areas masked crews rotated every 15 minutes. Any I that did not require insulation. The SRB insulation left after this operation was structure was mounted on a portable removed by hand using nonmetallic chisels turntable, which was cooidinated with the and mallets. Manual removal of the [] operation of the robot and spray gun. Then insulation from the two aft skirts required

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- i w /

Robot Arm Position for External Insulation Removal (MSA-2) w _ Robot Arm Position for External Insulation Removal (MSA-2) Robot Arm Position for Internal Insulation Removal (Insta-Foam)

Figure 1. Example Robot FaciBty: SRB Insulation Removal w

w Page OPS-13 Robotic Removal and Application of SRB Thermal Systems, Page 4 m Technique OPS-3

approximately 400 man-hours. considered in areas where the water has a I high mineral content. Since the water used in Procedures for Robotic Removal the insulation removal process is recycled, Robot•zing the removal of the insulation the water must be filtered prior to reuse to I reduced the man-hours for two aft skirts to approximately 64 man-hours. The Table 3. Best Practices for Robotic Systems w hydrolaser is mounted on a gantry robot I which is located in the removal cell. The 1. Gear Specifications to the environment and the m pressure to the hydrolaser has been application O D, adapt•on to a solvent or water m il increased to 12,000 to 15,000 psi. spray and debris-laden environment). Z Pay close attention to the ergonomics for o_ratorz Technicians have been eliminated from the (L_, convenience ofconu'ob,visibility, manual [] hazardous environment. The robot is override, and toaching procedures). 3. Provide SUffu__.nt sit_ac¢ in robotic facilitles for m controlled by computer. A turntable (also sapport equipment, mechanisms, personne_ and controlled by computers) is mounted flush op_ational control stations. 4. Design-_ automated shutdown to be activated in with the floor. ARer removal of the the event of excessive flow, pressures, temperatures, m insulation, the robot is programmed to clean or inadv_nt ingress of personne& 5. Consider the use of visinn systems for alignment, the hydrolaser cell. completion status, inspex_n, and thickness menxur_. Provide oveslaad sensing and tao_la feedback for Table 2 lists typical reasons for using delicate operaffons. automated robot cell to apply and remove 7. Retain manual capability for emergency and backup ot_rations. SRB insulation. Table 3 is a list of the 13 8. Establish precise automatic indexing of fi._ur_ I best practices in the design of robotic with workpiece and robot to minimize setup time. 9. Provide electrical grounding of all system elements. systewg for removal and application of 10. Purchase over-rated equipment Use only 75% or design insula:.on. The most predominant less of the capa_ in the _ to provide | grovteh potential and operatlonal/maintenance consideration was the high pressure water margins. 11. Protect robot e2ements from solvents in the spray and debris environment encountered in environment to ensure continued robot iubricatlOrL the hydrolaser insulation removal process. 12. Train and use dedicated penonnel for robotic i operations. Operational maintenance, as well as design, 13. Establish preveutive maintenance requirements is important in maintaining a safe and during the design phase based on designed-in ease of maintenance features (t _, proper panel access, calibration test ports, eq_meut clearances, ct_). table 2. Typical Reasons for Using Robots

m 1. Man out-of-the-loop for hazardous and toxic environments. prevent erosion and corrosion of pumping 2. Eff'wien_" robot does not get tire& u 3. Will do whatever it is programmed to do and spray equipment. and will do it repeatedly. 4. WHl handle various end effectors for For the SRB insulation system removal, the sanding, cleaning, inspection, spraying, m and thickness measurements. water is filtered tc, contain particles no greater than 5 microns. On a quarterly basis, or every 100 operating hours, high pressure U water pumps are inspected and overhauled if efficient operation. Potable water is used to necessary to repair or replace the pump reduce corrosion in thepumps, valve_,_ and head, pistons, dr brass _s[eeves. Preventive U lines. The use of de-ionized water should be maintenance is performed regularly.

m Page OPS-14

u Robotic Removal and Application of SRB Thermal Systems, Page 5 Technique OPS-3

Facility Requirements be considered for material removal w A robotic facility of the type used for SRB operations. insulation removal and application must L allow operator visibility of the process Special Design Considerations and careful design for personnel safety and Robotic systems lend themselves to the access provisions. During the noisy removal effective application of automated process, personnel within a 50 tt. radius are emergency shutdown, automatic end-effector required to wear ear protection. Operators changeout, overload sensing, tactile entering the area during or immediately after feedback, and manual override. These w spray operations are required to wear features should be designed into the robotic protective suits with self-contained breathing system at the outset with participation of the apparatus to prevent inhalation or contact robot vendor. Setup time can be minimized w with toxic fumes. by providing pre-engineered or automatic indexing and relative positioning between the Facility design must be carefully coordinated work piece, support tooling or equipment, u with robot design and robotic operations and robot. While mechanical systems should planning. A concurrent engineering be over-designed for extra margins of safety approach is desirable in the design of robotic against wear and malfunctions, Care Should systems to ensure use of the correct robot, be taken not to grossly overdesign control operating in an optimally designed facility, system memory, particularly if a bubble for the target application. A team of memory is used. This could result in slower engineers and technicians representing all robot control system operation. applicable disciplines should be assigned full

w time to the project throughout design and References operations. Three levels of drawings of the robot/facility complex representing: (1) 1. Rice, Robert: Process Report on the w components, (2) subsystems, and (3) the Automated Hydro Removal of TPS, Report # integrated system should proceed through USB-ATG-003, USBI Booster Production 30, 60, and 90 percent design reviews. Company, Inc., NASA/MSFC contract # w Three-dimensional solid modeling NAS8-36300, January 1986. simulations using computer-aided design i : techniques will dramatically speed up the 2. Loshe, Thomas: Hydrolyzing Operations W design process. (See the MSFC Guideline in High Pressure Wash Facilities, titled, "Concurrent Engineering Guideline for Maintenance Manual # B8598, USBI -_-__ Aerospace Systems," in NASA TM 4322, Document Prepared for Kennedy Space "NASA Preferred Reliability Practices for Center, October 4, 1991. Design and Test"). The facility must contain support equipment, pumping systems, 3. Loshe, Thomas: Solid Rocket Booster w material storage, control stations, and Thermal Protection Removal System personnel dressing and clean-up. Software Users Guide, Document # 10MNL- [J 0044, United Technologies, USBI, April 2, Particular attention should be paid to debris 1990. handling. Sloped concrete subfloors provide for easy debris collection and clean-up. 4. Babai, Majid: Robot Simulation and Automated cell clean-up techniques should Manufacturing, Aerospace Engineering,

w Page OPS- 15 Robotic Removal and Application of SRB Thermal Systems, Page 6 I Technique OPS-3

SAE, October 1992, pp 11-13. I

5. Fertig, Alan R. and Tony S. Humble: Robots Refurbish Space Shuttle Hardware, I TABES Conference Proceedings, Huntsville Association of Technical Societies (HATS), Huntsville, AL, 1987. tim

6. Special Goyermn. en_t Pub li_cations: _,_ _: MM B8601, Preventive Maintenance Gantry Robot and Controller MM B8604, Preventive Maintenance/ g Validation Robot End Effectors MM B8611, SRB Insulation Manufacturing Manual (Forward Assembly) MM B8616, SRB Aft Skirt Assembly-MSA-2 TPS Operations Manual ...... m MM B8630, MSA-2 Tunnel Cover Assembly : _ . i Operations Manual STP 513, Cleaning Sprayable MSA-2 Insula_o n Spray _ ___ STP 621, MSA Control Room Operation | STP 622, Installation and Removal of Robot

End Effector Adapters Im STP 634, Sprayable MSA-2 Insulation Control Room and Mix Operations TP 741, MSA-2 Spray System Preparation- m ARF [] SESP (Safety Engineering Standard Procedure) 23405, Safety Requirements for Robot Systems u

Ill

i Page OPS- 16

I GHe Purging of Hz Systems, Page 1 Technique OPS-4

Technique Prior to venting a hydrogen (H2) system, initiate a gaseous helium (GHe) sweep purge to evacuate air from the vent line. After venting operations are complete, initiate a second GHe sweep purge to evacuate the vent system of residual H r Use a flapper valve or check valve on the vent line to prevent air intrusion into the line during low or intermittent flow conditions.

=_-= r w Benefits

w Key Words Purge, Hydrogen, H_, Helium, GHe

L_. Application National Space Transportation System (NSTS) Experience

w Technical Use of dilution purges when venting explosive gases such as hydrogen Rationale is not necessarily desirable.

• Mixtures of H2/I-Ie do not become non-flammable until the mixture is 91% He.

For "fuel rich" hydrogen/helium mixtures in air, the flammability limit increases with increasing He content, until 85% He mixture is obtained.

Contact Center Kennedy Space Center (KSC)

Page OPS- 17 GHe Purging of H_ Systems, Page 2 i Technique OPS-4

GHe Purging of H_ Systems Reference Technique OPS-4 H. Hannah, LSOC 32-30, FCSS Hazardous

Commodity Purge Study, dated September J This technique recommends initiating a GHe 1991. sweep purge to evacuate air from a vent line prior to venting a i-i2_s-ystem. After the initial Ill venting operation is complete, a second GHe sweep purge_should be_ conducted to ;_ II evacuate the Ventsystem o_re_duaiH2. The ...... upper flammability limits of a gaseous H2/ai r

_ure iS lower _th'no GHe_r_sen_(_g/_ _-.... ! Figure 1). A flapper valve or check valve used on the vent line will prevent_ air_...... ---:-

- -;2; ZZS intrusion into the line during low or _ _ .... IB intermittent flow conditions.

This practice should be included in all -new- i systems operating procedures and changes initiated to applicable existing procedures. aim System design should be reviewed to include the following as recommended by NASA TM X-52454 (Lewis Research Center): _ ...... i . | Include a check valve/flapper valve or other suitable mechanism to exclude air from vent stacks at low or intermittent m flow conditions. N I m Extend vent stacks 15 tL above a II building roof.

w Discontinue use of ordinary hydrocarbon flame arresters which are incapable of quenching a H2 flame.

• Provide a minimum of a 3-volume

exchange (pulse purges) to sweep system u prior to introducing hydrogen.

M Five to 10 volume exchanges to purge a vent m system is a commonly acceptable industry practice. ull

m Page OPS-18

w GHe Purging of H_ Systems, Page 3 Technique OPS-4

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Figure 1. Limits of Flammability-Mixtures of H2and He

Page OPS- 19 z

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I Programmable Logic Controllers, Page I Technique OPS-5

Technique Use solid state Programmable Logic Controllers (PLC's) in system/equipment design to control and monitor systems and processes.

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:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ..:::: _i!i___i;!:!_i_!_!_::_i_q_ilili_.'.:!i_@!T'F#ii_i:_!i...... _:"_::_!._!i_ilii_i_ii_#_i_:;ii;i_!Y'_i_':"!!!._:':'r_:_i!i_i__i_:'_.<_i_ili_i!iiil_!!_!!iiii_i_;_ili !i_@_iii_Ii_i_i_i_!_ii_ii!@i_ii_!iii@iiii!i_i_!iii_iiii@]iiiIi_i_Iiiiiiiiii@iii_i_)_i_ii_iiiiiiii_iiIiiiiii_1_iIiiiii_iii_iiii_!@ ::::::::::::::::::::::::::::::::::::::::::::::: iii]!l!!i!li!iiii@liii!iI! e r .

W Benefits System/equipment design using PLC's is a prime example of the application of maintainability design objectives. PLC's are designed with ease of maintenance and troubleshooting as a major function. W When virtually all components are solid state, maintenance is reduced to the replacement of a modular, plug-in type component. Fault detection circuits and diagnostic indicators, incorporated in each major component, can tell whether the component is working properly. With the programming tool, any programmed logic can be viewed to see if input or outputs are on or off. w

Key Words Controller, Programmable i

Application Space Transportation System (STS), Facilities and Ground Support Experience Systems. w

Technical Conventional relay-based control systems are more subject to failure Rationale and cannot handle complex processing as efficiently as PLC'S. Use of PLC's in system design will reduce failure rates and subsequent

= downtime, ultimately saving a program money.

Contact Center Kennedy Space Center (KSC)

z •

Page OPS-20 w Programmable Logic Controllers, Page 2 i Technique OPS-5

m Programmable Logic Controllers Table 1. Typical Programmable Logic I Technique OPS-5 Controller FeaturesBenefits

..... Features .,, Benefits I PLC'S provide control capabilities not Solid State Components High reliability possible in the past. Control systems ProgrammableMemory Simplifies changes m incorporating programmable controllers are Flexible control I now able to operate machines and processes with an efficiency and accuracy never before Small Size Minimal space achievable with conventional relay-based requirements Ill control systems. Usually, PLC architecture Microprocessor Based Communications capability is modular and flexible, allowing hardware Higher level of performance : = and software elements to expand as the Higher quality products application requirements change. If an Multi-function capability application outgrows the limitations of the Software Timers/Counters Eliminate hardware PLC, the unit can easily be replaced with a Easily changed presets unit having greater memory and input/output capacity, and the old hardware can be reused Software Control Relays Reduced hardware wiring for a smaller application. COSts Reduced space g requirements PLC attributes make installation easy and I cost effective. Their small size allows PLC'S Modular Architecture Installation flexibility II to be located conveniently, often in less than Easily installed half tt_ pace required by an equivalent relay Hardware purchases minimized u contro: _,anel. On a small scale changeover i Expandability from relays, the PLC'S' small and modular construction allows it to be mounted near the Variety of I/O Interfaces Controls variety of devices relay enclosure and pre-wired to existing Eliminates custom control | terminal strips. Actual changeover can be Remote I/O Stations Eliminates long wiring made quickly by simply connecting the conduit runs input/output devices to the pre-wired w terminal slrips. Table 1 lists some features Diagnostic Indicators Reduced troubleshooting time available and benefits of PLC'S. Proper operation of signal

w In large installations, remote input/output ModularI/O Interface Neat appearance of control stations are placed at optimum locations. panel The remote station is connected to the Easily maintained i processor by a pair of twisted wires. This Easily wired configuration results in a considerable Quick I/O Disconnects Service w/o disturbing reduction of material and labor cost that wiring i would have been associated with running All System Variables Stored Useful management/ multiple wires and conduits. in Memory maintenance Data can be output w PLC Components and Operation PLC'S, regardless of size, complexity, or or programs. Figure 1, identifies the basic _-I cost, contain a basic set of parts. Some of parts of the PLC. In addition to a power I the parts are hardware; others are software supply system and a housing that is

Page OPS-21 i

II w Programmable Logic Controllers, Page 3 Technique OPS-5

--[PARTS OF A PROGRAMMABLE CONTROLLER]--

Signals From Process

INPUT INTERFACE I

. J w PROGRAMMING TOOL z s 1 w

PROGRAMMING LANGUAGE

Signals to Process

Figure 1. Parts of a Programmable Controller

appropriate for the physical and electrical The Processor and Memory. provide the main environment, PLC's consist of the following intelligence of the PLC. Fundamental parts: an input interface, central processor operating information is stored in memory as unit (CPU), memory section, programming a pattern of bits that is organized into language, programming tool, and an output working groups called words. Each word interface. stored in memory is either an instruction or piece of data. The data may be reference The Input Interface provides connection to data or a stored signal from the process that the machine or process being controlled. has been brought in through the input The principal function of the interface is to interface. The operation of the processor receive and convert field signals into a form and memory of the PLC can be described as that can be used by the central processing fairly_simple repetitive sequence: unit.

Page OPS-22 Programmable Logic Controllers, Page 4 Ig Technique OPS-5

. Look at the process being controlled. still popular. Alternative languages use t This is accomplished by examining the Boolean representation control schemes as information from the input interface. the base of the computer representation. m IB

° Compare the information with control The Progr.amming Tools provide connection information supplied by and stored in the between the programmer and the PLC. The i program. programmer devises the necessary control concepts and then translates them into the

3. Decide whether any control action is particular program form required by the m I needed. selected PLC. The tool produces the pattern of electrical signals that corresponds to the

. Execute the control action by symbols, letters, or numbers in the version of m Ill transmitting signals to the output the program that is used by humans. interface.

Process Improvements m 5. Look again at the inputs. The use of control and monitor equipment with the benefit ofa PLC could lead to:

The processor continually refers to the m program stored in memory for instructions • Increased system availability concerning its next action and for reference u data. • Decreased downtime requirements to il recover from a failure The Output Interface takes signals from the processor and translates them into forms that • Decreased cost in materials and man- I are appropriate to produce control actions by hours for installation external devices. • Increased system visibility M The Pjo_am and Pro_am Lan_age. The program is written by the user and stored in • Increased flexibility to meet new the PLC. The program is a representation of requirements. the actions that are necessary to produce the desired output control signals for a given Reference process condition. The program includes sections that d_e_t_h - bfi_nging_the- prgccss National Technology Transfer Inc. (PLC data into the controller memory, sections Seminar, Aurora, Colorado, 1992) that represent decision making, and sections that deal with converting the decision into physical output action. Progi'amming languages have many forms. Early versions were restricted to mat_ch the conventions of relay logic which consisted of ladder diagrams that specified contact closure types and coils. This type 0fprogramconsistsgf a representation of a relay logic control _ scheme. The relay ladder language types are

Page OPS-23 DC Drive - Solid State Control Page 1 Technique OPS-6

Technique During the design of new (or upgrades to) motor generator set type DC drives, consider the use of solid state assemblies for control functions.

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_iii_-_i;_t_i!::i!-_i!_!'_'_:::_::._:'.._.":'.':,.'_:!!;_-".:-":;_'i_.:_."_:.:_:i!ii_!:_i_: :_::_:5_;_:_:_[_::_;_:_¢_:_:_;_;_;_;_:_:_:_:_;_;_;_;:_:_:_;_:;;_;_: i_;.'.Z:i_i_iii .:.:<.>:<.,-:.::-:.::-:.:-:.::::.:::::::::::::::::::::::::::::::::.:-::-:::.., w Benefits Use of solid state controls instead of magnetic amplifiers can improve system restoration time in the event of a failure. Features such as fault detection, modular construction, and packaging can be easily employed. Diagnostics for system health status and problem resolution can also be readily provided. Incorporation of these features can result in improved

= , system performance and availability.

Key Words Solid State Assemblies, System Restoration, Maintainability, Performance, Availability

w _ Application National Space Transportation System Shuttle Ground Support Experience Systems.

w Technical At KSC the 175- and 250-Ton Bridge Cranes in the Vehicle Assembly Rationale Building (VAB) were using metadynes (electromechanicai rotating amplifiers) for control function. The metadyne had a long history of maintenance problems because of brush wear, contamination and corrosion. It required extensive pre-operation maintenance attention to -:_._: support Shuttle processing. In addition, the metadyne units often required maintenance during processing operations impacting processing schedules. KSC replaced the metadynes with solid state controller units resulting in decreased maintenance actions including pre-operation maintenance and improved system performance and r availability. Fault isolation and removal and replacement of failed components is easier and less time consuming. Since failures occur at a less frequent rate, the need for numerous operating spares is reduced. Furthermore, the "off equipment" in-shop maintenance of failed units requires much less time and money to effect a repair. Reduced maintenance and downtime allow for the crane to be ready and operating to support Shuttle processing in a more timely manner.

r Contact Center Kennedy Space Center (KSC)

L .

Page OPS-24 DC Drive - Solid State Control, Page 2 I1 Technique OPS-6

DC Drive - Solid State Control acceptable response rate. However, they g Technique 0P5-6 were rugged and highly reliable once in satisfactory operation.

The use of solid State assemblies for control m I functions represents a great improvement During the early 1960's the thyristor or SCR over previous control methods. Historically, became readily available. This device is

the first methtd-tfob_taml"_figadjustabl_ ..... -gi-m_I_iribperati0h to a thyiatron tube. I speed using DC motors was the constant Today it dominates the direct current drive potential I)(2 supply using fie! d adjustment._, field_S_ci_ c_cuits enable=the SCR to This provided a small range of adjustment. regenerate and reverse readily. Larger and m This method was followed by the rotating less expensive SCR's have extended the M-G system of Ward Leonard patented in range to well over 1000 HP. Figure 2 the 1890's. This drive used an AC motor illustrates a controlled rectifier drive. Note g driving a DC generator to convert AC to DC that the gateing control and SCR bridge have replaced the M-G set of Figure 1, resulting in power. The motor and generator may be m combined in a single frame and use a reduced rotating machinery. m common shaft, or separate coupled units (See Figure 1). The output DC voltage is Solid State Operation El controlled by adjusting the field excitation of Figure 3 shows the assemblies comprising a the DC generator. Depending on the solid state control system for DC drives. A accuracy required, armature voltage or a Single phase thyristor power conver(e-t- m tachometer may be used as a feedback signal supplies up to 200 volts positive or negative in a closed loop system. An important at 20 amperes to the generator field. A aspect of this drive is that power flow is closed-loop controller (speed regulator) l I reversible. The motor acts as a generator, provides for armature voltage with IR drop driving the generator as a motor, which compensation or AC/DC tachometer drives the AC motor which then pumps feedback speed control and linear U power back into the AC lines. This ability, acceleration and deceleration. A firing called regenerati0n, _isa useful feature !n circui t prov!des an isolated gate drive to the decelerating large inertias or holding back power converter. A bi-directional adapter m overhauling loads. This is a very important used in conjunction with the fuing circuit consideration when replacing the M-G with a assembly provides bi-directional current to conventional packaged silicon-controlled the field of a DC generator for contactoriess I rectifier (SCR) drive. reversing or to regulate to zero output voltage in the presence of residual

In the late 1940's, electronic tube drives magnetism of the DC generator. Protective m began to replace M-G drives. These used circuitry includes a voltage sensing relay for vacuum, thyratron, excitron, or ignitron safety interlocking and an isolator for tubes for armature circuit control. They had isolated armature current feedback. w limited acceptance because of tube life limits and water cooling requirements on larger References ratings. By the early 1960's the tubes were replace with the solid state thyristor drives. 1. KSC Electrical Drawing for VAB 250 Magnetic amplifier drives were developed in Ton Cranes, 250-69-K-L-11388. the mid-1950's when silicon diodes became I popular. They were never as widely used 2. KSC Electrical Drawing for VAB 175 because of difficulties of reactor design and Ton Crane, 175-67-K-L-11348. I

Page OPS-25 DC Drive - Solid State Control, Page 3 Technique OPS-6

3-Phase AC Supply

-I- w I , x Ic,cer

w i I....lo°oenora'orlI

Figure 11 Rotating M-G System

SCR GATING DC AND MOTOR POWER Supply CIRCUITRY u r_ t_

Armature Voltage Feedback

Figure 2. Controlled Rectifier Drive

Page 0PS-26 DC Drive - Solid State Control, Page 4 Technique OPS-6

I lUnum 11

SIGNAL +6V -6V ISOLATOR

SPEED

SPEED CONTROL INTERLOCK

1 M AC/DC TACH (OPTIONAL)

Figure 3. M-G Control-Reversing Simplified Schematic Motor Generator

Page 0PS-27 AC - Variable Frequency Drive Systems, Page 1 Technique OPS-7

Technique During the design of new or modifications to existing systems requiring motor speed control, consider the use of alternating current (AC) variable frequency drive systems for motor control.

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• Improved system maintainability, reliability, and performance. • Reduction of preventive and corrective maintenance (manhours and materials) by elimination of mechanical devices. • Increased system availability. • Self-contained diagnostic test capability. • Reduced size and mechanical complexity. i..; • Reduced life cycle costs. iJ Key Words AC Variable Frequency Drive, System Performance, Availability

Application Launch Complex 39A & B, Main Propulsion System, Liquid Oxygen Experience Subsystem

I I Technical Variable frequency drive systems are installed at the Shuttle launch pads Rationale at KSC. The system allows for a direct coupling between the main r • propulsion system liquid oxygen pump and drive motor. This eliminates the motor clutch system, a high maintenance item, and gaseous nitrogen lines used to purge the clutch system.

Contact Center Kennedy Space Center (KSC)

Page OPS-28

w AC - Variable Frequency Drive Systems, Page 2 Technique OPS-7

AC - Variable Frequency Drive Systems The control circuitry in the drive turns the Technique OPS-7 SCR's on 60 times per second to obtain the desired current flow. Each time a new SCR

The use of A/C variable frequency drive is gated, it then forces a previous one to shut I systems provides greater efficiency for motor off. If it is necessary to turn off all the speed control than mechanical devices with SCR's, all gate signals are removed and the DC or AC motors. AC variable frequency SCR's then turned off naturally when the AC I drive systems allow for direct coupling and input voltage is reversed. eliminates the need for mechanical devices= 7 7= such as clutches and pulleys. Elimination of The DC link module is so called because it is m these mechanical devices results in decreased a device that connects the inverter and maintenance downtime and repair costs. converter modules. Electronically it is an i Adjustable speed AC drives also offer many inductor or choke that filters the output of advantages over DC drives because of the converter module and provides a more simplicRy, high-speed capability, andi0w i u_f0rm flow Of current to the inverter maintenance requirements of induction module. Since the inductor tries to maintain motors. These motors are suitable for a constant flow of current through it, this adverse conditions such as dirty air, allows the=voltage source converter to I explosive atmospheres, and inaccessible function as a current source to the inverter locations. module.

I The inverter module takes the filtered DC Components Typically, an adjustable frequency drive from the DC link module and converts it S system for an AC induction motor will back to AC. Here the SCR's are gated, one consist of a converter module, DC link after the other, steering this DC into and out module, and inverter module. The following of each of three input lines to the motor. is a description of an adjustable frequency The faster the SCR's are fired, the faster the drive system. The configuration shown and motor turns. Since the AC line is not present the type of control scheme used classify the here, external commutating capacitors are = = used to ensure that each time a new SCR is drive as a current source inverter type. I Figure 1 illustrates three fundamental steps fired, an old or previously conducting one is used in converting the AC input into a shut off. variable AC output. g Drive Operation The converter module can be thought of as a The following paragraphs briefly discuss programmable DC voltage source where the some of the characteristics of the drive: W three AC input lines are rectified by silicon controlled rectifiers (SCR's) to provide a a. Output voltage and current normally variable DC output. An SCR can be thought delivered to a motor from the AC input line W of as a controlled rectifier or switch that lets are both sinusoidal. This is not true when current flow in the forward direction when operating the motor from a current source [] lid gated or opened. Then it cannot shut off inverter (see Figure 1). The voltage waveform is closely sinusoidal with again until the flow reverses or ceases. At m_ wml this point the SCR regains its forward disturbances called commutation spikes. The I blocking capability until gated again. output current is a high quality quasi-square

Page OPS-29 II

m m g AC - Variable Frequency Drive Systems, Page 3 Technique OPS-7

ConveNer D.C. Link Inverter

t_t'yy_ i i or Inductor or DC Choke

L _. -Typical SCR AC Line

Reactor

=_ r_

diJdt Reactors & Resistors

L--_ Typical Commutation Spike

Figure 1. Simplified Adjustable Speed Drive

waveform. The current source inverter b. Crowbar: Since during normal operating makes no attempt to define the shape of the conditions the DC link or choke is carrying a output motor voltage. The output voltage is large current, which implies a large amount simply a result of the current and rotation of of stored energy, it is worth discussing what the motor. The shape of the current happens should the input or output to the waveform is def'med and its level is increased drive be suddenly disconnected. The or decreased to obtain the required voltage. inductor would normally develop whatever Stated more simply, the control circuitry voltage is needed to maintain the constant L_ contains an inner current regulator loop with flow of DC. To mitigate the danger of these an outer voltage regulator loop that ensures damaging voltage levels, protective circuits that the proper current and voltage are are incorporated within the drive to provide supplied to the motor. a path for this DC. The protective schemes w are based on the capability of both the

Page OPS-30 A C - Variable Frequency Drive Systems, Page 4 m Technique OPS- 7

very low speeds, the motor appears to move inverterandconvertermodulesto providea [] pathfor thiscurrentby firing two series in discrete steps rather than smoothly rotate. SCR'sin theconverterandinvertermodules, At a frequency of 1 Hertz, for example, a two-pole machine would perform one thusgeneratinga directshortcircuit path i throughwhichthecurrenttrappedin the complete rotation in six distinct steps at a inductormayflow. Theprocessof firing rate of six steps per second. This effect is theseSCR'sto providea currentpathis reduced depending on the inertia of the i called"crowbar." connected load. The visual effect completely disappears at speeds above a few Hertz. I c. Outputclamp: With anabmptlossof i load,theprotectivemechanismoperatesas References follows. Theinverteroutputleadsto the motorareequippedwith adevicecalledan 1. KSC Electrical Advanced Schematic I "outputclamp." If themotoris abruptly Drawing 79K06382. disconnected,theoutputcurrentfrom the inverterwill transferto thisclampcircuit 2. KSC Electrical Advanced Schematic B until its levelhits 950voltsDC. At this Drawing 79K40029. point, thecontrolcirc_uitrywflIforcea- [] i "crowbar"andshut off the converter module. This prevents any further increase in output voltage; an orderly shutdown is I i performed.

d. Commutation: Commutation is a process U by which an SCR is forced out of a conducting state by reverse biasing. Two

types of commutation normally occur in the i power circuit, natural and forced.

e. Regeneration: The SCR converter is a m two-quadrant device capable of accepting power from the DC bus and returning it to -'-=_ the line when the DC bus potential is i negative. This capability makes the current source inverter one of the few inverter types

that are inherently regenerative without am excessive circuit complication.

f. Low speed cogging: Each commutation in the inverter module causes the current flow to the motor to be abruptly stopped in one phase and started in another. This action H forces the motor to turn one-sixth of a rotation on a 2-pole machine, one-half on a 4-pole machine, etc. This explains why, at

[] Page OPS-31 []

2 Fiber Optic Systems, Page 1 Technique OPS-8

Technique During new design or upgrades to existing transmission systems, consider the use of fiber optic systems in place of metallic cable systems.

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t..... Benefits Properly designed fiber optic transmission systems will last for long periods of time without any preventive maintenance and can offer reduced maintenance downtime and repair costs. Well-built optical w transmission lines and couplers are relatively immune to electromagnetic interference, adverse temperature, and moisture conditions and can be -i, used for underwater cable. An optic fiber can be 20 times lighter and five times smaller than copper wire and still carry far more energy. r Using fiber optic control circuits provides electrical isolation for safety in hazardous environments. Because optical cables carry no current they are safe to use in explosive environments and eliminate the hazards of short circuits in metal wires and cables.

Key Words Fiber Optics, Maintainability

Application Kennedy Space Center Ground Support Systems (e.g., Launch Experience Processing System, Ground Communications System). w

Technical Fiber optics can enhance the transmission quality, capacity, and safety Rationale environment of the system. The system designer should carefully weight the pros and cons of fiber optics vs. copper, microwave, or satellite for the transmission medium. Optical fiber, if cabled and installed properly, will last for years without any preventive maintenance. Reliability of optical cable is very good, and will enhance system availability, minimize downtime for maintenance, and reduce repair costs.

Contact Center Kennedy Space Center (KSC)

Page OPS-32 Fiber Optic Systems, Page 2 m Technique OPS-8 Z

Fiber Optic Systems cable expands and Shrinks with changes in i Technique OPS-# temperature, it does not affect the fiber as much. A fiber has a lower temperature coefficient th_most cable elements, l Components and Operation meaning that it expands and contracts less. The basic elements found in fiber optic The tight buffer has a plastic directly appfied " S),stems-_area tr_Smitter, flf_er 0_ti_cable, over thefiberc0ating | receiver, and connectors. Figure 1 illustrates the main parts of a fibe r optic system. The This construction provides better crush and following is a brief description of these' ' impac-t reS_s_anCeihowever, it does not i elements and their function: protect the fiber as well from stresses of temperature variations. Because the plastic lz • The Transmitter converts _ electrical expands and contracts at a different rate than i signal to a light signal. The transmitter the fiber, contractions caused by variations in consists of a driver and a source. The temperature can result in loss-producing input to the driver is the signal from the microbends. Tight buffers are more flexible equipment being served. The driver circuit and allow tighter turn radii. Therefore; tight chang_es=the input signal int_a'form tube i:;u-ffers are useful for indoor | required to operate the source. The applications where temperature variations source, either a light-emitting diode (LED) are minimal and the capability to make tight or laser diode, does the actual conversion. turns inside walls is desired. |

• The Fiber Optic Cable is the medium for Strength members add mechanical strength m carrying the light signal. The main parts of to the fiber cable. The most common [] a fiber cable are the optical fiber, cladding, strength members are Kevlar Aramid yarn,

buffer jacket, buffer, strength members, steel, and fiberglass epoxy rods. During and m and jacket. Figure 2 illustrates the main after installation, the strength members [] parts of a single fiber cable. The optical handle the tensile stresses applied to the fiber contains two concentric layers called cable so that the fiber is not damaged. the core and the cladding. The inner core Kevlar is most commonly used when J is the light-carrying part. The surrounding individual fibers are placed within their own cladding provides the difference in jackets. Steel and fiberglass members find refractive index that allows tOtal internal use in multi-fiber cables. Steel offers better I reflection of light through the core. The strength than fiberglass, but may not be the buffer is the plastic coating applied to the best choice for maintaining an all dielectric i cladding. cable. Steel also attracts lighting, whereas fiber does not. The jacket-like wire Cable buffers are one of two types, loose or insulation provides protection from the i tight. The loose buffer uses a hard plastic effects of abrasion, oil, ozone, acids, alkali, tube having an inside diameter several times solvents, etc. The choice of jacket material that of the fiber. One or more fibers lie depends on the degree of resistance required i within the buffer tube. The tube isolates the for different influences and costs. fiber from the rest of the cable and the mechanical forces acting on_it_ -The buffer • The Receiver accepts the light signal and becomes the load bearing member. As the converts it back to an electrical signal. The

w Page OPS-33 === : i Fiber Optic Systems, Page 3 Technique OPS-8

receiver contains a detector, amplifier, and with conventional systems and for short an output section. The amplifier enhances hauls of less than 10 km, no repeaters are the attenuated signal from the detector. necessary. In the absence of electrical The output section performs many current, the life of a fiber optic system's functions such as: separation of the clock components equals the useful life of the and data, pulse reshaping and timing, level control system, the light source, and the shitting to ensure compatibility (TTL, electronics. Maintenance and repair costs ECL, etc.) and gain control. are reduced dramatically. Installation costs of fiber optic cables are lower than metal w Connectors and splices, which link the cables because the shipping and handling various components of a fiber optic costs are about one-fourth and labor costs system, are vital to system performance. A one-half that of current metal cables. connector is defined as a disconnectable

device used to connect a fiber to a source, References detector, or another fiber. It is designed to w be easily connected and disconnected many 1. RADC-TR-88-124, Impact of Fiber times. A splice is a device used to connect Optics on System Reliability and one fiber to another permanently. Maintainability, June 1988. w Connection by splices and connectors couples light from one component to 2. RADC-TR-80-322, Failure Rates for another with as little loss of optical power Fiber Optic Assemblies, October 1980. as possible. The key to a fiber optic connection is precise alignment of the 3. AWP, Technician's Guide for Fiber mated fiber cores (or spots in single-mode Optics, 1987. fibers) so that nearly all the light is coupled from one fiber across the junction to the other fiber. Contact between the fibers is not required. However, the demands of precise alignment on small fibers create a w challenge to the designer of the connector or splice.

Maintainability design features that should be addressed in the design for fiber optic systems should provide for fault localization and isolation, modular replacement, and built-in test and check-out capability.

Improvements Fiber optics systems offer many benefits. In

F_L sensing systems, sensitive electronics can be isolated from shock, vibration, and harsh environments, resulting in more economical _z packaging. The number of repeaters required for low attenuation cable is less than

Page OPS-34 Fiber Optic Systems, Page 4 -- Technique OPS-8

t - - -- __em..,_r.... ', _,

I I, DR_VERI--Ii = SOURCEI---I= I TOSOURCEF_BER I--II 'OP _CALI------SIGNAL I I I [ I [ CONNECTION [ I FIBER / = IN I I

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OUT I =1 ,_ _ m m • • m m m m m _ m m m m m m _ m m , Figure 1. Basic Fiber Optic Link

i 8LACK POLVU_Er.ANt OUTEa.JACCEV_

STRENGTH x / MEM

\ \ -S,UCON(COAT,NO \ \ CL_,.a IS,.,CAJ] \ coRE m,w.A_ _Op,,CAL,,SEA

Figure 2. Parts of a Fiber Optic Cable

i Page 0PS-35 Pneumatic Systems -- Pilot-Controlled Pressure Regulator Loadingo Page 1 Technique OPS-9

_m_ Technique Use a separate, hand-operated, spring-loaded, vented regulator in pneumatic system designs to provide reference pressures for pilot controlled pressure regulators. Specify application in system/equipment specifications, requirements documents, and design policies and practices.

mm_.m

Benefits Design of a pneumatic systems using vented pressure regulators offers r . z tl the following maintainability advantages: • Requirement for a separate relief valve in the pilot-loading circuit is eliminated. • Logistics support requirements (materials, parts, tools) are decreased by elimination of additional relief valves. • System availability is increased by elimination of additional components and their maintenance/downtime requirements. • Elimination of components enhances maintainability and increases reliability. • Overall life cycle costs are improved by decreased maintenance and downtime requirements, and increased system availability.

Key Words Pneumatic, Regulator, Pressure

r _ Application Apollo, National Space Transportation System (STS), Pneumatic Experience Ground Support Systems

Technical When pneumatic system requirements mandate the use of pilot operated Rationale pressure regulators, the use of vented pressure regulators to supply reference pressure is mandatory. This reduces the system component count and associated logistics requirements.

Contact Center Kennedy Space Center (KSC)

Page OPS-36 w Pneumatic Systems -- Pilot-Controlled Pressure Regulator Loadinb Page 2 Technique OPS-9

Pneumatic Systems - Pilot-Controlled m Pressure Regulator Loading Technique OPS-9

Pressure in Pneumatic systems must be controlled. Primary points of control are downstream of the source (compressor) and I the system_eceive_ank). :_2on_trol of " _=_ = ...... pressure is required downstream of the compressor for system safety and ...... downstream of the receiver to m_aintai_na _-_ .... _--:: :: _: ::: _ _ :: : -: :: .... ::_:i -::,:_ :: _ steady pressure source for efficient operation of other system components. Pneumatic : ...... systems use pressure regulators to provide ..... this control. For those systems using standard dome-loaded (pilot-operated) :: :: ..... ::::=: : :::: -_ -_-_:/- -:: : : regulators, this practice requires use of ...... - separate vented regulator for loading the pilot operated regulators. Figure 1 shows a regulator system with separate relief valves. A venting type regulator limits downstream pressure to a level lower than that of the upstream (receiver) pressure. It also acts as a relief valve for its leg of the circuit in the event of pressure build up. This method _ _ eliminates the need for a separate relief valve in the dome-loading circuit. Figure 1 also shows an example of a vented system which illustrates this method.

References

1. KSC-SD-Z-0005A, Standard for Design of Pneumatic Ground Support Equipment.

2. Parker-Hannifin Corp., Bulletin 0225- B 1, Fluid Power.

Page OPS-37 Pneumatic Systems- Pilot-Controlled Pressure Regulator Loadinb Page 3 Technique OPS-9

REGULATOR (NON-VENTING) NON-VENTING SPRING LOADED

---_ RELIEF VALVE (VENT)

PNEU. F __ REGULATED [ : INPUT w LT_IJ :>OUTPUT PILOT OPERATED (DOME LOADED) REGULATOR

! :

REGULATOR (VENTING) SPRING LOADED

VENTINGPNEU. [VENT) _ J

INPUT _ " I> ;:> OUTPUT

PILOT OPERATED t (DOME LOADED) REGULATOR

=--

THIS APPLICATION ELIMINATES THE RELIEF VALVE

= =

I.,,#

Figure 1. Examples of Non-Vented and Vented Regulator Systems (Schematics)

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H mm Modular Automated Power Switching Device, Page 1 Technique OPS-IO

Technique Incorporate modular, fault tolerant power switching devices in new system designs and system upgrades. Specify application in system/ equipment specifications, requirements documents, and design policies and practices.

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Benefits Miniaturizing of conventional electronic components and assembling them in convenient groupings provides the following benefits: • More efficient base of maintenance can be achieved. • Logistics support requirements (materials, parts, etc.) are reduced by stocking modules as opposed to piece parts. • Keeping modules at lowest level of maintenance (throw-away) will minimize the requirements for sophisticated test equipment and highly skilled technicians. • Modular design will result in improved fault detection by isolating the problem at the module level instead of at the piece part level. • Module design can be sized to accommodate various loads. • Sealed modules provide increased environmental protection. _'_=_

Key Words Power, Switching, Modular

Application National Space Transportation System Experience

Technical Incorporation of the technique will achieve the goal of avoiding high Rationale maintenance costs from premature failure of hardware due to moisture ! or sand intrusion and other severe environmental conditions. Shuttle program operations around the world have shown that this switchover device has been extremely reliable even under conditions that are W normally detrimental to electrical equipment.

Contact Center Kennedy Space Center (KSC)

Page OPS-39 ModularAutomated Power Switching Device, Page 2 u Technique OPS- IO

m Modular Automated Power Switching: I Device Technique OPS-I O I This technique recommends providing modular, single-fault tolerant, p0Wer _/witching devices that e_ance ease of El maintenance and expedite system restoration. i Application _:= _ The design of lighted visual Landing Aids presently install_ at sever_-SpaceShu/tie ::_:_ ii landing sites around the world specified that the Ball/Bar lights for the Inner Glideslope .... w ....must be powered by a p_rim_ary/rod 5acku_ _ : - - :- power source with automatic switchover in the event of primary source failure. The R.eliability/Maintainability Engineers had to m l ensure the system would not prematurely fail and that the switchover mechanism was

relatively inexpensive, self-contained, and I easy to install/maintain. As a result of this effort, the modularized automated power

l switching device was developed and I implemented (see Figure 1).

Failure to utilize this technique could result Ill in excessive cost if commercial Automatic Transfer Switches are utilized instead. The Ball/Bar light system is critical to Shuttle g landing operations. These systems must be up and operational prior to a Launch Commit decision. Failure prior to launch could result in a very costly delay to the Shuttle program. W

References

1. NSTS 07700, Vol. X, Space Shuttle Flight & Ground System Specification, R.ev. J, June 14, 1990.

2. KSC Dra_ng No. 80K52361, Au!omatic Transfer Switch Wiring Diagram for BallBar Lights.

g Page OPS_0

m Modular Automated Power Switching Device, Page 3 Technique OPS-IO

LI _ L2 L1 _ L2

START L K2A •SWITCH -- --K1A KIB --

sl I- ! K1 T AUX -_- 7'

L_ 1 _LT1

=4 , ,'oo, o, MODULE ENCLOSURE

L1 L2

IF K1A OR KIB FAILS OPEN - K2 DROPS OUT CAUSING THE BACK-UP POWER SUPPLY TO COME ON LINE.

• IF THE PRIMARY POWER SUPPLY FAILS - K2 DROPS OUT CAUSING THE BACK-UP POWER SUPPLY TO COME ON LINE.

• S1 IS USED TO SUPPLY THE PRIMARY LINES AND IS ALSO USED TO BY-PASS K2A & K1 AUX TO ACTIVATE AND LOCK ON K1.

Figure 1. Modularized Automatic Power Source Switching Device

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m m B w Pneumatic System Contamination Protection, Page 1 Technique OPS-11

Technique Install filters immediately upstream of all interfaces in pneumatic systems to control dirt and water contamination.

ii_iiiiiiilitiiii_i/iii_iii_ii_i_iiilitit_!i!lii_ ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :::_. ::':::_.:::::::::::::::::::::::::::: _:: .'.':_:_::::::: _ _:_:._ _:?-:: .'.'_.:::_:..'._:: :_::_::: :i:i:_:_::_:_:_:__:i:_:_:i:i:i:i:i:_:_:_:i_:_:i:i:_:?..:_:_:i:_:i:i:i:i:i:_::::i:i:i:!:i:::i:!:::i:i_:::::i:_i_;::i: :!:': :: :i:_::_:_: :..'.:,_:: ,_:_: _: ::: :::: _:.'...':::_::: :i_'_::

1 ..%.._._.::_-______:.:!i__!!.,:._:,.:..,:_

+._- ..... _..,: : : :_ _:: :: :_.::::.:::: :: _: _:.::_:: ::, ::::::::::::::::::::::: ...... :,,...... _::_:_._:_._:_:_:_:_:_:_:_:.:_:_+:_:_:_:+:_:_:_.:.:::_::_:.::.:_.:..:_:_,_::.'.. _ +..._.+..+_:::...+...._._..¢..¢ +..._.....,..¢...... <._<..._._.,...._.-.._...... _...... ::::::_::::_.,,_....., _...... _ _...... _:_.¢::..,._: : .¢. _._::._._...... :: :...,..::.'.::•..._+:::._..:_._...... _ ...... _....._...,_._.._ ..... _ .•.".' ._'." _' ,_i_,.": _ i i i ! ! :::::::::::::::::::::::::::::::::::::::: ::_:!:.:_:::::_:_::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::_:._i:::_:`.::::::._:::`._:::::.`.:_::_:i:_:::_:'_._::::_:::: _:_ ::_::::::'.::::::_ :_!:::_ ::::::::: _-'.':_!i_i:iiii_!."-'_:_i_i_:i_._i _:.¢i_i _ i?...'!_i ...... -..:::::_:::::_: :_ ::::._ _:_'_ :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::_:."._: _..'..:'._:: ::::::_.:::_.:_::'__:: .":::::: : :_ : ::'.-"::::::: :: : :: :_:::."..'.'_::::::: ::: :_:::: : _:::: : : :.:::i::::: ::: ::: :_ _: :: : ::: :::: :_.":_:_:.:_:: :_i: :i:i:!:_:i_._:_:i:_:_:_:_:"_::. _:l_:_._,_ ...... _:_,..:::._.:.:.__::"::_:::: :_.:'_:::::-_:'_._: _::: : ::'):: ::: ::: :::-'.':.::::-::::::::,'.'::::_:'::_:_::::_.'.':_:::_:?.: _: :_::_: ::::i_::::::i::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::._::::::.':::::: _:._:: : :::._:_ ::::::::::::::::::::::::::::::::::::::: :::: _ :::::: :_ _:: :: ::: ::: _._.:::: t: _.::._._: : _:_:t:: _:.__:_ _::: _..'.:_: : :: ::: ::_'._:::?,.'.'.':_ : :: _:_:_:_:_:_$_:_:..`._:_:_:_:._:_:::_:.:_:_:_:_:i:_:_:_:_:_::`._:i:i:_:_:i:i:::i:i:_.._:i:_:i:i:_:_:_:i:_:[::!:_:_:!:i:"._::."._:_._'._::_ ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::::::::::::::::: j" ... . . :: .':

:_.:::..:::.:.:.:.:.:.:.:.,.::." _.....:.._+..:_ .... :..::_:.._..¢::: ,..:..::::_:...... :...; ...... :¢..:....:..:.....:. : .,.:..... :_..:_ ...... ::...: ...... :::::::::::::::::::::::::: :::::::::::::::::::::::::: .: : :,_...,_.:,,..::...... :.:.+...+: :,,...:.: ....: ...-.. :.....:.. :...... : .:..,.:.....::::...,.:.. :.- :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: : ._:::::_::::: :::::::::::::::::::::::::::::::::::::::::::::::::::::::: __:it_:.:'_'"_...... __'"' "_'_ ...... ".":__ ':" "'_'"" _"":'::¢ """'" '_'_i!i_ "" """"_" """:+"<""""":':_:::":_:'_:_':''_"_"" "" "_" " "" "" "...... _'" " "_"'_"' "" _'_ _'...... "_'"" _'" _¥"" wL_ __:::_..:!2{ '_ ...... :::::_:::::_:::' _:._::.::::.¢ _:::::'.'::::' ...... _::: _:_ :::: _::_ ...... '.::::::_ _...... :_ _:::::_ ::._...... ::::_._:_::: : • _:,:::_.:::.:,:.:__:_ ::_ _:::: ::_ :::::_:::::_i_.::.:::: ::..-: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :::_: _::_._ I_ : _.,. _:: .,.': _ i:_i_:L.'.,_..'._:_:.::..'i

Benefits Proper use of filters, prevents contaminated gas from interfacing with component and system operation, provides the following benefits:

E • Decreased component failure caused by contamination.

• Efficient and effective means of servicing system/equipment by filter cleaning or replacement.

• Increased system availability due to reduction in system maintenance.

Key Words Pneumatic, Protection, Contamination

Application Apollo, National Space Transportation System, Pneumatic Ground iml Experience Support Systems

L Technical System gas must be conditioned before it is allowed to enter a new Rationale system. Installing filters immediately upstream of interfaces achieves this objective and also reduces dirt and water contamination that can -:! interfere with component and system operation.

Contact Center Kennedy Space Center (KSC)

L J

Page OPS-42 Pneumatic System Contamination Protection, Page 2 i Technique OPS-I1

Pneumatic System Contamination and element clogged to its maximum iii Protection design capability). Technique OPS-11 =,_ Providing unconditioned gas in a pneumatic i No matter how well a system is designed or system will have the following effects: how expensive, particulate-contaminated gas interferes with component and system • Degraded System performance because of B operation. System gas must be conditioned; contamination. it must be decontarninated before it is =-:_:_::_ - _ _ - i allowed to enter a pneumatic system. The • Increased maintenance cost and downtime i KSC design standard for pneumatic systems to recover from problems induced by defines the following requirements for filters: contamination. I

• Filters shall be installed immediately • Decreased system availability. upstream of all interfaces where control of particulate matter is critical and at other References appropriate points as required to control

particulate migration. 1. KSC-SD-Z-0005A, Standard for Design m of Pneumatic Ground Support Equipment. • Selection of filters shall be made only after

i analysis of overall system performance 2. Parker-Hannifin Corp., Bulletin 0225-B 1, i requirements. This ensures maximum Fluid Power.

protection of critical components and l i minimal performance penalty (pressure g drop).

• Filter housings and elements shall be g constructed of 300 series stainless steel to reduce particulate contamination due to corrosion. Seal materials shall conform to D manufacturer's recommendations and the requirements specified herein. The element D construction should be welded instead of soldered whenever possible to simplify

cleaning. Where 300 series stainless steel r _ is specified, type 303 and other austenitic stainless steels should be avoided whenever possible because of susceptibility to stress i corrosion cracking. However, overall cost should be the deciding factor.

• Filter elements shall maintain filtering quality and not be damaged in any way

when subjected to worst-case system i conditions (i.e., maximum design flow rate

M Page OPS-43

= Q8-1@-1995 15:14 P.@2 "" F_. App+ow_ REPORT DOCUMENTATION PAGE oMlNo, Public mportl_+; b_+--_o_ thll collection of Informetlqn le o_Jfn,I t_l to mverfg9 I ho'ar Fm.rrmupnn.H, I.,,alud!nll _ t.kl_ f_ revle.wlng Ingtm_/onm, _,L_I+n__ IXll_k'lU dl_.l SOUPINg0glt._ll IrlE .nd r_..mlntalnlns the alike nomclml, el+_l oompllUl'_l ins rlv+lWll_ _ .oo_i+i.._:lOnIsT M11.o,rm,ITlOfi, .Imlna ©ol._rmlnll mjlmmmg 'mew burd,n **tim,t, or ,my omit iipem of _1, oollemlon _ Inform,tiroL In .dudln_ luOgp_nn+ f,r ,_ly.m,g Im.*..numpntp .w_l_*_nm0_n.m.,uq_ul_e_, ue_r__1. _. Dlriloforlll for Infm, mut}an C _lrltllml ind Papm'tw. I | 1 li J/|flrlMI DIVII Mlgrlwly, UiJI_i 1 ;[_, AfllrloTorl+ YA Z++u;I-6.3uz, Erie 118 lirlW _ilTItgl UI[ IMlrlalilmmln[ NK_01t. P+l_vMk Rodu_Jo | PrOJl(X (0704_1U). WNhlngton, DC 20503,

1. AOENCYUiEON_ _ b_n_ |.REPO_ DATE 2. RI_ORT TYPE AND DATE8 COVERED December 1994 Technical Memorandum

4.7_LEANDSUBTffLE 8, FUNDIN tu NUM|ERE

_.AUTHO_(B) NASA Reliability and Maintainability Steering Committee

7. PERFORMiNeOR_ANRA_ONNAMEL|IANDADDREiIIEil REPORT NUMBER NASA Office of Safety and Mission Assurance, Safety and Risk Management Division

10, 8PONSOR_OIMONITOP_NO I. sPoNSOmNO_ONITONNGASENCTNAME(DIANDADDREES{ES) AGENCY REPORT NU_qBER National Aezonautice and 5pace A_inistratio_ Washington+ DC 20546 NASA TM-4628

1I. SUPPLEMENTARY NOTE8

Iaa. DISTNBUTION_VAI_LITYETATEM_T Igb. DISTNBU_ON CODE

Un¢las_ified - Unlimited

Subject Category 38

13, ABSTRACT (MaximUm 200 wwdal

This manual presents a series of recommended techniques that can increase overall operational effeetlvness of both flight and ground based NASA systems. It provides a set of tools that minimizes risk associated wi_h; - Restoring failed functions (both ground and fllgh_ based) - conducting co_plex a_d highly vlsiblemaintenance operations - Sustaining a technical capability to support the NASA mission using agin_ e_uipment or facilities It considers (i) program Rangement - key elements of an effective main_alnability effort; {2) design and developmen_ - techniques that have benefited previous programs; (3) analysis and teS_ - qu_tltative _d qualitative analysis processes and testing techniques; and (4) operations and operational design techniques that address NASA field experience. This d_cument is a valuable resource for continuous improvement ideas in executing _he systems development process in accordance with the NASA "better, faster, ,_aller, end cheeper" goal without +om_omlalng _afety.

1E, NUMBER OF PAGES 14. su_Ec'r_[_| maintainability, maintenance, design and test, • yet_me engineering, space eystem design, operational 104 effectiveness, ground-based systems, flight systems, life-cycle 10, PNCE CODE cost A05

7. SECUR_r_ CLASSIFICATION I1. IiCuRrrf CLAEEIFICA'rlON 1III. IECURITY CLASIIFICATION 20. LIMITATION OF ABE'TRACT OF REPORT OF THIS PAeE OF ABSTRACT Unclassified Uncleselfled Unclassified ndard Form 20E (Flev. 2-SQI NON 7540-01,2E0_51S00 ei©ribd by _d_ll_Ind. Z31-_il :IIII-102