Space Systems Engineering

Home , Spacecraft design, Systems design

Space Systems Engineering • Lecture #02 – August 29, 2019 • Background of Systems Engineering • NASA program planning phases • Scheduled milestones • Requirements document • Work breakdown structure • Technology readiness levels • Project management tools • Design reference missions and CONOPS • Decision analysis tools

© 2019 David L. Akin - All rights reserved • Risk tracking http://spacecraft.ssl.umd.edu U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 1 Overview of Systems Engineering • Developed to handle large, complex systems – Geographically disparate – Cutting-edge technologies – Significant time/cost constraints – Failure-critical • First wide-spread applications in aerospace programs of the 1950’s (e.g., ICBMs) • Rigorous, systematic approach to organization and record-keeping

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 2 NASA Lifecycle Overview

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 3 NASA Formulation Stage Overview

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 4 Space Systems Formulation Process

Pre-Phase A Conceptual Design Phase Development of performance goals and requirements Establishment of Science Working Group (science missions) Trade studies of mission concepts Feasibility and preliminary cost analyses Request for Phase A proposals

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 5 Space Systems Formulation Process

Pre-Phase A Preliminary Analysis Phase Proof of concept analyses Mission operations concepts Phase A “Build vs. buy” decisions Payload definition Selection of experimenters Detailed trajectory analysis Target program schedule RFP for Phase B studies

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 6 Space Systems Formulation Process

Pre-Phase A Definition Phase Define baseline technical solutions Create requirements document Phase A Significant reviews: Systems Requirements Review Phase B Systems Design Review Non-Advocate Review Request for Phase C/D proposals Ends with Preliminary Design Review (PDR)

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 7 Historical Implications of Study Phases

from J. A. Moody, ed., Metrics and Case Studies for Evaluating Engineering Designs Prentice-Hall, 1997 U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 8 Implementation Stage Overview

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 9 Space Systems Implementation Process Development Phase Pre-Phase A Detailed design process “Cutting metal” Phase A Test and analysis Significant reviews: Critical Design Review (CDR) Phase B Test Acceptance Review Flight Readiness Review Phase C/D Ends at launch of vehicle

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 10 Space Systems Implementation Process

Pre-Phase A Operations and End-of-Life Launch On-orbit Check-out Phase A Mission Operations Maintenance and Troubleshooting Phase B Failure monitoring End-of-life disposal

Phase C/D

Phase E/F

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 11 NASA Project Life Cycle - Milestones

from NASA SP-2007-6105 rev. 1, “NASA Systems Engineering Handbook” U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 12 NASA Project Life Cycle - Acronyms

from NASA SP-2007-6105 rev. 1, “NASA Systems Engineering Handbook”

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 13 Requirements Document • The “bible” of the design and development process • Lists (clearly, unambiguously, numerically) what is required to successfully complete the program • Requirements “flow-down” results in successively finer levels of detail • May be subject to change as state of knowledge grows • Critical tool for maintaining program budgets

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 14 Akin’s Laws of Spacecraft Design - #13

Design is based on requirements. There's no justification for designing something one bit "better" than the requirements dictate.

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 15 DYMAFLEX

Stowed Deployed Conﬁguraon Conﬁguraon

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 16 DYMAFLEX Program Mission Statement Investigate the coupled dynamics and associated control mitigation strategies for a free-flying vehicle with a high-performance manipulator performing tasks analogous to satellite servicing

Should be a clear, unambiguous, definitive statement of the purpose of the program, and what it will achieve when complete.

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 17 Apollo Program Mission Statement “I believe this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to Earth.”

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 18 DYMAFLEX Program Objectives • Develop a microsatellite in the university environment through a program which maximizes opportunities for students to be involved in all aspects of the development process. • Leverage three decades of advanced space robotics research in the development and flight demonstration of a space manipulator system • Investigate the coupled dynamics and associated control mitigation strategies for a free-flying vehicle with a high-performance manipulator performing tasks analogous to satellite servicing U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 19 DYMAFLEX Mission (L1) Requirements

M-1 DYMAFLEX shall include a robotic manipulator

DYMAFLEX shall be able to move the manipulator sufﬁciently fast as to cause larger dynamic M-2 coupling between manipulator and host vehicle than currently experienced on ﬂown systems

DYMAFLEX shall be able to downlink telemetry of experiments to validate success of M-3 algorithms on the ground DYMAFLEX shall operate in an environment where system dynamics dominates perturbations M-4 due to environmental effects DYMAFLEX shall be able to introduce unknown values to control system by changing the mass M-5 conﬁguration of its end effector

DYMAFLEX shall be able to return to a stable attitude after or during dynamic motions of the M-6 manipulator DYMAFLEX shall simulate a variety of payload motions to cover desirable sets of future M-7 trajectories M-8 DYMAFLEX shall maximize useful life on orbit by accepting new experiments from the ground

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 20 DYMAFLEX System (L2) Requirements

DYMAFLEX shall be able to perform a minimum set of trajectories: a single DOF, multi-axis S-1 linear and extended nonlinear S-2 DYMAFLEX shall meet launch program's requirements (see UNP7 Users Guide) DYMAFLEX shall be able to know its position, orientation, manipulator conﬁguration, and lock S-3 state of tip masses DYMAFLEX shall have sufﬁcient communications capability to downlink a minimum of TBD Mb S-4 of experiment data within life of spacecraft

DYMAFLEX shall generate sufﬁcient power (# watts TBD) to execute the minimum set of S-5 experiments and communicate results to ground

S-6 DYMAFLEX shall have multiple interchangeable tip masses for the manipulator

DYMAFLEX shall have sufﬁcient computational power to perform realtime kinematic and S-7 manipulator control calculations

S-8 DYMAFLEX shall be able to put itself into a safe mode in the event of a critical anomaly

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 21 DYMAFLEX ROBO (L3) Requirements

S1-1 ROBO shall have a 4 DOF manipulator

S1-2 ROBO shall be able to change tip masses

S1-3 ROBO shall be capable of minimum end effector velocity of TBD m/s

S1-4 ROBO shall sense joint position, velocity, and torque

S1-5 ROBO shall sense motor controller temperature and current draw

ROBO shall not extend below the Satellite interface plane (during or after S1-6 deployment)

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 22 DYMAFLEX STRM (L3) Requirements

S2-1 The STRM shall have a natural frequency of at least 100 Hz with a goal of TBD Hz

S2-2 The STRM shall withstand g's in the x,y,z direction

S2-3 The STRM shall have a factor of safety of 2.0 for yield and 2.6 for ultimate for all structural elements

S2-4 STRM shall have a mass less than TBD grams with a goal of less than TBD grams

S2-5 STRM shall interface with lightband at satellite interface plane with 24 #1/4 bolts

S2-6 STRM shall not extend below Satellite interface plane (during or after deployments)

S2-7 STRM shall provide system with solar panels that will provide sufﬁcient power for experiments STRM shall ensure CG for DYMAFLEX is within envelope (less than 0.5cm from lightband centerline, S2-8 less than 40cm above satellite interface plane) S2-9 STRM shall ensure ﬁnal dimensions of DYMAFLEX meet requirements (50cm x 50cm x 60 cm tall)

S2-10 STRM materials shall meet all outgassing and stress corrosion cracking requirements

STRM shall provide adequate venting such that the pressure difference is less then 0.5 psi with a factor of S2-11 safety of 2

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 23 Requirements Verification Matrix • Single spreadsheet tracking all requirements, sources, status, and documentation • Broken down to successively finer levels of detail (frequently 4-6 levels) • For a major program, the printed version can run to hundreds of pages • Ensures that nothing gets overlooked and everything is done for a purpose

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 24 Requirements Verification Matrix

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 25 Interface Control Documents • Used to clearly specify interfaces (mechanical, electrical, data, etc.) between mating systems • Critical since systems may not be fit-checked until assembled on-orbit! • Success of a program may be driven by careful choices of interfaces • KISS principle holds here (“keep it simple, stupid”)

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 26 Akin’s Laws of Spacecraft Design - #15

(Shea's Law) The ability to improve a design occurs primarily at the interfaces. This is also the prime location for screwing it up.

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 27 System Block Diagrams • Shows interrelationships between systems • Can be used to derive communication bandwidth requirements, wiring harnesses, delineation of responsibilities • Created at multiple levels (project, spacecraft, individual systems and subsystems)

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 28 Exo-SPHERES S/C Block Diagram Wiring Harness! COMM! RCS! High Bandwidth! Thrusters (x 16)! ADCS! Antenna! ! XPNDR! (TBD)! (TBD)! Valves! Reaction Wheel (TDB)! Antenna! ! (x3)! (TBD) ! Tank! Tank! Low Bandwidth! ! ! 9 DOF IMU (TDB)! Antenna! (x 3)! XPNDR! (TBD)! EPS! (TBD)! Antenna! Kibo Airlock! C&DH! SFT! (TBD) ! Charger! Disk OS! Storage! Scheduling! VIS! Batteries! ADCS! Forward Camera (x2)! RCS! ! Regulator! COMM! Aft Camera! CPU! ROBO! STRM! Lights (TDB)! Interfaces! THRM! AMP! Access Hatches! Sensors! Active (TDB)! (TDB)! Payload! Restraints! Cushioning! Passive (TDB)!

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 29 Exo-SPHERES RCS Block Diagram

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 30 Work Breakdown Structures • Detailed “outline” of all tasks required to develop and operate the system • Successively finer levels of detail – Program (e.g., Constellation Program) – Project (Lunar Exploration) – Mission (Lunar Sortie Exploration) – System (Pressurized Rover) – Subsystem (Life Support System) – Assembly (CO2 Scrubber System) – Subassembly, Component, Part, ...

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 31 NASA Standard WBS Levels 1 & 2

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 32 Standard WBS for JPL Mission

Project Name

Project Management Project Sys Eng Mission Assurance Science Payload Flight System Mission Ops System Launch System 1 01 02 03 04 05 06 07 08

Project Mgmnt Project Sys Eng MA Mgmnt Science Mgmnt P/L Mgmnt Spacecraft Contract Mission Ops Mgmnt Launch Services 2 01.01 02.01 03.01 04.01 05.01 06.00 07.01 08.01

Business Mgmnt Mission & Nav Design System Safety Science Team P/L Sys Eng Flt Sys Mgmnt MOS Sys Eng

WBS Levels WBS 3 01.02 02.02 03.02 04.02 05.02 06.01 07.02

Risk Mgmnt Project SW Eng Environments Sci Data Support Instrument 1 Flt Sys - Sys Eng Ground Data Sys 01.03 02.03 03.03 04.03 05.03 06.02 07.03

Project Plng Spt Information Systems Reliability Sci Investigatio Instrument N Power Subsys Operations 01.04 02.04 03.04 & Ops Spt 05.04 06.03 07.04 04.04

Review Support Config Mgmnt EEE Parts Eng Sci Environment Common P/L Systems Command & Data S/s MOS V&V 01.05 02.05 03.05 Characterization 05.05 06.04 07.05 04.05

Facilities Planetary Protection HW Q&A Education & Outreach P/L I&T Telecomm Subsys 01.06 02.06 03.06 04.06 05.06 06.05

Foreign Travel/ITAR Launch Sys Eng SW Q&A Mechanical Subsys 01.07 02.07 03.07 06.06

Project V&V Contamination Control Thermal Subsys 02.08 03.08 06.07

SW IV&V Propulsion Subsys 03.09 06.08

GN&C Subsys 06.09

Spacecraft Flt SW 06.10

Testbeds 06.11 U N I V E R S I T Y O F SpacecraftSpace assembly Systems Engineering test & verification ENAE 483/788D - Principles06.12 of Space Systems Design MARYLAND 33 Detail across JPL WBS Level II 1. Project Management 2. Project Systems Engineering 3. Mission Assurance 4. Science 5. Payload 6. Flight System 7. Mission Operations System 8. Launch System

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 34 Standard WBS for JPL Mission

Project Name

Project Management Project Sys Eng Mission Assurance Science Payload Flight System Mission Ops System Launch System 1 01 02 03 04 05 06 07 08

Project Mgmnt Project Sys Eng MA Mgmnt Science Mgmnt P/L Mgmnt Spacecraft Contract Mission Ops Mgmnt Launch Services 2 01.01 02.01 03.01 04.01 05.01 06.00 07.01 08.01

Business Mgmnt Mission & Nav Design System Safety Science Team P/L Sys Eng Flt Sys Mgmnt MOS Sys Eng

WBS Levels WBS 3 01.02 02.02 03.02 04.02 05.02 06.01 07.02

Risk Mgmnt Project SW Eng Environments Sci Data Support Instrument 1 Flt Sys - Sys Eng Ground Data Sys 01.03 02.03 03.03 04.03 05.03 06.02 07.03

Project Plng Spt Information Systems Reliability Sci Investigatio Instrument N Power Subsys Operations 01.04 02.04 03.04 & Ops Spt 05.04 06.03 07.04 04.04

Review Support Config Mgmnt EEE Parts Eng Sci Environment Common P/L Systems Command & Data S/s MOS V&V 01.05 02.05 03.05 Characterization 05.05 06.04 07.05 04.05

Facilities Planetary Protection HW Q&A Education & Outreach P/L I&T Telecomm Subsys 01.06 02.06 03.06 04.06 05.06 06.05

Foreign Travel/ITAR Launch Sys Eng SW Q&A Mechanical Subsys 01.07 02.07 03.07 06.06

Project V&V Contamination Control Thermal Subsys 02.08 03.08 06.07

SW IV&V Propulsion Subsys 03.09 06.08

GN&C Subsys 06.09

Spacecraft Flt SW 06.10

Testbeds 06.11 U N I V E R S I T Y O F SpacecraftSpace assembly Systems Engineering test & verification ENAE 483/788D - Principles06.12 of Space Systems Design MARYLAND 35 Detail in JPL “Flight Systems” Column 1. Spacecraft Contract 2. Flight Systems Management 3. Flight Systems - Systems Engineering 4. Power Systems 5. Command and Data Handling Systems 6. Telecommunications Systems 7. Mechanical Systems 8. Thermal Systems 9. Propulsion Systems 10.Guidance, Navigation, and Control Systems 11.Spacecraft Flight Software 12.Testbeds 13.Spacecraft Assembly, Test, and Verification U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 36 Akin’s Laws of Spacecraft Design - #24

It's called a "Work Breakdown Structure" because the Work remaining will grow until you have a Breakdown, unless you enforce some Structure on it.

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 37 Technology Readiness Levels

TRL 9 Actual system “flight proven” through successful mission operations TRL 8 Actual system completed and “flight qualified” through test and demonstration TRL 7 System prototype demonstration in the real environment TRL 6 System/subsystem model or prototype demonstration in a relevant environment TRL 5 Component and/or breadboard validation in relevant environment TRL 4 Component and/or breadboard validation in laboratory environment TRL 3 Analytical and experimental critical function and/or characteristic proof-of-concept TRL 2 Technology concept and/or application formulated TRL 1 Basic principles observed and reported

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 38 Gantt* Charts

September October November December ID Task Name Duration Start Finish Predecessors9/1 9/8 9/15 9/22 9/29 10/6 10/13 10/20 10/27 11/3 11/10 11/17 11/24 12/1 12/8 1 Design Robot 4w Tue 9/3/02 Mon 9/30/02 2 Build Head 6w Tue 10/1/02 Mon 11/11/02 1 3 Build Body 4w Tue 10/1/02 Mon 10/28/02 1 4 Build Legs 3w Tue 10/1/02 Mon 10/21/02 1 5 Assemble 2w Tue 11/12/02 Mon 11/25/02 2,3,4

*developed by Charles Gantt in 1917

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 39 PERT Charts*

*Program Evaluation and Review Technique U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 40 A Simple Approach to PERT Charts

Task Name Task Duration A 1 1 1 Earliest Start Time Latest Start Time

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 41 A Simple Approach to PERT Charts

B 2 E 4 B

A 1 C 4 F 1 H 2 1 F

D 3 G 2

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 42 Propagate Forward for Earliest Starts

B 2 E 4 2 B

A 1 C 4 F 1 H 2 1 2 F

D 3 G 2 2 U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 43 Propagate Forward for Earliest Starts

B 4 E 3 2 6B

A 1 C 2 F 1 H 2 1 2 6F 9

D 3 G 2 Completion=11 2 5 U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 44 Propagate Backward for Latest Starts

B 4 E 3 2 6B 6

A 1 C 2 F 1 H 2 1 2 6F 8 9 9

D 3 G 2 Completion=11 2 5 7 U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 45 Propagate Backward for Latest Starts

B 4 E 3 2 2 6B 6

A 1 C 2 F 1 H 2 1 1 2 4 6F 8 9 9

D 3 G 2 Completion=11 2 4 5 7 U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 46 Difference Starts for Slack Time

B 4 E 3 2 2 6B 6 0 0 A 1 C 2 F 1 H 2 1 1 2 4 6F 8 9 9 0 2 2 0 D 3 G 2 Completion=11 2 4 5 7 U N I V E R S I T Y O F 2 2 Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 47 Identify Critical Path(s)

B 4 E 3 2 2 6B 6 0 0 A 1 C 2 F 1 H 2 1 1 2 4 6F 8 9 9 0 2 2 0 D 3 G 2 Completion=11 2 4 5 7 U N I V E R S I T Y O F 2 2 Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 48 Akin’s Laws of Spacecraft Design - #23

The schedule you develop will seem like a complete work of fiction up until the time your customer fires you for not meeting it.

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 49 Design Reference Missions • Description of canonical mission(s) for use in design processes • Could take the form of a narrative, storyboard, pictogram, timeline, or combination thereof • Greater degree of detail where needed (e.g., surface operations) • Created by eventual users of the system (“stakeholders”) very early in development cycle

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 50 Concept of Operations • Description of how the proposed system will accomplish the design reference mission(s) • Will appear to be similar to DRM, but is a product of the design, rather than a driving requirement • Frequently referred to as “CONOPS”, showing DOD origins

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 51 Space Systems Architecture • Description of physical hardware, processes, and operations to perform DRM • Term is used widely (e.g., “software architecture”, “mission architecture”, “planning architecture”), but refers to basic configuration decisions • Generally result of significant trade studies to compare options

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 52 ESAS Final Architecture/CONOPS

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 53 Success Criteria • Part of program formulation phase is to clearly identify observable metrics that will define success • Generally consists of two sets – “Full mission success” represents the minimum case for success in a nominal mission – “Minimal success” represents success criteria in the event of degraded capacity • Important to recognize that even “full mission success” is far below aspirational goals

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 54 Decision Analysis Tools • A number of different approaches exist, e.g. – Decision Matrices (aka Pugh Method) – Quality Function Deployment – Six Sigma – Analytic Hierarchy Process (details in notes) • Generally provide a way to make decisions where no single clear analytical metric exists - “quantifying opinions” • Allows use of subjective rankings between criteria to create numerical weightings • Not a substitute for rigorous analysis! U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 55 Analytical Hierarchy Process • Considering a range of options, e.g., ice cream – Vanilla (V) – Peach (P) – Strawberry (S) – Chocolate (C) • Could ask for a rank ordering, e.g. (1) vanilla, (2) strawberry, (3) peach, (4) chocolate - but that doesn’t give any information on how firm the rankings are • Use pairwise comparisons to get quantitative evaluation of the degree of preference

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 56 Pairwise Comparisons • Ideally, do exhaustive combinations – Vanilla >> chocolate (strongly agree) – Vanilla >> peach (agree) – Vanilla >> strawberry (agree) – Peach >> chocolate (strongly agree) – Peach >> strawberry (disagree) – Strawberry >> chocolate (strongly agree) • Number of required pairings out of N options is (N)(N-1)/2 - e.g., N=20 requires 190 pairings! • Can use hierarchies of subgroupings to keep it manageable

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 57 Evaluation Metric • Create a numerical scaling function, e.g. – “strongly agree” = 9 – “agree” = 3 – “neither agree nor disagree” = 1 – “disagree” = 1/3 – “strongly disagree” = 1/9 • Numerical rankings are arbitrary, but often follow geometric progressions – 9, 3, 1, 1/3, 1/9 – 8, 4, 2, 1, 1/2, 1/4, 1/8 U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 58 Evaluation Matrix • Fill out matrix preferring rows over columns

C S P V

C Note: if you have multiple people performing an AHP evaluation, S 9 populate a matrix like this for each of them, then add the matrices together P 9 1/3 and use that summary matrix as you proceed with the rest of the analysis. V 9 3 3

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 59 Evaluation Matrix • Fill out matrix preferring rows over columns • Fill opposite diagonal with reciprocals

C S P V C S P V

C C 1/9 1/9 1/9

S 9 S 9 3 1/3

P 9 1/3 P 9 1/3 1/3

V 9 3 3 V 9 3 3

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 60 Normalization of Matrix Elements • Normalize columns by column sums

C S P V C S P V

C 1/9 1/9 1/9 C 0.032 0.018 0.143

S 9 3 1/3 S 0.333 0.491 0.429

P 9 1/3 1/3 P 0.333 0.097 0.429

V 9 3 3 V 0.333 0.871 0.491

27 3.44 6.11 0.78

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 61 Evaluation of Hierarchy Among Options • Average across the populated row elements

C S P V

C 0.032 0.018 0.143 0.048

S 0.333 0.491 0.429 0.313

P 0.333 0.097 0.429 0.215

V 0.333 0.871 0.491 0.424 ⇐ Top ranking

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 62 Risk Tracking • There are two elements of risk – How likely is it to happen? (“Likelihood”) – How bad is it if it happens? (“Consequences”) • Each issue can be evaluated and tracked on these orthogonal scales • This is not an alternative to probabilistic risk analysis (PRA) ⇒ discussed in a later lecture

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 63 Likelihood Rating Categories 1.Improbable (P<10-6) 2.Unlikely to occur (10 -3>P>10 -6) 3.May occur in time (10 -2>P>10 -3) 4.Probably will occur in time (10 -1>P>10 -2) 5.Likely to occur soon (P>10 -1)

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 64 Consequence Rating Categories 1.Minimal or no impact 2.Additional effort required, no schedule impact, <5% system budget impact 3.Substantial effort required, <1 month schedule slip, >2% program budget impact 4.Major effort required, critical path (>1 month slip), >5% program budget impact 5.No known mitigation approaches, breakthrough required to resume schedule, >10% program budget impact U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 65 Risk Matrix

1 9 4

6 7

3 8 2

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 66 Akin’s Laws of Spacecraft Design - #38

Capabilities drive requirements, regardless of what the systems engineering textbooks say.

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 67 Today’s Tools You should understand and be able to create and use • Project scheduling (PERT and Gantt charts, critical path determination) • Requirements definition and flow-down • Work breakdown structures • Risk definition charts • Design reference missions • Concept of operations • Analytical hierarchy process • Earned value management (slides only) U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 68 References (Available Online)

• NASA Systems Engineering Handbook - SP-6105 - June, 1995 [2.3 Mb, 164 pgs.] (Obsolete, but nice description of NASA's systems engineering approach) • NASA Systems Engineering Processes and Requirements - NPR 7123.1A - March 26, 2007 [3.6 Mb, 97 pgs.] (Current version - pages are almost impossible to read without a magnifying glass) • NASA Space Flight Program and Project Management Requirements - NPR 7120.5D - March 6, 2007 [2.7 Mb, 50 pgs.] (Current version - pages are almost impossible to read without a magnifying glass) • NASA Program and Project Management Processes and Requirements - NPR 7120.5C - March 22, 2005 [1.9 Mb, 174 pgs.] (Older, superceded version, but includes more figures and is readable by mere mortals) • NASA Goddard Space Flight Center Procedures and Guidelines: Systems Engineering - GPG 7120.5B - 2002 [1.7 Mb, 31 pgs.] • NASA Goddard Space Flight Center Mission Design Processes (The "Green Book") [860 Kb, 54 pgs.] • NASA Systems Engineering “Toolbox” for Design-Oriented Engineers - NASA RP-1538, December 1994 [9.1 Mb, 306 pgs] U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 69 Earned Value Management • Method of tracking progress on large programs • Initially supported by DOD • Assesses “earned value” by fraction of task completed vs. cost allocated to task • Earned value tracked against expenditures to see where program compares to nominal schedule • Details will not be covered in class, but are in the lecture notes online • You will be held responsible for this material

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 70 Earned Value Management • Consider a simple program with four two-month tasks that are expected to cost various amounts

$4 M

$10 M

$6 M

$8 M

$2M $7M $8M $7M $4M Planned monthly costs 1 2 3 4 5 Months

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 71 Program Cost Accounting • Traditionally monitored by “burn rate” - cumulative expenditures with time

15 Cumulative 10 Costs ($M) Costs 5

0 0 1 2 3 4 5 Months

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 72 Earned Value Management - Month 1 • In the first month, you complete 60% of task 1 and 10% of task 2 • Actual costs for month 1 = $3 M EV=$3.4 M

$4 M EV(1)=0.6*4=$2.4 M

$10 M EV(2)=0.1*10=$1 M

$6 M

$8 M

1 2 3 4 5 Months

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 73 Earned Value Management - Month 2 • In the second month, you complete 100% of task 1 and 60% of task 2 • Actual costs for month 2 = $10 M EV=$10 M

$4 M EV(1)=1.0*4=$4 M

$10 M EV(2)=0.6*10=$6 M

$6 M

$8 M

1 2 3 4 5 Months

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 74 Earned Value Management - Month 3 • In the third month, you complete 100% of task 1, 80% of task 2, and 40% of task 3 • Actual costs for month 3 = $16 M EV=$14.4 M

$4 M EV(1)=1.0*4=$4 M

$10 M EV(2)=0.8*10=$8 M

$6 M EV(3)=0.4*6=$2.4 M

$8 M

1 2 3 4 5 Months

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 75 Program Cost Accounting - Tracking • Plotting actual costs vs. time shows how money is spent, but doesn’t tell anything about how much work has been accomplished

15 Cumulative 10 Actual Costs ($M) Costs 5

0 0 1 2 3 4 5 Months

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 76 Program Cost Accounting - Tracking • Earned value tracks accomplishments against their planned costs • Variation shows schedule performance

15 Cumulative 10 Earned Value Costs ($M) Costs 5

0 0 1 2 3 4 5 Months

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 77 Program Cost Accounting - Tracking • Comparing earned value to actual costs shows “apples to apples” comparison of money spent and value achieved

15 Cumulative Earned Value 10 Actual Costs ($M) Costs 5

0 0 1 2 3 4 5 Months

U N I V E R S I T Y O F Space Systems Engineering ENAE 483/788D - Principles of Space Systems Design MARYLAND 78