Guide to Verifying Safety-Critical Structures for Reusable Launch and Reentry Vehicles

Guide to Verifying Safety-Critical Structures for Reusable Launch and Reentry Vehicles Version 1.0 November 2005 HQ-033805 Guide to Verifying Safety-Critical Structures for Reusable Launch and Reentry Vehicles Version 1.0 November 2005 Federal Aviation Administration Commercial Space Transportation 800 Independence Avenue, SW, Room 331 Washington, DC 2059 NOTICE Use of trade names or the names manufacturers or professional associations in this document does not constitute an official endorsement of such products, manufacturers, or associations, either expressed or implied, by the Federal Aviation Administration. TABLE OF CONTENTS 1.0 INTRODUCTION ...........................................................................................................1 1.1 Purpose ..........................................................................................................................1 1.2 Scope .............................................................................................................................1 1.3 Acronyms.......................................................................................................................1 1.4 Definitions .....................................................................................................................2 2.0 GENERAL RECOMMENDATIONS: STRUCTURAL AND MECHANICAL VERIFICATION.......................................................................................................................4 2.1 General Structural Systems Recommendations...............................................................4 2.2 Structural Verification Approaches for Design and Test Factors of Safety......................5 2.2.1 Prototype Testing: Design and Test Factors of Safety..............................................5 2.2.2 Protoflight Testing: Design and Test Factors of Safety............................................5 2.2.3 Verification by Analysis ..........................................................................................5 2.2.4 Probabilistic Methods ..............................................................................................6 2.3 Reliability and System Safety.........................................................................................6 3.0 DETAILED RECOMMENDATIONS: STRUCTURAL AND MECHANICAL VERIFICATION.......................................................................................................................6 3.1 Applicability ..................................................................................................................6 3.2 Design and Test Factors of Safety ..................................................................................7 3.2.1 Metallic Structures...................................................................................................7 3.2.2 Fasteners and Preloaded Joints.................................................................................7 3.2.3 Composite and Bonded Structures............................................................................8 3.2.4 Structural Glass........................................................................................................8 3.2.5 Bonds for Structural Glass .......................................................................................9 3.2.6 Pressure Vessels, Lines, Fittings, and Components ..................................................9 3.3 Fatigue and Creep Life Recommendations ...................................................................10 3.4 Facture Control ............................................................................................................10 3.4.1 Damage Tolerance Analysis...................................................................................11 3.4.2 Damage Tolerance Testing.....................................................................................11 4.0 ALTERNATE STRUCTURAL AND MECHANICAL VERIFICATION METHODOLOGIES ..............................................................................................................11 5.0 SUMMARY ...................................................................................................................11 6.0 BIBLIOGRAPHY..........................................................................................................12 iii TABLES Table 1. Recommended Minimum Design and Test Factors for Metallic Structures....................7 Table 2. Recommended Minimum Design and Test Factors for Fasteners and Preloaded Joints.8 Table 3. Recommended Minimum Design and Test Factors for Composite and Bonded Structures .............................................................................................................................8 Table 4. Recommended Minimum Design and Test Factors for Structural Glass ........................9 Table 5. Recommended Minimum Design and Test Factors for Structural Glass Bonds ............9 Table 6. Recommended Minimum Design and Test Factors for Pressurized Lines, Fittings, and Components........................................................................................................................10 Table 7. Recommended Minimum Design and Test Factors for Pressurized Vessels ................10 iv 1.0 INTRODUCTION 1.1 Purpose This guide provides acceptable methods of verifying safety-critical structures for reusable launch vehicles (RLV’s). It defines structural safety factors and methodologies for demonstrating compliance with the Federal Aviation Administration (FAA), Office of Commercial Space Transportation (AST), regulations and for the safe operation of the applicant’s proposed vehicle. This guide serves as a companion document to the three FAA/AST publications listed below. It provides very specific guidance on verifying safety-critical structures per the guidelines refer- enced in the following documents. • Guide to Reusable Launch Vehicle Safety Validation and Verification Planning, Version 1.0, September 2003 (see http://ast.faa.gov). • Advisory Circular 431.35-2A – Reusable Launch and Reentry Vehicle System Safety Process, July 2005 (see http://ast.faa.gov). • Guide to the Identification of Safety-critical Hardware Items for Reusable Launch Vehi- cle (RLV) Developers (see http://ast.faa.gov). An applicant may use this document or an acceptable equivalent process to demonstrate compliance with 14 CFR 431 – Launch and Reentry of a Reusable Launch Vehicle and 14 CFR 437 – Experimental Permits. This guide makes no distinction between inhabited or uninhabited vehicles; however, structures of inhabited vehicles may be subjected to additional verification and safety requirements that are consistent with 14 CFR 460 – Suborbital Reusable Launch Vehicle Operations with Space Flight Participants and Crew. Potential RLV operators are strongly en- couraged to start a pre-application dialogue with FAA/AST in the development phase of a proposed RLV program, so that any potential public safety concerns can be addressed as early as possible. 1.2 Scope This guide provides a compilation of recommended structural design and acceptable methods of verification for RLV developers to use in demonstrating that their proposed vehicle’s design and operations satisfy regulatory licensing requirements. This list of vehicle structural analysis and design criteria provides an acceptable basis for demonstrating that the structural systems can sur- vive and perform to an adequate level of safety in all operating environments, including launch, flight, on-orbit, reentry, and recovery. 1.3 Acronyms AIAA – American Institute of Aeronautics and Astronautics AST – Office of Commercial Space Transportation COPV – Composite Overwrapped Pressure Vessels FAA – Federal Aviation Administration MEOP – Maximum Expected Operating Pressure MS – Margin of Safety NDE – Nondestructive Evaluation NASA – National Aeronautics and Space Administration RLV – Reusable Launch Vehicle 1.4 Definitions Acceptance test – A test performed on each article of the flight hardware to verify workmanship, material quality, and structural integrity of the design. In the protoflight structural verification approach, acceptance, proof, and protoflight tests are synonymous. Acceptance test factor – A multiplying factor applied to the limit load or maximum expected operating pressure (MEOP) to define the acceptance test load or pressure (i.e. Acceptance test load = Acceptance test factor Limit load or MEOP). Allowable load – The maximum load or combination of loads which a structure or a component of a structural assembly can sustain during its service life under all expected conditions of operation or use without potential rupture, collapse, or detrimental deformation. Creep – Time-dependent permanent deformation under sustained load and environmental conditions. Detrimental yielding – Yielding that adversely affects the fit, form, function, or integrity of the structure. Factors of safety (safety factors) – Multiplying factors to be applied to limit loads or stresses for purposes of analytical assessment (design factors) or test verification (test factors) of design ade- quacy in strength or stability. Fatigue – Cumulative irreversible damage incurred in materials caused by cyclic application of stresses and environments resulting in degradation of load-carrying capability. Fracture (safe-life) control – Rigorous application of engineering processes and methodologies, such as assurance management, manufacturing, and operations technology, dealing with the analysis and prevention

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