JSC-67723_Propulsion_Standard_Basic_Final.pdf

JSC-67723

BASIC

27 APRIL 2025

STANDARD FOR THE CONTROL OF

CATASTROPHIC HAZARDS IN HUMAN-

RATED SPACECRAFT PROPULSION

SYSTEMS

Abstract: Building safe, reliable, high performance, and successful spacecraft propulsion systems for human spaceflight by appropriate application of the necessary standards, practices, and hazard mitigations early in the design and test phase.

Engineering Directorate Office of Primary Responsibility: EP / Propulsion and Power Division

Compliance is Mandatory

National Aeronautics and Space Administration

Public Release Statement

This document has been reviewed for Proprietary, SBU, and Export Control (ITAR/EAR) and has been determined to be non-sensitive. It has been released to the public via the NASA Scientific and Technical Information (STI) Process DAA# 20250001287.

Revision: Basic Document No: JSC-67723

Date: 27 April 2025

Title: STANDARD FOR THE CONTROL OF CATASTROPHIC HAZARDS IN

HUMAN-RATED SPACECRAFT PROPULSION SYSTEMS

APPROVED FOR PUBLIC RELEASE — DISTRIBUTION IS UNLIMITED

Change Record

Revision

/DCN

Date Originator Approvals Description

Basic 27 April

Eric Hulbert /

EP4

Per EA MRCB CR/D

EA-0296

Initial Release.

Prepared by:

John Albright, Subject Matter Expert (SME), Spacecraft Propulsion Systems Date TriVector Services, Inc.

Eric Hurlbert, Propulsion Technical Discipline Lead Date EP4 / Propulsion and Fluid Systems Branch

Approved by:

Clemente Quintana, Chief Date EP4 / Propulsion and Fluid Systems Branch

Richard Schoenberg, Division Chief Engineer Date EP1 / Propulsion and Power Division

Edgar Castro, Chief Date EP / Propulsion and Power Division, EP

Julie Kramer White, Director Date EA / Engineering Directorate, EA

John Albright (affiliate) Digitally signed by John Albright (affiliate) Date: 2025.05.09 08:50:32 -05'00'

ERIC HURLBERT Digitally signed by ERIC HURLBERT Date: 2025.05.09 10:24:11 -05'00'

Clemente Quintana Digitally signed by Clemente Quintana Date: 2025.05.09 13:37:50 -05'00'

Richard Schoenberg Digitally signed by Richard Schoenberg Date: 2025.05.12 14:19:59 -05'00'

Edgar Castro Digitally signed by Edgar Castro Date: 2025.05.12 16:13:10 -05'00'

Gerald Lebeau Digitally signed by Gerald Lebeau Date: 2025.05.12 17:49:22 -05'00'

Table of Contents

1 INTRODUCTION

1.1 PURPOSE AND SCOPE

1.2 BACKGROUND

1.3 PROPULSION SYSTEM FAILURE MODES AND HAZARDS

1.4 SPACECRAFT AND PROPULSION SYSTEM RELIABILITY

2 HUMAN RATED SPACECRAFT PROPULSION SYSTEMS

2.1 APPLICABLE TECHNICAL STANDARDS FOR SPACECRAFT PROPULSION

SYSTEMS

3 HUMAN RATED PROPULSION SYSTEM STANDARDS AND REQUIREMENTS

3.1 VEHICLE AND PROPULSION SYSTEM REQUIREMENTS

3.1.1 VEHICLE AND PROPULSION SYSTEM PERFORMANCE

3.1.2 CRITICAL MATH MODELS

3.1.3 REUSABLE VEHICLE PROPULSION SYSTEMS

3.1.4 REDUNDANCY AND FAULT TOLERANCE

3.1.5 FAILURE TOLERANCE EXCEPTIONS IN PROPULSION SYSTEMS

3.1.6 SEPARATION OR PROTECTION OF REDUNDANT FUNCTIONS

3.1.7 GN&C AND THRUSTERS/ENGINE PERFORMANCE AND SERVICE LIFE ICD... 30

3.1.8 PLUME IMPINGEMENT LOADS, DYNAMICS, HEATING, AND CONTAMINATION

3.1.9 PROPELLANT SLOSH COUPLING WITH GN&C & STRUCTURE

3.1.10 DIFFERENTIAL DRAINING IMPACT ON VEHICLE CENTER OF GRAVITY ... 34

3.1.11 LOADS AND STRUCTURAL DYNAMICS REQUIREMENTS

3.1.12 UNSTABLE DYNAMIC COUPLING OF ENGINE/THRUSTER, FEED SYSTEM,

AND VEHICLE STRUCTURE

3.1.13 THERMAL CONTROL OF THE PROPULSION SYSTEM

3.1.14 PROPULSION SYSTEM VENTS AND UNINTENDED LEAKS - EXTERNAL

AND INTERNAL

3.1.15 ANOMALY, ISSUES, PROBLEM TRACKING AND RESOLUTION

3.2 PROPULSION SYSTEM, SUBASSEMBLY, AND COMPONENT TESTING

3.2.1 GENERAL TESTING APPROACH

3.2.2 PROPULSION SYSTEM LEVEL QUALIFICATION TEST

3.2.3 PROPULSION SYSTEM DEVELOPMENT SYSTEM LEVEL TEST

3.2.4 PROPULSION SYSTEM ACCEPTANCE, ASSEMBLY, INTEGRATION, AND

TEST (AI&T)

3.2.5 PROPULSION SYSTEM ALLOWABLE LEAK RATE ASSESSMENT AND

VERIFICATION FOR FLIGHT AND QUALIFICATION ARTICLES

3.3 FLIGHT OPERATIONAL FLUIDS; PROPELLANT, PRESSURANTS, PNEUMATIC;

PROCUREMENT AND USAGE SPECIFICATION

3.3.1 GENERAL FLUID PROCUREMENT AND USAGE REQUIREMENTS

3.3.2 GENERAL FLUID INTERFACE FILTRATION AND SAMPLING REQUIREMENTS 56

3.3.3 OPERATIONAL FLUIDS: PRESSURANT, PNEUMATIC, PURGE, AND COLD GAS

PROPULSION GASES

3.3.4 OPERATIONAL FLUIDS: MONOPROPELLANTS (MAY ALSO BE USED IN

BIPROPELLANT OR DUAL MODE PROPULSION SYSTEMS)

3.3.5 MONOPROPELLANT HAZARDS

3.3.6 OPERATIONAL FLUIDS: BIPROPELLANTS

3.3.7 BIPROPELLANT MMH/NTO HYPERGOLIC SYSTEMS HAZARDS

3.3.8 BIPROPELLANT CRYOGENIC SYSTEMS HAZARDS

3.3.9 PROPELLANT AND PRESSURANT DATA PROPERTY TRACEABILITY

3.4 MATERIALS AND PROCESSES (M&P) AND FLUID COMPATIBILITY

3.4.1 MATERIALS AND PROCESSES STANDARD

3.4.2 TEST AND ASSEMBLY FLUIDS; CLEANING, FLUSHING, AND DRYING

3.4.3 COMPONENT FLUID COMPATIBILITY AND CORROSION ASSESSMENT TEST70

3.4.4 PROPELLANT OXIDIZER AND MATERIAL IGNITION AND COMBUSTION

3.4.5 SOFT GOODS MATERIAL SELECTION, PROPELLANT AND CLEANING FLUID

EXPOSURE

3.4.6 SYSTEM AND COMPONENT CONTAMINATION CONTROL

3.4.7 EXTERNAL FOD, WATER, OR AMBIENT AIR INTRUSION CONTROL

3.4.8 WELDS AND BIMETALLIC JOINTS

3.5 PROPULSION SYSTEM PRESSURIZED HARDWARE

3.5.1 MAXIMUM DESIGN PRESSURE (MDP) AND FACTORS OF SAFETY

3.5.2 FRACTURE CONTROL REQUIREMENTS FOR SPACEFLIGHT HARDWARE

3.5.3 NONDESTRUCTIVE EVALUATION REQUIREMENTS FOR FRACTURE-

CRITICAL METALLIC COMPONENTS

3.5.4 THREADED FASTENERS

3.6 PRESSURE VESSELS AND PROPELLANT TANKS

3.6.1 INTEGRATED PROPELLANT TANK DESIGN AND ANALYSIS

3.6.2 TYPE I METALLIC PRESSURE VESSELS

3.6.3 TYPE II AND III COMPOSITE OVERWRAPPED PRESSURE VESSELS

(COPVS)

3.6.4 TYPE IV. COMPOSITE PRESSURE VESSELS WITH PLASTIC LINER

3.6.5 TYPE V ALL COMPOSITE PRESSURE VESSEL

3.6.6 LIQUID PROPELLANT MANAGEMENT DEVICE (PMD)

3.6.7 TANK SLOSH MITIGATION REQUIREMENT

3.6.8 PROPELLANT QUANTITY GAUGE

3.7 PRESSURIZATION SUBSYSTEM

3.7.1 PRESSURE REGULATION AND ISOLATION

3.7.2 OVERPRESSURE PROTECTION – PRESSURE RELIEF

3.7.3 CONTROL OF CORROSIVE AND REACTIVE PROPELLANT LIQUID AND

VAPORS IN THE PRESSURIZATION SYSTEM

3.8 PROPULSION SYSTEM VALVES

3.8.1 GENERAL REQUIREMENTS

3.8.2 DIMENSIONAL ANALYSIS AND CLEARANCES

3.8.3 TORQUE/FORCE MARGIN ANALYSIS

3.8.4 CYCLE LIFE

3.8.5 VALVE ELECTRICAL

3.9 PROPELLANT FEED SYSTEM

3.9.1 PROPELLANT FEED SYSTEM AND ENGINE INTERFACE CONDITIONS

3.9.2 PROPELLANT FEED SYSTEM ACTIVATION; PRIMING AND REPRIMING

3.9.3 PROPELLANT FEED SYSTEM MAXIMUM DESIGN PRESSURE TRANSIENTS 103

Date: 27 April 2025 Page 7 of 189

Title: STANDARD FOR THE CONTROL OF CATASTROPHIC HAZARDS IN

HUMAN-RATED SPACECRAFT PROPULSION SYSTEMS

APPROVED FOR PUBLIC RELEASE — DISTRIBUTION IS UNLIMITED

3.9.4 FEED SYSTEM MODEL VERIFICATION AND VALIDATION

3.9.5 PROPELLANT ISOLATION – INHIBITS TO BULK PROPELLANT LOSS

3.9.6 FEED SYSTEM BACK PRESSURE RELIEF

3.9.7 FLUID LINE DESIGN, ROUTING, AND INSTALLATION

3.10 GENERAL REQUIREMENTS FOR MECHANICAL FITTINGS, JOINTS, AND

FLANGES

3.10.1 USE OF MECHANICAL FITTINGS/JOINTS VS. BRAZING OR WELDING

3.10.2 MECHANICAL FITTING, JOINT, AND FLANGE DESIGN, QUALIFICATION,

AND ACCEPTANCE

3.11 IN-SPACE FLUID TRANSFER AND SEPARABLE SPACECRAFT MODULES

3.11.1 IN-SPACE FLUID TRANSFER

3.11.2 SEPARATION OF SPACECRAFT MODULES

3.12 FILTERS AND FILTRATION

3.12.1 IDENTIFICATION OF SOURCES AND QUANTITIES OF CONTAMINATION 113

3.12.2 SENSITIVITY TO CONTAMINATION

3.12.3 INCORPORATION OF FILTERS

3.12.4 FILTER SPECIFICATION, QUALIFICATION, AND ACCEPTANCE TEST

REQUIREMENTS

3.12.5 ALTERNATE TO THE USE OF WIRE CLOTH AND ETCHED DISC

FILTERS

3.13 PYROTECHNIC VALVES

3.13.1 NORMALLY CLOSED (NC) PARENT METAL HERMETIC SEALING VS.

NORMALLY OPEN (NO)

3.13.2 GENERAL REQUIREMENTS FOR PYRO VALVES

3.14 THIN WALL FLEXIBLE PRESSURE BOUNDARY (TWFPB) HARDWARE ITEMS:

BELLOWS, FLEX HOSES, AND DIAPHRAGMS

3.14.1 TWFPB FAILURE MODES AND EFFECTS ANALYSIS

3.14.2 TWFPB DESIGN, ANALYSIS, AND TEST REQUIREMENTS

3.14.3 FLOW INDUCED VIBRATION

3.15 SPACECRAFT ENGINES AND THRUSTERS

3.15.1 OPERATING CONDITIONS AND HERITAGE

3.15.2 STRENGTH AND LIFE REQUIREMENTS, SERVICE LIFE QUALIFICATION 128

3.15.3 REUSABLE ENGINES

3.15.4 SMC-S-025, EVALUATION AND TEST REQUIREMENTS FOR LIQUID

ROCKET ENGINES & SMC-S-016

3.15.5 DELTA -QUALIFICATION

3.15.6 COMBUSTION STABILITY

3.15.7 THERMAL LIMITATIONS AND CONTROL

3.15.8 ENGINE/THRUSTER IGNITION SYSTEMS

3.15.9 OVERPRESSURES; CONTROL OF HARD STARTS, ZOTS, AND POPS

3.15.10 ENGINE AND VALVE LEAK DETECTION

3.15.11 THRUST VECTOR CONTROL (TVC)

3.16 FDIR, INSTRUMENTATION, DATA RATES, AND SOFTWARE

3.16.1 FAULT DETECTION ISOLATION AND RECOVERY (FDIR)

3.16.2 INSTRUMENTATION DATA RATES

3.16.3 SYSTEM LEAK DETECTION – INTERNAL AND EXTERNAL

3.16.4 INSTRUMENTATION TYPES AND HAZARDS

3.17 PROPULSION SYSTEM ELECTRICAL

3.17.1 PROTECTIVE

3.17.2 ELECTRICAL BONDING

3.17.3 PROPULSION DEVICE POWER SWITCHING

3.17.4 CORONA SUPPRESSION

3.18 FLIGHT AND GROUND OPERATIONS INTERFACE

3.18.1 HARDWARE TIME AND CYCLE TRACKING

3.18.2 FLIGHT OPERATIONS

3.18.3 FLIGHT HARDWARE-TO-GROUND INTERFACE PROTECTIONS

3.18.4 HARDWARE WARNING SIGNS, LABELS, AND MARKINGS

APPENDIX A: REQUIREMENTS APPLICABILITY MATRIX

APPENDIX B: LIST OF ACRONYMS AND ABBREVIATIONS

APPENDIX C: LIST OF REFERENCES INCLUDING LESSONS LEARNED AND REPORTS

List of Figures

FIGURE 1: ORGANIZATION OF PROPULSION STANDARD CONTENT

List of Tables

TABLE 1 HUMAN SPACECRAFT ONBOARD CHEMICAL PROPULSION SYSTEMS WORKED BY

THE PROPULSION TECHNICAL DISCIPLINE AT NASA

TABLE 2: LIST OF TYPE 2 STANDARDS FOR THE CONTROL OF CATASTROPHIC HAZARDS

IN HUMAN-RATED SPACECRAFT PROPULSION SYSTEMS

TABLE 3 LIST OF TYPE 3 REFERENCE DOCUMENTS FOR THE CONTROL OF CATASTROPHIC

HAZARDS IN HUMAN-RATED SPACECRAFT PROPULSION SYSTEMS

Foreword and Acknowledgements

This document was prepared with the review and inputs from many engineers representing disciplines across the agency such as propulsion, structures, guidance, navigation, and control (GN&C), materials and processes (M&P) over a couple of years. The requirements and information were gathered from as many different sources as possible. Without these inputs the document could not have been prepared up to this point. The intent is to release this document to gather further inputs from industry and government in order to further improve this document. An update will be provided in a revision.

1 INTRODUCTION

1.1 PURPOSE AND SCOPE

The gaps in requirements that control spacecraft propulsion systems hazards are a particular emphasis of this document with a strong belief that up-front communication and clarity in the standards, which consider the many costly lessons learned over time, will reduce technical, cost, and schedule issues and improve overall safety. The National Aeronautics and Space Administration (NASA) Procedural Requirements (NPR) document NPR 8705.2C, Human-Rating Requirements for Space Systems, defines requirements for the control of catastrophic hazards in human-rated space systems. The NASA Technical Authority (TA) and the NASA Design and Construction standards are the foundation of the process. Some of the applicable standards are owned by NASA, some are owned by iother United State (U.S.) Government agencies, and some are owned by private industry.

Collectively, these TA standards provide a structured and repeatable means of designing, analyzing, manufacturing, assembling/integrating, testing, servicing/maintaining, and operating a human-rated spacecraft successfully. Despite the existence of these TA standards, there are still some significant gaps in the content, understanding, and application of requirements that are relevant to the control of catastrophic hazards associated with human-rated spacecraft propulsion systems.

Spaceflight history is full of lessons learned related to failure modes and hazards of propulsion systems which have been codified into the many technical standards and guidelines publications that are in use today, whether owned by NASA, the U.S. military, or the aerospace industry. Incorporating lessons learned into a project upfront has been shown to have significant benefit to its success. This document, which is specific to human-rated spacecraft propulsion systems, identifies failure scenarios, hazards, specific standards/requirements, and the source of one or more driving lesson(s) learned. The sources for lessons learned include publicly available reports from the cognizant engineers and the NASA Lessons Learned Information System (LLIS), with topics such as LLIS 21501. “Projects Benefit from Lessons Learned on Previous Spaceflight Projects” (LLIS-21501, 2017)

In summary, this document is intended to define the key requirements and address known requirement gaps needed to control catastrophic hazards associated with onboard chemical propulsion systems of any type on a human-rated spacecraft, including liquid abort systems. Note that the scope does include all orbital, transit, and lander vehicles but not boosters or upper stages.

The goal is to ensure that the collective body of knowledge reflected by the existing TA standards, in addition to the supplemental requirements contained herein which have been gathered over a period of many years of spacecraft propulsion systems engineering, are applied efficiently and effectively without resulting in the catastrophic events and costly technical issues needing rework that can occur late in a project/program.

The scope covers gaseous, earth storable liquid, and cryogenic liquid and gaseous propellants and propulsion systems. It does not cover solid propellants or electric propulsion systems, though the fluid systems that deliver oxidizer for hybrid propulsion systems and gaseous propellants to electric thrusters would need to meet the requirements contained herein. Some additional requirements may apply to supporting subsystems, such as active refrigeration for long duration spacecraft, specific Xenon (Xe) propellant procurement and use specification, or electric propulsion system thrusters and their interfacing power systems. However, it is expected that those types of systems would still need to meet many of same hazard control requirements contained herein, such as service life, maximum design pressures, material compatibility, ignition hazards, etc., while noting that there may be additional hazard control requirements imposed on hybrid and electric propulsion systems.

1.2 BACKGROUND

The propulsion technical discipline at NASA, shared across multiple centers, has been heavily involved in the design, development, testing, and evaluation (DDT&E); failure modes and hazards analyses; assembly, integration, and testing (AI&T); ground checkout and servicing; launch preparations; flight operations; and sustaining engineering and maintenance for chemical propulsion systems on human-rated spacecraft and importantly on other non-human rated vehicles spanning multiple projects/programs over the last six decades. A list of the human rated propulsion systems, dating back to the beginning of the US human spaceflight program, is shown in Table 1. This document represents a set of knowledge and lessons learned from the propulsion engineering and flight/ground operations teams, who have provided technical support for propulsion systems of the past, to inform similar propulsion systems of the future. NASA programs and projects should assess their compliance with NASA lessons learned at each major program or project milestone. Reference Each NASA Project Should Assess Its Compliance with NASA Lessons Learned. (LLIS-2042, 2009)

TABLE 1 HUMAN SPACECRAFT ONBOARD CHEMICAL PROPULSION SYSTEMS WORKED BY

THE PROPULSION TECHNICAL DISCIPLINE AT NASA

PROJECT/PROGRAM ELEMENT/VEHICLE/PAYLOAD PROPULSION SYSTEM DETAILS STATUS

PROPELLANT(S) VACCUM THRUST LEVEL(S)

MERCURY SPACECRAFT CAPSULE 90% H2O2 1 LBF, 6 LBF, 24 LBF

(REF) (NASA, 1963, PP.

54,283)

FLOWN

GEMINI CAPSULE ORBIT ATTITUDE

AND MANEUVERING SYSTEM

(OAMS) AND REACTION

CONTROL SYSTEM (RCS)

MMH / NTO 8 X 25 LBF OAMS

8 X 100 LBF OAMS

16 X 25 LBF RCS

(REF) (BLATZ, 1964, PP. 14,

FIG 13)

FLOWN

APOLLO LUNAR MODULE (LM) A50 / NTO 10500 LBF (DME)

(REF) (HAMMOCK, 1973, P. 7)

FLOWN

APOLLO LUNAR MODULE (LM) A50 / NTO 1 X3500 LBF (AME)

(REF) (HUMPHRIES, 1973, P. 2)

16 X 100 LBF (RCS)

(REF) (VAUGHAN, 1972, P. 2)

FLOWN

APOLLO SERVICE MODULE RCS MMH / NTO SM: 16X 100 LBF (REF)

(TAEUBER, 1973, PP. 6, PARA.

4)

FLOWN

APOLLO COMMAND MODULE (CM)

RCS

MMH / NTO CM: 12X 100 LBF (REF)

(TAEUBER, 1973, PP. 9,39, FIG.

18)

FLOWN

APOLLO SERVICE MODULE (SM) MAIN

ENGINE

A50 / NTO 21,500 LBF (SME) (REF)

(GIBSON C. R., 1973, PP. 5,

PARA 3)

FLOWN

SSP ORBITER MAIN PROPULSION

SYSTEM (MPS)

LH2 / LO2 3 X 512,000 LBF (REF)

(MARTINEZ, 2011, P. 2), SSME

RS25

FLOWN

SSP ORBITER ORBITAL

MANEUVERING SYSTEM

(OMS)

MMH / MON3 2 X 6000 LBF (REF) (GIBSON

C. , 1985, PP. 13, FIG 10)

FLOWN

SSP ORBITER REACTION

CONTROL SYSTEM (RCS)

MMH / MON3 38 X 870 LBF, 6 X 25 LBF

(VERNIER) (PRIMARY) (REF)

(HERNANDEZ, 2011, PP. 23,

PARA 2)

FLOWN

GEMINI, APOLLO, SSP LO2/LH2 POWER REACTANT

STORAGE AND

DISTRIBUTION (PRSD)

SYSTEM

LOX/LH2

(SUPERCRITICAL)

UP TO 3 X UP TO 16 KW (REF)

(HERNANDEZ, 2011, P. 28),

(REF) (DAVIS, 1970), (REF )

(SIMON, 1985, PP. 15, TABLE

3), FLOWN

ORION MPCV CREW MODULE (CM) HYDRAZINE 12 X 160 LBF (REF) FLOWN

ORION MPCV SERVICE MODULE (SM) MMH / MON3 1 X 6225 LBF (27.7 KN) (OMS-

E)

8 X 110 LBF (490N) (AUX)

24 X 50 LBF (220N) (RCS)

(REF) (PHILIPPE BERTHE,

2017, PP. 4-5)

FLOWN

ISS SOYUZ ON-ORBIT UDMH / N2O4 28 X 30 LBF (REF) (BOWMAN,

2016, P. 6:07)

FLOWN

ISS SOYUZ DESCENT MODULE

(DM)

H2O2 8 SMALL THRUSTERS (REF)

(NASA PRESS KIT, 2004, P.

PARA 6)

FLOWN

ISS CRS H-II TRANSFER

VEHICLE (HTV)

MMH / MON3 4 X 110 LBF MAIN

28 X 25 LBF ACS (REF)

(MATSUO, 2012, PP. 1-2)

FLOWN

ISS CRS AUTOMATED TRANSFER

VEHICLE (ATV)

MMH / MON3 4 X 110 LBF MAIN

28 X 50 LBF ACS (REF)

(EUROPEAN SPACE AGENCY,

N.D.)

FLOWN

ISS CRS CYGNUS HYDRAZINE

(N2H4) / MON3

DUAL MODE N2H4 AND MON3

OR N2H4 (REF) (GRUMMAN,

N.D.)

FLOWN

ISS CCP / CRS DRAGON MMH / MON3 8 X 16K LBF LIQUID ABORT

16 X 90 LBF DRACO (REF)

(SPACEX, N.D.)

FLOWN

ISS CCP CST-100 STARLINER MMH / MON3 4X 40K LBF LIQUID ABORT,

20 X 1500 LBF ORBITAL,

28 X 85 LBF RCS (REF)

(L3HARRIS, N.D.)

FLOWN

As evident in this table, the bulk of historical experience involves pressure-fed, earth storable hypergolic propellant systems, which are the primary source of requirements and best practices appearing in this document. However, other propellant combinations have also been the subject of significant development, test, certification, and flight operations over the course of time. While there are many commonalities among propulsion systems in terms of design, construction, testing/checkout, ground/flight operations, and hazard analyses, there are also some unique attributes associated with certain propellants that must be considered in that context. The recent advent of high thrust (128,000 lbf+ total) pressure-fed liquid abort systems integrated with orbital maneuvering systems is also evident.

The body of work outlined above represents a high level of practical experience and subject matter expertise needed to effectively identify, document, and control the catastrophic hazards associated with spacecraft propulsion systems.

1.3 PROPULSION SYSTEM FAILURE MODES AND HAZARDS

The hazards are typically grouped into 4 major categories associated with a spacecraft propulsion system that could result in loss of mission (LOM), loss of vehicle (LOV), and/or loss of crew (LOC), as listed below:

• Rupture

• Leakage – external, internal

• Fire/explosion

• Loss of Control – translation and/or attitude

Of course, there are many possible causes for each of these catastrophic hazards and the controls are typically rooted in the use of appropriate design and construction standards; rigorous qualification, acceptance, and integrated system testing; and functional redundancy built into the system. For spacecraft propulsion systems, the failure modes associated with these hazards include leakage/release of fluid commodities from weld flaw or mechanical fittings, pressure vessel rupture, engine burn through, flammable environments, over-pressurization of the system or surrounding compartments/volumes, structural failure of the interfacing primary or secondary structure, fracture of thin wall membranes, thruster inadvertent firings due to avionics or wiring fault, loss of thrust vector control (TVC), thruster failure to fire or shut down due to valve sticking, etc. A table of requirements, applicability, and catastrophic failure modes/hazards, and lessons learned references is contained in Appendix A.

1.4 SPACECRAFT AND PROPULSION SYSTEM RELIABILITY

Reliability of the propulsion system, inclusive of the associated hardware and software, is established thru the various design, analysis, assembly/integration, and test requirements contained in these standards. The goal is to keep it ‘Safe, Simple, Lightweight, Reliable, and Robust.’ Of course, that is a very challenging task full of critical design decisions and process optimization to meet the mission requirements with minimum practical risk and adequately controlled hazards, within the physics prescribed by the rocket equation. Extra mass and extra margin above that required are not extra good. For example, added mass in the propulsion system might be better spent to improve safety or performance in some other system within the spacecraft. A probabilistic risk assessment (PRA) that assigns a probability to LOM, LOV, and/or LOC requires test data on failure modes, anomalies, how often it occurs, and consequences etc. that is specific to the hardware being used and considers the details of its application (ref NASA/SP-2011-3421 Probabilistic Risk Assessment Procedures Guide for NASA Managers and Practitioners). The requirements included herein provide that test data, however the PRA is beyond the scope of this document. Capture of Apollo Lunar Module Reliability Lessons Learned: Reliability Engineering) (LLIS 1835, 2008)

2 HUMAN RATED SPACECRAFT PROPULSION SYSTEMS

This propulsion system standard, and other standards, derives from NASA Procedural Requirements (NPR) 8705.2C, Human-Rating Requirements for Space Systems and NASA-STD-8719.29 NASA Technical Requirements for Human-Rating, specifically:

• NPR 8705.2C, paragraph 2.2.3 requires a process to be defined for identifying, assessing, and mitigating failure scenarios and hazards thru a formal safety analysis process.

• NPR 8705.2C, paragraphs 2.4.3 and 2.4.4 require a definition of how critical system level performance characteristics and critical system level interactions will be verified/validated, respectively, to avoid catastrophic hazards.

• NASA-STD-8719.29, paragraph 4.3.1 provides general requirements for the control of catastrophic hazards.

• NPR 8705.2C also describes the process for a project/program to define the standards to be implemented for the activity.

NASA-STD-8719.29 paragraph 4.3.1 states that the space system shall provide at least single failure tolerance to catastrophic events, with specific levels of failure tolerance and implementation (similar or dissimilar redundancy) derived via an integration of the design and safety analysis (required by

NPR 8705.2). Notable exceptions include pressure vessels and primary structure, where redundancy of a structural nature is not practically achievable. In some cases, mission architecture may provide a form of dissimilar redundancy (a.k.a. unlike redundancy), but its use as a hazard control must be formally established by a given project/program and it does not provide effective control of certain catastrophic hazards associated with a propulsion system that are characterized by a short ‘time to effect’ due to rapid events.

2.1 APPLICABLE TECHNICAL STANDARDS FOR SPACECRAFT PROPULSION SYSTEMS

The technical standards shown in Table 2 each play a role in addressing the catastrophic failure modes associated with human rated spacecraft propulsion systems and have all been cited in one or more requirement statements in subsequent sections of this document. Therefore, they are considered as ‘applicable’ Type 2 standards (i.e. meets or exceeds) for use by all projects/programs charged with developing such systems, with tailoring and/or substitution considered possible via an adjudication process to be defined by the NASA project/program and supporting NASA Technical Authorities.

The technical standards and other documents shown in Table 3 also play a role in hazard control for human rated spacecraft propulsion systems but have only been cited in the text and/or rationale paragraphs that accompany the requirement statements in this document. The intent is to provide a source of additional clarification/information on a given topic. Therefore, they are considered as Type 3 (reference only) documents for use by all projects/programs charged with developing such systems.

Note that all entries in both tables are listed in alphabetical/numerical order by document number.

Also note that the philosophy here is to provide a pointer to the appropriate technical standards, in whole or in part, and avoid repeating the detailed requirements language of those standards, unless there is a specific need to clarify, modify, or expand the content to address common misconceptions or identified gaps in the implementation for the control of specific hazards.

Despite the existence of these standards, there are still some significant gaps in the requirements relevant to the control of catastrophic hazards for spacecraft propulsion systems. This statement is based on the many past and recent technical issues experienced during propulsion system development and operations. These gaps and clarifications are the main source of requirements included herein this document. In addition, each requirement is annotated with a description as shown below:

The revisions for each standard, which have been used for the clarification and gap assessments herein, are shown in table 2. Substitution or a conflict with a more recent version of a given standard, or use of another standard altogether, would be subject to an adjudication process and could be influenced by other project/program considerations.

This document uses the word ‘shall’ for requirements that must be implemented and verified to control catastrophic hazards, ‘should’ for items that represent a recommended best practice but are not mandatory, ‘will’ for items that represent an expected outcome or statement of fact but are not verified, and ‘are’ or ‘is’ for items that represent informative/descriptive material.

Tailoring of the requirements in this standard for application to a specific project/program is acceptable when formally documented and approved by the delegated NASA Technical Authority in accordance with NPR 7120.5, NASA Space Flight Program and Project Management Requirements.

TABLE 2: LIST OF TYPE 2 STANDARDS FOR THE CONTROL OF CATASTROPHIC HAZARDS

IN HUMAN-RATED SPACECRAFT PROPULSION SYSTEMS

Document # Document Title Rev TA Type Publi c

A-A-59150 Cleaning Compound, Solvent, Hydrofluoroether (HFE)

A, 02/14/2003 Eng 2 Y

AIAA G-082 Guide: Space Systems – Composite Overwrapped Pressure Vessels with a Plastic Liner

2022 Eng 2 Y

AIA/NAS412 Foreign Object Debris (FOD) Prevention Guidance Document

3,2023 Eng 2 Y

AIAA SP-084-

Fire, Explosion, Compatibility, and Safety Hazards of Hypergols – Hydrazine

1999 w/ 12/05/2001 Correction

Eng 2 Y

AIAA SP-085-

Fire, Explosion, Compatibility, and Safety Hazards of Hypergols – Monomethylhydrazine

1999 Eng 2 Y

AIAA SP-086-

Fire, Explosion, Compatibility, and Safety Hazards of Nitrogen Tetroxide

Jan 2001 Eng 2 Y

AFRL-RZ-ED-

TP-2008-184

Nitrous Oxide Explosive Hazards 05/19/2008 Eng 2 Y

ANSI/AIAA G-

Guide to Safety of Hydrogen and Hydrogen Systems

A-2017 Eng 2 Y

ANSI/AIAA S-

Space Systems - Metallic Pressure Vessels, Pressurized Structures and Pressurized Components

A-2018 Eng 2 Y

ANSI/AIAA S-

Space Systems - Composite Overwrapped Pressure Vessels

B-2018 Eng 2 Y

AIAA-S-157 In Space Storable Fluid Transfer for Prepared Spacecraft

-2024 Eng 2 Y

ARP901 Bubble-Point Test Method Rev B Eng 2 Y

ARP599 Aerospace - Dynamic Test Method for Determining the Relative Degree of Cleanliness of the Downstream Side of Filter Elements

Rev D Eng 2 Y

Document # Document Title Rev TA Type Publi c

ASTM D1193 Standard Specification for Reagent Water

11/1/2024 Eng 2 Y

ASTM MNL 36 Safe Use of Oxygen and Oxygen Systems: Guidelines for Oxygen System Design, Materials Selection, Operations, Storage, and Transportation

Second Edition Eng 2 Y

CGA G-8.2 Commodity Specification for Nitrous Oxide

Seventh Edition Eng 2 Y

CGA G-11.1 Commodity Specification for Argon Eighth Edition Eng 2 Y

IEST-STD-

CC1246

Product Cleanliness Levels – Applications, Requirements, and Determination

E, Feb 2013 Eng 2 Y

ISO 14644-1 Cleanrooms and Associated Controlled Environments – Part 1: Classification of Air Cleanliness by Particle Concentration - Second Edition

Second Edition, 12/15/2015

Eng 2 Y

JANNAF-GL-

2022-0001 (Note:

Formerly CPIA 655)

Guidelines for Combustion Stability Specifications and Verification Procedures for Liquid Propellant Rocket Engines

Jan 1997 Eng 2 N

JSC-08080-2 JSC Design and Procedural Standards B w/ DCN 001, 08/04/2020

Eng 2 Y

JSC 28596 NASA Standard Initiator User’s Guide A, 02/29/2000 Eng 2 N

JSC 62809 Human Rated Spacecraft Pyrotechnic Specification

G, 11/08/2024 Eng 2 N

JSC 65828 Structural Design and Factors of Safety for Spaceflight Hardware

B w/ Chg 1, 07/15/2014

Eng 2 Y

JSC 65829 Loads and Structural Dynamics Requirements for Spaceflight Hardware

B, 03/01/2024 Eng 2 Y

JSC 67035 Best Practices and Guidelines (BP&G) for Thin Wall Pressure Boundaries (TWPB) for Human Spaceflight Applications

A, Aug 2017 Eng 2 Y

JSC ES

151001-1

Use of ASME Code or Code of Federal Regulations Title 49 Department of Transportation (DOT) Pressure Vessels for Space Applications

01/19/2016 Eng 2 N

MIL-PRF-

27401

Performance Specification, Propellant Pressurizing Agent, Nitrogen

H w/ Amd 2, 01/09/2024

Eng 2 Y

MIL-PRF-

27407

Performance Specification, Propellant Pressurizing Agent, Helium

E, 04/23/2024 Eng 2 Y

MIL-PRF-

26536

Performance Specification, Propellant, Hydrazine

G w/ Amd 1, 07/13/2021

Eng 2 Y

MIL-PRF-

16005

Performance Specification, Propellant, Hydrogen Peroxide

F, 08/01/2023 Eng 2 Y c

MIL-PRF-

27201

Performance Specification, Propellant, Hydrogen

F, 08/26/2022 Eng 2 Y

MIL-PRF-

25508

Performance Specification, Propellant, Oxygen

J, 03/02/2020 Eng 2 Y

MIL-PRF-

26539

Performance Specification, Propellant, Dinitrogen Tetroxide

G w/ Amd 1, 04/19/2017

Eng 2 Y

MIL-PRF-

27404

Performance Specification, Propellant, Monomethylhydrazine

D, 04/20/2012 Eng 2 Y

MIL-PRF-

27415

Propellant Pressurizing Agent, Argon D, 02/28/2023 Eng 2 Y

MIL-PRF-

32207

Performance Specification, Propellant, Methane

BL, 10/10/2006 Eng 2 Y

MIL-PRF-

25567

Leak Detection Compound, Oxygen Systems

E, 07/10/2015 Eng 2 Y

MIL-STD-461 Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment

G, 12/11/2015 Eng 2 Y

MIL-DTL-

25576

Detail Specification, Propellant, Rocket Grade Kerosene

F w/ Amd 1, 05/24/2023

Eng 2 Y

MSFC-SPEC-

Flow-Induced Vibration Assessment Requirements for Metal Bellows and Flex hoses

BL, 04/16/2020 Eng 2 Y

NASA-SPEC-

NASA Manufacturing and Test Requirements for Normally Closed Pyrovalves for Hazardous Flight Systems Applications

BL w/ Chg 2, 06/24/2015

Eng 2 Y

NASA-STD-

Electrical Bonding for NASA Launch Vehicles, Spacecraft, Payloads, and Flight Equipment

A w/ Chg 1, 01/16/2019

Eng 2 Y

NASA-STD-

Nondestructive Evaluation (NDE) Requirements for Fracture Critical Metallic Components

C, 08/03/2023 Eng 2 Y

NASA-STD-

Strength and Life Assessment for Liquid Rocket Engines

B, 06/16/2016 Eng 2 Y

NASA-STD-

Design and Development Requirements for Mechanisms

B, 12/06/2022 Eng 2 Y

NASA-STD-

Fracture Control Requirements for Spaceflight Hardware

A w/ Chg 4, 02/01/2016

Eng 2 Y

NASA-STD-

Requirements for Threaded Fastening Systems in Spaceflight Hardware

B, 08/06/2021 Eng 2 Y

NASA-STD-

Standard Materials and Processes Requirements for Spacecraft

C w/ Chg 1, 11/15/2023

Eng 2 Y

NASA-STD-

Standard for Models and Simulations A, 05/08/2019 Eng 2 Y

NASA-STD-

Leak Test Requirements A, 02/22/2023 Eng 2 Y c

NASA-STD-

8719.12

Safety Standard for Explosives, Propellants, and Pyrotechnics

A w/ Chg 2, 03/18/2021

Eng 2 Y

NASA-STD-

8719.24 and Annex

ANNEX TO NASA-STD-8719.24,

NASA Payload Safety Requirements:

Requirements Table

B, 03/30/2022 S&MA 2, In part Y

NASA-STD-

8719.29

NASA Technical Requirements for Human Rating

BL, 12/11/2023 S&MA 2 Y

NASA-STD-

8739.10

Electrical, Electronic, and Electromechanical (EEE) Parts Assurance Standard

BL, 06/17/2013 S&MA 2 Y

NASA/TM-

20210022275

Treatment of Transient Pressure Events in Space Flight Pressurized Systems

N/A Eng 2 Y

NESC-RP-19-

01498

Filtration of Spaceflight Propulsion and Pressurant Systems

N/A Eng 2 Y

NESC

Technical Bulletin No.

22-02

Revisiting Filtration Standards and Definitions for Spaceflight Propulsion and Pressurant Systems

N/A Eng 2 Y

NPR 6000.1 Requirements for Packaging, Handling, and Transportation for Aeronautical and Space Systems, Equipment, and Associated Components

H Eng 2 Y

NPR 8705.2 Human-Rating Requirements for Space Systems

C w/ Chg 2 N/A N/A Y

MIL-STD-1252

Inertia Friction Welding Process, Procedure and Performance Qualification

BL,03/11/1998 Eng 2 Y

SMC-S-016 Test Requirements for Launch, Upper- Stage, and Space Vehicles

09/05/2014 Eng 2 Y

SMC-S-025 Evaluation and Test Requirements for Liquid Rocket Engines

07/26/2017 Eng 2 Y

TOR-

2013(3909)-1

Objective Reuse of Heritage Products 04/30/2012 Eng 2 Y

TT-I-735 Isopropyl Alcohol A, 06/06/2007 Eng 2 Y

TABLE 3 LIST OF TYPE 3 REFERENCE DOCUMENTS FOR THE CONTROL OF CATASTROPHIC

HAZARDS IN HUMAN-RATED SPACECRAFT PROPULSION SYSTEMS

Document # Document Title Rev TA Type Publi c

AIAA 91-2172 Propellant Management Device Conceptual Design and Analysis: Vanes

1991 Eng 3 Y

AIAA 93-1970 Propellant Management Device Conceptual Design and Analysis: Sponges

1993 Eng 3 Y

AIAA 97-2811 Propellant Management Device Conceptual Design and Analysis: Galleries

1997 Eng 3 Y

AFRPL-TR-69-

USAF Propellant Handbook Hydrazine Fuels Vol I

March 1970 Eng 3 Y

AFRPL-TR-76-

USAF Propellant Handbook Nitric Acid/Nitrogen Tetroxide Oxidizers

Feb. 1977 Eng 3 Y

ANSI/AIAA S-

Mass Properties Control for Space Systems A-2015 Eng 3 Y

ARAED CR-

90002

Hazard Classification Testing of Liquid Propellants

May 1990 Eng 3 Y

CGA G-5.3 Commodity Specification for Hydrogen 8th Edition, Eng 3 Y

FED-STD-209 Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones

E, 09/11/1992 (cancelled 11/29/2001)

Eng 3 Y

JANNAF CPIA

Publication 246

Rocket Engine Performance Prediction and Evaluation Manual

April 1975 Eng 3 Y

KSC-STD-Z-

Design of Hypergolic Propellants Ground Support Equipment, Standard For, C Eng 3 Y

NASA-HDBK-

Spacecraft High Voltage Paschen and Corona Design Handbook.

Change 3, 2020-12-29

Eng 3 Y

NASA-HDBK-

Fracture Control Implementation Handbook for Payloads, Experiments, and Similar Hardware, Vol I and II

Vol I: A, 12/15/2023 Vol II: A, 01/09/2024

Eng 3 Y

NASA-HDBK-

Pyrovalve Applications and Performance Handbook

A w/ Chg 2, 12/27/2021

Eng 3 N

NASA-HDBK-

NASA Handbook for Models and Simulations: An Implementation Guide for NASA-STD-7009A

A, 05/08/2019

Eng 3 Y

NASA-HDBK-

8739.19-2

Measuring and Test Equipment Specifications. 2010-07-13 Baseline

S&M A

3 Y

NASA-HDBK-

8739.19-3

Measurement Uncertainty Analysis Principles and Methods, NASA Measurement Quality Assurance Handbook - ANNEX 3

2010-07-13 Baseline

S&M A

3 Y

NASA SP-8055 Prevention of Coupled Structure-Propulsion Instability (POGO)

Oct 1970 Eng 3 Y

NASA-STD-

NASA-STD-6001, Flammability, Offgassing, and Compatibility Requirements and Test Procedures.

B w/ Chg 2, 04/21/2016

Eng 3 c

NASA/TM-

20210022275

Treatment of Transient Pressure Events in Space Flight Pressurized Systems

Oct 2021 Eng 3 Y

NASA TN D-

Fundamental Techniques of Weight Estimating and Forecasting for Advanced Manned Spacecraft and Space Stations

May 1971 Eng 3 Y

NESC

Technical Bulletin 19-02

90/95 POD Radiography Concern for COPVs and Metal Tank Welds

N/A Eng 3 Y

NESC

Technical Bulletin 20-06

Material Compatibility Assessment of Spacecraft Oxidizer Systems

N/A Eng 3 Y

NESC

Technical Bulletin 20-07

Evaluating and Mitigating Liner Strain Spikes in COPVs

N/A Eng 3 Y

NESC

Technical Bulletin 21-01

Experimental and Computational Study of Cavitation in Hydrogen Peroxide

N/A Eng 3 Y

NESC

Technical Bulletin 22-03

Treatment of Transient Pressure Events in Space Flight Pressurized Systems

N/A Eng 3 Y

NESC

Technical Bulletin 22-07

Helium Solubility in MMH and NTO N/A Eng 3 Y

NESC

Technical Bulletin 22-08

Contamination Reduction in High Purity Hydrazine

N/A Eng 3 Y

SAE AS85421 Fittings, Tube, Fluid Systems, Separable, Beam Seal, 3000-4000 psi, General Specification for

C, May 2021 Eng 3 Y

3 HUMAN RATED PROPULSION SYSTEM STANDARDS AND REQUIREMENTS

The following sections call out the existing technical standards and additional requirements aimed at filling gaps to address the failure modes and controlling the associated catastrophic hazards of a human-rated spacecraft propulsion system. These requirements are broadly applicable to many types of liquid and gaseous spacecraft propulsion systems and can be tailored accordingly.

This section is structured as follows, from the vehicle and system level down to the components of the system as shown in Figure 1. Many of the most significant propulsion system failures can be traced back to the vehicle or propulsion system initial sizing or conceptual design selections or can be related to vehicle level interactions with avionics, Guidance, Navigation, and Control (GN&C), flight software (FSW), structures, thermal control, and other interfacing systems on the spacecraft, or can be traced to the application of ‘heritage’ components in manner for which it was not capable.

Detrimental interactions within the propulsion system itself can also lead to hardware failures and associated hazards. Recent examples include, but are not limited to, the following: (1) the operation of components, in series and/or in parallel, causing transient pressures that result in leakage or uncommanded state changes of other valves, (2) the combined effects of external ground environment exposure (e.g. moist air) and internal propellant exposure (e.g. MON propellant) resulting in permeation through seals that drives unexpected corrosion of ‘non-wetted’ component parts, (3) MON propellant exposure in combination with elevated pressure and temperature conditions resulting in Teflon seal swell that adversely affects component flow area/delta P and leakage performance, and (4) transient liquid propellant flow during water-hammer events caused by propulsion system activation sequences, line/manifold priming steps, thruster firings, etc. which damages components exposed to the excessive surge pressures. These types of interactions may occur for nominal, dispersed, and/or fault cases and conditions, necessitating a methodical and thorough assessment of all relevant scenarios.

In many cases, these types of issues are discovered late in the program and drive a complex and costly redesign, additional analysis and/or testing, operating procedure workarounds, or an increased level of risk acceptance for the technical authority (TA) and project/program. The goal is early detection of any issues during pre-preliminary design review (PDR) tests, and successful completion of the component level qualification tests and propulsion system level qualification tests with those components included. Ultimately, a series of development, acceptance, and qualification tests will be necessary to verify the requirements.

FIGURE 1: ORGANIZATION OF PROPULSION STANDARD CONTENT

3.1 VEHICLE AND PROPULSION SYSTEM REQUIREMENTS

3.1.1 Vehicle and Propulsion System Performance

3.1.1.1 The critical propulsion system performance parameters, including delta-V, engine specific impulse (Isp), propellant load, propellant mass fraction of the total propulsion system mass, and mission duration including nominal values, tolerances, and margins shall be specified at the conceptual design phase for all options being considered, with confirmation at the system definition review (SDR) and continued tracking throughout the remainder of the project to ensure that the vehicle and propulsion system with the required fault tolerance closes. [PSR- 01G]

Rationale: Improper upfront definition and subsequent monitoring of these key propulsion system performance requirements, such as the total amount of propellant or thrust levels, may later stress the propulsion system resulting in catastrophic failures of the pressure vessels, valves, and/or engines/thrusters as more performance is required and margins are reduced. Mission planners, vehicle designers, propulsion engineers, and GN&C engineers are collectively responsible for these inputs, which need to be in place exiting SDR and entering the PDR phase of propulsion system development. Guidelines for engine/thruster specific impulse (Isp) estimation is to follow JANNAF CPIA Publication 246, Rocket Engine Performance Prediction and Evaluation Manual. Guidelines for propulsion system mass estimation is to follow ANSI/AIAA S-120A-2015, Mass Properties Control for Space Systems, which recommends a 10-20% mass growth allowance (MGA) at the ‘E2’ level of design maturity (i.e. conceptual designs (equivalent to layout drawings or models) prior to initial sizing), a 5-15% MGA at the ‘C3’ level of design maturity (i.e. preliminary designs based on calculations that occur after initial sizing but prior to final structural/thermal/manufacturing analyses, assumes minor modifications to existing hardware, generally equivalent to PDR), and a 2-7% MGA at the ‘C4’ level of design maturity (i.e. released production drawings, assumes very minor modifications to existing hardware, generally equivalent to critical design review (CDR)). Note that applying a (MGA) plus dry mass margin (DMM) totaling >20% or more to the propulsion system and structure early in a project will cause excessive growth in the size/mass of the propulsion stage due to the mathematical nature of the rocket equation. Guidelines for propellant load estimation is to use historical spacecraft, propulsion system, and propellant mass fraction performance data using techniques described in NASA TN D-6349, Fundamental Techniques for Estimating and Forecasting for Advanced Manned Spacecraft and Space Stations, or actual heritage component masses with appropriate mass growth allowance.

3.1.1.2 Spacecraft propulsion systems shall be designed to accommodate the applicable natural environments defined in SLS-SPEC-159, Cross-Program Design Specification for Natural Environments (DSNE). [PSR-02S]

Rationale: The cited standard defines critical natural environments which can greatly affect the performance and life of propulsion system hardware on a human rated spacecraft.

3.1.2 Critical Math Models

3.1.2.1 The critical math models and analysis products for a human rated spacecraft Propulsion

System listed in section 3.1.2.2 that are used as a control for a catastrophic hazard, shall meet the requirements of NASA-STD-7009, including documentation (data book) that is maintained under configuration control at the project/program level. [PSR-03S]

Rationale: The cited NASA standard, along with the accompanying NASA-HDBK-7009, NASA Handbook for Models and Simulation: An Implementation Guide for NASA-STD-7009, provides a comprehensive set of requirements governing the creation, verification, and configuration management of critical math models and analysis products. This content is especially relevant for math models and analysis products that are used as a control for a catastrophic hazard. Specific requirements are in applicable sections. This documentation and the associated data books must be updated as changes affecting hazard control are made.

3.1.2.2 For a human rated spacecraft propulsion system, the following critical models and simulations, inclusive of all nominal and contingency in-flight operating scenarios and worst-case single failure cases, as a minimum shall be generated, updated as changes to system design and operating conditions occur, and maintained under configuration control over the life of the project/program [PSR-04G]:

a) Performance Model

b) Maximum Design Pressure Models

c) Thermal Model

d) GNC and Thruster Math Models with thruster limits and faults (Monte Carlo)

e) Structural Dynamic Math Models including, but not limited to, slosh, vibratory, and pogo.

f) Controls Math Models, including the effects of slosh, pogo, and vibration.

g) Electrical power models for motor-driven components including, but not limited to, pumps, valves, and TVC actuators.

Rationale: A spacecraft propulsion system that meets the mission requirements from a performance standpoint, while avoiding the realization of catastrophic hazards during in-flight operation, begins with a comprehensive set of critical models and simulations, sometimes referred to as ‘critical math models.’ These items are intended to ensure that key performance requirements are met while the propulsion system hardware is maintained within its qualified operating bounds for pressure, temperature, cycle count, duty cycle, etc. This is especially important for avoiding catastrophic failures involving the engines/thrusters, which can progress rapidly, be highly energetic, and have severe consequences. Examples include steady state and transient feed system transient models used to establish internal fluid flow velocities and maximum design pressure (MDP) values; steady state and transient thermal models to evaluate minimum/maximum temperatures and ensure the required thermal margins are maintained in service; static and dynamic structural models to verify the required structural factors/margins are maintained; duty cycle/electrical pulse width (EPW)/duration engine/thrust response; etc. Of course, all of these models and analysis products must continue to evolve as changes to propulsion system design and operating conditions occur and be maintained under configuration control over the life of the project/program.

3.1.3 Reusable Vehicle Propulsion Systems

3.1.3.1 For a reusable spacecraft, the design and qualification (which includes the service life factors required herein) of the propulsion systems and associated components shall account for the effects of repeated exposure to all relevant environments and operating cycles/conditions, associated with in-flight usage, including landing environment, and ground turnaround testing, checkout, inspection, and maintenance tasks/activities across the designated number of missions to be certified. [PSR-05SC]

Rationale: A properly designed and qualified propulsion system on a reusable spacecraft must account for the worst case cumulative effects, with service life margins as defined herein and NASA D&C standards, of repeated exposure to all relevant environments (e.g. vibration, shock, thermal (especially cryogenic temperatures), depressurization/repressurization, radiation, propellant exposure (especially at sealing interfaces involving humid air and cryogenic or hypergolic propellants) and operating cycles/conditions (e.g. tank pressure cycles, valve actuation cycles, pressurant regulator slam-start cycles, propellant manifold priming cycles, propellant drain/decontamination cycles, etc.)

that are associated with in-flight usage, including landing environment, and the ground environment exposure and turnaround testing, checkout, inspection, and maintenance tasks/activities across the designated number of missions to be certified. That broad scope is consistent with the succinct definition of ‘service life’ in section 3.44 of SMC-S-016, Test Requirements for Launch, Upper Stage, and Space Vehicles. Additional factors to consider that can adversely affect hardware life include cryogenic pumping and condensation/freezing of water vapor from the surrounding ambient air, torque relaxation of fasteners due to cold-flow/compression-set of soft goods and/or thermal cycles to cryogenic temperatures, general wear and tear of fasteners caused by reuse, etc. Experience has shown that these considerations, particularly those involving ground turnaround activities, have sometimes been under-represented or completely neglected during hardware qualification for multiple flights, which can lead to premature failure of the hardware and the realization of catastrophic hazards in service.

3.1.3.2 For a reusable spacecraft, the design of propulsion systems and components shall comply with the requirements of the following additional paragraphs from JSC-08080-2, JSC Design and Procedural Standards. [PSR-06S]

a) G-1, Equipment Accessibility for Maintenance

b) G-52, Reuse of Flight Equipment

Rationale: The requirements of paragraphs G-1 and G-52 are considered critical to the successful planning and execution of the typical ground turnaround testing, checkout, inspection, and maintenance tasks/activities needed to address safety-of-flight risks and ensure flight readiness for the propulsion system across multiple flights on a reusable spacecraft. Note that some of these paragraphs may also have applicability to single use vehicles. Also note that other paragraphs, including G-3 (Electrical and Fluid Systems Checkout Provisions), G-5 (Prevention of Debris – Electrical & Mechanical Systems), G-8 (Design for Redundancy Verification), G-10 (Time/Cycle Critical Part Control) , and F-12 (Protection of Pressurized Systems from Damage Due to Pressurant Depletion – Support Equipment) are considered applicable to this requirement but they were excluded here due to being levied elsewhere in this document.

3.1.3.3 For a reusable spacecraft, an Operations and Maintenance Requirements and Specifications Document (OMRSD), or equivalent, shall define all initial and recurring ground tests, checkouts, inspections, and maintenance tasks/activities, each with qualified pass/fail criteria, to be performed on the propulsion system prior to the first flight and between flights. [PSR- 07G]

Rationale: The ability to perform initial and recurring tests, checkouts, inspections, and maintenance tasks/activities, each with qualified pass/fail criteria, is considered critical to controlling hazards and ensuring flight readiness of a spacecraft propulsion system across multiple missions on a reusable vehicle.