National Academies Press: OpenBook

Space Nuclear Propulsion for Human Mars Exploration (2021)

Chapter: Appendix B: Findings and Recommendations

« Previous: Appendix A: Statement of Task and Additional Guidance
Suggested Citation:"Appendix B: Findings and Recommendations." National Academies of Sciences, Engineering, and Medicine. 2021. Space Nuclear Propulsion for Human Mars Exploration. Washington, DC: The National Academies Press. doi: 10.17226/25977.
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Page 82
Suggested Citation:"Appendix B: Findings and Recommendations." National Academies of Sciences, Engineering, and Medicine. 2021. Space Nuclear Propulsion for Human Mars Exploration. Washington, DC: The National Academies Press. doi: 10.17226/25977.
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Page 83
Suggested Citation:"Appendix B: Findings and Recommendations." National Academies of Sciences, Engineering, and Medicine. 2021. Space Nuclear Propulsion for Human Mars Exploration. Washington, DC: The National Academies Press. doi: 10.17226/25977.
×
Page 84
Suggested Citation:"Appendix B: Findings and Recommendations." National Academies of Sciences, Engineering, and Medicine. 2021. Space Nuclear Propulsion for Human Mars Exploration. Washington, DC: The National Academies Press. doi: 10.17226/25977.
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Page 85

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B Findings and Recommendations All of the findings and recommendations that appear in the report appear below. Those that apply specifically to NEP or NTP systems appear in Table A.1, with corresponding findings and recommendations appearing side-by-side. The table is followed by those findings and recommendations that are not specific to NEP or NTP systems. TABLE A.1 Findings and Recommendations Specific to Nuclear Thermal Propulsion (NTP) or Nuclear Electric Propulsion (NEP) Systems Findings and Recommendations Findings and Recommendations Specific to NTP Systems Specific to NEP Systems FINDING. NTP Fuel Characterization. A significant amount of characterization of reactor core materials, including fuels, remains to be done before NASA and DOE will have sufficient information for a reactor core design. RECOMMENDATION. NTP Fuel Architecture. If NASA plans to apply NTP technology to a 2039 launch of the baseline mission, NASA should expeditiously select and validate a fuel architecture for an NTP system that is capable of achieving a propellant reactor exit temperature of approximately 2700 K or higher (which is the temperature that corresponds to the required Isp of 900 sec) without significant fuel deterioration during the mission lifetime. The selection process should consider whether the appropriate fuel feedstock production capabilities will be sufficient. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 82

APPENDIX B 83 TABLE A.1 Findings and Recommendations Specific to Nuclear Thermal Propulsion (NTP) or Nuclear Electric Propulsion (NEP) Systems (continued) Findings and Recommendations Findings and Recommendations Specific to NTP Systems Specific to NEP Systems FINDING. NTP Storage of LH2. NTP systems for the baseline mission will require long-duration storage of LH2 at 20 K with minimal boiloff in the vehicle assembly orbit and for the duration of the mission. RECOMMENDATION. NTP Storage of LH2. If NASA plans to apply NTP technology to the baseline mission, NASA should develop high-capacity tank systems capable of storing LH2 at 20K with minimal boiloff in the vehicle assembly orbit and for the duration of the mission. FINDING. NEP Power Scaling. Developing a MWe-class NEP system for the baseline mission would require increasing power by orders of magnitude relative to NEP system flight- or ground-based technology demonstrations. FINDING. NTP Modeling and Simulation, FINDING. NEP Modeling and Simulation, Ground Testing, and Flight Testing. Ground Testing, and Flight Testing. Subscale in-space flight testing of NTP Subscale in-space flight testing of NEP systems cannot address many of the risks and systems cannot address many of the risks and potential failure modes associated with the potential failure modes associated with the baseline mission NTP system and therefore baseline mission NEP system. With cannot replace full-scale ground testing. With sufficient M&S and ground testing, including sufficient M&S and ground testing of fully modular subsystem tests at full scale and integrated systems, including tests at full scale power, flight qualification requirements can and thrust, flight qualification requirements be met by the cargo missions that will can be met by the cargo missions that will precede the first crewed mission to Mars. precede the first crewed mission to Mars. Fully integrated ground testing may not be required. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION

84 SPACE NUCLEAR PROPULSION FOR HUMAN MARS EXPLORATION TABLE A.1 Findings and Recommendations Specific to Nuclear Thermal Propulsion (NTP) or Nuclear Electric Propulsion (NEP) Systems (continued) Findings and Recommendations Findings and Recommendations Specific to NTP Systems Specific to NEP Systems RECOMMENDATION. NTP Modeling and RECOMMENDATION. NEP Modeling Simulation, Ground Testing, and Flight and Simulation, Ground Testing, and Testing. To develop an NTP system capable Flight Testing. To develop an NEP system of executing the baseline mission, NASA capable of executing the baseline mission, should rely on (1) extensive investments in NASA should rely on (1) extensive M&S, (2) ground testing, including investments in M&S, (2) ground testing integrated system tests at full scale and (including modular subsystem tests at full thrust, and (3) the use of cargo missions as a scale and power), and (3) the use of cargo means of flight qualification of the NTP missions as a means of flight qualification system that will be incorporated into the of the NEP system that will be first crewed mission. incorporated into the first crewed mission. FINDING. NTP Prospects for Program FINDING. NEP Prospects for Program Success. An aggressive program could develop Success. As a result of low and intermittent an NTP system capable of executing the investment over the past several decades, it baseline mission in 2039. is unclear if even an aggressive program would be able to develop an NEP system RECOMMENDATION. NTP Major capable of executing the baseline mission in Challenges. NASA should invigorate 2039. technology development associated with the fundamental NTP challenge, which is to RECOMMENDATION. NEP Major develop an NTP system that can heat its Challenges. NASA should invigorate propellant to approximately 2700 K at the technology development associated with reactor exit for the duration of each burn. the fundamental NEP challenge, which is NASA should also invigorate technology to scale up the operating power of each development associated with the long-term NEP subsystem and to develop an storage of liquid hydrogen in space with integrated NEP system suitable for the minimal loss, the lack of adequate ground- baseline mission. In addition, NASA based test facilities, and the need to rapidly should put in place plans for (1) bring an NTP system to full operating demonstrating the operational reliability temperature (preferably in 1 min or less). of an integrated NEP system over its multi-year lifetime and (2) developing a large-scale chemical propulsion system that is compatible with NEP. RECOMMENDATION. NEP Pace of Technology Development. If NASA plans to apply NEP technology to a 2039 launch of the baseline mission, NASA should immediately accelerate NEP technology development. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION

APPENDIX B 85 Findings and Recommendations Applicable to Both NTP and NEP Systems FINDING. Trade Studies. Recent, apples-to-apples trade studies comparing NEP and NTP systems for a crewed mission to Mars in general and the baseline mission in particular do not exist. RECOMMENDATION. Trade Studies. NASA should develop consistent figures of merit and technical expertise to allow for an objective comparison of the ability of NEP and NTP systems to meet requirements for a 2039 launch of the baseline mission. FINDING. NEP and NTP Commonalities. NEP and NTP systems require, albeit to different levels, significant maturation in areas such as nuclear reactor fuels, materials, and additional reactor technologies; cryogenic fluid management; modeling and simulation; testing; safety; and regulatory approvals. Given these commonalities, some development work in these areas can proceed independently of the selection of a particular space nuclear propulsion system. FINDING. Enrichment of Nuclear Fuels. A comprehensive assessment of HALEU vs HEU for NTP and NEP systems that weighs the key considerations is not available. These considerations include technical feasibility and difficulty, performance, proliferation and security, safety, fuel availability, cost, schedule, and supply chain as applied to the baseline mission. RECOMMENDATION. Enrichment of Nuclear Fuels. In the near term, NASA and DOE, with inputs from other key stakeholders, including commercial industry and academia, should conduct a comprehensive assessment of the relative merits and challenges of HEU and HALEU fuels for NTP and NEP systems as applied to the baseline mission. FINDING. Synergies with Terrestrial and National Defense Nuclear Systems. Terrestrial microreactors, which operate at a power level comparable to NEP reactors, are on a faster development and demonstration timeline than current plans for space nuclear propulsion systems. Development of microreactors may provide technology advances and lessons learned relevant to the development of NEP systems. Similarly, technology advances within the DARPA DRACO program could potentially contribute to the development of NTP systems for the baseline mission. RECOMMENDATION. Synergies with Terrestrial and National Defense Nuclear Systems. NASA should seek opportunities for collaboration with the DOE and DoD terrestrial microreactor programs and the DARPA DRACO program to identify synergies with NASA space nuclear propulsion programs. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION

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Space Nuclear Propulsion for Human Mars Exploration identifies primary technical and programmatic challenges, merits, and risks for developing and demonstrating space nuclear propulsion technologies of interest to future exploration missions. This report presents key milestones and a top-level development and demonstration roadmap for performance nuclear thermal propulsion and nuclear electric propulsion systems and identifies missions that could be enabled by successful development of each technology.

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