NAS Report: For Humans to Reach Mars, Advances Are Needed in Space Nuclear Propulsion Technologies

Press Release From: National Academy of Sciences
Posted: Friday, February 12, 2021

Using nuclear propulsion technologies to support a human mission to Mars in 2039 will require NASA to pursue an aggressive and urgent technology development program, says a new report from the National Academies of Sciences, Engineering, and Medicine.

NASA should commit within the year to conducting an extensive and objective assessment of the merits and challenges of using different types of space nuclear propulsion systems and to making significant technology investments this decade. Such a program must include subsystem development, prototype systems, ground testing, and cargo missions as a means of flight qualification prior to first crewed use, the report says.  

Space Nuclear Propulsion for Human Mars Exploration assesses the primary challenges, merits, and risks for developing a nuclear electric propulsion (NEP) system and a nuclear thermal propulsion (NTP) system for a human mission to Mars. While NEP converts the thermal energy from a nuclear reactor into electrical energy to power electric thrusters, NTP uses the thermal energy from a nuclear reactor to heat a rocket propellant and create thrust. Each system has its own advantages and limitations for use in a crewed mission to Mars.

“Safely transporting astronauts to and from Mars will require advances in propulsion systems to develop spacecraft that are up to the challenge,” said Roger Myers, owner of R. Myers Consulting and co-chair of the committee that wrote the report. “Nuclear propulsion systems have the potential to substantially reduce trip time compared to non-nuclear approaches. Synergy with other space mission applications and terrestrial power programs is also significant and will bring about added value.”

Studies comparing NEP and NTP systems are needed to assess the viability of each system for a crewed mission to Mars. Given the need to send multiple cargo missions to Mars prior to the first crewed mission, NASA should use those cargo missions as a means of flight qualification of the selected nuclear propulsion system before it is incorporated into the first crewed mission.

NEP and NTP each have challenges, which are identified in the report.  The fundamental challenge for developing an NEP system is scaling up the operating power for each subsystem, something that requires power levels that are orders of magnitude greater than have ever been achieved to date. Another challenge is developing a compatible chemical propulsion system to provide the primary thrust when departing Earth’s orbit and when entering and departing Mars’ orbit. The fundamental challenge facing an NTP system is the ability to heat its propellant to the proper temperature, approximately 2,700 K. Other challenges include the long-term storage of liquid hydrogen in space with minimal loss; the need to rapidly bring an NTP system to full operating temperature, preferably in under one minute; and the need to develop full-scale ground test facilities that can safely capture the NTP exhaust.

“Space nuclear propulsion technology shows great potential to facilitate the human exploration of Mars,” said Bobby Braun, director for planetary science at the Jet Propulsion Laboratory and co-chair of the committee that wrote the report. “However, significant acceleration in the pace of technology maturation is required if NASA and its partners are to complete this mission within the stated timeline.”

The study — undertaken by the Space Nuclear Propulsion Technologies Committee — was sponsored by NASA. The National Academies are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln.

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