NASA Principal Technologist lays out strategy to develop advanced space propulsion over the next 25 years

NASA Principal Technologist Ronald J. Litchford looks at the strategic development of improved space propulsion.

Deep space transportation capability for science and exploration is fundamentally limited by available propulsion technologies. Traditional chemical systems are performance plateaued and require enormous Initial Mass in Low Earth Orbit (IMLEO) whereas solar electric propulsion systems are power limited and unable to execute rapid transits. Nuclear based propulsion and alternative energetic methods, on the other hand, represent potential avenues, perhaps the only viable avenues, to high specific power space transport evincing reduced trip time, reduced IMLEO, and expanded deep space reach. Here, key deep space transport mission capability objectives are reviewed in relation to STMD technology portfolio needs, and the advanced propulsion technology solution landscape is examined including open questions, technical challenges, and developmental prospects. Options for potential future investment across the full compliment of STMD programs are presented based on an informed awareness of complimentary activities in industry, academia, OGAs, and NASA mission directorates.

Advanced Propulsion Technology Development Strategy

For optimal outcome, it is recommended that the future development of advanced propulsion capability proceed along parallel technology development pathways, one near-term path for proven but immature technologies (TRL ≥ 3) based on proven processes and a second far-term path for unproven but high capability concepts (TRL < 3) that could completely revolutionize mission possibilities.

The near-term pathway would ideally have a four-prong emphasis:
(1) advanced chemical propulsion,
(2) electric/plasma propulsion,
(3) nuclear thermal propulsion, and
(4) hybrid nuclear thermal/electric propulsion.

The key technology focal points are as follows:
• Advanced Chemical Propulsion
– Long-term cryogenic propellant storage and handling
– In Situ Resource Utilization (ISRU)
• Robust High Power/Isp Thrusters
– Advanced Hall/Ion thrusters
– MPD thrusters
– Plasma & Pulse Inductive thrusters
• Nuclear Thermal Propulsion
– High-performance high-temperature reactor fuels
– Affordable &regulatory compliant nuclear engine system testing
• Dual Mode Reactor Propulsion and Power Systems

The key technology focal points of a combined near/far-term technology development strategy are as follows:
• Advanced Low-Specific-Mass Nuclear Electric Propulsion
– Advanced nuclear brayton/rankine powerplants
– Advanced power conversion subsystems
– Advanced high-temperature radiator and heat rejection subsystems

• Advanced Fission Thermal Propulsion
– Enhanced solid core and gas core configurations
– Fission fragment configurations
– Nuclear pulse fission configurations
• Fusion Propulsion
– Fission-driven-fusion configurations
– Pure continuous and pulsed fusion