IEEE Spectrum breed · Technologie

NASA's Synchronal Bimodal Nuclear Rocket Aims to Cut Mars Trip Times

NASA and industry engineers have proposed a new design for a nuclear rocket, the Synchronal Bimodal Nuclear Rocket (S-BNR), which combines nuclear thermal and electric propulsion. This innovative approach aims to significantly reduce travel times to destinations like Mars, potentially cutting transit time to 335 days or less, thereby enhancing astronaut safety and simplifying mission logistics.

The S-BNR design utilizes a single nuclear reactor with two independent fluid loops and optimized fuel zones, eliminating the need for complex mode-switching valves. This configuration allows for both high thrust for rapid acceleration and continuous electrical power generation for spacecraft systems. Previous bimodal concepts struggled with integrating these two functions due to the demanding requirements for fuel elements and valve systems operating in harsh radiation environments.

Historically, nuclear thermal rockets (NTRs) offer high thrust by heating a propellant like hydrogen to extreme temperatures, achieving specific impulses of 900 seconds or more, far exceeding chemical rockets. Nuclear electric propulsion (NEP), on the other hand, uses electricity generated by a reactor to accelerate ionized propellant, offering much higher specific impulses (2,200-4,600 seconds) but with very low thrust. Combining these capabilities in a single system has been a long-standing goal.

The S-BNR addresses this by dividing the reactor core into two zones: one with high-temperature fuel elements (HTFEs) for thermal propulsion and another with low-temperature fuel elements (LTFEs) for efficient electricity generation. These zones have separate fluid loops, removing the need for valves to switch between modes. The HTFEs, potentially using uranium-encased pebbles, heat hydrogen propellant, while LTFEs, using solid uranium fuel, heat a power-conversion fluid for electricity generation. This design ensures continuous electrical power and high thrust when needed.

Significant challenges remain for the S-BNR, including developing fuel elements that can withstand both high-temperature, short-duration thermal thrust maneuvers and lower-temperature, long-duration power generation. Ground testing also presents difficulties, as exhaust must be fully contained, unlike early nuclear rocket tests. Furthermore, nuclear launch safety protocols require reactors to remain subcritical until in space, a constraint that must be carefully managed.

Despite these hurdles, the S-BNR concept builds upon decades of research in nuclear propulsion and power. The proposed development plan includes extensive modeling, non-nuclear testing, component qualification, integrated reactor testing, and eventual in-space demonstrations. Success will necessitate close collaboration among NASA, the Department of Energy, the Department of Defense, industry partners, and the broader scientific community, focusing on advancements in materials, power conversion, heat transport, and control systems.

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