NASA and industry engineers are developing a nuclear spacecraft concept that could significantly reduce travel times to Mars and other destinations. Called the synchronal bimodal nuclear rocket, or S-BNR, the proposed system combines nuclear thermal propulsion and nuclear electric propulsion using a single reactor, tells IEEE Spectrum.
Reducing travel time is particularly important for crewed Mars missions. NASA’s shortest blueprint requires astronauts to spend 620 days in space and 30 days on Mars, exposing crews to prolonged microgravity, radiation, and other risks. The S-BNR concept could reduce total transit time to about 335 days or less.
Nuclear thermal propulsion provides the powerful thrust needed for critical maneuvers. Liquid hydrogen passes through a hot reactor core and exits at high velocity, potentially delivering a specific impulse of 900 seconds or more, roughly twice that of efficient chemical rockets. Nuclear electric propulsion works differently. Reactor-generated electricity powers thrusters that provide much lower thrust but can operate efficiently for extended periods.
Previous bimodal concepts attempted to combine these capabilities but depended on complicated valves and fuel elements required to operate under very different conditions. The S-BNR simplifies the architecture by using two independent fluid loops within one reactor. One zone contains high-temperature fuel elements for thermal propulsion, while another uses lower-temperature elements optimized for sustained electricity generation.
Significant engineering challenges remain. Researchers must demonstrate stable reactor control across a wide power range, develop durable fuels and materials, manage heat and neutrons, and prove that the system can generate power continuously for years. Ground testing must also safely capture potentially radioactive exhaust.
Development would progress from modeling and nonnuclear testing to component trials, fueled reactor testing, and eventually in-space demonstrations. Success could produce spacecraft capable of combining rapid maneuvers with sustained, efficient propulsion for missions throughout the solar system.
