Nasa selected a nuclear propulsion concept for Phase I development as part of its Innovative Advanced Concepts (NIAC) program for 2023.
The Nuclear Thermal and Nuclear Electric Propulsion (NTP/NEP) concept is a new class of bimodal nuclear propulsion system that uses a "wave rotor topping cycle", as per a Nasa blog post.
The scientist behind the proposal, Professor Ryan Gosse from the University of Florida, believes it could reduce travel time to Mars to a mere 45 days. If the technology does work as planned, it could drastically reduce travel times to Mars and make missions to the red planet innumerably safer for humans.
Is nuclear propulsion the future of human space flight?
The new proposal, titled 'Bimodal NTP/NEP with a Wave Rotor Topping Cycle', is one of 14 selected by the NIAC for Phase I development. It received a grant to the tune of $12,500 to research and develop the technology required.
Nasa has a long history of considering nuclear propulsion for spacecraft, according to Universe Today. This includes the Nuclear Engine for Rocket Vehicle Application (Nerva) concept, which was successfully tested but then defunded around the same time the Apollo Era came to a close in 1973.
More recently, Nasa also tested nuclear propulsion concept technologies with Project Prometheus in the early 2000s. Private firm Ad Astra, meanwhile, which is run by former Nasa astronaut Franklin R Chang Díaz, completed a record 88-hour high-power endurance test of its Vasimr VX-200SS plasma rocket at 80 kW in 2021. Ad Astra claims its nuclear rocket technology could eventually take humans to Mars at speeds of 197,950 km/h.
Nasa's new nuclear propulsion concept
Nasa's new NIAC grant recipient leverages two of the key concepts behind nuclear propulsion. Nuclear-Thermal Propulsion (NTP) utilises a nuclear reactor to heat liquid hydrogen propellant so that it is converted into plasma and channelled through a nozzle to generate thrust.
Nuclear-Electric Propulsion (NEP), meanwhile, uses a nuclear reactor to power a Hall-Effect thruster (ion engine) with electricity. This, in turn, generates an electromagnetic field that ionises and accelerates an inert gas to create thrust.
Gosse, who serves as the Hypersonics Program Area Lead at the University of Florida, combines the advantages of both NTP and NEP with his new concept. The engineer proposes a bimodal design based on a solid-core Nerva reactor that would provide a specific impulse (lsp) of 900 seconds. That is twice the performance of existing chemical rockets.
On top of that, Gosse also proposes using a Wave Rotor (WR) to further compress the reaction mass using pressure generated by the reactor's heating of the liquid hydrogen fuel.
According to the engineer, this has the potential to deliver thrust levels comparable to that of a Nerva-class NTP concept but with a higher Isp of 1,400-2,000 seconds. Combining this with an NEP cycle would produce even higher thrust levels.
Shorter travel times are vital for the well-being of astronauts
What all of that means is that Gosse's concept could drastically reduce the travel time to Mars for future astronauts. Using existing technologies, a crewed voyage to Mars could take about six to nine months to reach the red planet. So, reducing the travel time to about 45 days would mean Mars missions could last months instead of years.
This is vitally important as long missions to Mars would expose astronauts to high levels of radiation that could prove deadly. Not only that, the effects of microgravity on humans for such a long time period would also have negative health implications, meaning there is a strong incentive to reduce Mars mission times.
Other concepts awarded a grant by Nasa's NIAC program include a hybrid aircraft concept called TitanAir that could collect samples from the seas of Saturn's moon Titan.
A concept for a lunar pipeline could also improve the efficiency of oxygen delivery for Nasa's upcoming Artemis moon missions. The space agency has posted a full list of the impressive space concepts it is considering as potential game-changers for astronomy, Earth science, and human space exploration.