We're building nuclear spaceships again–this time for real

The U.S. military and NASA are reviving efforts to develop nuclear thermal rockets (NTRs) for space exploration, with a focus on creating demonstration hardware. The concept of using nuclear reactors for propulsion dates back to the mid-1950s, initiated by the U.S. Air Force's Rover program. NTRs promise significant fuel efficiency by using liquid hydrogen heated in a nuclear reactor, allowing for a specific impulse that is at least twice as efficient as traditional chemical rockets. However, challenges remain in adapting ground-based reactor technology for flight, including the need for fuel rods that can withstand extremely high temperatures and the corrosive nature of hydrogen at those temperatures. The program gained momentum when it transitioned to NASA and the Atomic Energy Commission in 1958, leading to the development of the Nuclear Engine for Rocket Vehicle Applications (NERVA). Despite past setbacks, including the Phoebus 2A reactor test in 1968, which did not lead to manned missions to Mars, current military interest suggests a renewed commitment to harnessing nuclear propulsion for future space missions. The potential applications include not only deep space exploration but also military uses, such as intercontinental ballistic missiles. The ongoing research aims to overcome the technical hurdles associated with flying nuclear reactors, which include the design of control systems and materials that can endure the extreme conditions of space travel.