They were developed more than 40 years ago and then almost forgotten but now Nuclear Rockets are set to make a comeback and possibly provide the fastest way to get around our solar system to date. Here look at their history and how they could be used in the next decade or so.
A nuclear thermal rocket (NTR) is a type of thermal rocket where the heat from a nuclear reaction, often nuclear fission, replaces the chemical energy of the propellants in a chemical rocket. In an NTR, a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor and then expands through a rocket nozzle to create thrust. The external nuclear heat source theoretically allows a higher effective exhaust velocity and is expected to double or triple payload capacity compared to chemical propellants that store energy internally.
NTRs have been proposed as a spacecraft propulsion technology, with the earliest ground tests occurring in 1955. The US maintained an NTR development program through 1973, when it was shut down to focus on Space Shuttle development. Although more than ten reactors of varying power output have been built and tested, as of 2019, no nuclear thermal rocket has flown.
Whereas all early applications for nuclear thermal rocket propulsion used fission processes, research in the 2010s has moved to fusion approaches. The Direct Fusion Drive project at the Princeton Plasma Physics Laboratory is one such example, although “energy positive fusion has remained elusive”. In 2019, the US Congress approved US$125 million in development funding for nuclear thermal propulsion rockets.