A Nuclear Thermal Rocket (NTR) is a type of spacecraft propulsion system that uses nuclear reactions to heat a propellant, typically hydrogen. The heated gas is then expelled through a nozzle to produce thrust, allowing the spacecraft to travel efficiently in space. NTRs are designed to provide higher performance than conventional chemical rockets, making them suitable for deep space missions. The core of an NTR is a nuclear reactor, which generates heat through fission reactions. This technology has been explored for missions to destinations like Mars and beyond, as it can significantly reduce travel time compared to traditional propulsion methods.