ELI5: Explain Like I'm 5

Nuclear thermal rocket

A nuclear thermal rocket is a type of rocket which uses heat from nuclear fission to make it go faster. Nuclear fission is the process of splitting atoms apart to release energy. The energy released creates heat and this heat is used to turn a gas into a hot gas that moves really quickly and creates a lot of force. This force pushes the rocket forward and makes it go much faster than a normal rocket.