Thermal propulsion is a method of generating propulsive force by heating a working fluid and expelling it through a nozzle. This process converts thermal energy into the kinetic energy of the expelled propellant, producing thrust via Newton's third law. As an academic concept and research field, it encompasses the study of systems that utilize diverse thermal energy sources, including chemical combustion, solar concentration, or nuclear reactions (fission or fusion), to achieve propulsion. Research in this area investigates the fundamental thermodynamic principles, heat transfer mechanisms, fluid dynamics of high-temperature propellants, material science challenges, and system design optimization for applications requiring high thrust or high specific impulse, particularly in aerospace engineering for rockets and spacecraft.