Chapter 13 - Space Propulsion

Abstract

Space propulsion systems are illustrated in terms of their specific impulse and specific mass. Electric propulsion systems are introduced and their operation characterized as electrothermal, electrostatic, or electromagnetic, depending on the mechanism by which they produce thrust. Electrothermal propulsion devices, including resistojets, arc jets, and RF or microwave excited jets, are shown to operate by heating a propellant and then accelerating the heated gas through a nozzle, just like chemical or nuclear rockets. Electrostatic propulsion devices do not require a physical nozzle to accelerate the propellant but instead employ an electric field to accelerate heavy positive ions to produce thrust, which is demonstrated by means of a one-dimensional analytical model. Ion engines and Hall Effect thrusters, electrostatic rockets of high specific impulse currently used in space applications, are described. Electromagnetic propulsion devices that use electromagnetic forces arising from crossed electric current and magnetic fields, like the magnetoplasmadynamic thruster and the pulsed plasma thruster are discussed. Nuclear thermal propulsion for space exploration is introduced and applications are illustrated. The past demonstration of the feasibility of operating large-scale nuclear rockets is outlined. The typical configuration of a solid core nuclear rocket motor and the improvements in specific impulse achievable compared to chemical rockets are analyzed. Nuclear reactors for rocket applications and the basic operation of solid and pebble bed core reactors are described. Improvements in nuclear rocket performance using gas core nuclear reactors and possible practical designs are illustrated.