Thermionic Spacecraft Design Study

This report presents the results of a design study of nuclear-electric propelled unmanned spacecraft. The electric power source is in-core thermionic reactors based on either the internally (flashlight) or externally fueled diode concept. The study guidelines and approach are defined. The characteristics of the candidate launch vehicles, thrust subsystem, and communications subsystem are presented. The definition of two spacecraft/powerplant configurations are presented which deliver 240 kWe net to the thruster array. This definition, presented for both the flashlight and externally fueled reactors includes the key items of spacecraft arrangement and a detailed weight breakdown. Power conditioning, heat rejection subsystem, shielding, and spacecraft structure are detailed. The results show about a 30 percent weight advantage for the spacecraft based on the externally fueled reactor. This is primarily due to a 120 vdc power output from the externally fueled reactor, as compared to a 15 vdc power output from the flashlight reactor. Weight reduction by improved technology could further reduce the weight by 5 to 15 percent.