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An integral space power concept provides both the electrical power and propulsion from a common heat source and offers superior performance capabilities over conventional orbital insertion using chemical propulsion systems. This paper describes a hybrid (bimodal) system concept based on a proven, inherently safe solid fuel form for the high temperature reactor core operation and rugged planar thermionic energy converter for long-life steady state electric power production combined with NERVA-based rocket technology for propulsion. The integral system is capable of long-life power operation and multiple propulsion operations. At an optimal thrust level, the integral system can maintain the minimal delta-V requirement while minimizing the orbital transfer time. A trade study comparing the overall benefits in placing large payloads to GEO with the nuclear electric propulsion option shows superiority of nuclear thermal propulsion.

Comparisons are given between various launch vehicles, transfer vehicles, and propulsion methods to launch satellites into low Earth orbital parking orbits and then into a final geosynchronous orbit. The studies indicate that a Thermionic Space Nuclear Power System (TI-SNPS) can have significant advantages over solar array power systems for both orbital transfer capabilities and mission applications. Also, by utilizing a relatively inexpensive Atlas IIAS launch vehicle, a particular TI-SNPS hybrid design with a specific impulse of 950 sec can place a satellite weighing 3,511 kg into GEO orbit, as compared to only a corresponding 1,104 kg satellite capability when using conventional chemical propulsion techniques.