Nuclear radiation problems, unmanned thermionic reactor ion propulsion spacecraft

A nuclear thermionic reactor as the electric power source for an electric propulsion spacecraft introduces a nuclear radiation environment that affects the spacecraft configuration, the use and location of electrical insulators and the science experiments. The spacecraft is conceptually configured to minimize the nuclear shield weight by: (1) a large length to diameter spacecraft; (2) eliminating piping penetrations through the shield; and (3) using the mercury propellant as gamma shield. Since the alumina material is damaged by the high nuclear radiation environment in the reactor it is desirable to locate the alumina insulator outside the reflector or develop a more radiation resistant insulator

Testing of Milliwatt Power Source Components

A milliwatt power source (MPS) has been developed to satisfy the requirements of several potential solar system exploration missions. The MPS is a small power source consisting of three major components: a space qualified heat source (RHU), a thermopile (thermoelectric converter or TEC) and a container to direct the RHU heat to the TEC. Thermopiles from Hi-Z Technology, Inc. of San Diego and the Institute of Thermoelectricity of Chernivtsi Ukraine suitable for the MPS were tested and shown to perform as expected, producing 40 mW of power with a temperature difference of about 170°C. Such thermopiles were successfully life tested for up to a year. A MPS container designed and built by Swales Aerospace was tested with both a TEC simulator and actual TEC. The Swales unit, tested under dynamic vacuum, provided less temperature difference than anticipated, such that the TEC produced 20 mW of power with heat input equivalent to a RHU

Local thermodynamic equilibrium study of H/sup -/ abundance in negative-ion source discharges

A local thermal equilibrium study of a hydrogen gas has been carried out for temperatures and densities relevant to the expected conditions in the Penning SAS source, which is a negative-ion source presently under investigation by AT-2 at Los Alamos National Laboratory. For the pure hydrogen mixture, it was found that the relative abundance of H/sup -/ ions peaks at about 10,000 K but is extremely low. The inclusion of cesium does improve the H/sup -/ abundance significantly only at low temperatures (less than or equal to5000 K), raising it to about several parts per million, which should be considered low in view of estimates from the sheath physics which is not based on the local thermodynamic equilibrium assumption. Incorporation of the enhancement of dissociative attachment from contributions by higher rotational-vibrational states associated with a nonthermal hot electron component has not been attempted, being an intrinsically nonthermal effect. The higher rotational-vibrational states themselves are, however, fully included