Aeronautics and Space Report of the President FY 1995 Activities

Space Flight and Space Technology


In FY 1995, the Department of Energy (DoE) continued its work in the fabrication of 3 General Purpose Heat Source Radioisotope Thermoelectric Generators (GPHS-RTG's) and 157 Radioisotope Heater Units (RHU's) for NASA's upcoming Cassini mission to Saturn. RTG's directly convert the heat from the decay of the radioisotope Plutonium-238 (Pu-238) into electricity without any moving parts; they have been employed successfully on more than 20 spacecraft of long-duration missions. Technicians completed all of the Pu-238 processing required for the RTG's and RHU's and completed fabrication of the first RTG's heat source during FY 1995. The prime system contractor completed the production of all thermoelectric elements and assembled and acceptance-tested the first thermoelectric converter. Finally, DoE supported NASA in developing environmental documentation and performing safety testing for the safety analysis reports required for the launch approval process of Cassini.

In addition, DoE took delivery in 1995 of 4.2 kilograms (for a total of 9.2 kilograms) of Russian-produced Pu-238 to supplement the existing U.S. inventory of Pu-238. This Pu-238 is to fuel the power sources for future planetary exploration spacecraft. This is the first foreign-produced material capable of being pressed directly into pellets to fuel RTG's.

DoE and NASA officials signed a Supplemental Agreement to the basic Memorandum of Understanding on radioisotope power systems for the Mars Pathfinder mission. DoE is to provide three Lightweight Radioisotope Heater Units (LWRHU's) from its inventory (these are actually spares from the Galileo and Ulysses missions) for this upcoming launch. DoE also began preparing a Final Safety Analysis Report on the LWRHU's for the Mars Pathfinder mission.

For NASA's Pluto Express mission, DoE engineers and scientists studied advanced converter technologies to provide high-efficiency and lightweight power sources. DoE engineers also initiated technology development work to investigate and demonstrate the viability of advanced power converters using thermophotovoltaic, alkaline metal, and Stirling engine technologies.

In conjunction with JPL, DoE has been exploring the use of a bimodal (power/propulsion) space reactor system to support NASA's New Millennium spacecraft program. In a joint program with the Air Force, DoE developed design concepts for three bimodal space reactor power systems.

DoE staff also participated in an interagency technical working group on space reactor systems sponsored by the Defense Nuclear Agency to review its Topaz International Program. This program is centered on a thermionic space power system developed in the former Soviet Union, called the Topaz II. Unlike RTG's, the Topaz reactor has moving parts like a ground nuclear powerplant. At the component level, under the DoE-managed 40-kilowatt (of electric power) thermionic space reactor program, technicians completed the initial evaluation of a single-cell thermionic fuel element that is to double the power of past designs. At the basic research level, work continued on the cesium effects on bulk and surface conductivity of seal insulators and collector sheath insulators and the cesium plasma erosion of interelectrode gap ceramic spacers.

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Curator: Lillian Gipson
Last Updated: September 5, 1996
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