Effect of fuel and design options on RTG performance versus PFF power demand

Previous publications by the author described detailed studies of a number of radioisotope power systems for the Pluto Fast Flyby (PFF) mission. The systems studied employed General Purpose Heat Source (GPHS) modules and a variety of conversion systems (thermoelectric, Stirling, and thermophotovoltaic) for transforming the isotope heat into electricity. The present paper confines its attention to the relatively conservative option employing standard thermoelectric unicouples, since that may be the only one flight-ready for the projected PFF launch in 2001. Instead of the previously studied parametric assumptions of thermal power, the present study examines three specific fuel options: the first option, with the lowest thermal power, is to use the heat source modules from the F5 RTG, which was a spare flight unit for the 1989-launched Galileo mission and also for the upcoming Cassini mission. The second fuel option is to use newly reprocessed fuel made at the end of the Department of Energy's (DOE's) current production run for NASA's Cassini mission. That production run is scheduled to be completed by the end of 1994. The third fuel option would be to use the Pu-238 obtained from Russia under the recently signed purchase agreement. The previous RTG design studies were based on the use of five standard GPHS modules per generator. In response to a request from JPL, the present study derives EOM power predictions for RTGs with five, six, and seven heat source modules, for each of the three fuel options described above, and compares the results with HPL's latest (February 1994) power demand goals, which are 10% higher than their 1992 baseline goals