Modified design of radioisotope thermophotovoltaic generator to mitigate adverse effect of measured cell voltage

Abstract

OSC has been investigating a number of generator design modifications to achieve additional improvements in system performance. Specifically, OSC found that the converter's performance could be significantly improved by increasing the heat flux incident on the PV cells. Since the thermal power input from the generator's heat source is fixed for a given number of General Purpose Heat Source (GPHS) modules, the only other way of increasing the converter's heat flux is to reduce its active area. This can be accomplished by covering only two of the heat source's six faces with TPV converter panels, instead of the four faces so covered in previous designs. The other four faces are covered with multifoil thermal insulation. For the 3-module 2-panel option, two cases were analyzed: placing the two converter panels on two of the generator's side walls, or on its smaller end covers. Analytical results show that even with EDTEK's improved March-96 PV cell, the generator would not meet JPL's EOM power demand goal with two GPHS modules, but would meet it comfortably with three heat source modules. For both the 2- and 3-module generators, they show that-for a given thermal power per heat source module-the option with two converter panels yields significantly higher output power than that with four panels. But this gain is achieved at the cost of higher heat source temperatures and consequently greater grain growth rates of the fuel capsules iridium clads, which could adversely affect their impact resistance in case of inadvertent Earth reentry.