Design, Analysis, and Optimization of RTG for Solar Polar Mission

Abstract

The paper presents the conceptual design of an RTG, employing stacked radioisotope heat source modules and silicongermanium thermoelectric couples, for use on the joint NASA/ESA International SolarPolar Mission, to be launched in early 1983,The use of stacked heat source modules in RTGs requires a structural support system which holds the stack together during launch, but allows it to disassemble when the generator housing melts during reentry. This is a much more difficult support problem than in the case of a monolithic heat source. A proposed, lightweight scheme for solving this problem is described and analyzed. A detailed analytical model of the RTG and the space craft to which it is attached was constructed, and a NASTRAN analysis was carried out to assess the structural performance of the heat source support scheme under differential thermal expansion and dynamic launch loads, to determine the system's characteristic frequencies, the loads transmitted to the RTG, and the resultant stresses and displacements. The analytical results presented con firm the structural feasibility of the heat source support scheme.The paper also describes a detailed thermal analysis and a computer program which, for a given set of assumptions and ground rules, can rapidly examine thousands of design variations and deter mine the combination of design parameters which will minimize the RTG weight for a given power output. Graphical results are pre sented to illustrate design trends and clarify the optimization procedure. The generated results lead to interesting and somewhat unexpected conclusions about optimum design parameters, the relative constancy of RTG specific power over a wide power range, comparisons between single and split RTGs, sensitivity to variations in heat source module design, weight comparisons with the MHW RTG, and com parative RTG weights for different housing and radiator fin materials, I.

RTG Impact Response to Hard Landing During Mars Environmental Survey (MESUR) Mission

“…The study reported last year [3] presented two illustrative RTG designs: a 9-watt design for direct communication to Earth and a 3-watt design for communication through an orbiting relay. Both designs strove to maximize the use of previously developed technology, including the General Purpose Heat Source (GPHS) [4] used in the Galileo and Ulysses RTGs [5]; the SiGe thermoelectric materials employed in the RTGs for the Voyager, LES 8/9, Galileo and Ulysses missions, and the multicouples developed for DOE's Mod-RTG program [6,7]. Modifications were introduced only where necessary to improve the RTG's Impact resistance and to meet other mission requirements.…”

RTG Impact Response to Hard Landing During Mars Environmental Survey (MESUR) Mission

“…The study reported last year [3] presented two illustrative RTG designs: a 9-watt design for direct communication to Earth and a 3-watt design for communication through an orbiting relay. Both designs strove to maximize the use of previously developed technology, including the General Purpose Heat Source (GPHS) [4] used in the Galileo and Ulysses RTGs [5]; the SiGe thermoelectric materials employed in the RTGs for the Voyager, LES 8/9, Galileo and Ulysses missions, and the multicouples developed for DOE's Mod-RTG program [6,7]. Modifications were introduced only where necessary to improve the RTG's Impact resistance and to meet other mission requirements.…”

Design modifications for increasing the BOM and EOM power output and reducing the size and mass of RTG for the Pluto mission

“…This arrangement is identical to that use in the 18-module RTGs successfully flown on the Galileo and Ulysses mission. 2 The predicted power profile of the above RTG during the 8.2-year PFF mission is depicted in Figure 2 for three specific fuel options, with respective BOM thermal powers of 254, 234, and 220 watts per heat source module. For each fuel option, the figure shows the BOM efficiency, the optimum RTV voltage, and the BOM and EOM hot- junction temperatures.…”