and expensive to manufacture new GPHS RTGs (although it may be possible to build two or three GPHS RTGs using leftover thermocouples). The RPS program is now focused on development of ASRGs; the current budget has no funding set aside to retain the ability to produce MMRTGs, although NASA has asked the DOE to determine what it would take to keep MMRTG production capabilities active for two years.

The central issue that threatens the future of RPS-powered missions is the short supply of 238Pu. Accordingly, RPS research and development should strive to meet NASA’s mission requirements for RPSs while minimizing NASA’s demand for 238Pu. In addition, a balanced program would develop RPS technologies and systems suitable for various applications, and it would support development of RPS technology for near- and far-term use.

Because the RPS program is focused on advanced development of a single RPS design for near-term application, the RPS program (in FY 2009) is not well balanced. However, this imbalance is appropriate given that (1) the FY 2009 budget is insufficient to sustain a well-balanced program and (2) the focus on ASRGs is well aligned with current programmatic priorities. The balance of the program would improve under the current out-year funding scenario (if enacted), as ASRG development is completed, the RPS budget is doubled, and funding for other RPS technologies is expanded. The planned development of a small RPS would be a good first step toward the goal of establishing a suite of RPSs with capabilities optimized for different mission scenarios.


FINDING. Programmatic Balance. Balance within NASA’s RPS program is impossible given the current (fiscal year 2009) budget and the focus on development of flight-ready ASRG technology. However, NASA is moving the ASRG project forward, albeit at the expense of other RPS technologies.

RPS SYSTEM CAPABILITIES

Figure 4.2 compares the performance of past, present, and future RPSs. The technology development cycle for new RPS technologies is typically 15 to 20 years long, and it is driven by perceived mission needs (rather than actual mission requirements) because, even for very large spacecraft and very important missions, it is impossible to predict with certainty what mission requirements will be 15 to 20 years in the future. Over such a long time span, space exploration priorities often change as changes occur in the leadership of the Administration and Congress.

FIGURE 4.2 Performance of past, present, and future radioisotope power systems. NOTE: ARTG, Advanced Radioisotope Thermal Generator; ASRG, Advanced Stirling Radioisotope Generator; BOM, beginning of mission; GPHS, general purpose heat source; MMRTG, Multi-Mission Radioisotope Thermoelectric Generator; RTG. radioisotope thermal generator; TPV, thermophotovoltaic. SOURCE: Modified from S. Surampudi, NASA, “Radioisotope Power Systems Technology Programs,” presentation to the Radioisotope Power Systems Committee, November 18, 2008, Washington, D.C.

FIGURE 4.2 Performance of past, present, and future radioisotope power systems. NOTE: ARTG, Advanced Radioisotope Thermal Generator; ASRG, Advanced Stirling Radioisotope Generator; BOM, beginning of mission; GPHS, general purpose heat source; MMRTG, Multi-Mission Radioisotope Thermoelectric Generator; RTG. radioisotope thermal generator; TPV, thermophotovoltaic. SOURCE: Modified from S. Surampudi, NASA, “Radioisotope Power Systems Technology Programs,” presentation to the Radioisotope Power Systems Committee, November 18, 2008, Washington, D.C.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement