foreign nations is not a viable option because of schedule and national security considerations. Fortunately, there are two viable approaches for reestablishing production of 238Pu in the United States. Both of these approaches would use existing reactors at DOE facilities at Idaho National Laboratory and Oak Ridge National Laboratory with minimal modification, but a large capital investment in processing facilities would still be needed. Nonetheless, these are the best options in terms of cost, schedule, and risk for producing 238Pu in time to minimize the disruption in NASA’s space science and exploration missions powered by RPSs.


On April 29, 2008, the NASA administrator sent a letter to the secretary of energy with an estimate of NASA’s future demand for 238Pu.1 The committee has chosen to use this letter as a conservative reference point for determining the future need for RPSs. However, the findings and recommendations in this report are not contingent on any particular set of mission needs or launch dates. Rather, they are based on a conservative estimate of future needs based on various future mission scenarios. The estimate of future demand for 238Pu (which is about 5 kg/year) is also consistent with historic precedent.

The orange line [hollow square data points] in Figure S.1 shows NASA’s cumulative future demand for 238Pu in a best-case scenario (which is to say, a scenario in which NASA’s future RPS-mission set is limited to those missions listed in the NASA administrator’s letter of April 2008, the 238Pu required by each mission is the smallest amount listed in that letter, and ASRGs are used to power OPF 1). The green line [solid square data points] shows NASA’s future demand if the status quo persists (which is to say, if OPF 1 uses MMRTGs).

Once the DOE is funded to reestablish production of 238Pu, it will take about 8 years to begin full production of 5 kg/year. The red and blue lines [triangular data points] in Figure S.1 show the range of future possibilities for 238Pu balance (supply minus demand). A continuation of the status quo, with MMRTGs used for OPF 1 and no production of 238Pu, leads to the largest shortfall, and the balance curve drops off the bottom of the chart. The best-case scenario, which assumes that OPF 1 uses ASRGs and DOE receives funding in fiscal year (FY) 2010 to begin reestablishing its ability to produce 238Pu, yields the smallest shortfall (as little as 4.4 kg). However, it seems unlikely that all of the assumptions that are built into the best-case scenario will come to pass. MMRTGs are still baselined for OPF 1, there remains no clear path to fight qualification of ASRGs, and FY 2010 funding for 238Pu production remains more a hope than an expectation. Thus, the actual shortfall is likely to be somewhere between the best-case curve and the status-quo curve in Figure S.1, and it could easily be 20 kg or more over the next 15 to 20 years.

It has long been recognized that the United States would need to restart domestic production of 238Pu in order to continue producing RPSs and to maintain U.S. leadership in the exploration of the solar system. The problem is that the United States has delayed taking action to the point that the situation has become critical. Continued inaction will exacerbate the magnitude and the impact of future 238Pu shortfalls, and it will force NASA to make additional, difficult decisions that will reduce the science return of some missions and postpone or eliminate other missions until a source of 238Pu is available.

The schedule for reestablishing 238Pu production will have to take into account many factors, such as construction of DOE facilities, compliance with safety and environmental procedures, and basic physics. This schedule cannot be easily or substantially accelerated, even if much larger appropriations are made available in future years in an attempt to overcome the effects of ongoing delays. The need is real, and there is no substitute for immediate action.

HIGH-PRIORITY RECOMMENDATION. Plutonium-238 Production. The fiscal year 2010 federal budget should fund the Department of Energy (DOE) to reestablish production of 238Pu.

  • As soon as possible, the DOE and the Office of Management and Budget should request—and Congress should provide—adequate funds to produce 5 kg of 238Pu per year.

  • NASA should issue annual letters to the DOE defining the future demand for 238Pu.


Advanced RPSs are required to support future space missions while making the most out of whatever 238Pu is available. Until 2007, the RPS program was a technology development effort. At that time, the focus shifted to development of a flight-ready ASRG, and that remains the current focus of the RPS program. The program received no additional funds to support this new tasking, so funding for several other important RPS technologies was eliminated, and the budget for the remaining RPS technologies was cut. As a result, the RPS program is not well balanced. Indeed, balance is impossible given the current (FY 2009) budget and the focus on development of flight-ready ASRG technology. However, the focus on ASRG development is well aligned with the central and more pressing issue that threatens the future of RPS-powered missions: the limited supply of 238Pu. The RPS program should continue to support NASA’s mission requirements for RPSs while minimizing NASA’s


Letter from the NASA Administrator Michael D. Griffin to Secretary of Energy Samuel D. Bodman, April 29, 2008 (reprinted in Appendix C).

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