TABLE 3.2 Best-Case Estimate of 238Pu Shortfall through 2028: 238Pu Demand Versus Supply Subsequent to Launch of Outer Planets Flagship 1


238Pu (kg)


Discovery 14



New Frontiers 4



Pressurized Rover 1






New Frontiers 5



Discovery 16



Pressurized Rover 2



Outer Planets Flagship 2



Pressurized Rover 3





Total 238Pu demand subsequent to OPF1



Remaining inventory of 238Pu after OPF1 (with ASRGs)



Best-case estimate of 238Pu production needed



Total 238Pu production if work starts in FY 2010



Best-case estimate of 238Pu shortfall

NOTE: ATHLETE, All-Terrain Hex-Legged Extra-Terrestrial Explorer; FY, fiscal year; OPF, Outer Planets Flagship.

because solar power is not feasible for some of the missions described in that report.

The report The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics (NRC, 2003) describes the solar probe mission as the highest priority in the large mission category, with implementation recommended as soon as possible. The Solar Probe mission, now scheduled for launch in 2015, has been rescoped to eliminate the need for an RPS. The rescoped mission will spend more time near the Sun, but the closest point of approach will be 8.5 solar radii from the surface of the Sun instead of 3 (JHU, 2008).

Similar considerations affect other missions. The mission planning teams for OPF 1 have been directed to minimize power and consider the use of ASRGs. The use of a mixed package of RPSs has also been considered. For example, MMRTGs could be used to provide a basic level of power, and ASRGs could be used for additional power for full mission capability. For the OPF 1 mission, concurrent science operations will have to be limited unless there are at least 4 or 5 MMRTGs (or the equivalent number of ASRGs).

The decadal survey for solar and space physics identifies the interstellar probe as another high-priority mission, although it has been deferred until necessary propulsion capabilities are available (NRC, 2003; 2004). Given the demise of Project Prometheus (NASA’s space nuclear reactor power and propulsion program), the interstellar probe is not possible without RPSs (which are far less expensive than space nuclear reactors).

The DOE’s budget does not currently include funds to reestablish production of 238Pu. Yet, even if funding does become available in fiscal year (FY) 2010, full-scale production of 238Pu (5 kg/year) is unlikely to be possible until 2018, and that will be too late to meet all of NASA’s needs. In fact, if the OPF 1 mission uses MMRTGs, as is currently baselined, even if the DOE starts work immediately to restore its 238Pu production capability, there will be a substantial shortfall in meeting NASA’s needs for 238Pu through 2028.

While it remains to be seen whether ASRGs can and will be flight qualified in time for OPF 1, if ASRGs can be used, NASA estimates that there will be 13 kg of 238Pu left from the available stockpile (including future deliveries of Russian 238Pu) to power missions after OPF 1. Those missions (through 2028) and their demand for 238Pu are listed in Table 3.2. They will require a total of 75.4 to 79.8 kg of 238Pu. Thus, the required production from now through FY 2028 is at least 62.4 to 66.8 kg.

Assuming that the DOE begins work in FY 2010 to establish the capability to produce 5 kg of 238Pu per year, it will be able to produce 1 kg of 238Pu in 2016, 2 kg in 2017, and 5 kg in 2018 and in each year thereafter. This amounts to a total production of 58 kg through the end of FY 2028. The net result is a shortfall of 4.4 to 8.8 kg. Thus, even in a “best-case” scenario that minimizes 238Pu demands and maximizes 238Pu supply—which is to say, even if it is optimistically assumed that (1) NASA’s future RPS mission set is limited to those missions listed in the NASA administrator’s letter of April 2008,10 (2) the 238Pu required by each mission is the smallest amount listed in that letter (for missions with a demand for 238Pu that is listed as a range of values), (3) ASRGs are flight qualified in time to use them instead of MMRTGs on OPF 1, and (4) funds for 238Pu production are included in the DOE’s budget for FY 2010—it would not be possible for the DOE to meet NASA’s total demand for 238Pu. Immediate action is required to minimize the mismatch between NASA needs and the DOE capabilities and to avoid


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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