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Plutonium shortage threatens future NASA missions |
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Written by Derek Kessler on
Sunday, 09 March 2008
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 For deep space exploration missions, no fuel quite matches the power of plutonium-238. The radioactive isotope is at the heart of the power systems for such long-distance probes like Cassini (studying Saturn) and New Horizons (on its way to Pluto). Missions beyond the inner planets have to rely on power sources other than solar power, for the further out you go, the less sunlight there is available. Speaking in front of a Senate panel on NASA's proposed 2009 budget, NASA chief administrator Mike Griffin revealed that all of the remaining US supply of plutonium-238 has already been allocated for current exploration missions, and with no plans or funds to produce more of the fuel, that's all that there is.
Plutonium-238 is valued by NASA and space scientists for its heat-generating properties. While it is of little use as a weapons base, plutonium-238 gives off constant and consistent heat which is harnessed to provide power for long-range spacecraft. Plutonium-238 is formed from the decay of neptunium-238 (which itself is created by artificially bombarding uranium-238 with loads of deuterium - an isotope of hydrogen with a neutron). The United States Department of Energy stopped producing plutonium-238 in 1988, and all NASA nuclear-powered missions since 1992 have used plutonium purchased from Russia.
In 2005, the Department of Energy planned to restart plutonium-238 production at the Idaho National Laboratory by 2011, at the cost of $250 million. The plan was shelved for reasons unknown, and starting today it would take seven years of construction, development, and testing before the lab could produce any new plutonium. The 2009 NASA budget does not include any funds to be transferred to the DoE for the production restart.
The latest figures on the US plutonium-238 stockpile date to 2005, when the DoE had 39.5 kg of the fuel on hand. At that point, projections of NASA and 'national security customer' use predicted that by 2010, all but 6.5 kg of the plutonium will have been used. To supplement the US supply, purchases of plutonium-238 have been made from Russia. Since 2005, the US has recieved 5 kg of plutonium from Russia, with an additonal 4.9 kg on order for this year.
With the current supply, NASA has enough fuel to power three more missions: the Mars Science Laboratory (due for launch in 2009), an outer planets exploration mission targeted for launch in 2017, and a Discovery-class mission (low-cost probes like Stardust, NEAR, Deep Impact, and Sojourner) sometime around 2014. Due to the lack of plutonium-238 to power any other missions, NASA's solicitation for the New Frontiers missions (frequent medium-sized probes, more expensive than Discovery-class missions, like New Horizons) requires that any proposals use a power source other than plutonium. The limitation severely hampers any missions destined to explore beyond Mars, as the predominant solar power used by inner solar system probes is not feasible for any missions to Jupiter, Saturn, or beyond.
Griffin has expressed his frustration in the past with NASA's future dependence on Russia for transportation to the International Space Station. With the retirement of the space shuttle fleet set for 2010, Russia will remain as the only nation capable of transporting crew to and from the ISS. The ESA's recently launched Automated Transfer Vehicle will be able to carry cargo to the station, but until the launch of the Orion CEV, no earlier than 2015, NASA will be reliant upon Russia's Soyuz craft for crew transfers.
Griffin described the further dependence of NASA should domestic plutonium-238 production not resume as "appalling." Even worse, Russia has advised NASA that it only has 10 more kg of plutonium-238 on hand. For comparison, Cassini launched with 32.7 kg of plutonium-238 fuel. As with the reliance on Russia for human space travel, some lawmakers are concerned about the reliance for nuclear fuel, citing potential political unrest in the country, Additionally, once the US stockpile of plutonium-238 is exhausted, Russia will be the only supplier on the planet, and as such, will be able to name its own price for the plutonium fuel.
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