[/caption]Decommissioning nuclear weapons is a good thing. But when our boldest space missions depend on surplus nuclear isotopes derived from weapons built at the height of the Cold War, there is an obvious problem.
If we’re not manufacturing any more nuclear bombs, and we are slowly decommissioning the ones we do have, where will NASA’s supply of plutonium-238 come from? Unfortunately, the answer isn’t easy to arrive at; to start producing this isotope, we need to restart plutonium production.
And buying plutonium-238 from Russia isn’t an option, NASA has already been doing that and they’re running out too…
This situation has the potential of being a serious limiting factor for the future of spaceflight beyond the orbit of Mars.
Exploration of the inner-Solar System should be OK, as the strength of sunlight is substantial, easily powering our robotic orbiters, probes and rovers. However, missions further afield will be struggling to collect the meagre sunlight with their solar arrays. Historic missions such as Pioneer, Voyager, Galileo, Cassini and New Horizons would not be possible without the plutonium-238 pellets.
So the options are stark: Either manufacture more plutonium or find a whole new way of powering our spacecraft without radioisotope thermal generators (RTGs). The first option is bound to cause some serious political fallout (after all, when there are long-standing policies in place to restrict the production of plutonium, NASA may not get a fair hearing for its more peaceful applications) and the second option doesn’t exist yet.
Although plutonium-238 cannot be used for nuclear weapons, launching missions with any kind of radioactive material on board always causes a public outcry (despite the most stringent safeguards against contamination should the mission fail on launch), and hopelessly flawed conspiracy theories are inevitable. RTGs are not nuclear reactors, they simply contain a number of tiny plutonium-238 pellets that slowly decay, emitting α-particles and generating heat. The heat is harnessed by thermocouples and converted into electricity for on board systems and robotic experiments.
RTGs also have astonishingly long lifespans. The Voyager probes for example were launched in 1977 and their fuel is predicted to keep them powered-up until 2020 at least. Next, the over-budget and delayed Mars Science Laboratory will be powered by plutonium-238, as will the future Europa orbiter mission. But that is about as far as NASA’s supply will stretch. After Europa, there will be no fuel left.
If plutonium-238 production is to be started again, a decision will need to be made soon. It will take eight years to start producing 5 kilograms of plutonium-238 per year, therefore any application for additional funding for plutonium-238 production for space exploration will need to be placed in next year’s budget.