Fuel Shortage threatens future NASA Deep Space Exploration

Due to a severe fuel shortage, we may soon no longer be going boldly where no one has gone before.

NASA and collaborative space programs have had some amazing successes over the years, delivering some of the most compelling and emotional moments in human history. Our deep space exploration programs have been a large part of that, allowing us to venture out into realms that we can barely dare to dream. Those same missions and their future spawns are in jeopardy, however not due to budget cuts or the like, but rather because we have almost run out of plutonium.

The recent announcement that Voyage 1 has actually reached interstellar space is a marvel to imagine, especially considering that the spacecraft is over 36 years old. A huge component of this monumental accomplishment is attributed to a special nuclear-powered generator that converts heat from the radioactive decay of plutonium-238 into electricity. This same power supply is used on the Cassini and New Horizons spacecrafts that are orbiting Saturn and headed out towards Pluto respectively, and the Mars Curiosity rover uses a very similar generator as well.

Now, although the engineering panache of those power supplies has brought us this far, their continued use is in question due to a shortage of plutonium-238. NASA’s supply had been simply a by-product of the manufacture of nuclear weapons during the Cold War, as plutonium-238 can no longer be found in nature. However, with no new nuclear weapons being produced in the past 25 years, supplies are dwindling. A partnership between the Department of Energy and NASA has led to production specifically tailored to make more plutonium starting up once again, however it could take nearly a decade to see any results from these efforts.

“By the end of the calendar year, we’ll have a complete plan from the Department of Energy on how they’ll be able to satisfy our requirement of 1.5 to 2 kilograms a year,” said NASA’s Planetary Science Division Head Jim Green at the 44th Lunar and Planetary Conference earlier this year.

Sixteen kilograms, the amount of useable plutonium-238 currently accessible by NASA, could disappear in the blink of an eye when considering that nearly twice as much as that was required just for the Cassini spacecraft, which launched in 1997 and reached Saturn in 2004.

“We’ve been living off of the material that we had produced up until [the end of the Cold War], and if you keep using material and you have a finite supply, eventually you run out and that’s where we are right now,” stated Ralph McNutt, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory, in 2009.

Plutonium-238 itself is an extremely efficient, but extremely expensive, fuel source. The isotope is made in a nuclear reactor and can produce small quantities of electricity consistently for several decades. A single gram, or about .002 pounds, of plutonium-238 can produce .5 watts of power. A 10-pound chunk of plutonium can produce about 2,268 watts of power.

As the isotope breaks down, or decays, it releases energy. So much energy, in fact, that its temperature can reach 2,300 degrees Fahrenheit. A plutonium-238 battery is rigged in a way that turns this heat into power. This is called a multi-mission radioisotope thermoelectric generator, or MMRTG.

Future Mars missions might be able to switch to solar power. The Juno spacecraft is one such example and should successfully reach Jupiter in 2016, but only via the use of three enormous 2.7 x 8.9 metre solar panels. This technology, though adequate for this mission, would not be feasible for deep space missions sent to the outer solar system, which cannot depend on the sun. Newer models of the radioisotope thermoelectric generator are also in development and will be more efficient, and thus use less fuel, but still, each new mission will pick away at the remaining supply.


Image: NASA, ESA and the Hubble SM4 ERO Team

Written by Andrés Markwart, a Contributor at Vancity Buzz. Connect with Andrés on Twitter at @AMarkwart.