Will NASA Run Out of Plutonium-238?

Here at NEI, we like to keep an ear to the ground when it comes to what's being discussed on Twitter and make sure to respond if/when folks direct reasonable questions our way.

Earlier this afternoon, Baltimore resident Dan Ewald posed the following question to us via Twitter:

"Y'all doing anything to help with the impending Plutonium-238 problem for @NASA?

Dan very helpfully included a link to a story from Wired describing the problem. To get an answer, I turned to Leslie Barbour of NEI:

We have long supported the DOE program for space exploration in appropriations, especially Cassini. The funding has always been provided by the Office of Nuclear Energy until this year when DOE and NASA agreed that space reactor funding be included in NASA budget. We can look at this again if needed.

For more information on how NASA spacecraft utilize radioisotope thermoelectric generators (RTGs) for the power they need, see our website.

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A Nuclear-Powered Space Rover Lands on Mars, Brings New Hope for Space Exploration

“If anybody has been harboring doubts about the status of U.S. leadership in space, well, there’s a one-ton, automobile-size piece of American ingenuity, and it’s sitting on the surface of Mars right now.”

This statement came from John Holdren, President Obama’s science advisor, this morning following the landing of a 2,000-pound nuclear-powered space rover, Curiosity, on the surface of Mars. This marks the first time that NASA has ever safely landed a human-made object of this size and weight on the surface of Mars, a notable feat in American engineering.

Early reports from The New York Times describes the rover’s landing on the Red Planet like a scene in a movie script:

As the drama of the landing unfolded, each step proceeded without flaw. The capsule entered the atmosphere at the appointed time, with thrusters guiding it toward the crater. The parachute deployed. Then the rover and rocket stage dropped away from the parachute and began a powered descent toward the surface, and the sky crane maneuver worked as designed. 

“Touchdown confirmed,” Allen Chen, an engineer in the control room, said at 1:32 a.m. Eastern time, followed by cheers, hugs and high-fives. 

Two minutes later, the first image popped onto video screens — a grainy, 64-pixel-by-64-pixel black-and-white image that showed one of the rover’s wheels and the Martian horizon. A few minutes later, a clearer version appeared, and then came another image from the other side of the rover.

This pivotal moment in space exploration is even more exciting because of the far-reaching implications Curiosity’s mission has for the nuclear energy field. The space rover is fully outfitted with an advanced nuclear power system called the Multi-Mission Radioisotope Thermoelectric Generator, or MMRTG (for those who like acronyms), to power its large frame over the two-year mission.

Ashwin Vasavada, deputy project scientist for the Mars Science Laboratory, explains that Curiosity needed a good, strong, reliable source of power to keep it going over its two-year mission. Other Mars Exploration Rovers—Spirit and Opportunity—have used solar panels for a source of power, but the engineers have found that they did not have enough power at times to complete their objectives because of dust settling on the panels or during the short days of winter. With Curiosity measuring two times bigger, five times heavier, and holding 15 times the weight in scientific equipment than the former space rovers, Vasavada said that the space rover needed a power generator that would be guaranteed to charge its battery year-round in all types of harsh conditions, which is why the laboratory turned to nuclear energy.

Curiosity’s generator serves a dual purpose: it provides electrical power and heat to the rover. The generator has a capacity of 110 watts of electrical power, which is used to continuously charge the rover’s battery and keep the rover moving and operating its technical devices. The heat that is created can then be pumped off using pipes, but maintain the warmth on the inside of the rover, including the scientific instruments.

Vasavada explains the reasons for selecting the nuclear-powered generator and how it works in the following video:


For a more technical explanation on how the generator works, see this description by Canadian Energy Issues:

Curiosity’s electronics are powered by what’s called a radioisotope thermoelectric generator (RTG). An RTG is a device that uses the heat from disintegrating radioisotopes to generate an electric current. In Curiosity’s case the radioisotope is plutonium-238, a strong alpha emitter with a half-life of around 88 years. A disintegrating Pu-238 atom ejects an alpha particle from its nucleus with an energy of 5.5 million electron volts. The ensuing collision between that ultra-high-energy particle and the first material it encounters generates a lot of heat.  

All missions to Mars and beyond are powered with Pu-238. By the time you get out to Mars, solar energy is too weak to generate meaningful amounts of electricity.

Over the course of its mission, Curiosity will be searching for indications that Mars was once habitable, such as examining rocks and other organic matter and sending images and samples back to Earth. The Washington Post says this is the first time NASA has embarked on a mission to Mars since the Viking missions in the 1970s. Since then, scientists have discovered that the planet was once wetter and warmer, which signals improved possibilities for life on the planet.

Photos from Curiosity’s first day on Mars are available on NASA’s website. You can also follow the space rover’s mission on Twitter: @MarsCuriosity and on Facebook: NASA’s Curiosity Mars Rover.

Have thoughts to share about Curiosity? Join the conversation about the space rover on NEI’s Facebook page.

For more information on nuclear energy’s applications in outer space, see NEI’s website.
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Photo captions: Image #1: One of the first test images from NASA’s space rover Curiosity upon landing on Mars to signal that everything was operational (credits: NASA TV, via The New York Times).

Image #2: Engineers work on a replica of NASA’s space rover Curiosity at the Jet Propulsion Laboratory (credits: Damian Dovarganes, Associated Press, via The Los Angeles Times).

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