Mars rover gets 'engine' upgrade: Curiosity fueled by nuclear power
The next Mars rover, Curiosity, is scheduled to launch Saturday. It's the first Mars rover to jettison solar panels for nuclear power, meaning it can go places and do things others couldn't.
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Gone are the fly's-wing-like solar panels that provided electricity for earlier rovers Spirit and Opportunity.
Instead, the rover for the Mars Science Laboratory, Curiosity, carries 10.6 pounds of plutonium-dioxide pellets. The system is designed to allow the vehicle to operate where sunlight is so weak or the spacecraft's mission is so demanding that solar panels are impractical.
"You can operate with solar panels on Mars, you just can't operate everywhere," said Stephen Johnson, who heads the space nuclear systems technology division at the US Department of Energy's Idaho National Laboratory in Idaho Falls, in a statement. "This gives you an opportunity to go anywhere you want on the planet, not be limited to the areas that have sunlight, and not have to put the rover to sleep at night."
The power source is known as a multimission radioisotope thermoelectric generator (RTG), and other versions have been incorporated into spacecraft designs since the 1960s. In January 2006, NASA launched an RTG on the New Horizons spacecraft, which is now more than half way to its planned 2015 flyby of Pluto. Even the Mars rovers Sojourner, Spirit, and Opportunity have carried small plutonium-fueled heaters to keep the vehicles' electronics warm.
The RTG on Curiosity uses the contrast between heat of plutonium's radioactive decay and the chilly temperatures on Mars to generate electricity.
What are the launch risks?
The form of plutonium used, plutonium-238, is unsuitable for nuclear explosive. The primary risk, according to physicists, comes if finely ground plutonium is inhaled or ingested along with with food.
The units housing the plutonium-dioxide pellets have undergone rigorous tests under conditions one might expect to see if a rocket carrying an RTG-bearing spacecraft has to be destroyed before it reaches orbit, NASA and US Department of Energy officials have said.
By some accounts, six missions since the 1960s, including the aborted Apollo 13 mission and Russia's Mars 96 mission, have ended with RTGs burning up high in the atmosphere or plunging into the ocean after surviving reentry. While early models released radioactive material as craft burned up on reentry, later models appear to have survived reentry and impact intact without releasing radioactive material.
NASA's environmental-impact statement for this launch puts the risk of a release from a launch-area accident at 1 in 420. But the agency's calculations put the risk of adverse health effects to any single individual from an accident near the launch site at less that 1 in 1 million.