Original URL: http://www.theregister.co.uk/2011/11/22/curiosity_nuclear_battery/

Nuclear power will let NASA Mars rover beat 1970s Soviet record

The throbbing plutonium heart of Curiosity

By Lewis Page

Posted in Science, 22nd November 2011 16:22 GMT

Everyone knows the famous NASA Mars rovers "Spirit" and "Opportunity": but not everyone knows that for all their renowned longevity they do not hold the record for robot rover distance rolled on an extraterrestrial body.

That honour belongs to the Soviet Moon rover Lunokhod-2, despite the fact that it was launched more than a decade before the NASA Martian ones and was much less sophisticated. The comparatively primitive Lunokhod was able to roll much faster - and so much farther - than today's Mars rovers for the simple reasons that Mars is much farther from the Sun, and Spirit and Opportunity make little use of nuclear power.

This is why NASA's new Martian explorer, Curiosity, has a plutonium-powered "space battery" at its core and carries no solar panels. On Mars, sunlight is weak and temperatures are low - often bitterly so. Much of the paltry amounts of juice that Spirit and Opportunity have been able to generate has had to be used in heaters to keep equipment from failing in the fierce Martian cold, severely limiting what could be given to propulsion and instruments. The rovers have to be put into hibernation on a slope tilting towards the Sun in order to survive the winter, so that much of their long lifespans have in fact been largely wasted.

But Curiosity will generate both heat and power from its Multi-Mission Radioisotope Thermoelectric Generator unit, build by the nuclear-space boffins of the Idaho National Lab. A radioisotope generator isn't a reactor - it doesn't use a chain reaction to accelerate fission in its plutonium. Rather it simply harvests the heat of the heavy element's natural decay, pumping it around using a central-heating system to keep the rover healthy: Curiosity won't need to hibernate in the winter. Meanwhile thermocouples exploit the big difference between hot battery and cold exterior to generate more than 100 watts of electricity for years on end, all of which can go on propulsion and instruments.

The Lunokhods of the 1970s used nuclear power too: though they generated their electricity from a flip-top solar panel lid, this naturally ceased during the cold-enough-to-freeze-nitrogen, fortnight-long lunar nights. When the Sun set, the Lunokhods would close the lid over their bathtub-like bodies and wait - kept warm by an internal polonium-powered radioisotope heater.

Now, at last with Curiosity, the 37km distance record set by Lunokhod 2 looks set to be broken at last.

We here on the Reg space desk will be bringing you more on Curiosity and its departure for the Gale crater later this week. ®