There is a cool article today in New Scientist that describes an old cooling method with a bleeding edge application: a rover to Venus. Venus is a picture of the greenhouse effect gone wild. Average temperatures are about +260 degrees Celsius (500 degrees Fahrenheit). This is hot enough to melt lead and destroys most modern electronics. Previous rover attempts to Venus by the US and Russia lasted less than 2 hours. So if we are to put a rover on Venus for the kind of time we have spent on Mars, we’ll need to find a way to cool the onboard electronics long enough that they can operate well.
Enter two NASA boffins, Geofferey Landis and Kenneth Mellott. By applying a refrigeration technique invented by a clergyman nearly two centuries ago, they have found a way to keep a rover cool for about fifty Earth days (a Venutian day is 243 Earth days, about 19 days longer than its year!). The Stirling cooler (invented by Reverend Robert Stirling) works by compressing a gas with a piston. As it compresses, it gets hotter. The temperature is dissipated with a radiator (which would be placed on the back of the probe). As the gas expands, it gets cooler (causing the refrigeration effect). In order for this to work, the radiator must be hotter than the outside air.
Interestingly, the Stirling cooler is energy efficient and is being incorporated into some of the newer energy efficient refrigerator models. To power the cooler on the rover, they propose using a plutonium battery. This type of device is known as a radioisotope thermoelectric generator. As the radioactive material decays, it release heat, and this heat is converted into electricity. These batteries are common on satellites and in unmanned situations where a long duration power source is necessary and solar cells are not viable (the massive cloud cover on Venus prevents solar cells from being very effective, plus the atmosphere is very caustic and I think it would probably damage them).
Well, if there is somehow intelligent life on Venus, let’s hope they don’t confuse this rover for the first case of interplanetary terrorism.