Antique Fridge Could Keep Venus Rover Cool

Hugh Pickens writes "In the 1970s and 80s, several probes landed on Venus and returned data from the surface but they all expired less than 2 hours after landing because of Venus' tremendous heat. It's hard to keep a rover functioning when temperatures of 450 C are hot enough to melt lead but NASA researchers have designed a refrigeration system that might be able to keep a robotic rover going for as long as 50 Earth days using a reverse Stirling engine. NASA has not committed to a Venus rover mission, but a 2003 National Academies of Science study recommended that high priority be given to a robot mission to investigate the Venusian surface helping to answer such questions as why Venus ended up so different from Earth and if the changes have taken place relatively recently."

Stirling coolers

[EaglemanBSA]

While stirling engines are certainly old, the idea of using them as refrigerators is just recently catching on. Here in sleep Athens, OH a company called Global Cooling is the forefront producer of such devices (and is still hand-making a good number of them).

The nice little advantage to these coolers is that they operate with very high COP's, and are limited in lower temperature merely by available power and the boiling point of the working gas. In global cooling's case, Helium is typically used, so temperatures down to around 5K are obtainable (at which point the helium liquifies. Yeah. Cold.) Also, control of the device can be very precise, in that instead of a compressor kicking on and off, it operates constantly, quietly, and with good variable control.

LG is beginning to outfit refrigerators with Stirling pumps because they're so much better than current designs - only problem is they're not mass produced yet. Coleman has a portable unit shown here [coleman.com] that is quite a nice unit, albeit very pricey.

One of my professors here at school is one of the pioneers of Stirling refrigeration, so I've been exposed to it a lot. If the whole country switched their refrigerators to stirling compressors, California could shut off its power grid and we'd still have a surplus of energy country-wide.

Re:i've always said

[calebt3]

Isn't Venus outside Sol's habitable zone? (the region around a star where liquid water is possible)

Re:i've always said

[evanbd]

Well, in terraforming terms, finding stuff to make up the Martian atmosphere probably isn't that hard. There are significant CO2 ice caps, and there may be significant water available with modest effort. CO2 plus plants gives you O2. Also, there is some good evidence to suggest that the icecaps' existence is bistable -- that is, if you could mostly evaporate them, the additional greenhouse effect would warm the planet enough to finish the job and keep it that way.

Basically, the problem of terraforming is to find resources that are already available in almost the form you want, and find some way to leverage your input effort. You don't want to have to process every single megaton of atmosphere you want to add / remove. It's far easier to (for example) dust carbon black on the poles and add a few orbiting mirrors.

Of course, the only reference I have handy is Zubrin's The Case for Mars which is a bit dated but (I think) still basically correct. The details may well have changed thanks to newer lander data.

Re:i've always said

[larry bagina]

Prior to the global warming, Venus is generally believed to had surface water.

Re:Stirling coolers

[EaglemanBSA]

No, actually they're using the stirling design as the actual pump - that's the beauty of it. They're looking at using CO2 or helium as the refrigerant as well as the working fluid in the stirling cooler - especially with respect to helium, getting the gas-phase bubbles out of the fluid is as simple as letting it evaporate and leak back into the cooler itself. The design is much simpler this way, and leaks are quite benign.

That being said, helium is a bit more expensive than other refrigerants, and CO2 requires intensely high pressures, so much work is yet to be done. As a heat pump, Stirling cycle engines operate on the theoretical threshold (we evaluate them using the Carnot cycle) of efficiency, so they...well, blow other designs out of the water. For numbers, I don't have any here. To give you some perspective though, I've seend a 40 watt unit freeze the water in the air around it within seconds of being turned on.

Re:i've always said

[Loke the Dog]

They both lack magnetic fields which makes long term terraforming pointless which means we can just drop the whole idea.

Re:Stirling coolers

[Geoffrey.landis]

in sleep Athens, OH a company called Global Cooling is the forefront producer of such devices (and is still hand-making a good number of them).

... and, in fact, Global Cooling licensed their free-piston Stirling engine technology from Sunpower (also of Athens, Ohio), and Sunpower works with NASA Glenn on the Stirling engine development. So they really are the cousins of the Venus engines.

Re:Water and Plate Tectonics

[Geoffrey.landis]

Water lowers the viscosity of magma.

Re:i've always said

[QuantumG]

Yes, but it takes thousands of years for the solar wind to blow away the atmosphere. If we one day have the ability to make the atmosphere of Mars suitable for human habitation then surely we will also have the ability to maintain the atmosphere over such a long time period.

Re:why nuclear?

[Anonymous Coward]

Second Law of Thermodynamics: It takes a temperature differential to convert heat into usable energy.