Page last updated at 14:41 GMT, Tuesday, 19 August 2008 15:41 UK

A thermostat for mini-spacecraft

space shuttle launch
Fewer big launches makes for many small issues

Researchers in the US are showcasing a new approach to temperature control for spacecraft.

The technique is a welcome advance for miniature spacecraft, for which temperature regulation technologies employed in larger craft cannot be adapted.

The scheme uses razor-thin films that can adjust the amount of heat radiated by spacecraft.

The films are robust, inexpensive, and consume very little power.

Ever smaller

The push towards smaller spacecraft and satellites has a number of motivations. Launch costs scale directly with weight, so there is always a push toward the small.

But it is also about independence. As those costs fall, an increasing number of developing countries is looking to launch small, dedicated satellites for monitoring and security.

Companies that, for instance, provide digital television share time on satellites to send signals earthward, resulting in more software and electronics to manage communications. As a result, companies are opting for their own satellites.

Defence applications also benefit from smaller craft, as they are less detectable and more difficult to target.

Spacecraft can be in blazing sunlight or in the cold shadow of Earth or further out in space, and different operating conditions generate different amounts of heat from electronics. That makes temperature control difficult for craft of all sizes.

"For large spacecraft, this is done with mechanical louvers—basically glorified window blinds—that open and close to allow in or reflect heat," says Prasanna Chandrasekhar of Ashwin-Ushas, an American tehnology firm.

"But as satellites get smaller, these systems get too heavy and bulky."

Firms that make smaller satellites like Surrey Satellite Technology Limited (SSTL) have had to make do with simpler systems.

"We've used thermal insulation—similar to what you'd find in a fridge—and we're finding that we need better ways than purely insulating layers to make sure that our spacecraft maintain the right temperature," says SSTL engineer Adam Baker.

"There are lots of ways to cool and heat things, but they all tend to be complicated and require power, and could potentially break down."

Thin skin

Chandrasekhar and his colleagues, reporting at this week's American Chemical Society meeting in Philadelphia, believe they have found the solution.

These materials are surprisingly inexpensive
Prasanna Chandrasekhar
The team has developed a "skin" that can be placed on spacecraft to actively control the amount of heat that they radiate by controlling a property called emissivity.

Polymers in the skin can change their emissivity when electricity is applied to them, retaining heat in cold conditions and radiating it away in hot ones. That leads to an active temperature control that can be maintained with very little power.

The skin is just a few tenths of a millimetre thick, has been tested to withstand the rigours of the vacuum and temperature extremes of space, and can be bent and cut to fit craft of any shape without losing its properties.

"These materials are surprisingly inexpensive," adds Dr Chandrasekhar—around $300 per square metre—because they are made primarily from commercially available components. That means the approach is equally applicable to larger spacecraft.

"Something very simple like this requiring minimal power and with minimal mechanical things to go wrong could be quite a useful thing to put on small spacecraft," says Dr Baker.

"It looks like these things are a product that we could take off the shelf and apply to our spacecraft."

Microsatellites 'pose global threat'
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19 Jun 00 |  Science/Nature

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