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SPHERES hope to show that small is beautiful

April 27, 2006 By Mark Peplow This article courtesy of Nature News.

Tiny satellite makes debut inside the space station.

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A miniature satellite has arrived at the International Space Station (ISS), where it will take its first space flight in indoor comfort rather than in the harsh conditions outside the station.

Its inventors hope that the volleyball-sized probe will be the forerunner to a new generation of small satellites that can fly in formation, and possibly act as servicing robots for the ISS.

The probe arriving at the ISS this week is one of just three built by the SPHERES project at the Massachusetts Institute of Technology, Cambridge. The Synchronized Position Hold Engage Re-orient Experimental Satellite is designed to float in space while holding a precise position.

A flotilla of such satellites could eventually act as parts of a giant telescope, maintaining their position by communicating with each other using radio links, suggests David Miller, who leads the MIT team.

Inside job

The probes went through a preliminary round of testing 6 years ago on the 'vomit comet' jet plane, which flies on a roller-coaster path through the skies to give astronauts a taste of weightlessness during freefall. But delays to the Space Shuttle programme have prevented the SPHERES making its space debut until now. It arrived in an unmanned Progress 21 cargo ship that docked with the ISS on 26 April, which also brought more than 2 tonnes of supplies.

The two astronauts onboard the ISS have been trained to test the capabilities of the SPHERES, and will begin their experiments on 18 May. They'll be putting the probe through its paces, checking that it can maintain its position using tiny jets of CO2 and dock with the ISS wall or, later this year, with a twin satellite. The tests will last for at least 8 months, and Miller expects to upload new versions of the probe's software every 2 or 3 weeks, making improvements as they go.

Testing the SPHERES inside the station offers the obvious benefits of allowing astronauts to keep a close eye on it and tinker with its hardware, all while in microgravity but not in the cold and airless environment of outdoor orbit.

Little helpers

As the technology develops, similar probes could be used to refuel larger satellites, or even double as robotic assistants for the ISS crew. "Space walks are extremely expensive and you can't send someone out quickly," explains Max Meerman, director of research at Surrey Satellite Technology Limited, Guildford, UK.

SPHERES is just part of a growing trend for launching several smaller, single-task satellites, rather than one giant satellite carrying a dozen different instruments, says Bill Levett, an engineer at the technology company Qinetiq based in Farnborough, UK.

Spreading instruments over several smaller satellites means that if one malfunctions, there is less risk that the whole mission is ruined, says Levett. And it's easier for smaller satellites to hitch a ride on rocket launches that have spare capacity, adds Meerman, which helps to keep costs down.

But formation flying has a lot of technical hurdles to clear before astronauts would be confident enough to rely on miniature probes that might accidentally crash into each other in space. "You need to have a lot of faith in the system," says Levett, "and that takes a lot of time and flight trials."

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