On space station, droids get a workout

Cue the John Williams theme and roll the vanishing intro – Obi-Wan Kenobi's Jedi-training droids have arrived on the International Space Station (ISS).

Or at least David Miller's versions have arrived. The free-floating spheres are set to test new concepts for "smart" satellites. Able to fly in precision formation, the robots may one day hold the key to building everything from huge space telescopes that can peer deeply into the universe to constellations of small, cheap satellites that can monitor changes on Earth.

The shuttle Discovery last week brought the second of three droids that are undergoing experiments as they arrive.

If the experiment, dubbed SPHERES, sounds like science fiction, perhaps that's because it was inspired in part by it. While working on formation "flying" for satellites, Dr. Miller, director of MIT's Space Systems Laboratory, challenged his students to build prototypes.

"I rented the first 'Star Wars' movie and showed the class the scene where Luke is practicing the use of the Force with a floating droid," he explains. "I said: 'I want three of those. How do we start doing this?' "

The result: spheres the size of bowling balls crammed with computers, position sensors, and tiny thrusters made to maneuver with precision.

After years of testing – including trials aboard a NASA jet whose flight path allows occupants a brief experience of weightlessness – the first of three spheres arrived in April aboard a Russian Soyuz spacecraft. A second arrived with Discovery, currently docked at the International Space Station, and the third is slated to arrive on Discovery in December.

Each orb weighs nearly nine pounds. Twelve thrusters use gentle puffs of carbon dioxide to change the orb's orientation and location. Each orb can figure out where it is by using 24 tiny microphones to listen for chirps from pager-size ultrasonic beacons placed on the station's walls.

The satellites communicate with one another via radio, and an additional radio channel lets ISS crewmember Col. Jeffrey Williams send software to the satellites and retrieve test data from them.

In May, Colonel Williams put the first droid through its paces, running tests to see how well the droid's sensors did in reporting changes in position.

The mini-sat also performed some rudimentary docking maneuvers. Once the second orb is checked out, the research team can begin testing more complex maneuvers.

The project is funded by the Defense Advanced Research Projects Agency and NASA. These agencies are interested in intelligent docking systems that can autonomously sense trouble and use their thrusters to compensate.

Robert Mah, a research scientist in the intelligent systems division at NASA's Ames Research Center in Moffett Field, Calif., cites a collision between Russia's Mir space station and a Progress resupply vessel as an instance where "fault-tolerant" docking would have helped.

After unloading the supplies, he says, the cosmonauts filled Progress with trash to be incinerated on reentry. Then they decided to back Progress away and practice docking maneuvers.

But the models they used to determine how much thrust Progress should apply didn't compensate for the capsule's changed mass after being loaded with refuse. The result: a dangerous collision between Progress and Mir.

For astronomers, one potential application for the precision-flying aspects of the SPHERES project comes in building space-based telescopes called interferometers – telescopes with several mirrors spread out over large distances.

For a space interferometer to work properly, the position of each element with respect to the others needs to be accurate within an inch or so as they shift their gaze from one object to another, Miller says.

After the third mini-sat arrives in December, Miller adds, he plans to test some basic interferometer configurations to see how precisely the mini-sats can hold their positions.