Today, when satellites break in space, there’s nothing to be done but wave buh-bye. A new generation of spacecraft that could diagnose and repair ailing satellites is on the horizon, though. Both NASA and the U.S. Air Force will soon launch experimental craft designed to autonomously hunt down another object in space and circle around it while snapping pictures. Next year, the Pentagon’s Defense Advanced Research Projects Agency will go a step further by launching a craft that will find a satellite and then dock to it.

Low-cost, self-directing robots that could haul cargo to the moon, for instance, or make repairs to instruments in orbit, such as the Hubble Space Telescope, are essential to the future of space exploration. But some experts warn of ulterior motives: Sidling up to another craft would also allow you to spy on it, and possibly even destroy it. “These missions offer the ability to modify, inspect, and refuel other satellites,†says arms-control and space policy expert Jeffrey Lewis of the University of Maryland. â€It´s very clear that they also offer the ability to attack foreign satellites.â€

NASA´s Demonstration for Auto-nomous Rendezvous Technology mission, known as DART, is slated to launch this month. According to project manager Jim Snoddy, DART will use GPS receivers to track down its target object, a retired communications satellite. Closer in, DART´s Advanced Video Guidance Sensor will identify the satellite and help the computerized guidance system to fire the appropriate thrusters, bringing the craft within five meters of its target. Snoddy points out that DART can´t be used offensively because it needs a cooperative target: The retired communication satellite was fitted with easy-to-spot reflectors before launch.

The Air Force´s Experimental Satellite System mission (XSS-11), also due for launch this spring, is attempting something more ambitious. It will spend a year in space, carrying out navigational tests around several targets-many of them derelict rockets. To home in, XSS-11 will use a combination of a laser-scanning system. Although the Air Force emphasizes the peaceful uses of this technology, the XSS project was born of the old â€Star Wars†missile-defense program.

Meanwhile, civilian satellite builders are also getting into the game. Surrey Satellite Technology in the U.K. built the 6.5-kilogram SNAP-1 as an exercise in miniaturization. Launched in 2000, SNAP-1 crept to within nine meters of the satellite Tsinghua-1 and then took pictures. Surrey is now working on an even smaller shutterbug, dubbed PalmSat.

Like the Air Force, Surrey insists that its craft are for peaceful uses only, although its collaboration with the Chinese government on the 2000 mission has raised a few eyebrows among U.S. military officials, prompting some to speculate on whether China is secretly developing â€parasitic satellites†as space weapons. Of course, China may be wondering the same thing about the U.S.

While the 1967 Outer Space Treaty bans weapons of mass destruction in orbit, there are no international laws governing the use of robots in space, and Lewis believes it´s time to establish some ground rules. Simple measures-such as making public any experiments carried out in space-would make a big difference, he says. “Just having a discussion would be a big step forward.â€