Even while orbiting high above the atmosphere in the International Space Station, astronauts will work under the watchful eyes of ground-based investigators. A semiautonomous, miniature space vehicle will let the principal investigator observe experimental results and will free up some time for the astronauts. When the multibillion-dollar space station is operational, the cost of an astronaut's time will be staggering. Timesaving tools will be not only appreciated but absolutely necessary. Engineers at NASA's Ames Research Center have developed the softball-size Personal Satellite Assistant (PSA) to improve the efficiency of on-orbit operations. For example, if warning flags indicate a potential problem with a fluid flow line, a ground team can remotely guide the robot to the area in question, freeing the astronauts to concentrate on their research tasks. Small enough to operate in the shirtsleeve environment of the space station, the Personal Satellite Assistant -- using its ducted-fan propulsion system, with feedback from an inertial measurement system and a stereoscopic pair of complementary metal oxide semiconductor (CMOS) imagers -- will remain at a desired location while it transmits images and other information on a 3-Mb/s wireless Ethernet link. Dedicated diode detectors can watch for hot spots, allowing rapid response to a potentially disastrous fire or contaminant leak. The robot should satisfy the earthbound investigator's need to observe experimental results and to communicate with the experimenters. "The PSA acts as a remote-controlled camera," said Hans Thomas, optical systems engineer for the device, "which the [principal investigator] can use to watch over the astronaut's shoulder." The optical system is used not only to provide a virtual presence on the station, but also to increase the robot's autonomy. The CMOS cameras produce range and velocity information, and are used for orientation by comparing visual fiducial marks with an onboard map. "The PSA can also use real-time visual 'servoing' to station-keep in a given location," Thomas said. "In conjunction with the inertial measurement unit, we track features in the environment to resolve out long-term drift."