Microsatellites are gaining acceptance in the aerospace community as potential replacements for conventional satellites. These spacecraft can be as small as a Coca-Cola bottle, so it would be far less expensive to deploy them. One challenge, however, is developing the tiny thrusters that would deliver the 0.1 to 10 mN for orbital changes and attitude control. For fine maneuvers, the required thrust is less than a sneeze, at 10 to 100 µN. Micro-optics can help to monitor the performance of these propulsion systems. An integrated optics chip, built into the nozzle of a microthruster, may serve as a diagnostic sensor to identify potential problems, such as contamination from incomplete combustion. Rice Systems Inc. is at the forefront of this technology. Rice's president, Colleen Fitzpatrick, explained that the concept for micropropulsion diagnostics evolved from its integrated optics rotation sensor, an optical gyroscope developed with funding from the US Defense Advanced Research Projects Agency. 'Virtual' satellites A benefit of microsatellites is that they can be deployed in a distributed architecture to form "virtual" satellites at one-third the cost of conventional systems and with a threefold increase in capability. One application is in synthetic-aperture radar for space applications, similar to radio telescope arrays on Earth. Because networked arrays of microsatellites are highly reconfigurable, however, they can be adapted for many other uses, such as geolocation and environmental applications. "The essential advantage of using microsatellites over conventional technology is that if you combine the data from each member of a microsatellite array, you can mimic the geometry of something that is much larger and harder to launch," Fitzpatrick said. She said that the micropropulsion diagnostic sensors have been designed and are ready for testing in realistic environments. As the thrusters themselves advance, the company will tweak the sensors to accommodate more sophisticated performance requirements. Rice hopes to test the sensors in a microsatellite flight experiment within two years.