Technical challenges and science benefits of using astrometric devices to track laser-carrying spacecraft

Research and development related to the use of lasers for optical communication links with planetary spacecraft is now being pursued vigorously by NASA and other organizations worldwide. Baseline models envision a 1-Watt, frequency-doubled Nd:YAG laser (532 nm) firing through a 30-cm telescope aboard spacecraft as early as the late 1990's. At Saturn or Neptune, for example, such a laser would look to typical broadband astrometric detectors like a Sun-like star of apparent visual magnitude 12 or 15, respectively. JPL has been looking into the use of astrometric techniques to locate and track the angular motion of the spacecraft relative to nearby quasi - stationary stars or solar-system objects. This talk will discuss some of the technical challenges and advantages associated with the use of single-telescope (e.g., with Ronchi gratings) and interferometric astrometric techniques for tracking spacecraft, both from the ground and from space. Also to be discussed are some of the potential science benefits that would result from a laser on board a spacecraft and a precise astrometric tracking capability.