1 ISTS 2006-d-50 USE OF VERY LONG BASELINE ARRAY INTERFEROMETRIC DATA FOR SPACECRAFT NAVIGATION

Very Long Baseline Interferometric (VLBI) techniques have been used to support numerous interplanetary missions since the late 1970s. These techniques involve the simultaneous tracking of two or more sources, at least one of them a spacecraft, by widely separated ground antennas. The recordings from the sources are correlated and differenced to obtain very precise estimates of the angular separation between the sources. The main VLBI technique that is used at JPL is known as the Delta Differential One-way Ranging (ΔDOR). Two DSN antennas simultaneously track a source, and alternate between sources. The signals recorded at the antennas from each source are correlated to obtain the delay in arrival to the two antennas, and the delays are differenced to remove common-source errors. An alternative technique is to use carrier phase differences between antennas. This is routinely done by the Very Large Baseline Array (VLBA) as part of source imaging. The VLBA capabilities are used for scientific research, but also have the potential to be used for navigation. Two main experiments were performed with the VLBA and JPL spacecraft. This paper describes and analyzes these experiments and discusses the possible uses of VLBA tracking for spacecraft navigation