Abstract:
Radio interferometric techniques for measuring spacecraft angular position play a role of increasing importance in today's missions of interplanetary exploration. Several national and international space agencies have or are developing operational systems to support spacecraft navigation using interferometric measurements. NASA's Deep Space Network has provided Delta Differential One-way Range (ΔDOR) or this purpose since 1980. Steady improvements in system performance and operability have taken place with accuracy today approaching the 1-nrad level. In this paper the current performance of NASA's ΔDOR system is presented. Recent data from the Mars Reconnaissance Orbiter cruise from Earth to Mars are used to illustrate system performance at 8.4 and 32 GHz. Technical feasibility and requirements for combining tracking stations from different agencies to support ΔDOR observations are discussed. The advantages of having additional stations to form baselines for measurements are presented. Results of a covariance study for encounter targeting are given for a candidate mission that may need ΔDOR data from additional baselines.
