In-Beam Phase Referencing with the Deep Space Network Array

The Deep Space Network Array of the future provides an intriguing possibility of using the techniques of in-beam phase referencing to determine the position of spacecraft with accuracy at the level of 0.1 nrad. In this article, we discuss the prospects for carrying out such measurements at both 8.4 GHz (X-band) and 32 GHz (Ka-band). Our study suggests that at X-band in-beam calibration may be available as an astrometric tool over 20 to 30 percent of the sky. We point out that this estimate depends strongly on the number density of compact sources at the 1-mJy flux level. The prospects at Ka-band, on the other hand, are not very hopeful. We also discuss issues related to phase cycle ambiguity resolution and potential techniques to resolve them.