Progress on the VLBI2010 Proof-of-Concept Geodetic VLBI System

In order to make a significant improvement in the accuracy and precision of geodetic VLBI measurements, a new system has been proposed by a working group of the International VLBI Service for Geodesy and Astrometry (IVS). The goals with the new system are to obtain approximately 1 mm position accuracy in 24 hours, to observe continuously, and to provide analysis of each 24 hour session within one day. The principal change recommended, compared to the current system, is to use faster-slewing antennas in order to sample the atmosphere more frequently. Although faster usually means a smaller antenna, and thus lower sensitivity, for the same cost, this has been overcome by improvements in both radio-frequency electronics and data acquisition that allow more instantaneous bandwidth coverage and much higher recording rates. Thus smaller (twelve meter diameter or larger) and less expensive antennas can be used to obtain satisfactory sensitivity. To demonstrate the feasibility of such a system NASA has funded the development of a new broadband microwave (2-12 GHz) VLBI system by the MIT Haystack Observatory, in collaboration with personnel from HTSI and NVI, Inc. This broadband system is intended to supercede the majority of operational S/X-band systems currently deployed in the global geodetic VLBI network. However those legacy antennas that continue to operate with S/X-only capability and that have sufficient sensitivity will be utilized for their unique contributions. Key components of the new system are a feed and receiver that cover the full 2-12 GHz range, and digital electronics that provide sample rates up to 4 gigabits per second. By recording four bands simultaneously, rather than the two bands (S and X) currently in use, relatively small (~12m) but fast-slewing antennas can be used. A proof-of-concept system has been implemented with the installation of prototype feed, receiver, and data acquisition systems on two existing antennas: the 18m antenna at Westford, MA, and the 5m MV3 antenna at the Goddard Space Flight Center (GSFC) at Greenbelt, MD. Observations on this baseline have led to improvements in the calibration system while the second generation feed and data acquisition systems were being developed. A new 12m antenna is being installed at GSFC. In this presentation we will describe the new geodetic VLBI system and discuss first results with the new antenna and broadband equipment.