Development History and Future Prospects of VLBI Terminals

This paper mainly describes the development history and future prospects of the VLBI (Very Long Baseline Interferometry) technique. The VLBI technique began in 1960s. Its developments have exerted a profound influence on various fields such as the Geodesy, Geodynamics, and Astrometry. The VLBI terminal system (i.e. data recording system), which is an important part of a VLBI system, has been undergoing massive renewal and dramatic developments during the last few decades. The progress from the first Mark 1 system to a Mark 5 system today, and that from the first tape-recording device to a hard-disk digital recorder then to the real-time data transmission through the Internet today, all show that tremendous changes have taken place for VLBI terminal systems.Since the adoption of reform and opening policies, China has entered a new era of rapid development, and the VLBI technology in China is also developing amazingly. China has the world's most advanced observation equipments, with its technological capability in VLBI at the global advanced level. The Chinese VLBI Network (CVN) project was proposed in 1979, and since then research of VLBI has been actively carried out in the Shanghai Observatory (SHAO). The project plans to cover geodetic, geodynamic, astrometric, and astronomical VLBI applications. The Shanghai Sheshan 25m Telescope, the Urumqi Nanshan 25m Telescope, the Kunming 3m mobile VLBI station, the Kunming 40m Telescope, and the Beijing Miyun 50m Telescope are constructed in 1987, 1994, 1999, 2005, and 2006, respectively; and the first CVN correlator was estabilished in 2000. At present, the CVN consists of these four radio telescopes and a data processing center located in Shanghai. The resolving power of a VLBI in the CVN is equivalent to that of a 3000-kilometer synthesis-aperture radio telescope, with the angular resolution at a few hundredths of an arcsecond or better.In 2007 the VLBI technique was employed for the first time in the Chinese lunar exploration program, the ChangE'1. As a subsystem of the lunar exploration-program monitoring system, the specific task of the VLBI system is to measure motion of the spacecraft and obtain data including those for time delay, time delay rate, and angular position, which are useful in orbit determination and prediction. This task has been successfully accomplished as a result of the concerted effort and full cooperation of all parties. In 2010, based on the experience with the ChangE'1, the VLBI technique was once again successfully applied, to the ChangE'2. Being a key part of VLBI observation, the VLBI terminal system has contributed tremendously to the Chinese lunar exploration programs. Currently, the latest type—Mark 6 is being developed and perfected in the USA. We believe that this type will be widely used in the field of astronomy and space science in the near future.