With over fifty years of experience in radio astronomy and uniquely located within the National and West Virginia Radio Quiet Zones, the National Radio Astronomy Observatory’s Green Bank, West Virginia site is home to seven large radio telescopes ranging in size from 14m – 100m in diameter. The site also has significant infrastructure which allows for the installation of any instrument which may benefit from the radio quiet location of the site, as well as an excellent test range for receivers and other hardware and a large anechoic chamber outfitted for testing antenna beam patterns and radio emissions from all types of equipment. The primary function of the Green Bank site is for scientific research of all types. As a result the facility telescopes have been used in a wide variety of ways, including satellite tracking, spacecraft tracking, atmospheric studies, monitoring of astronomical and planetary phenomenon, and educational programs. A full description of the telescopes, and their uses, is below.
The 13.7m (45ft) diameter telescope was built in 1995 as a tracking station for NASA’s Very Long Baseline Interferometry (VLBI) satellites. With an aperture efficiency of 38% at 15 GHz the telescope is designed to work well at the common up and downlink frequencies for satellite systems. As a tracking station the 43m transmitted a maser referenced timing tone to the orbiting satellites and also received astronomical data sampled by the orbiting space crafts. Per the preference of the NASA mission, the tracking stations recorded the received data on wideband magnetic tape and ship it to correlators for further processing. Once the NASA VLBI mission was complete the telescope found subsequent use monitoring the sun for solar activity, offering publicly available research quality dynamic spectra of the sun during daylight hours.
Construction and original use of the 20m diameter telescope was funded by the United States Naval Observatory (USNO). The telescopes was part of the National Earth Orientation Service telescope network and the USNO Navy Network participating in a global program of Earth Orientation very long baseline interferometry measurements in cooperation with the International Earth Rotation Service and with the NASA Space Geodesy program. The USNO program was shut down in June, 2000, due to budget cutbacks at USNO. It has since been used as an educational telescope (part of the University of North Carolina’s SkyNet project) and as a test telescope for new technology to build cameras on radio telescopes using the “phased array feed” concept. As with the 13.7m telescopes, this instrument is optimized for use through 18GHz.
Three 26m diameter (85-ft) antennae also reside at the Green Bank site. The first Antenna, known as the 85-1, was built in 1958 for research into Radio Astronomy. Soon thereafter the remaining two 26m telescopes, 85-2 and 85-3 were built. While able to be run independently, the three telescopes can also be used together, as a three element interferometer. Use of the last of these three telescopes ended in 2000. As a result all three telescopes are in need of some level of refurbishment before they can become fully operational.
Built for Radio Astronomy research, the 43m (140ft) diameter telescope is an equatorial mount telescope, which allows it to avoid having any tracking, or “zone of avoidance” issues when tracking objects at or near the zenith. The 43m worked as an astronomical research instrument from 1965 through 1999 when it was retired as a general user facility. Six years later, in 2005, the 43m telescope was put back into use, this time as part of a satellite tracking program to study the ionosphere instituted by the Massachusetts Institute of Technology’s Lincoln Laboratory. The Lincoln Laboratory work continued until 2011, and the telescope has since been refurbished to act as a satellite data downlink station for a new space-based astronomy satellite (Spektr-R).
The by far most sensitive of the telescopes in Green Bank, the 100m Robert C. Byrd Green Bank Telescope is the largest fully steerable telescope in the world. The telescope’s unblocked aperture and excellent surface result in an extremely sensitive telescope from 0.1 through 100 GHz. While its primary purpose is radio astronomy research, the GBT is designed to enhance many types of scientific pursuits. The telescope’s high sensitivity allows it to receive direct communications from small spacecraft exploring the solar system. Recent use of the telescope for this activity includes monitoring the direct signal from NASA’s Mars Phoenix lander as it entered descended through the Martian atmosphere to successfully land. The telescope is also often used as a receiving station for the planetary radar experiments performed with the Arecibo 305m telescope and Goldstone 70m antenna.
|Diameter||Performance (Efficiency)||Tracking Speed (°/min)||Pointing Accuracy (°)||Sky Coverage||Azimuth/Declination||Status|
|13.7m||38% at 15 GHz||35-40||0.01-0.03||+3 to +112||-162 to +373||Operational|
|20m||60% at 10 GHz||120||0.01||+1 to +90||-270 to +270||Operational|
|26m (3)||TBD||201||TBD||+5 to +90||-270 to +270||Needs Refurbishment|
|43m*||50% at 7.2 GHz, 32% at 15 GHz||10-20||0.01-0.04||-40 to +88||-105 to +105||Operational|
|100m||70% at 7.2 GHz, 35% at 90 GHz||18-35||0.001||+5 to +90||-270 to +270||Operational|
|*43m is an equatorially mounted telescope, coverage is given in declination and hours angle (degrees).|