NATIONAL RADIO ASTRONOMY OBSERVATORY
RADIO TELESCOPES IN GREEN BANK,WV
With over fifty years of experience in radio astronomy and uniquely located within the National and WestVirginia
Radio Quiet Zones, the National Radio Astronomy Observatory's Green Bank 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.
13.7mTelescope: The 13.7m 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.
20mTelescope: 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.
26mTelescopes: Three 26m diameter 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.
43mTelescope: Built for Radio Astronomy research, the 43m 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).
100mTelescope: The by far most sensitive of the telescopes in Green Bank, the 100m
Robert C. Byrd Green BankTelescope 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.
Site Facilities: The NRAO Green Bank,WestVirginia site lies within both the National and WestVirginia Radio
Quiet zones, providing a unique level of protection against radio interference for all projects which occur on site.
Facilities on the site also include an indoor and outdoor antenna test range and a large anechoic chamber which can
be used for the determination of radio emissions from many types of equipment.
With 100s of acres of managed land, good network connectivity, and reliable power, numerous groups have also
taken advantage of the infrastructure and radio quiet to deploy their own instruments on site. Currently these
instruments include two small telescope arrays operating from 20-100 and 100-200 MHz,one station from a nationwide magnetometer array,and a GPS sensor deployed as part ofWestVirginia's geo-spatial array.
Diameter
Performance
(Efficiency)
13.7m
20m
26m
(3 telescopes)
43m**
38% at 15 GHz
60% at 10 GHz
TBD
100m
50% at 7.2 GHz
32% at 15 GHz
70% at 7.2 GHz
35% at 90 GHz
NRAO Telescopes in Green Bank, WV*
Tracking
Pointing
Sky Coverage
Status
Speed
Accuracy
Elevation
Azimuth
(°/min)
(°)
(°)
(°)
35‐40
0.01‐0.03 +3 to +112 ‐ 162 to +373
Operational
120
0.01
+1 to +90 ‐
270 to +270
Operational
20*
TBD
+5 to +90 ‐
270 to +270
Needs
Refurbishment
10‐20
0.01‐0.04 ‐ 40 to 88* ‐ 105 to +105* Operational
18‐35
0.001
+5 to +90 ‐
270 to +270
Operational
* Original specifications
**43m is an equatorially mounted telescope; coverage is given in declination and hours angle (degrees).
www.nrao.edu