When the NRAO was first founded, and the Green Bank site was chosen, the United States’ new national radio observatory had no radio telescopes. Plans for a giant telescope were underway, but no working telescope was on site. An order was placed with the Blaw-Knox Corporation in Pittsburgh, Pennsylvania for the purchase of one of their new 85-foot dish telescope kits. In the meantime, a 12-foot replica was used to test receivers and feeds for the 85-foot’s imminent arrival.
The kit arrived in summer of 1958, and the telescope was completed in early 1959. It was dedicated on October 16, 1958 and named in honor of Howard E. Tatel. Tatel designed the giant gearing of the telescope, presenting a scale model to Blaw-Knox that used his wife’s cereal bowl in place of the 85-foot dish. The new design increased the precision of the telescope’s movement and also made the kit much more affordable.
The Tatel Telescope began 24-hour a day observations on February 13, 1959, starting with the brightest radio objects known: Cygnus A, Cassiopeia A, and Taurus A. One of the first major observing projects performed was the first detailed mapping of the center of our Milky Way Galaxy by staff astronomer Frank Drake. He discovered that the heart of our Galaxy contains several sources of radio waves and is a lot more complex than ever seen before.
In 1960, Drake initiated a two-month observing program on the Tatel which he called Project Ozma, after the Queen of Oz, to aim the big telescope on two of the nearest, Sun-like stars in our galaxy to listen for possible signals from extraterrestrial civilizations. He and his team observed stars Tau Ceti and Epsilon Eridani with a receiver tuned to the 21-cm line of hydrogen, the most common radio signal in the Universe. Despite a brief excitement over what later turned out to be an airplane, the project did not pick up any signs of intelligent life around those stars.
The Tatel quickly gave astronomers more accurate positions and brightnesses for known radio objects. Astronomers also used the Tatel to measure surface temperatures for Venus and the Moon. Studies were done of Jupiter’s radiation belts, the envelope of charged particles that are trapped in the enormous magnetic field of our Solar System’s largest planet.
In the mid 1960s, two more 85-foot telescopes were built to the same design as the Tatel to become the three-element Green Bank Interferometer (GBI). A succession of smaller, portable telescopes was added to the interferometer to give it another axis and turn it into an array prototype for what would become the Karl G. Jansky Very Large Array.
Radio interferometers help astronomers study the fine structure and positions of radio objects, because the separation of the telescopes creates a powerful binocular vision.
The precision of the GBI allowed it to make the first radio measurement that confirmed, to high accuracy, the prediction by general relativity of the bending of light (i.e. any electromagnetic radiation) near a massive body.
From 1978 to 1996 the Tatel, as part of the GBI, was operated by the USNO for studies of Earth rotation and monitoring of variable radio sources. From 1996 until October 6, 2000, the Tatel Telescope was in continuous use as part of the GBI, funded partly by NASA, for radio studies of X-ray and Gamma-ray sources.
- Reflector: 85-foot diameter paraboloid; Surface is 0.125 inch thick aluminum panels; Surface area is 5700 square feet with better than 0.125 inch RMS tolerance.
- Focus: 36 feet above reflector surface and 115 feet above ground; Carries 600 pounds of receiving equipment; position relative to paraboloid stable to 0.25 inch.
- Mount: Equatorial (polar and declination axis, mutually perpendicular)
- Declination Axis: Shaft is 40 feet long, 16 inches diameter; gear is 40 feet diameter; Travel is 132 degrees total, 48 degrees north of stow and 84 degrees south of stow.
- Polar Axis: Shaft is 23 feet long, 28 inches diameter; Gear is 48 feet diameter; Travel is about 90 degrees either way from stow.
- Drive Rates, Both axes: Slew is 20 degrees per minute; Scan is up to 4 degrees per minute.
- Material: Painted steel superstructure.
- Brakes: Electrical set and spring set hydraulic release.
- Total Weight: 210 tons.
- Pointing Precision: About 30 arc seconds (about a quarter at 600 feet).
The 45-foot portable radio telescope at the NRAO in Green Bank was a 1973 replacement for the retired 42-foot radio telescope that had been hauled around Pocahontas County in West Virginia since 1967 as the outlying fourth member of the Green Bank Interferometer.
Over its 15-year tour of duty in the GBI, the 45-foot was disassembled, packed, hauled to and reassembled in a few nearby locations in the county, most notably in Huntersville. It was critical in helping to prove that the proposed Very Large Array project would be feasible and an extremely valuable tool for astronomy.
Antenna of All Trades
At the conclusion of its successful nomadic phase, the 45-foot settled on piers at Green Bank in 1988 where NASA converted it into a tracking station for orbiting satellites.
GEOTAIL, a joint NASA-Institute of Space and Astronautical Science (ISAS, in Japan) satellite sent up to study the magnetic stream off of the Earth, was the first orbiting craft to benefit from the 45-foot’s space communications. The second was a Very Long Baseline Interferometry (VLBI) test satellite called SURFSAT-1, built by undergraduates and NASA’s Jet Propulsion Laboratory in California.
In 1995 the 45-foot began to send NASA mission controllers the timing signals for orbital corrections, and also it received their scientific data.
In 1996, Comet Hyakutake C/1996 B2 raced across our skies, and the 45-foot was used to examine the molecular-rich ice ball for interesting chemistry.
In 1997, after the launch of Japan’s VLBI Space Observatory Program (VSOP, aka MUSES-B, aka HALCA) carrying an 8m radio telescope, space VLBI became a brief reality. The 45-foot and NRAO’s VLBA participated in creating the largest telescope ever used – over 60,000 miles across! Coordination with the VSOP mission ended in 2001.
In between its late 20th-century tracking duties, the 45-foot telescope conducted the Galactic Plane A survey, mapping the entire Milky Way galaxy in the microwave wavelengths of 8.35 GHz and 14.35 GHz frequencies.
The versatile 45-foot was once again adapted for a new purpose: solar observing. Retrofitted, the 45-foot began taking daily spectral observations of the Sun from decimeter to decameter wavelengths in 2004. As the Green Bank Solar Radio Burst Spectrometer, this little telescope functioned as a state-of-the-art instrument for discovering and monitoring solar radio bursts until 2012. It worked with a smaller partner antenna as the prototype for FASR, the Frequency Agile Solar Radiotelescope, a next-generation instrument for observing solar phenomenon.
The 20-meter telescope arrived as a guest at our site in Green Bank, West Virginia in 1994. The telescope was built by RSI, funded by the US Naval Observatory (USNO) as part of their Earth orientation observing programs.
Engineers in Green Bank built its receiver and installed it on January 11, 1995. The 20-meter observed with other telescopes to test its systems during the next few months, but had to give up some of its parts to help a twin 20-meter in Hawaii. By October 1995, the 20-meter was in regular operation by the USNO.
The USNO uses antennas around the world to measure small wobbling motions of the Earth’s polar axis and irregularities in the Earth’s rate of rotation with reference to positions of quasars (distant bright explosions in nuclei of galaxies). Quasars are the most distant point-like radio sources known, and therefore form a good set of stable reference points. This telescope network is part of the the International Earth Rotation Service (IERS) and supplies data needed for high accuracy world-wide navigation systems.
The data are also used for studies of continental drift and of atmospheric and oceanic currents, in collaboration with the NASA Geodetic VLBI program. Prior to the completion of the 20-meter, these geodetic VLBI experiments had been using telescope 85-3, part of the Green Bank Interferometer.
The USNO shut down their use of the 20-meter in June 2000 due to funding cutbacks. Although the Green Bank 20-meter is no longer used for the USNO project, USNO monitoring of Earth rotation and motions continues using the NRAO VLBA antenna array as well as telescopes in Hawaii and Germany.
In 2008, an L-band frequency array receiver feed, destined for use on the Robert C. Byrd Green Bank Telescope, was installed and tested on the 20-meter. It successfully observed the radio emissions around the famous Cygnus X-1 black hole complex.
The 20-meter was refurbished in 2012 as the first radio telescope in the Skynet Robotic Telescope Network project run out of the University of North Carolina, Chapel Hill.
Old receivers formerly used on the 140-foot telescope were revived and adapted for use on the 20-meter, providing receivers sensitive to 1.3-1.8 GHz, and 8-10 GHz.
The 20-meter telescope is used for a combination of educational and research projects. Anyone may apply to use it.
Automated through the University of North Carolina’s Skynet program, it is in regular use for educational activities around the U.S. and around the world. Via Internet remote control, students use the 20-meter to observe the invisible Universe from their classrooms and homes.
In addition, students and teachers participating in the Pulsar Search Collaboratory program use the 20-meter to conduct follow up research on candidate pulsars found in archived Green Bank Telescope (GBT) data. Students have discovered several new pulsars and become published authors before they leave high school!
After the onset of the COVID-19 pandemic, the Observatory’s Radio Astronomer for a Day program began using the 20-meter, instead of the 40-foot telescope, due to its remote operating capabilities. If you’re interested in scheduling this virtual opportunity for your student group, complete this form or contact us at gro.y1708601842rotav1708601842resbo1708601842bg@sn1708601842oitav1708601842reser1708601842.
A project with Virginia Tech and West Virginia University has used the 20-meter to search for the mysterious “fast radio bursts”, flashes of radio energy that happen seemingly at random spots in the sky at random times. Many observatories, including the one in Green Bank, are trying to gather more information to understand what is making these signals.
Height: 85 feet
Weight: 150 tons
Receivers: 1.3 to 1.8 GHz and 8 to 10 GHz at the prime focus
Slew Speed: 2 degrees per second, each axis.
Surface Accuracy: 0.8 mm rms.
Focal Ratio (F/D): 0.43
Geodetic Position: 38 26 12.661 N.Lat, 79 49 31.865 W.Long.
In 1961, a 40-foot telescope was ordered from Antenna Systems, Incorporated and delivered to our growing observatory in Green Bank, West Virginia. This inexpensive aluminum telescope took only two days to set up and began observations on December 14, 1961.
The 40-foot telescope can only move in one direction, up and down. It relies on the Earth’s rotation to swing it underneath the space objects it observes. With a control system designed and built by NRAO staff, on February 1, 1962 the 40-foot became the world’s first fully automated telescope.
The 40-foot provided us with an unmanned observing program focused solely on radio sources whose brightness changes over time. Its five-year mission observed eight radio sources every day: 3C 48, 3C 144 (Taurus A, aka Crab Nebula), 3C 218 (Hydra A), 3C 274 (Virgo A), 3C 295, 3C 358, 3C 405 (Cygnus A), and 3C 461 (Cas A). As far as we know, it was the first completely automated telescope. After sitting idle for nearly 2 decades, the 40′ was recommissioned in 1987 as an educational telescope.
Cool fact: We repurposed the Tatel Telescope’s 1960 feed, which was created by Frank Drake for Project Ozma, the world’s first scientific search for extraterrestrial intelligence.
More than 1,500 students ranging from 5th graders to graduate students use the telescope to investigate the radio universe every year.
Receiver bandpass: 1340 MHz to 1580 MHz
When the National Radio Astronomy Observatory was first founded, it was with the understanding that, fairly quickly, it should be able to offer the world a large, single dish radio telescope. The radio astronomy community was hoping for a massive moving telescope, perhaps 1000 feet in diameter! However, until engineers could deem such a monstrosity feasible, the National Science Foundation funded the design and installation of a 140 foot radio telescope on a polar-aligned mounting – a telescope that would be unique in its own right.
A polar-aligned telescope, also called an equatorial-mounted telescope, parallels the axis of the Earth for its spin axis. The spinning of the Earth causes the rising and setting of sky objects, and the imaginary northern axis of the Earth’s spin (its North Pole) is below the North Star, appropriately called Polaris.
The 140 Foot telescope rides on a giant gear whose axis is also aimed at Polaris. As the Earth spins toward the east, the 140-foot telescope spins to the west to follow the sky’s apparent movement. The 140 Foot easily tracks objects in space this way.
A robust design for the world’s largest polar-mounted telescope stymied engineers for years, and a few false starts delayed the progress of this telescope. The original polar mount used a welded steel shaft and a 22-foot diameter welded bearing on top that was assembled like segments of an orange.
However, inspectors found over 70 minute cracks in these critical pieces, a condition known as “brittle fracture.” The cold Green Bank winters would have spelled doom for this bearing, and resulted in the loss of the entire telescope. This design was abandoned in 1962 for a smaller cast bearing. The steel from the sphere was taken to Long Island to shield the particle accelerator at Brookhaven National Laboratory, and the original and ill-fitting polar mount is buried as a culvert under the road leading from the 140 Foot to the GBT.
From its earliest observations, this giant telescope proved to be worth the wait.
Tool of Astrochemistry
Chemistry is a scientific exploration of the assembly and reactions of the basic structures of everything we know. Chemists study atoms, molecules, and the energies that are required to break them and make them, in labs on Earth.
In space, however, the conditions for chemistry are cold, full of destructive radiation, and fairly empty. Few chemists even considered it a place where they could explore the same activities they watched in molecules on Earth.
However, astronomers without the burden of knowledge in chemistry wanted to try to hunt for molecules anyway. From a physics point of view, they felt that every time a space-based molecule spins around, its electrons should cough up weak radiation in a radio frequency.
In the mid-1960s, looking at the center of our Galaxy, astronomers in California found the signal of ammonia. Soon, the 140 Foot telescope, with its huge collecting dish and receivers that were tuned to many molecules’ predicted frequencies, was put into service to hunt for more species of molecules. In 1968, it found formaldehyde, the first complex molecule ever found in space.
Formaldehyde’s discovery overturned the long-held assumptions about the conditions required for chemistry. In good spirit, chemists joined astronomers to help target new and wonderful signals from space-based molecules. Thanks to this new interdisciplinary pursuit of astrochemistry, the 140 Foot went on to discover formic acid (you know it as insect venom), methanol, acetaldehyde (the chemical responsible for hangovers), and cyanoacetylene (a possible precursor to the DNA acid cytosine).
Tool of VLBI
Very Long Baseline Interferometry is a technique that combines the views of two separate telescopes, separated by large distances, to capture the finest details of an object in space. In radio astronomy, the two telescopes observe the same radio source for hours at a time, and their data is written to tape or hard drive. Those data must be stamped with a timecode to make them accurate to within 1/1000th of a second or better, or else they cannot be combined.
Technicians send the data to a central computing facility to be merged. The waves of data are added, and the interference pattern created by their overlap refines true peak signals into sharper points and flattens the random noise. The result is a highly-detailed picture of distant, compact sources such as quasars deep inside the hearts of galaxies and clouds of hyper-glowing gas, called masers.
VLBI experiments with the 140 Foot telescope and others around the United States commenced within a couple of years of this giant telescope coming online. In 1967, the 140 Foot and the 85-foot Maryland Point telescope, run by the Naval Research Laboratory on the shore of the Potomac River, worked together for the very first time. They formed a telescope 226 miles across!
Later that year, the 140 Foot and the 120-foot telescope in Westford, Massachusetts successfully worked together as a single unit, 845 miles long, to observe a quasar. Throughout 1967, the 140-foot paired with American telescopes farther and farther away, eventually succeeding in simulating a telescope the size of the United States when it paired with the 25-meter Mk2 telescope in Jodrell Bank, near Manchester in England.
The first US-USSR experiments, between the 140 Foot telescope and a 22-meter USSR telescope in Crimea were conducted in September and October 1969, with follow-up experiments in 1971.
In 1999, this giant telescope officially ceased observations as an open-access instrument and was mothballed to await a new benefactor. In 2004, it was retrofitted with a new receiver to become MIT’s Lincoln Laboratories receiver station for the study of the Earth’s ionosphere, a high layer of our atmosphere that acts like a mirror for bouncing radio broadcasts around the planet.
MIT’s Millstone Hill Observatory’s radar station in Westford, Massachusetts bounced radar signals off orbiting spacecraft for the 140 Foot to receive. Scientists using the data measured the density of the ionosphere from the change in the radar signal.
During breaks in its MIT schedule, the 140 Foot was also used for pulsar hunting and monitoring. In particular, it regularly checked on the Crab pulsar, searched for new changing sources, and mapped pulsars across the entire sky.
When MIT ended its contract with the NRAO for use of the 140 Foot in 2011, once again, the giant telescope lay waiting – but not for long. For years, scientists from NRAO had been consulting with Russian scientists about a space-based radio astronomy project called RadioAstron.
On July 18, 2011, the Russian Space Agency launched a satellite into orbit that unfolded into a 10-meter (33-foot) dish radio telescope called Spektr-R. This telescope observes as a space-based radio telescope, but also can be used with other radio telescopes on Earth for what is called Space Very Long Baseline Interferometry.
Our telescopes in Green Bank were the first to participate in Space VLBI decades ago, when we worked with the HALCA radio telescope launched and operated by Japan in the 1990s.
In 2012, telescope technicians adapted the 140 Foot to become an Earth station for tracking and downlinking data from Spektr-R, including a high-frequency receiver and a fiber optically-controlled secondary mirror system that could fine tune the focus of the telescope quickly and remotely.
Until Spring, 2019, the 140 Foot has served to help the RadioAstro team in Russia to keep track of the position, navigation, and health of their orbiting radio telescope. The GBT has joined Spektr-R in several observations of active galactic nuclei, the supermassive black holes lurking inside galaxies that are bright in radio waves.
On May 30, 2019, the Russian RadioAstron satellite — the farthest element of an Earth-to-space radio-telescope system — ended its service. During its mission, RadioAstron helped to capture some of astronomy’s highest-resolution images and studied previously the extreme physics of astronomical objects by working with telescopes around the world, including the Green Bank Telescope in Green Bank, W.Va.
Once again, the giant sleeps, awaiting the next mission to expand our knowledge of the Universe.
Height: 60 feet; 41 feet 6 inches to observation deck
Contains: 5700 tons of concrete and 140 tons of steel
Wall thickness: 3 feet. Houses control room, hydraulic and electric equipment, transformer vault, and electronic workshop
Total Moving Weight: About 2,500 tons
Mount: Equatorial – Two mutually perpendicular axes
Pointing Precision: 10 arc seconds – about the diameter of a dime at 400 yards
Receivers: Generally at wavelengths between 2cm and 40cm.
Paraboloid Diameter: 140 feet.
Surface: 1/8 inch aluminum plate.
Surface tolerance: 0.030 inches at zenith.
Contains: 350 tons of aluminum, 35tons of concrete ballast, 5 tons of balancing blocks.
Focus:60 feet above the surface. Carries 1/2 tons of receiving equipment
Stability: Position relative to paraboloid stable to 1/4 of an inch.
Shaft: Length: 67-1/2 feet overall; 57 feet between bearings.
Diameter: 2 feet.
Material: composite aluminum and steel shaft running in two spherical roller bearings.
Rotates 145 degrees to -53 degrees north of zenith and 92 degrees south.
Yoke: Serves to support the declination shaft and to rotate the antenna east and west about the polar axis by means of the polar gear.
Shaft Length: 67 feet
Diameter: 12 feet
Weight: 555 tons of steel; 170 tons of high density concrete ballast
Rotates 220 degrees (-110 degrees east of meridian and 110 degrees west)
Diameter of polar gear sector: 84 feet
Diameterof declination gear sector: 71 feet
Spherical Bearing Diameter: 17-1/2 feet
Surface tolerance: 0.003 inches
Floats on oil film 0.005 inches thick