140 Foot (43m) Telescope

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.

Ionospheric Studies

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.

RadioAstron

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.