28-05-2025
EXCLUSIVE: An up close look at the Green Bank Telescope
GREEN BANK, (WBOY) — In May, 12 News took a special tour of the National Science Foundation (NSF) Green Bank Telescope (GBT), the largest fully-steerable radio telescope in the world.
At 485 feet tall with a 2.3-acre dish, the NSF Green Bank Telescope weighs 17 million pounds, or about 8,500 tons. But why does the GBT need to be so big in the first place and why is the fact that it's 'fully steerable' such a big deal?
Green Bank Observatory software engineer Nathaniel Sizemore explained the dish on the telescope is like 'a giant bucket.'
'The bigger the dish, the more signal we can collect and the better chances we have of finding the signal we're looking for,' Sizemore said.
But size isn't GBT's only advantage. The fact that it's fully steerable means that it can point to just about any target in the night sky, and can even track objects for multiple hours during extended observations. This is especially useful for observations on things like pulsars, where scientists are trying to make multiple precise time measurements during a single observation.
GBT's large size, paired with its ability to track objects, is what makes the telescope so valuable to scientists. In some cases, it's the only telescope capable of making certain observations, like when the telescope was used to look for liquid oceans in Jupiter's orbit.
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'Between the size of the antenna and the fact that we can track that source for hours at a time, theoretically horizon to horizon if we wanted to, we can give [scientists] that data and let them get enough signal to then process that and do the science that they want to do,' Sizemore said.
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Moving such a massive telescope requires equally massive machinery. The telescope rests on 16 wheels on a circular track, giving it 360 degrees of rotation. Further up is a large arc-like structure that acts as a hinge and counterweight, letting the telescope tilt back and forth.
Although the telescope is movable, there are several safety measures to make sure no one is on top of the telescope while it is in motion. Radios are used to notify the control room when people move onto and off the telescope, and each person attaches a safety key near the entrance to the telescope to physically stop it from moving while anyone is aboard.
The telescope also has a second manual lock along the arc, which has gaps scientists can use to keep the telescope in a specific orientation.
Although you could take the stairs if you wanted, a pair of elevators on the telescope are used to carry people and scientific instruments up and down the GBT. The first one starts at the ground level and goes halfway up, close to the main dish of the telescope. A second elevator begins at the bottom of the telescope's arm and at the top of the GBT.
The second-highest level of the telescope is the main reflector dish level. There, maintenance workers can access the underside of the dish using narrow catwalks below the reflective panels that make up the telescope. Using multiple smaller panels instead of a single reflective dish makes maintenance on the telescope cheaper and easier. For example, if a panel at the center of the dish is damaged and a spare isn't on hand, a panel from the edge of the dish can be used to replace it.
Using lots of smaller panels has another benefit as well; hundreds of actuators underneath the dish can be used to make small adjustments to individual panels. This means that instead of moving the entire telescope, the panels themselves can be moved to fine-tune the telescope's orientation.
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At the very top, just below the telescope's sub-reflector, is where the telescope's instruments are kept. At the time of our visit, all the observation equipment had been removed from the telescope in preparation for an upcoming repainting project in June. Normally, the telescope can freely switch between different measuring tools, like a microscope switching between different magnifying lenses.
Unsurprisingly, the top of the telescope also has some of the best views of any level on the GBT.
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