North Liberty telescope peers into deep space

Few know of its existence or role in giant array

Gregg Hennigan
Published: October 8 2013 | 5:30 am - Updated: 28 March 2014 | 9:31 pm in

It’s part of a system that collectively forms the most powerful telescope in the world, but it’s virtually invisible in its own backyard.

This despite being 10 stories high, 25 meters in diameter and looking like the largest satellite dish you’ll ever see.

It’s a radio telescope, and it’s found in a small open field in a wooded area between North Liberty and Coralville Lake. It’s only slightly visible from a few spots on the water, and the only indication on land is an easily missed sign at the entrance to the hole-ridden drive that leads to it off Mehaffey Bridge Road.

“I have very little knowledge of it myself, so I don’t know if the community knows much about it,” said North Liberty City Administrator Ryan Heiar.

In astronomy, though, it is huge — figuratively and literally.

The North Liberty telescope is one of 10 radio telescopes in the Very Long Baseline Array, or VLBA, spread across 5,351 miles from Hawaii to the Virgin Islands and overseen by the National Radio Astronomy Observatory from a control center in New Mexico.

When used together, they provide the same angular resolution as a telescope 5,351 miles big. Angular resolution is the ability to see fine detail.

By that measure, it is 100 times more powerful than any other dedicated instrument, said Robert Mutel, a University of Iowa astrophysicist and an expert in radio telescopes.

Say an astronaut was on the moon, waving a cell phone. He would have to walk 100 meters for the best optical telescope to determine he moved, Mutel said. With the VLBA, the astronaut would just need to take one big step.

“There’s no other instrument that has anywhere near as much angular resolution,” Mutel said.

The VLBA is used to explore galaxies, black holes, pulsars and much more. It’s helped provide the most accurate measurements ever to distant objects, including galaxies. It’s been used to map our own galaxy, the Milky Way. It also helps make global positioning systems more accurate.

The VLBA is offline indefinitely following the closure of the National Radio Astronomy Observatory Friday night because of the federal government shutdown. The NRAO is operated by a nonprofit organization but is a facility of and is funded by the National Science Foundation, which is a federal agency.

The VLBA cost $85 million and became operational in 1993. The telescope in North Liberty is the only one in the array in the Midwest.

That’s thanks in part to the University of Iowa’s history with radio telescopes, including partnering in an earlier network using technology similar to the VLBA.

“We were one of the groundbreakers, I would say, of the VLBA,” Mutel said.

The UI gets no special access to the array, however. Research proposals are submitted from scientists worldwide, with between one-third and one-half getting time on the VLBA, Mutel said.

Two technicians, Mike Burgert and Dave Alderman, work at the North Liberty site and maintain sophisticated electrical, refrigeration and heating, ventilation and air-conditioning systems, among other duties.

“A little bit of everything,” said Burgert, who has worked there since 1999. “We mow the grass.”

The telescope is controlled remotely from New Mexico. On a Wednesday in September, it was facing south and pointed at an angle toward the sky, occasionally making small movements.

It works by collecting radio waves that hit the surface of the dish, bounce up 30 feet to a subreflector and then are directed to feed cones in the center of the dish that each capture a different wavelength.

Radio receivers in a room just below the dish are chilled to nearly 433 degrees Fahrenheit below zero — the idea being to quiet the electrons in the receiver so only those from the signal are moved through an amplifier.

The radio waves then go to equipment in a control building next to the telescope and are recorded on hard drives, which are shipped to New Mexico.

In astronomy there are many types of telescopes, each observing different wavelengths of light. What is used depends on the science.

One advantage of radio, said Walter Brisken, a scientist at the National Radio Astronomy Observatory, is with an optical telescope you cannot see through stuff that absorbs light. For example, there is something called a dark cloud, he said, where stars likely form. That phenomenon could not be seen by the Hubble Space Telescope, he said.

“So the optical kind of tells us where to look in that case and then gives us a scale of how much material there is and how big it is,” he said, “and the radio is actually pointing at the gasses that are actually doing the work inside the cloud.”

This type of science requires precision in its instruments.

Personnel know the exact height of every point of the rail upon which a VLBA telescope rotates. If even one bolt is tightened, the dozens of others are surveyed.

Each of the 10 telescope stations stays in sync with an atomic clock, which maintains accuracy within one second in a million years. The air around the clock, which looks like a black case a few feet high with several switches and knobs but no time display, is regulated to within two-tenths of a degree to keep it stable.

The control building is shielded to keep unwanted radio signals from disturbing the telescope. Some of the equipment is further encased to prevent radio frequency interference.

There is a mixture of old and new equipment used in this process. For example, an older data collection system with eight 2-terabyte disk modules is still used, along with a new version that has 16-terabyte modules.

“It’s like the difference between black-and-white television and high definition,” said Alderman.

The VLBA just underwent a major upgrade, and scientists are constantly testing new ways of using it. Brisken was doing just that when the telescope was moving at the start of The Gazette’s tour.

There’s an “endless appetite for bigger and better” with radio astronomy, he said, and a long-term goal that as yet is unfunded is to combine the VLBA with another array and add 10 more antennas to increase the resolution and tuning capabilities.

They also want to connect all 10 of the telescopes to the New Mexico facility with fiber optic to eliminate the need to ship the hard drives.

The recent upgrade and renewed interest in the VLBA from other fields means the array will stay relevant for years to come, Brisken said.

“The VLBA’s best science is actually just getting started, in my opinion,” he said.

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