An enormous radio telescope may soon be a powerful tool for planetary defense

In Overmatched, we take a close look at the science and technology at the heart of the defense industry—the world of soldiers and spies.

A HIGH VALLEY in the mountains of West Virginia is home to one of the world’s largest radio telescopes: a white-paneled behemoth called the Green Bank Telescope whose dish is bigger than a football field and whose topmost point is almost as high as the Washington Monument’s. That telescope typically collects radio-wave emissions from cosmic phenomena such as black holes, pulsars, supernova remnants, and cosmic gases. When doing that work, it receives those emissions passively. But now it has had experience with a new, more active tool: a radar transmitter.

Thanks to defense contractor Raytheon, the telescope has gotten practice emitting its own radio waves, using the big dish to direct them, and bouncing them off objects in space. The reflected signals were then collected by more radio telescopes—antennas spread across the planet that are part of a collection of instruments called the Very Long Baseline Array. Data from those radar signals can be used to produce detailed pictures of, and to learn more details about, the moon, the planets, asteroids, and space debris—a set of targets of interest to both science and the defense community.

Radar genesis

The collaboration is Steven Wilkinson’s fault. “I’m the instigator,” Wilkinson, principal technical fellow at Raytheon, confesses jokingly. Back in 2019, Wilkinson was working on ultraprecise clocks but needed to find a new funding stream. So he went to the American Astronomical Society meeting, hoping to talk to someone from the National Radio Astronomy Observatory (NRAO) about those clocks—a technology integral to the instrumentation of radio telescopes. The NRAO is a set of federally funded telescopes that astronomers from all over the world can use.

At the meeting, Wilkinson met the director of NRAO, Tony Beasley, and Beasley did indeed want a partner—but not in timekeeping. He wanted a radar collaborator. “That is our core competency as a company,” says Wilkinson. “I just could not believe my ears.”

Always game for a new experiment, Wilkinson went back to Raytheon and attempted to convince the bosses to put a radar transmitter on the giant Green Bank Telescope—formerly part of the NRAO, now its own separate facility but often a partner in NRAO projects. (Disclosure: I worked at the Green Bank Observatory, which is where the Green Bank Telescope is located, as an educator from 2010 to 2012.)

“For radar, you’re worried about sending a signal and then receiving it,” says Patrick Taylor, head of NRAO’s and Green Bank Observatory’s joint radar division. “So you lose a lot of your power going out and then coming back again. … In that sense, you need really large telescopes. And the largest telescopes in the world are radio telescopes.” The array of telescopes that would catch the returning signal, conveniently, belongs to NRAO.

By October of 2020, the joint Raytheon radio observatory team had built a 700-watt prototype transmitter—about as powerful as a household microwave oven—and placed it at the prime focus of the telescope.

With the system in place, the joint team has since performed three kinds of tests: experiments involving the moon, an asteroid, and space debris. “Those are the three main fields that we want to look at,” says Taylor. “Planetary-scale bodies, like the moon; small bodies, like asteroids and comets, for planetary science and planetary defense; and space debris, for, essentially, safety, security, and awareness of what’s out there around the Earth.”

The system that illuminates all of these objects—natural and synthetic—is the same: Radar signals leave the telescope, bounce off the objects, and return to be collected by other telescopes.

Over the moon

The moon tests returned perhaps the most striking results, showing portraits of the Apollo 15 landing site and Tycho Crater in detail such as you might find on a United States Geological Survey quadrant map of Earth. The pictures, taken from hundreds of thousands of miles away, boast a similar level of detail to those shot with the high-tech camera aboard the Lunar Reconnaissance Orbiter, which, as its name suggests, is in orbit around the moon.

Later, the team shot radio waves at an asteroid 1.3 million miles from Earth. The rocky body was just about 0.6 miles wide—small enough to make for impressive pictures from afar, but too big for comfort if it were on a collision course with Earth. Finding such asteroids, keeping track of their orbits, and understanding their characteristics could help scientists both know if a global catastrophe is careening toward the planet and develop mitigation strategies if one is—a capability the Double Asteroid Redirection Test recently demonstrated. (That mission involved slamming a spacecraft into an asteroid in orbit with another asteroid, to see if the bump could change its trajectory. It was successful.)

“Radar is not great for finding asteroids in the sense of discovering them,” says Taylor, “but radar is great for tracking, monitoring, and characterizing them after they are discovered by optical or infrared observatories.”

Importantly, though, both sides of the team—those from Raytheon and those from Green Bank Observatory and the NRAO—are also interested in using the radar system to check out space debris. Those objects would be ones that are far out, between geostationary orbit (around 22,000 miles from Earth) and lunar orbit. “With so many more payloads going to the moon, there’s going to be more and more junk out there,” says Taylor. “Especially if we start sending human payloads, which we’re obviously planning to do, you’re gonna want to be able to track that debris.”

Wilkinson cites as an example the recent rocket booster from the Artemis I mission, a precursor to sending humans back to the moon. “That would be something that we would try to go and find and image and do some cool stuff,” he says.

Knowing the nature of debris is of interest to scientists and to civil projects that may venture far out, but it’s also relevant to defense: The Space Force, for instance, is keeping an eye on the problem, and the Air Force Research Lab (AFRL) is even working on a program called the Cislunar Highway Patrol System (CHPS), which according to an AFRL statement will “search for unknown objects like mission related debris, rocket bodies, and other previously untracked cislunar objects, as well as provide position updates on spacecraft currently operating near the moon or other cislunar regions that are challenging to observe from Earth.”

Sure, you don’t want pieces of space trash to hurt astronauts or damage or destroy spacecraft. But military and intelligence officials are also, in general and specifically through programs like CHPS, trying to find out more about everyone’s spacecraft out there and what they’re up to. Powerful Earth-based radar, if it’s capable of surveilling debris, would be technologically capable of doing the same to active satellites too.

Let’s dish

The team’s hope is that a higher-powered radar system would be a permanent fixture on the telescope now that the low-power prototype has done its demo job. The work can feed back into Raytheon’s other projects. “We could take a little bit more risk to develop technology and the things that we’re learning here and then fold that back into our other products,” says Wilkinson. This system could be a test bed, he says, for the company’s future tracking work in the space between geostationary orbit and the moon—a science experiment that could lead to the next generation of “space situational awareness” technology.

Both sides of the team are working on a conceptual design for the higher-power system with funding from the National Science Foundation. Flora Paganelli, a project scientist in NRAO’s radar division, says it’s the first time she’s been able to help craft a ground-based telescopic tool as it’s being built. Previously, she was a member of the Cassini Radar Science Team, and she also worked at the SETI Institute before joining NRAO.

Having such input on this instrument is very significant right now. For researchers like Paganelli, such an instrument would augment science in a more significant way than it would have even just a few years ago. That’s because a few years ago, the US had two “planetary radars,” or systems that did work like surveilling the moon, planets, and asteroids.

Today, there’s just one—Goldstone, in California—because the other, at the iconic Arecibo Observatory in Puerto Rico, is no longer usable. Sadly, the telescope collapsed in 2020: The platform that hung above the dish crashed into its panels. Taylor worked there for years, before he did a stint at the Lunar and Planetary Institute and then came to NRAO. “Having a radar on the Green Bank Telescope, it’s something we considered for many years, essentially as a way to complement the other existing systems,” he says.

Because there are no firm plans to rebuild Arecibo or something like it, Green Bank represents the best hope for a second such radar system in the United States. “It kind of went from something that could complement Arecibo to something that could step in and fill the void,” Taylor says of Green Bank’s system. Paganelli notes that the scientific community’s radar expertise could now coalesce there.

Wilkinson, though he comes from the corporate national security sphere, also has an inherent interest in astronomy, which makes this dual-use project exciting to him. Also exciting: astronomy’s openness. “A lot of the things we do here, typically, we can’t talk about,” says Wilkinson, of Raytheon. The universe’s secrets, on the other hand, are there to be discovered and shared, not kept.

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