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Asteroid hunting using heliostats?

BY KENNY VIGIL

THURSDAY, JULY 24, 2025

Sandia scientist says heliostats can be valuable at night

NIGHTTIME EXPERIMENT — Scientist John Sandusky stands in the field of heliostats at the National Solar Thermal Test Facility. John conducted research at night showing that heliostats might be able to detect asteroids. (Photo by Craig Fritz)
NIGHTTIME EXPERIMENT — Scientist John Sandusky stands in the field of heliostats at the National Solar Thermal Test Facility. John conducted research at night showing that heliostats might be able to detect asteroids. (Photo by Craig Fritz)

Sandia scientist John Sandusky believes he has found a way to put heliostats, which typically turn solar energy into electricity, to work in the dark.

He proposes that these large mirrors could help find asteroids at night.

“The heliostat fields don’t have a night job. They just sit there unused. The nation has an opportunity to give them a night job at a relatively low cost for finding near-Earth objects,” John said. “If we knew ahead of time that an asteroid was coming and where it might hit, we’d have a better chance to prepare and reduce the potential damage.”

Most planetary defense efforts use observatory-grade telescopes to produce images of the stars. Within those images, computational methods identify streaks, which are asteroids. This process is precise but time-consuming, and building new observatories is expensive.

The nighttime experiment

As part of a Laboratory Directed Research and Development project, John spent summer nights working at the National Solar Thermal Test Facility. He used one of the 212 heliostats in the field for his experiment.

NIGHT WORK — While heliostats can collect energy from the sun, Sandia scientist John Sandusky put the heliostats to work at night. His findings could help detect near-Earth objects, such as asteroids. (Photo by Craig Fritz)
NIGHT WORK — While heliostats can collect energy from the sun, Sandia scientist John Sandusky put the heliostats to work at night. His findings could help detect near-Earth objects, such as asteroids. (Photo by Craig Fritz)

“Solar towers collect a million watts of sunlight,” John said. “At night, we want to collect a femtowatt, which is a millionth of a billionth of a watt of power of sunlight that’s scattered off of asteroids.”

In simpler terms, he believes the heliostats can measure the speed at which asteroids pass by the stars, rather than using conventional imaging methods.

“I’m trying to detect the asteroid by its speed relative to the stars,” John said.

The heliostat he used was not retrofitted with any new equipment for the experiment. John used existing software to oscillate the heliostat’s direction relative to the stars.

“We changed the direction the heliostat was pointing gradually so it would sweep back and forth about once per minute,” John said.

As dusk turned to night, John sat up on the solar tower, 200 feet above the ground, and used standard optical instruments to detect the light the heliostat was concentrating on the solar tower.

“You spend a lot of time waiting. There was about 20 minutes between the collection of data points. I would collect data until dawn,” John said. “We did not set out to find asteroids. We demonstrated the heliostat can be swept back and forth and that it can see stars.”

More advantages

John said this is early-stage technology. In addition to being more cost-effective than building new observatories, this method may offer other advantages.

“It may help the U.S. Space Force with its job of trying to find spacecraft, especially in the cislunar area. Orbits near the moon can be difficult to track from the ground,” he said.

John presented his findings at a conference for the International Society for Optics and Photonics, and a paper was published. At this stage, he said, feedback is important.

“We want to hear from our peers in optics and the asteroid hunting community,” John said. “Getting peer feedback provides an opportunity to understand what the concerns are about how this technology will work.”

He said the next step might involve using the heliostat to find a known planet, which would help understand the technology’s limitations.

“We’re looking for opportunities to scale up from one heliostat to many and try to demonstrate that we can help find near-Earth objects,” John said. “We also want to demonstrate we can scale up the technology to detect even smaller asteroids.”

Lingering question helps Sandia scientist discover how heliostats can be used in the dark

A question posed nearly 20 years ago — early in his Sandia career — had been stuck in the back of John Sandusky’s mind. At the time, John was asked if the heliostats at the National Solar Thermal Test Facility could be used to do imaging.

The answer was simple.

“No. They’re not high enough optical quality to form an image,” John said.

But the heliostats do collect a lot of light.

“Isn’t there a way to use that?” was the lingering question in the back of John’s mind.

John worked at NASA’s Jet Propulsion Laboratory after graduate school in laser communication.

“Communication theory is heavily into looking for repetitive events that we call frequencies. Those frequency domain techniques have been a mainstay of communication since radio first came to town,” he said.

He explained that the current method of finding asteroids by looking at streaks in imagery is related to a frequency shift problem. The asteroids move at a slightly different rate than the stars.

“We have very precise methods for measuring frequency,” John said. “Even frequency changes as small as one-one-millionth of one cycle per second are measurable thanks to frequency standards that can be commercially procured and locked to references like GPS signaling. I knew it was possible to measure the very small rate differences of an asteroid passing relative to the stars.”

This insight led John to consider how heliostats could do that job.

“All I needed to do was sweep the heliostat pointing relative to the stars at a fixed rate,” he said. “If I can map all of the stars to one frequency, anything moving relative to the stars will appear at a neighboring frequency but still be separable.”

Nearly 20 years after that lingering question about how the heliostats could be used, John received Laboratory Directed Research and Development funding and began his nighttime experiments at the solar tower.

“What I did for the experimental phase was demonstrate that the heliostats can be swept back and forth and respond to the stars,” John said. “No surprise. They can see stars.”

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