John Sandusky, a scientist at Sandia National Laboratories, has proposed using heliostats—large mirrors usually dedicated to collecting solar energy—for detecting asteroids during nighttime hours. According to Sandusky, these heliostat fields are typically idle at night and could be repurposed at a relatively low cost for finding near-Earth objects.
“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,” Sandusky 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.”
Traditionally, planetary defense relies on observatory-grade telescopes that create images of the stars; computational methods then identify moving streaks in those images as asteroids. While this approach is accurate, it can be slow and building new observatories comes with significant costs.
As part of a Laboratory Directed Research and Development project, Sandusky spent several nights working at the National Solar Thermal Test Facility in Albuquerque. He conducted his experiment using one of the facility’s 212 heliostats without adding any new equipment, instead relying on existing software to oscillate the direction of the mirror relative to the stars.
“Solar towers collect a million watts of sunlight,” Sandusky 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.”
Sandusky’s method involves measuring how fast asteroids move compared to background stars rather than taking traditional images. “I’m trying to detect the asteroid by its speed relative to the stars,” he explained.
For his experiment, he gradually changed the direction in which the heliostat pointed so it would sweep back and forth about once per minute. From atop the 200-foot-high solar tower, he used standard optical instruments to observe concentrated light reflected by the heliostat onto the 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,” Sandusky 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.”
Sandusky described this research as early-stage technology but noted potential benefits beyond cost savings compared with building new observatories. He suggested it may also support U.S. Space Force efforts in tracking spacecraft near lunar orbits—an area challenging for ground-based observation.
“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.
He presented his findings at an International Society for Optics and Photonics conference and published them in an academic paper; peer feedback is now being sought.
“We want to hear from our peers in optics and the asteroid hunting community,” Sandusky said. “Getting peer feedback provides an opportunity to understand what the concerns are about how this technology will work.”
The next phase could involve using heliostats to locate known planets as another step toward evaluating technological limitations.
