Space-based sensor will help in detection of hypersonic missiles


A sensor that can help satellites detect hypersonic missiles is one of the experiments aboard an uncrewed spacecraft that recently docked at the International Space Station (ISS).

The payload aboard the Cygnus NG-16 supply vessel included the Prototype Infrared Payload (PIRPL), which was developed jointly by the U.S. Department of Defense’s Space Development Agency (SDA) and Missile Defense Agency in partnership with the Northrop Grumman Corp.

Cygnus, pictured, was captured by astronauts wielding the space station’s robotic arm on August 12, 2021.

PIRPL is designed to study the Earth’s infrared background. It would be used in the “tracking layer” of an envisioned “constellation made of hundreds of small satellites mostly operating in low-Earth orbit” less than 1,200 miles above the planet, according to an August 11 SDA news release. The SDA said it plans to construct the warning system in “two-year tranches,” beginning with an initial constellation of about 30 satellites to start launching in 2022.

PIRPL, which is a multispectral infrared camera, is the first experiment in that capability, the SDA said.

“The satellites will be able to provide missile-tracking data for hypersonic glide vehicles and the next generation of advanced missile threats,” Derek Tournear, the SDA director, said in a 2020 release from Department of Defense News.

But PIRPL is designed to help detect, rather than to track, incoming threats. It provides a first look at the infrared background noise of the Earth’s surface, oceans and atmosphere. The ability to characterize that “bright” infrared background is the first step needed to “pull out the dim signal” of a hypersonic missile and feed it to detection and tracking sensors, said an SDA official cited by the online magazine Breaking Defense on August 10, 2021.

“It’s imperative we have the capability to look down on the warm Earth and pick targets out of that scene,” the SDA said in a statement to Defense One published August 9.

Such targeting can be done through a technique known as “clutter suppression.”

“So, that means I’m trying to subtract the unwanted background from the picture that I took and see what’s left,” the SDA official said, according to Breaking Defense. “And what’s left is going to show … was there a bright infrared source that might be a missile or it might be a forest fire or might be a meteor?”

Now that PIRPL has arrived at the space station, it is “collecting infrared data and expanding detection capabilities that will aid in the development of algorithms for the next generation of tracking satellites,” according to a Northrop Grumman news release.

The Northrop Grumman-built Cygnus cargo vessel was christened the S.S. Ellison Onizuka in honor of the first Asian American astronaut, Air Force Lt. Col. Ellison Onizuka, who died in the Challenger shuttle disaster in 1986.

PIRPL will operate primarily from within Cygnus while docked to the ISS for about three months, according to Breaking Defense. But when the spacecraft leaves the space station, PIRPL will be ejected into space to take more pictures until it reenters the atmosphere and burns up, according to the SDA.