Tracking Space Debris Requires Special Computational Methods

Robert Plemmons, Wake Forest University professor of computer science and mathematics, has developed computational methods scientists are using to identify and track objects in space. (WFU/Ken Bennett)

The challenge of getting a clear image of objects in space in order to identify them and understand what they are there for has been a lifelong interest for Robert Plemmons, Z. Smith Reynolds Professor of Computer Science and Mathematics at Wake Forest University. Plemmons has been working on the challenge of identifying objects in space since 1983 with funding from the Air Force Office of Scientific Research. One big challenge, he says, is getting a clear image of the space object through the turbulence of the Earth’s atmosphere.

Two large satellites collided in Earth’s orbit on Feb. 10, leaving trails of debris in space that may threaten other satellites and the Hubble Space Telescope. Specialists at the Maui Air Force Space Surveillance Center are monitoring the clouds of debris in order to identify the pieces and project their path.

Using a variety of imaging systems and computer algorithms, Plemmons is able to identify the composition of a tiny piece of debris in space and what it came from using information as small as a single pixel of information. His ongoing work is also funded by U.S. intelligence agencies, and is being used by Air Force and NASA specialists following the debris clouds from the satellites.

“Atmospheric effects are continuously changing so when you deblur an image, you have to do billions and billions of computations fast,” said Plemmons, Z. Smith Reynolds Professor of Mathematics and Computer Science at Wake Forest. “When we look at a distant galaxy, [for example], the light from it travels, say, several million years to reach Earth but only gets blurred in the last few microseconds. That’s the basic problem of atmospheric imaging.”

Plemmons algorithms, developed in more than 30 years of research for the Defense Department, are also being used to overcome wind, hot air and other atmospheric turbulence that could affect the aim of the Air Force¹s $1.1-billion Airborne Laser Weapons System (ABL), designed to fire a laser through the nose of an aircraft to zap enemy missiles.

Astronomer Horace Babcock first proposed the idea of adaptive optics in 1953, but the first experiments did not begin until the 1970s. Only in the 1980s, with the Strategic Defense Initiative (SDI), or “Star Wars,” did Plemmons and other adaptive optics researchers gain substantial funding. Ironically, the declassification of SDI work in 1991 has revolutionized ground-based astronomy.

“Whether you are trying to shine a laser on a target or get a sharp image of something in orbit, you have the same problems,” said Maj. Scott Shreck, manager of the AFOSR’s computational mathematics program.

Better eyes for the heavens also help the Air Force keep better tabs on spy satellites or protect space shuttle crews and satellites from orbiting space junk. “Some of this space junk will cause trouble when it comes down,” Plemmons said. “Some U.S. and old Soviet satellites have nuclear power systems, so we want to know where they are.”

Author of more than 150 papers and five books on computational mathematics, Plemmons envisions the day when the math of adaptive optics will allow ground-based telescopes to possess the same imaging accuracy as the Hubble.