Professor’s Math Clears View of Telescopes, Lasers
The Hubble Space Telescope isn’t the only stargazer getting better eyes to view the universe.
A Wake Forest University professor’s applied mathematics are part of new adaptive optics technology producing “Hubble-like” improvements in the sight of ground-based telescopes and new laser weapons.
Adaptive optics combines powerful lasers, high-speed computers, active mirrors that can rapidly alter their shape, and Robert J. Plemmons problem-solving mathematical algorithms to reconstruct images distorted by Earth’s atmosphere. By analyzing light returning from bright stars such as Vega or artificial stars created by shining a laser into the night sky, scientists can diminish the distorting effects of Earth’s atmosphere.
The result: telescopes able to see 50 to 100 times more detail and laser-guided weapons better able to zap enemy missiles.
“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, 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.”
No fewer than 10 telescopes are adding adaptive optics systems to improve their view, including what is now the highest-resolution telescope on Earth: the Air Force Phillips Laboratory’s 3.5-meter, $27 million instrument at the Starfire Optical Range in New Mexico. Equipped with adaptive optics in January under a project supported by the Air Force Office of Scientific Research (AFOSR) and the National Science Foundation, the telescope can track softball-sized objects traveling 1,000 miles above the surface.
Plemmons’ algorithms, developed in more than 25 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 Force’s $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.”
Twinkling stars and other annoying effects of the Earth’s atmosphere on light has confounded stargazers since the invention of the telescope. It was Christian Huygens, the inventor of the pendulum clock, who first noticed in the 17th century that heavenly bodies quivered in telescopic view through no fault of the telescope. Sir Isaac Newton observed in 1704: “The only remedy is a most serene and quiet air.”
Iraqi Scuds and other missile threats have now made Newton’s “remedy” a national defense priority. “We don’t yet have a good ballistic missile defense system against Scud-type threats,” said Plemmons, who testified before Congress last spring on the need for more basic science research to avoid the kind of mathematical errors that sent an Iraqi Scud into a U.S. Army barracks in Dhahran, Saudi Arabia , on Feb. 25, 1991, killing 28 Americans.
“It’s not enough to just hit a target,” Plemmons said. “The idea behind the ABL program is to image the nose cone of an incoming missile and fire the laser from the aircraft at the fuel supply behind the nose cone — where it’s most vulnerable — and before the missile reaches its zenith, when it’s still over enemy territory.”
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.
For now, he said both the Hubble and ground-based telescopes have roles in the exploration of the universe’s mysteries. The larger mirrors of ground-based telescopes allow them to see the bigger picture of celestial bodies, whole planets and stars. The pristine vacuum of space allows the Hubble to better inspect individual areas and gather ultraviolet, X-ray and other light Earth’s atmosphere blocks out.
“One doesn’t exclude the other,” Plemmons said. “We need both.”
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