Watching the Action in Orbit

A new eagle-eyed satellite-tracking network takes shape

Ever since Sputnik was rocketed into space nearly 23 years ago, the heavens have become increasingly crowded.

At last count, the U.S. Air Force's North American Air Defense Command, the watchdog of all objects in orbit, listed 4,552 pieces of hardware--ranging in size from a Soviet space station to such bits of space junk as an astronaut's glove, stray cameras, and even nuts and bolts. In the coming years NORAD's job will become still harder. By the mid-1980s, the number of orbital objects may double, making it more difficult to tell what is up, and whether it belongs to friend or foe.

Now M.I.T.'s Lincoln Laboratory, to gether with researchers elsewhere, has come to the rescue of the overtaxed satellite watchers. Using the latest in silicon-chip wizardry, it is setting up a worldwide network of monitoring stations that should vastly expand NORAD's ability to keep tabs on orbiting objects.

The first station is being built at the White Sands Missile Range in New Mexico. Others will be located near Taegu, South Korea, on the Hawaiian island of Maui, and at sites in the Indian Ocean and the Eastern Atlantic regions. Known as GEODSS (for ground-based electro-optical deep space surveillance), the system will provide almost live-action portraits of distant satellites and permit virtually instantaneous identification of any mysterious intruders in the night sky.

Such near "real time" observations are a giant step forward in satellite tracking. Until now, the U.S. has been relying on standard telescopic techniques using Baker-Nunn cameras, which provide fast, short-exposure pictures of wide swatches of the sky. The optics and the film have been vastly improved over the years, but each film strip must still be chemically processed and tediously analyzed, which can take an hour or more.

GEODSS takes some remarkable short cuts. The installations, which resemble small, domed astronomical observatories, will be equipped with two powerful 101-cm (40-in.) telescopes and a smaller 38-cm (15-in.) auxiliary telescope. As the instruments scan the skies, the images they capture will be focused onto sensitive photo-imaging tubes rather than film. An outgrowth of the military's night-vision devices, these tubes convert even the faintest flickers of light into electronic impulses, which are then fed into computers. There GEODSS performs its real prestidigitation. It separates from the myriad stars in the background any tiny man-made objects passing into the telescope's field of view.

How? GEODSS takes in rapid succession several separate electronic snapshots of each sector of the sky. Because the telescopes are geared to sweep the heavens at a rate that will exactly counter the rotation of the earth, the distant stars appear as sharp pinpoints of light in precisely the same positions in each of the images; if the telescope were fixed, the earth's rotation would cause apparent movement of these stars. But satellites, even those placed in so-called geosynchronous orbits over a fixed point on earth, move against the background stars, however slightly. Thus they change position in successive pictures.

Everything that the computer finds in the same position in each picture is wiped out of the final image, while objects that have moved between exposures are allowed to remain. Thus the stars vanish and only the tiny blurs created by any satellites are left for display on GEODSS's video screens. All this is accomplished in a flash, and the information is relayed by microwaves and satellites to NORAD'S master computers at its headquarters deep within Cheyenne Mountain at Colorado Springs, Colo., where the location, size and other characteristics of the object are quickly determined.

The network, scheduled to be completed in 1982, will cost $62 million. But the Air Force, already hard pressed in its role as orbital traffic cop, figures the price is something of a bargain. Training its eagle eyes on the heavens, GEODSS should be able to spot--and identify--an object as small as a soccer ball 40,000 km (25,000 miles) away.

This file is automatically generated by a robot program, so viewer discretion is required.