Theproliferation of garbage in low Earth orbit has reached a point where it willincrease in the coming decades even if all rocket launches were canceledstarting now, according to research by NASA's Johnson Space Center.
Thesatellites and rocket stages designed and launched before the seriousness ofthe problem was recognized are like time bombs, waiting to break apart in thecoming years on combustion of their remaining fuel thereby multiplying thepieces of space garbage.
At somepoint, the growing population of orbiting debris increases the likelihood thatpieces will collide into each other, spawning still more space junk.
The problemis especially acute at altitudes of between 900 and 1,000 kilometers.
Research byNASA's Nicholas L. Johnson and J.C. Liou concludethat even if all launches were stopped immediately, the debris population wouldremain constant for about 50 years, then increasing noticeably after that as aresult of in-orbit collisions.
No less anexpert than Arthur C. Clarke, who first discovered the virtues of geostationaryorbit 36,000 kilometers above the equator for communications satellites, warnedthat space exploration is more likely to be shut down by low-orbit debris thanby anything else.
In responseto Space News inquiries, Johnson said July 26 that while removal of largepieces of debris might be the only answer to the problem, "no cost-effectivemeans to remove derelict large objects from Earth orbit has yet beenidentified. This remains an area of research."
The breakupin May and June of two Russian rocket stages illustrates the problem.
In May, thethird stage of a Russian Tsyklon rocket spontaneously exploded, creating morethan 50 pieces of debris large enough to be tracked by the U.S. SpaceSurveillance Network of ground-based sensors. The network can identify objectsin low Earth orbit as small as 10 centimeters. For objects in geostationaryorbit, objects of 1-meter-diameter and larger can be tracked.
In June, amotor from a Russian Proton rocket engine launched in the late 1980s broke up.The engine was in a highly elliptical orbit with a perigee of 655 kilometersand an apogee of 18,410 kilometers, according to a NASA study of SpaceSurveillance Network data.
Tsyklon andProton rocket stages and motors are well-known among those tracking orbitaldebris. The May breakup was the fifth of its type since 1988 for a Tsyklonstage. Simulations of the trajectory of the 50-plus pieces of junk created inthe May event suggest that nearly half of them will re-enter Earth's atmosphereand burn up this summer.
The JuneProton motor breakup was the 34th of its kind and created more than 70detectable pieces of debris.
Trackingrelatively small pieces of debris needs to be done regularly because theirtrajectory can be predicted only for a few days, Johnson said. "Hence, it isnot possible to determine if any Tsyklon or Proton breakup debris might comeclose to any operational spacecraft for other than very short periods," hesaid.
Tsyklon andProton once both employed a design that did not permit their upper-stageengines to be rendered passive in orbit, meaning they would not explode fromthe combustion of their remaining fuel, or following a collision with anotherpiece of debris.
Johnsonsaid Tsyklon vehicles, built by the Yuzhnoye DesignBureau of Ukraine, continue to feature the kind of upper stage that makes themdangerous as debris generators. The Proton vehicle upper stage has beenredesigned, he said, and now features engines that are rendered passive inorbit.
Johnsonsaid there remain slightly more than 100 Tsyklon stages and more than 50 Protonstages orbiting the Earth with the same debris-generating design.
TheInter-Agency Space Debris Coordination Committee, whose members include most ofthe active space-faring nations, has developed guidelines for satellites androckets to reduce the chance that they will contribute to the debris problemonce in orbit.
The U.S.Federal Communications Commission, which licenses U.S. satellites, also hasdeveloped mandatory rules for debris mitigation.
NASA keepswhat it calls a "box score" of nations responsible for the current debrispopulation as measured by ground-based radars and telescopes. As of July 4, theU.S. Space Surveillance Network was tracking 9,680 pieces of debris.
Notsurprisingly, the former Soviet Union and the United States are running a closerace for first and second place among the nations responsible for debris, with4,151 and 4,058 pieces, respectively.