Junk-Yard Threat For Space Near Earth

Press, Volume CV, Issue 31003, 8 March 1966, Page 11

Junk-Yard Threat For Space Near Earth

Space near the earth is in danger of becoming a junk-yard. At this moment there are nearly 1000 separately-identified objects in orbit. Most are useless pieces of debris. In addition there are thousands of smaller fragments too small to be registered on the sensitive radar networks operated for space surveillance by both the United States and Russia.

All of these bits and pieces are orbiting around the earth like bees swarming around a honey pot.

Although the earth is large and is surrounded by plenty of empty space, the likelihood of a collision between two satellite objects travelling in different directions is steadily increasing. As the number of objects in orbit is doubled the chance of a collision is roughly quadrupled. This is something that must be remembered in the planning of manned spaceflight operations in the future. A collision between a manned space vehicle and even a tiny piece of space debris could be disastrous. The impact of an object colliding in earth orbit produces an explosive force roughly equal to that of the same quantity of dynamite. Not only would the airtight spacecraft be punctured but the pyrotechnics on board, such as retro rockets for return to earth, might be ignited. Any crew members surviving the decompression could find themselves marooned in space unless help was at hand.

The chances of such a catastrophe are not very great for the Gemini flights which orbit at altitudes below 200 miles. Other objects orbiting at these heights have lifetimes measured in weeks or months at the most, hence their numbers remain small. Future manned space stations, on the other hand, need to be in more permanent orbits and must therefore remain above 200 miles altitude. However, the orbiting lifetime of debris is also higher at higher altitudes, so there is an altitude where the chance of a collision is greatest before the number of objects thin out as the distance from the earth increases. This height is probably close to 400 miles. Estimates of the collision probability for a manned space station vary widely, and at first sight seem too small to worry about, but several American aerospace firms have already been giving thought to.the problem. One proposal describes a spacecraft for conveying a disposal team to rendezvous with an unwanted satellite object and fasten portable retro-rockets to it. The rocket’s thrust modifies the satellite orbit to make it plunge into the earth’s atmosphere where is is destroyed. The cost of such spaceclearing operations would be comparable with the cost of placing the objects in orbit in the first place. It would be justified only when the potential danger is very high. However, some future satellites may be equipped with such retro-rockets to clear them out of the way when their useful life is ended. Demolition charges are no good for clearing the clutter i.i space. Unless the explosion could be relied upon to vaporise the object completely, the result would be a shower of small fragments and an increased hazard. This

has already happened unintentionally on three separate occasions. The first occurred in 1961 when the final stage of the rocket which boosted Transit 4A (one of America’s prototype navigational satellites) and the solar research satellite, Injun 3. into orbit mysteriously exploded. Fortunately the two satellites had been released before the explosion, which completely shattered the rocket casing. Nearly 206 separate fragments are being regularly tracked and there must be many more pieces too small to be detected. The fact that United States space surveillance radar systems can detect so many fragments of a five-foot rocket at altitudes of more than 500 miles gives some idea of the extreme sensitivity of these radars. The Russians had the next accident early last year when they placed Cosmos 61, 62 and 63 in orbit with a single launch vehicle. Again it appears that the final rocket stage exploded after payload separation and at least 131 fragments have been catalogued. The latest mishap occurred last October when a U.S.A.F. Titan lIIC broke up in orbit and contributed another 111 fragments to the growing list of debris.

All of these pieces of debris will remain in space for centuries because there is no easy way of sweeping them up. The only way of minimising the hazard they present to manned space flights would appear to be in the use of computers. It is not beyond the capabilities of modern computers to calculate for manned vehicles safe orbits which dodge the larger fragments of space debris. But the pieces that are just below the limit of detection will always be a problem. They are too small and too numerous to follow but large enough to do serious harm to a spacecraft. The extremely small specks of debris do little damage and in addition they do not remain long in orbit. The two sets of needles sent into oirbit by the U.S. fall into this category. They are so small that the force of the solar wind—the stream of particles blown out from the sun—pushes them into more elongated orbits which, after a few years, dip into the earth’s atmosphere, causing the needles to bum away. If the larger pieces of space debris met their end as rapidly there would be no problem but the force exerted by the solar wind is so small that a half-ounce fragment in a 400-mile circular orbit can stay aloft for centuries.