Orbiting junk complication for space missions

Early risers a week ago today were treated to a spectacular celestial display as a derelict Soviet rocket body, launched in 1975, burned up in the atmosphere. None of the material reached the ground, which was not the case with the Russian Mir space station, whose descent into a remote area of the Pacific Ocean was monitored closely last March.

These types of incidents, while they gain attention, are rare. This might lead you to think that the space debris that cause them is also rare but this is not the case. Small pieces of space debris enter the atmosphere on a daily basis, where the brief flash from their destruction is often mistaken for a meteor. The fact is that there is an orbiting junkyard above our heads that is certain to cause problems for communications satellites, the space shuttle and International Space Station, and astronomical instruments such as the Hubble Space Telescope in the years ahead.

Just how prevalent is space debris or, as it is more commonly called, space junk? A recent report from NASA says that more than 9,000 objects larger than 10 centimeters, or about 4 inches, are in orbit. The number smaller than 4 inches is estimated to be in the millions.

According to Richard Panek, writing in the March issue of Natural History, about 2,500 of the larger objects are satellites. Many of these are still operating but many others are shut down and listed as orbital debris. The rest of the larger pieces are fuel tanks, burned-out rocket bodies, and other materials related to launches. The oldest known piece is from the U.S. Vanguard 1 satellite launched in 1958. Other items range from an astronaut’s glove to a one-third-scale model of Sputnik 1 released by the Mir cosmonauts in 1997 to commemorate the 40th anniversary of the satellite’s launch.

Space debris orbits in three distinct regions above the earth. Robert Coontz Jr. describes these in the December 2000 issue of Astronomy. The first region extends from about 200 miles to 350 miles and is where the shuttle, space station and Hubble Space Telescope operate. Coontz says the lower end of this spectrum is relatively self-cleaning as the debris burns up in the atmosphere but that in the upper levels it can orbit for centuries. This consists mainly of fragmentation debris resulting from the breakup of larger objects. For example, a Pegasus rocket blew up in 1996 generating more than 300,000 tiny fragments.

At 600 miles to 900 miles is a second band that contains the highest density of debris. This is where most of the mission-related debris is located. A third band is found at 22,400 miles, where the geosynchronous orbit houses hundreds of satellites. Coontz says these communications satellites are “well-behaved” and travel in the same direction at a sedate 6,700 miles per hour much like rush hour on a freeway.

The U.S. Space Command’s Space Control Center tracks around 9,500 objects greater than 10 centimeters. Some of the SCC’s two dozen tracking stations can monitor pieces of debris as small as 2 inches in low-earth orbit. Most pieces of tracked debris are logged daily and cover altitudes from 350 miles to 1,200 miles. SCC gives NASA a 72-hour “space junk forecast” before a mission launch. In addition, shuttles fly in an “alert box,” says Coontz, which is a 3-mile by 3-mile by 15.5-mile volume of space. Anytime a piece of debris enters the “box,” the shuttle crew is alerted.

At the moment, NASA says the chances of two large objects colliding are very low, with only one recorded hit in 40 years. This, according to a report in the Sept. 6, 1996, issue of Science, took place between a French military satellite and a burned-out rocket shell in July 1996. The satellite was destroyed. Hits from tiny bits of debris are much more frequent. The Long Duration Exposure Facility, launched in 1984 and retrieved in 1990, sustained more than 20,000 hits from tiny bits of debris.

Even tiny particles, because of their high rate of speed, can inflict significant damage. A fleck of paint gouged a 1/4-inch wide pit in the window of a space shuttle a few years ago. Depending upon its orbit, says Coontz, an object can be traveling up to 22,000 miles per hour and pack energy equivalent to 20 times its weight in TNT. A small ball bearing could smash through a satellite or punch a hole in the side of a shuttle or the space station.

Years ago Donald Kessler of NASA’s Johnson Space Center warned of the consequences of the uncontrolled buildup of space junk. Barbara Wood-Kaczmar wrote of the “Kessler Syndrome” in the Oct. 13, 1990, issue of New Scientist. Kessler sees an eventual buildup of space debris to the point where an avalanche effect will take place from repeated collisions, forming an impenetrable blanket of debris about the planet. This would, in effect, make it impossible to launch any new space missions. When the article was written a decade ago, Kessler predicted humanity would become earthbound in 30 years. Unfortunately, with only 20 years left on Kessler’s timetable, no government has any comprehensive policy to minimize space junk.

Clair Wood taught chemistry and physics for more than 10 years at Eastern Maine Technical College in Bangor.