Satellite Collision Adds to 'Space Junk' Problem
Saturday, February 14, 2009
Satellite 33442 orbits Earth every 91 minutes, circling at an inclination of 56.1 degrees to the equator and gradually slowing down, destined to fall into the atmosphere in late spring or summer and burn up. Aficionados of satellites know that 33442 is a tool bag. A spacewalking astronaut let it slip last year, adding one more tiny, artificial moon to the junk in low Earth orbit.
The military has a running catalog of more than 19,000 pieces of orbital debris. This week, the census of space schmutz suddenly jumped by 600 -- the initial estimate of the number of fragments from Tuesday's stunning collision of two satellites high above Siberia.
Space is now polluted with the flotsam and jetsam of a satellite-dependent civilization. The rubbish is increasingly a hazard for human spaceflight and has put important equipment such as the Hubble Space Telescope and communications satellites at risk of being struck by an object moving at hypervelocity.
The military's radar can spot objects about four inches in diameter, roughly the size of a softball, or larger. This collision, however, may have produced many thousands of small, undetectable pieces of debris that would still carry enough kinetic punch at orbital velocities to damage or destroy a spacecraft.
"We expect there will be tens or hundreds of thousands of pieces down to a centimeter or a millimeter," said Nicholas Johnson, NASA's chief scientist for orbital debris.
This is not a new problem. Garbage has been accumulating in space for decades, hurtling through the void alongside about 900 working satellites. Some of the dross is in the form of spent rocket boosters. There are defunct satellites tumbling to nowhere. The oldest is the Vanguard I satellite launched by the United States in 1958.
China dramatically increased the trash in space when, in January 2007, it destroyed an aging satellite to demonstrate a new missile's capability. Rather than obliterate the old hardware, the missile strike converted the satellite to about 2,500 fragments, Johnson said.
A bad situation got worse Tuesday. The two satellites, an American Iridium and a Russian Cosmos, came together 491 miles above Earth at about 22,000 mph. They struck one another at a 90-degree angle. It was probably a glancing blow, as the military is still tracking "parent" objects, according to Navy Capt. Mack Insch, chief of staff of the Joint Functional Component Command for Space of the U.S. Strategic Command (Stratcom).
NASA immediately checked to see whether there was any danger to the international space station. The risk of the station being struck was determined to be "very small" but "elevated."
NASA is also concerned about the safety of its scientific satellites, including five Earth-observing spacecraft, collectively known as the A-Train, that fly in a close formation about 438 miles above the surface. A sixth satellite for that mission, the Orbiting Carbon Observatory, is scheduled to be launched Monday.
The Hubble is about 350 miles above the surface, while the space station orbits 220 miles up. The debris could eventually spread to those lower orbits, though NASA has said that, for the moment, it believes there is a very small risk to those spacecraft.
At higher orbits, space doesn't flush out its contaminants very quickly. At lower orbits, in the range of 200 miles or so, there is atmospheric drag as the friction of air molecules reduces the speed of the objects and causes them to fall to Earth to burn up upon reentry. But 500 miles or so above Earth, the drag is vanishingly slight.