The September 24, 2011 uncontrolled reentry of NASA’s UARS satellite places a spotlight on a problem that has been building for decades, the problem of debris in orbit around Earth.
The bus-sized Upper Atmosphere Research Satellite (UARS) satellite plunged to Earth over the Pacific, apparently causing no damage or injuries. Less publicized was another space debris incident – called a “scare” by some – that took place on June 28, 2011, when orbital debris came within a couple of hundred yards of the International Space Station (ISS).
According to a June 2011 post by Richard Ingham at Phys.org, millions of chunks of metal, plastic and glass are moving in orbit around Earth. These bits and pieces of space debris – plus many intact orbiting satellies – are left from 4,600 launches in 54 years of space exploration, Ingham said.
He points out that the collision risk is clearly low, since collisions between major satellites and debris to not happen often. But space junk travels at high speeds in orbit. Even a small piece can cripple an orbiting satellite that make have cost tens of millions to launch.
The U.S. Army, Navy and Air Force operate the U.S. Space Surveillance Network. It consists of ground-based radar and optical sensors at 25 sites worldwide, and it does the following jobs:
- Predict when and where a decaying space object will re-enter the Earth’s atmosphere;
- Prevent a returning space object, which to radar looks like a missile, from triggering a false alarm in missile-attack warning sensors of the U.S. and other countries;
- Chart the present position of space objects and plot their anticipated orbital paths;
- Detect new man-made objects in space;
- Produce a running catalog of man-made space objects;
- Determine which country owns a re-entering space object;
- Inform NASA whether or not objects may interfere with the space shuttle and Russian Mir space station orbits.
The U.S. Space Surveillance Network tracks roughly 16,000 objects bigger than four inches across, while 19,000 are known to exist.
Meanwhile, according to according to the NASA Orbital Debris Program Office website, there are approximately 500,000 pieces ranging in size between half an inch and four inches (1 to 10 cm), while the total of particles smaller than half an inch “probably exceeds tens of millions.”
Collisions are relatively rare, considering how much debris is up there. Past collisions have included these:
- In 2009, a disused Russian military satellite, Cosmos 2251, smacked into a U.S. Iridium communications satellite, generating a debris cloud.
- In 2005, the upper stage of a U.S. Thor launcher hit debris from a Chinese CZ-4 rocket.
- In 1996, a fragment from an exploded Ariane rocket launched in 1986 damaged a French spy micro-satellite, Cerise.
- In 1991, a Russian navigation satellite, Cosmos 1991, collided with debris from a defunct Russian satellite, Cosmos 926, although this event came to light much later, in 2005.
- In June 1983, the windscreen of the shuttle Challenger had to be replaced after it was chipped by a paint fleck just 0.01 inch (0.3 mm) across that hit at 2.4 miles (4 km) per second.
Europe, Japan, Russia and the United States have issued guidelines for mitigating the debris problem, such as designing satellites and spacecraft so they can de-orbit rather than drift in space. NASA now designs large orbiting craft in this way. Leading space agencies have also formed a panel to address the problem, and the U.N.’s Committee on the Peaceful Uses of Outer Space (COPUOS) is discussing the issue.
Bottom line: The September 24, 2011 uncontrolled reentry of NASA’s UARS satellite places a spotlight on a problem that has been building for decades, the problem of debris in orbit around Earth.
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