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27 Oct 14 22:44:00 GMT
27 Oct 14 18:44:00 EDT

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Countering the Threat Posed by Orbital Debris

In this computer simulation, the sheer amount of orbital debris becomes apparent - as does the need to find a way to prevent it. Image Credit: NASA

In this computer simulation, the sheer amount of orbital debris becomes apparentas does the need to find a way to prevent it. Image Credit: NASA

There’s a lot of junk up there. Around 20,000 bits and pieces of satellites and old rocket parts, bigger than 5 cm (2 inches) across, are floating around in orbits less than 2,000 km high—and that’s just the stuff that can be tracked from Earth. It’s estimated that there’s another half a million unwanted items, up to 1 cm across, orbiting in regions where there’s a danger of collision with active spacecraft. Even an object as small as a dime, traveling at a relative speed of several thousand kilometers per hour, could knock out a valuable functioning satellite or pose a threat to astronauts in low-Earth orbit. 

The first-ever piece of space junk would be high on the wanted list of any space museum. It’s Vanguard 1the fourth satellite to be launched (March 17, 1958) and the second by the United States. It’s still silently circling our planet every 134 minutes, and its orbit isn’t expected to decay for another 200 years.

There are around 1,000 active satellites going around the Earth at this moment, including everything from “nanosats” of just a few kilograms to the International Space Station (ISS), weighing in at 450 metric tons. But the problem is what happens to these spacecraft when they end their working lives?

One of the more infamous pieces of orbital debris is Ed White's glove - which drifted out of the Gemini 4 spacecraft in 1965. Photo Credit: NASA

One of the more infamous pieces of orbital debris is Ed White’s glove, which drifted out of the Gemini 4 spacecraft in 1965. Photo Credit: NASA

There have already been collisions in orbit. The most spectacular of these happened on February 10, 2009, when an active satellite in the Iridium constellation of comsats, the 560-kg Iridium 33, smacked into the 950-kg Kosmos 2251, a defunct Russian Strela-2M comsat, at roughly 35,000 kilometers per hour (about 32 times the speed of a bullet). Both were shattered into numerous parts. By July 2011, the U.S. Space Surveillance Network had cataloged over 2,000 debris fragments from the impact. One of the fragments of Kosmos 2251, being tracked from the ground, narrowly avoided the ISS on March 24, 2012. As a precaution, the six crew members on board took refuge inside the two docked Soyuz rendezvous spacecraft until the debris had passed. Another potential disaster was avoided just over a week later, when the Fermi Gamma-ray Space Telescope fired its thrusters to put some distance—9 km—between itself and an incoming Russian Cold-War spy satellite.

The fallout from the Iridium-Kosmos incident highlights the danger posed by orbital debris. The problem is not just the potential risk to material assets and astronauts, but the fact that every collision spawns a shower of fresh debris which could lead to a chain reaction of collisions, possibly bringing down many spacecraft and making near-Earth space inaccessible for decades. This is the feared “Kessler syndrome,” named after NASA scientist Donald Kessler who, in 1978, envisaged a situation in which the density of objects in low-Earth orbit became high enough that a major collision between two objects could trigger a cascade. If such a domino effect does happen—and some are warning that we may be close to it—then a generation or more of space exploration could be lost until the mess is cleared up.

The solution must be twofold: to be more responsible about disposing of any new stuff we send up, and to clear away the garbage that’s already out there. Designers of new launch vehicles or satellites are already required, in many instances, to show that they have plans for eventual safe disposal—for example, by use of controlled atmospheric re-entry or a means to boost the spacecraft into a so-called graveyard orbit. Beyond that, schemes are on the drawing board for bringing in the garbage. In the case of small fragments, in the 1 cm to 10 cm range, this might involve a “laser broom” – —a powerful ground-based laser that would target fragments and, by radiation pressure, alter their orbits so that they would quickly re-enter the atmosphere and burn up harmlessly. For larger stuff, dedicated space missions would have to be launched to capture the hardware and drag or deflect it into a path where it would incinerate on re-entry.

 

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