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Written by Andrew Parker   
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Tuesday, 27 September 2011

Space Pollution
There are many types of pollution in our environment:  water pollution, air pollution, noise pollution, and more. But one of these – space pollution – is in a category all by itself. Space pollution refers to the gathering debris in orbit around the Earth, made up of discarded rocket boosters, broken satellites, and more. And just like the other types of pollution, space pollution is a cause for increasing concern as the amount of material continues to grow.

“Big Sky” or “Kessler Syndrome”? Several decades ago, as the U.S. was just beginning to launch items into space, NASA officials relied on the “big sky theory” when faced with the question of accumulating debris. According to the theory, objects left in space would disperse and eventually re-enter the Earth’s atmosphere, where they would burn up before hitting the ground. Following this logic, there was no reason to be concerned about over-crowding the space around our planet.

The big sky theory was challenged in 1978 by a NASA scientist named Donald Kessler. Kessler published a paper titled “Collision Frequency of Artificial Satellites: The Creation of a Debris Belt,” which argued that the increasing number of man-made objects in space posed a huge threat. It wasn’t just the slow growth of these objects, Kessler wrote, but the way in which inevitable collisions would create a domino-like effect. One big collision could generate thousands of pieces of debris, each of which might go on to strike other objects, leading to a chain reaction that would exponentially increase the number of items in space. This phenomenon, later dubbed the “Kessler Syndrome,” would produce a “growing belt of debris.”

The development of this “belt of debris” would have significant consequences, beginning with damage to existing satellites, as more and more are pelted with sharp objects traveling at high speeds. This could eventually disrupt satellites tasked with communication and weather observation functions, causing a noticeable impact for people on Earth. Even worse, any future space exploration missions – or even service missions to repair existing objects in orbit – would become far more dangerous.

Orbital Bebris
Computer model of debris in low-Earth orbit

Monitoring Space Pollution
Right now, NASA’s Orbital Debris Program Office is monitoring about 19,000 pieces of space debris larger than 10 centimeters. Because these are the biggest objects, they pose the greatest risk to Earth. This risk includes surviving re-entry into Earth and causing damage here, of striking a spaceship or the International Space Station, or of colliding with another piece of debris and causing the effect predicted by Kessler.

Unfortunately, there are also half a million items between one and 10 centimeters, and an almost incalculable number (projected at over 10 million) that are smaller than a centimeter. And it is not just the large pieces that create a risk—the International Space Station (ISS) is considered to be vulnerable to impact by objects only one centimeter across. The ISS was wisely designed with the ability to move out of the path of oncoming debris and has had to executive five such maneuvers in the last 30 months alone. Officials at NASA now believe that such debris poses the greatest threat to the ISS.

Evidence of the Kessler Syndrome at Play
Writing in 1978, Kessler predicted that the cascading effect of debris collisions would begin in 30 to 40 years. And now, right on time, we are starting to see evidence. The first event, in 2007, was not exactly what Kessler had expected; it was caused when China launched a rocket at one of its own defunct satellites, presumably as a show of military force. The rocket hit its target, and in the process created about 3000 pieces of debris that are now shooting through space and causing additional collisions. One large chunk came very close to hitting both the space shuttle Atlantis and the Hubble Space Telescope.

The second event was more in line with Kessler’s original argument – the idea that space would simply become more and more crowded until collisions became inevitable. On February 10, 2009, a U.S. communications satellite named Iridium 33 was struck by an out-of-service Russian satellite called Cosmos 2251. Both were traveling at 18,000 miles per hour, or five miles per second, and the impact created a “cloud of debris” consisting of thousands of individual pieces.

This collision and the Chinese rocket vastly increased the amount of debris in orbit around the Earth. Kessler said that these two events alone “doubled the amount of fragments in Earth orbit and completely wiped out what we had done in the last 25 years” to manage the threat generated by space pollution. Kessler’s efforts included a set of rules and guidelines, which were subsequently adopted by many other nations, specifying which types of objects could be left in space.

Re-Examination and Clean-Up
After the satellite collision in 2009, NASA and the U.S. military began to take the issue of space pollution much more seriously. These organizations had previously been watching only 120 satellites for potential collisions, and Iridium 33 wasn’t even on the radar. They quickly expanded their capacity and now monitor thousands of satellites and tens of thousands of pieces of debris.

In December 2009, Kessler and his colleagues organized the Conference on Orbital Debris Removal, which sought out a broad range of inventions and concepts for cleaning up the polluted space around our planet. Kessler was impressed with the results, saying “I’ve gone from being totally skeptical to thinking maybe something will work…We can bring things down; it’s just going to cost a lot.” NASA is pursuing a variety of avenues right now, and its 2011 budget proposal included funds for research grants in this area.

The proposed clean-up methods are numerous, and they are all still in the design and development phases. With that being said, here are a few of the most promising ideas:
  • DARPA, the Defense Advanced Research Projects Agency, has outlined plans for an Electrodynamic Debris Eliminator featuring 200 nets, all of which are connected to a central unit. Debris captured in the nets could be sent back toward Earth to burn up in the atmosphere or even recycled on the spot. DARPA is planning test flights for 2013.

  • The CubeSail, designed in Britain, is based around sail technology that relies on the force of sunlight to move. In the short term, the project team envisions a sail attachment for new satellites that could be used to move the object away from the “debris belt” – either toward Earth or out into space. Further down the road, they hope to create special debris cleaners that use solar sails to navigate through space and gather objects.

  • Tethers Unlimited, a space company in Seattle, proposed a vehicle named “Rustler” that would connect a miles-long attachment made of wire mesh to debris in space. Electrical current could be sent through the attachment and, relying on the principles of electromagnetic forces, the item would be pulled in by Earth's magnetic field and eventually burn up in the atmosphere.
http://blogs.discovery.com/.a/6a00d8341bf67c53ef01310fef4acc970c-pi
A prototype CubeSail

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1 http://www.huffingtonpost.com/2011/09/01/space-pollution-junk_n_945020.html
2 http://www.wired.com/magazine/2010/05/ff_space_junk/all/1
3 http://webpages.charter.net/dkessler/files/Collision%20Frequency.pdf
4 http://www.wired.com/magazine/2010/05/ff_space_junk/all/1
5 http://www.space.com/7956-space-junk-mess-messier-orbit.html
6 http://www.huffingtonpost.com/2011/09/01/space-pollution-junk_n_945020.html
7 http://orbitaldebris.jsc.nasa.gov/photogallery/beehives/LEO640.jpg
8 http://orbitaldebris.jsc.nasa.gov/faqs.html
9 Id.
10 http://orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv15i3.pdf
11 http://www.wired.com/magazine/2010/05/ff_space_junk/all/1
12 http://www.wired.com/magazine/2010/05/ff_space_junk/all/1
13 http://satellite.tmcnet.com/topics/satellite/articles/50489-when-
satellites-collide-iridium-33-meets-kosmos-2251.htm
14 http://www.wired.com/magazine/2010/05/ff_space_junk/all/1
15 http://www.huffingtonpost.com/2011/09/01/space-pollution-junk_n_945020.html
16 http://www.wired.com/magazine/2010/05/ff_space_junk/all/1
17 Id.
18 Id.
19 Id.
20 Id.
21 http://www.popsci.com/technology/article/2010-08/darpas-space-
junk-remover-will-net-orbiting-debris-leo
22 http://www.space.com/8296-solar-sails-clean-space-junk.html
23 http://www.wired.com/magazine/2010/05/ff_space_junk/all/1
24 http://news.discovery.com/space/cubesails-to-drag-space-junk-from-orbit.html



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