Space Junk

Space junk, space debris, space waste — it has many different names, but just as junk and waste cause problems here on Earth, in space spent booster stages, nuts and bolts from ISS construction, various accidental discards such as spacesuit gloves and cameras, and fragments from exploded spacecraft could soon turn into a serious problem for the future of spaceflight. The European Space Operations Centre is urging action to mitigate the threat and is displaying some startling images to highlight the issue. They have noted objects in both in low Earth orbit (LEO–appearing as a fuzzy cloud around Earth) and geostationary Earth orbit (GEO — farther out, approximately 22,240 miles above Earth) -- and all points in between.

Between the launch of Sputnik in October 1957 and January 2008, approximately 4600 launches have placed some 6000 satellites into orbit; about 400 are now travelling beyond Earth on interplanetary trajectories, but of the remaining 5600 only about 800 satellites are operational - roughly 45% of these are both in LEO and GEO. Space debris comprise the ever-increasing amount of inactive space hardware in orbit around the Earth as well as fragments of spacecraft that have broken up, exploded or otherwise become abandoned. About half of all trackable objects are due to in-orbit explosion events (about 200) or collision events (less than 10).

Officials from the space shuttle program have said the shuttle regularly takes hits from space debris, and over 80 windows had to be replaced over the years. The ISS occasionally has to take evasive maneuvers to avoid collisions with space junk. And of course, this debris is not just sitting stationary: in orbit, relative velocities can be quite large, ranging in the tens of thousands of kilometers per hour.

For the Envisat satellite, for example, the ESA says the most probable relative velocity between the satellite and a debris object is 52,000 kilometers per hour. If a debris objects hits a satellite, the ISS or the Shuttle, at those speeds it could cause severe damage or catastrophe.

But how does debris end up in orbit? Even after the end of the mission, batteries and pressurised systems as well as fuel tanks explode. This generates objects which contribute to a growing population of materials ranging from less than a micrometer to 10 centimeters or more in size. About 40% of ground-trackable space debris come from explosions, now running at four to five per year. In 1961, the first explosion tripled the amount of trackable space debris. In the past decade, most operators have started employing on-board passive measures to eliminate latent sources of energy related to batteries, fuel tanks, propulsion systems and pyrotechnics. But at present rates, in 20 or 30 years, collisions would exceed explosions as a source of new debris.