How many space debris objects are currently in orbit?

For Giotto designers, one of the most difficult problems was how to ensure that the spacecraft survived long enough to snap close-up pictures of Halley's comet nucleus when the spacecraft and the comet were heading towards each other at a combined speed of 245 000 km/hour (equivalent to crossing the Atlantic Ocean in 11 minutes!). At this speed, a 0.1-gram dust particle would be able to penetrate 8 cm of solid aluminium.
Giotto in 1985, with Whipple shield at bottom

Scientific models estimate the total number of space debris objects in Earth orbit to be in the order of:

•             29,000 - for sizes larger than 10 cm

•             670,000 - for sizes larger than 1 cm

•             More than 170 million - for sizes larger than 1 mm.

Any of these objects can cause harm to an operational spacecraft. For example, a collision with a 10-cm object would entail a catastrophic fragmentation of a typical satellite, a 1-cm object would most likely disable a spacecraft and penetrate the ISS shields, and a 1-mm object could destroy sub-systems on board a spacecraft. Scientists generally agree that, for typical satellites, a collision with an energy-to-mass ratio exceeding 40 J/g would be catastrophic.

Last update: 25 July 2013

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