If you’re not familiar with the Kessler Effect, Wikipedia describes it as “a scenario in which the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade – each collision generating debris which increases the likelihood of further collisions.” In other words, if we keep putting crap in orbit the crap will inevitably collide with other crap exploding in to thousands of smaller pieces of crap which will also collide with crap and the smaller crap making it dangerous for anything to travel to or through Earth’s orbit.
It may seem like the problem solves itself: big, dangerous pieces of debris are smashed into smaller harmless specks… This just isn’t the case; You need to consider speed. Typical orbital velocities can be tens of thousands of kilometres per hour, making even the smaller pieces extremely hazardous.
The Kessler Effect has been a hot topic on and off since the 70′s, but in 2009 it became a bit of a scary reality when defunct Russian military communications satellite Kosmos 2251 struck the solar panel of Iridium 33, a commercial American communications satellite. The explosion and resulting thousands of pieces of debris have forced NASA and other international agencies to develop a plan moving forward… failure to do so doesn’t just put the safety of future missions and astronauts a risk, it puts our ability to even travel into space at risk.
Scary stuff! Anyway, check out the awesome recreation of the Kosmos/Iridium collision below. For more info on the current state of our lower Earth orbit, check out this article from Stuart Clark, author of The Big Questions: The Universe.