There's all kinds of asteroids and other debris cruising through space, but a lot of the really dangerous stuff is stuff we put there ourselves. NASA's cosmic bubble-spotting Fermi telescope almost had an intergalactic fender bender, but not with some epoch-old rock floating through the cosmos. No, it almost got crushed by some Cold War-era trash.
On March 29th 2012, NASA scientists were alerted that their precious telescope was going to get a close visit from Cosmos 1805, an outdated spy satellite which has been careening around the globe since its death decades ago. While a collision wasn't certain, the potential for one was disastrous; a 27,000 mph crash with the 3,100 pound hunk-of-junk would have been like the detonation of two and half tons of high explosives. And Fermi cost to build and deploy $200 million dollars, so NASA decided it was better to be safe than sorry.
In a maneuver that really just involved firing Fermi's previously unused thrusters for a mere second, NASA altered the satellite's orbit ever-so-slightly to avoid the potential disaster. Though it was a risk that Fermi's thrusters might be useless afterwards, the trick paid off, leaving the telescope safe and sound.
As our little corner of space gets increasingly crowded, issues like this are only going to become more and more common, especially as more and more countries blast satellites into space and lose control of them (looking at you, North Korea). The ISS has had to pull of stunts like this too. There are preliminary plans to blast space debris back into the atmosphere so it can burn up on its way down, but for the moment, the most effective strategy is just to keep dipping and diving. It's a high-stakes zero-g ballet up there. Hopefully no one screws up anytime soon. [NASA via Gizmag]