Outer space seems vast and empty, but the space directly above Earth is quite crowded with satellites and ... space junk!
Between the launch of Sputnik on 4 October 1957 and 1 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 percent 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 50 percent 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.
Falling to earth isn't the big deal. It's mission survivability.
http://www.kongregate.com/games/Neopolita/debris-hunter
This is a typical human problem. Lets do what we want without thinking about the consequences till we really have to. Similar to Nuclear Power. Hey we get all this FREE energy. So what if theres a little waste left behind, we'll worry about figuring out what to do with it latter. Well latter is here and we better start dealing with this junk soon. Or every ship we launch will be in danger of hitting something.
Look at the bright side. Maybe all this space junk will protect us from an Alien invasion. Who would want to try to drive thru all this stuff just to get to a planet that is even more polluted?
The problem is that every time one of our "retired" (read DEAD) orbiting satellites breaks apart, the debris is traveling at about 20,000 miles/hour. At that speed, if the space shuttle (for example) is hit by a paint-chip, it takes significant damage. I'm not making this up; this is recorded data. "Space junk" flying out into space is not a problem, as you say. However, space junk STUCK IN ORBIT is a HUGE problem for us. Several solutions have been recently proposed by NASA but none are really that great yet. Some are as loony as putting up in orbit a MASSIVE mylar sheet to catch or slow down debris so it stops and falls to earth... which would work if you can spare like a million square miles of mylar...
Shooting down a satellite breaks it into smaller debris, which are harder to track. This is the reason everyone was against the Chinese missile launch. (And of course the fact that it gives them practice shooting down satellites)
The spy satellite shot down by the US government was in a much lower orbit, so the debris field fell to Earth instead of becoming a problem.
If you look at those objects in the pic, they'd have to be thousands of times larger than ANYTHING ever launched into space.
In reality if you shrank each dot down to actual size, you wouldn't see anything there at all.
The total area of the LowEarthOrbit 'sphere' encompasses many hundreds of millions of cubic miles and there is MUCH more room there than the photo would lead you to believe.....