The U.S. Air Force is spending nearly $4 billion to build a S-Band radar on Kwajalein Island in the Pacific. This will make it easier and cheaper to find and track small (down to 10mm/.4 inch) objects in orbit around the planet. Such small objects are a growing threat and Space Fence will make it possible to track some 300,000 10mm and larger objects in orbit.
Getting hit by an object 100mm (4 inch wide), if it’s coming from the opposite direction in orbit, results in an explosion equivalent to 20 kg (66 pounds) of TNT. That's all because of the high speed (7 kilometers a second, versus one kilometers a second for high-powered rifles) of objects in orbit. Even a 10mm object hits with the impact of 50-60 g (2 ounces) of explosives. In the last 16 years eight space satellites have been destroyed by collisions with one of the 300,000 lethal (10mm or larger) bits of space junk that are in orbit. As more satellites are launched more bits of space junk are left in orbit. Based on that, and past experience, it's predicted that ten more satellites will be destroyed by space junk in the next five years. Manned space missions are at risk as well. Three years ago a U.S. Space Shuttle mission to fix the Hubble space telescope faced a one in 229 chance of getting hit with space junk (that would have likely damaged the shuttle and required a backup shuttle be sent up to rescue the crew). Smaller, more numerous, bits of space junk are more of a danger to astronauts (in space suits) working outside. The shuttle crew working outside to repair the Hubble satellite had a much lower chance of being killed by space junk because a man in a space suit is much smaller and the space suits are designed to help the person inside survive a strike by a microscopic piece of space junk.
The U.S. is spending nearly a billion dollars a year in an attempt to better identify, and track, the larger more lethal bits of space junk. Two years ago the U.S. Air Force put a special Space Based Space Surveillance system (SBSS) satellite into orbit. This $830 million system uses a satellite that contains a digital camera to take pictures of space debris and make it easier to count and track the growing quantity of space junk. Getting a better and timelier look at space junk has become a priority.
The U.S. has proposed using a space based laser to destroy much of the space junk. The laser either vaporizes debris or damages the larger bits so that its orbit "decays" and the junk moves down into the atmosphere and burns up. Many nations object to this proposal, as such a laser system could also be used as an anti-satellite weapon. However, if the growing swarm of space junk destroys a lot more satellites, that attitude may change.
After over half a century of humans putting objects into orbit there is a lot of junk circling the planet. There are nearly 18,000 objects 100mm (4 inches) or larger. These can do some catastrophic damage to satellites or spacecraft. There are millions of objects smaller than 10mm, and these are responsible for many satellites failing early because of cumulative damage from getting hit by a lot of these micro objects.
SBBS has a military purpose, to spot and track hostile KillSats sent up to destroy American satellites. If the initial SBBS continues to be successful more will be launched, to provide real time surveillance of orbital space. But most of the time SBBS will serve to make space safer from catastrophic accidental collisions. The two or three ground based Space Fence radars will complement the satellites in finding and tracking dangerous space junk.