Anti-satellite missile
From Citizendium, the Citizens' Compendium
An anti-satellite missile (ASAT) is a weapon intended to destroy satellites in orbit, which has similarities to, and differences with, an anti-ballistic missile (ABM). Since satellites are in a continuing orbit, the ASAT potentially has more than one chance to hit the target in different orbits. ABMs, in contrast, have only one point where their trajectory will intersect with the parabolic path of a ballistic missile.
Not all orbits are within the range of current or near-term ASATs.
Orbit
Low earth orbit is within the range of Chinese, Russian, and U.S. interceptors, all of which have demonstrated kills of unneeded satellites. Only the U.S. system is known to be mobile.
Capabilities beyond LEO are not known in the open literature, although it is fairly likely that nothing exists that can hit satellites in geosynchronous or higher orbit.
Kill mechanism
While demonstrations have used a hit-to-kill single kinetic interceptor, it is also possible to put a number of small interceptors into orbit. As long as their orbit will eventually intersect that of the satellite, they need not even be individually powered and guided, although "dumb" interceptors would present a long-term hazard to space navigation.
