This is an interesting article (pdf) on the weaponization of space and averting a US-China space race..

The United States is extraordinarily dependent on space for its national security. The U.S. military has integrated space technologies into virtually all aspects of military operations, dramatically improving U.S. military power.

A strength and a weakness. Lots of things can threaten our space based equipment. One of the more interesting threats involves parasitic satellites. These are satellites that piggyback on legitimate enemy satellites and then at a later time break off and attach themselves to our GPS or communications satellites. When a dispute arises and hostilities erupt, or as a preemption, a signal is sent and our gear goes down.