The vulnerability military space systems depends on their orbits, functions, and other characteristics. The high-altitude satellites needed for warning and communications in particular could be vulnerable to prompt destruction by certain space-based systems and, in the future, possibly by ground-based high power lasers. A combination of passive countermeasures and arms control agreements could give these satellites some protection against such attack. Deployment of strategic defensive systems with the capability to reach far into space would invalidate this approach.