How is striking a satellite in orbit different from trying to strike at an incoming missile?

Question

I've heard of people complaining of the failure of missile defense systems,but both China and the U.S. have each successfully missiles against their obsolete satellites,what does actually work and/or what still needs to be worked upon?

Answer 1

Satellites have a trajectory that can be calculated years ahead of time. Missiles don't give you that kind of warning. You can really take your time to ensure accuracy when downing a satellite, but after you get all the clearance and such you have maybe an hour to set up a missile hit. Less if you don't have an early enough detection.

Answer 2

On one hand, orbital speeds are greater than a falling missile and they are usually smaller so it would seem easier to hit the incoming one. On the other hand, the orbits of these test targets are well known so speed and trajectory are known precisely while all computations on an attacking missile would have to be made from scratch.