Brilliant Pebbles works very effectively, taking out all ICBMs in launch phase, and it is not inherently vulnerable, as it takes more missiles to shoot it down than the number of missiles in orbit.

For others, Brilliant Pebbles is a system of 10,000 kinetic kill vehicles, all in independent orbit around the earth, and capable with IR sensors to detect the launch of any sizable rocket and guide itself to impact the thin-skinned body of the rockets. No explosives needed. The ultimate clean weapon. The warheads are not armed then and will not suffer re-entry, so no radioactive substances will be released.

It is Bush's desired space defense program. The ground-based stuff does not work and is just a foot in the door.

The only undesirable thing about this system is that it automatically shoots everything down. If it is designed to be turned off, then there is the possibility that anyone can hack in and turn it off.

The system may be vulnerable to EMP however. So we may be able to conceptually shoot it down as vulnerable to EMP.