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Scalenut,

SM3 and GMD are unrelated

SM3 (or Standard Missile 3) is the Navy's Aegis anti-missile system and last heir of the Tartar/Terrier system that dates back to the 1950's, but it was also used last year to shoot down a wayward US spy satellite as a response to the Chinese shooting down one of their own. The anti-sat version replaces the warhead of a standard SM3 with a "4th stage" exo-atmospheric hit-to-kill vehicle that looks sorta like an Apollo SM thruster with a seeker head on top. You don't need a warhead if you smack something at several thousand miles an hour.

An SM3 replaces the Terrier booster of the SM2 with a finless 21" solid booster. SM3 is slated to be replaced by an SM4 with a new 21" second and third stage which will eliminate any visual vestige of the old system.

The GMD is a land-based anti-missile system that is designed to hit-to-kill an ICBM or IRBM (like the one, oh, say, the North Koreans have) during the boost phase there by eliminating the need to differentiate between the warheads, decoys and anything else coming off during the reentry phase. This is what was supposed to be stationed in Poland and other Eastern European countries that really angered the Russians. All the overseas deployments been cancelled but there are operational installations in Alaska, at Vandenburg in California and probably on Kwajalein. There are a number of pictures on the web but I believe most of them show the target drone developed by Orbital Systems which looks like the second and third stages of a Minuteman with fins, used to test the system rather than the actual intercepter missile itself. The intercepter may look like Midgetman. Perhaps the development of Midgetman as an ICBM was cancelled in 1991 but the program proceeded as black program ABM. When it looked successful, the US withdrew from the ABM treaty in 2001.

Did I over-share?