To put it bluntly you don't know what you are talking about. Reagan did not define any system. Unlike the leftists he did not believe that the president automatically became the fount of all knowledge. He started a program that looked at many approaches to missile defense. The first successful defense was actually a missile that could hit an incoming missile. There is currently a system that uses lasers to destroy the missile early after lift off. That system is apparently being axed by O'bama rex.
I know we don't consider Wiki as gospel but I think it will do here...
Remember SDI... Strategic Defense Initiative...
http://en.wikipedia.org/wiki/Strategic_Defense_Initiative
The initial focus of the strategic defense initiative was a nuclear explosion-powered X-ray laser designed at Lawrence Livermore National Laboratory by a scientist named Peter L. Hagelstein who worked with a team called 'O Group', doing much of the work in the late 1970s and early 1980s. O Group was headed by physicist Lowell Wood, a protégé and friend of Edward Teller, the "father of the hydrogen bomb".
<snip>
The concept for the space-based portion was to use lasers to shoot down incoming Soviet intercontinental ballistic missiles (ICBMs) armed with nuclear warheads. Nobel Prize-winning physicist Hans Bethe went to Livermore in February 1983 for a two-day briefing on the X-ray laser, and "Although impressed with its scientific novelty, Bethe went away highly skeptical it would contribute anything to the nation's defense."[3]
Either way we spent a ton of cash on SDI and it never amounted to anything...