ologies ▁such ▁as ▁X - ray ▁las ers ▁were ▁not ▁feas ible ▁with ▁then - current ▁technology . ▁As ▁research ▁continued , ▁S DI ▁evol ved ▁through ▁various ▁concepts ▁as ▁design ers ▁strugg led ▁with ▁the ▁difficulty ▁of ▁such ▁a ▁large ▁complex ▁defense ▁system . ▁S DI ▁remained ▁a ▁research ▁program ▁and ▁was ▁never ▁deployed . ▁Several ▁post - S DI ▁techn ologies ▁are ▁used ▁by ▁the ▁present ▁Miss ile ▁Def ense ▁Agency ▁( MD A ). ▁ ▁Las ers ▁originally ▁developed ▁for ▁the ▁S DI ▁plan ▁are ▁in ▁use ▁for ▁astronom ical ▁observations . ▁U sed ▁to ▁ion ize ▁gas ▁in ▁the ▁upper ▁atmosphere , ▁they ▁provide ▁teles cope ▁operators ▁with ▁a ▁target ▁to ▁cal ibr ate ▁their ▁instruments . ▁ ▁T act ical ▁AB M s ▁deployed ▁in ▁ 1 9 9 0 s ▁The ▁Isra eli ▁Ar row ▁miss ile ▁system ▁was ▁tested ▁initially ▁during ▁ 1 9 9 0 , ▁before ▁the ▁first ▁G ulf ▁War . ▁The ▁Ar row ▁was ▁supported ▁by ▁the ▁United ▁States ▁throughout ▁the ▁ 1 9 9 0 s . ▁ ▁The ▁Patri ot ▁was ▁the ▁first ▁deployed ▁tact ical ▁AB M ▁system , ▁although ▁it ▁was ▁not ▁designed ▁from ▁the ▁out set ▁for ▁that ▁task ▁and ▁consequ ently ▁had ▁limitations . ▁It ▁was ▁used ▁during ▁the ▁ 1 9 9 1 ▁G ulf ▁War ▁to ▁attempt ▁to ▁intercept ▁Ira qi ▁Sc ud ▁miss iles . ▁Post - war ▁anal ys es ▁show ▁that ▁the ▁Patri ot ▁was ▁much ▁less ▁effective ▁than ▁initially ▁thought