▁use ▁of ▁Saf egu ard ▁in ▁ 1 9 7 5 / 1 9 7 6 ▁The ▁U . S . ▁Saf egu ard ▁system , ▁which ▁util ized ▁the ▁nuclear - ti pped ▁LIM - 4 9 A ▁Spart an ▁and ▁S print ▁miss iles , ▁in ▁the ▁short ▁oper ational ▁period ▁of ▁ 1 9 7 5 / 1 9 7 6 , ▁was ▁the ▁second ▁counter - IC B M s ▁system ▁in ▁the ▁world . ▁Saf egu ard ▁protected ▁only ▁the ▁main ▁fields ▁of ▁US ▁IC B M s ▁from ▁attack , ▁theoret ically ▁ens uring ▁that ▁an ▁attack ▁could ▁be ▁respond ed ▁to ▁with ▁a ▁US ▁launch , ▁enfor cing ▁the ▁mut ually ▁assured ▁destruction ▁principle . ▁ ▁S DI ▁experiments ▁in ▁the ▁ 1 9 8 0 s ▁ ▁The ▁Re agan - era ▁Str ateg ic ▁Def ense ▁In iti ative ▁( o ften ▁referred ▁to ▁as ▁" Star ▁Wars "), ▁along ▁with ▁research ▁into ▁various ▁energy - be am ▁weapon ry , ▁brought ▁new ▁interest ▁in ▁the ▁area ▁of ▁AB M ▁techn ologies . ▁ ▁S DI ▁was ▁an ▁extremely ▁am bit ious ▁program ▁to ▁provide ▁a ▁total ▁shield ▁against ▁a ▁massive ▁Soviet ▁IC B M ▁attack . ▁The ▁initial ▁concept ▁en vision ed ▁large ▁s oph istic ated ▁orbit ing ▁las er ▁battle ▁stations , ▁space - based ▁relay ▁mirror s , ▁and ▁nuclear - p ump ed ▁X - ray ▁las er ▁sat ell ites . ▁Later ▁research ▁indicated ▁that ▁some ▁planned ▁techn