▁safety ▁reasons . ▁IC B M s ▁have ▁various ▁special ▁launch ing ▁facilities . ▁ ▁A ▁launch ▁is ▁often ▁restricted ▁to ▁certain ▁launch ▁windows . ▁These ▁windows ▁depend ▁upon ▁the ▁position ▁of ▁cel est ial ▁bodies ▁and ▁or bits ▁relative ▁to ▁the ▁launch ▁site . ▁The ▁biggest ▁influence ▁is ▁often ▁the ▁rotation ▁of ▁the ▁Earth ▁itself . ▁Once ▁launched , ▁or bits ▁are ▁normally ▁located ▁within ▁relatively ▁constant ▁flat ▁plan es ▁at ▁a ▁fixed ▁angle ▁to ▁the ▁axis ▁of ▁the ▁Earth , ▁and ▁the ▁Earth ▁rot ates ▁within ▁this ▁orbit . ▁ ▁A ▁launch ▁pad ▁is ▁a ▁fixed ▁structure ▁designed ▁to ▁dispatch ▁air bor ne ▁vehicles . ▁It ▁generally ▁consists ▁of ▁a ▁launch ▁tower ▁and ▁fl ame ▁tren ch . ▁It ▁is ▁surrounded ▁by ▁equipment ▁used ▁to ▁ere ct , ▁fuel , ▁and ▁maintain ▁launch ▁vehicles . ▁Before ▁launch , ▁the ▁ro cket ▁can ▁we igh ▁many ▁hundreds ▁of ▁t onnes . ▁The ▁Space ▁Sh utt le ▁Columbia , ▁on ▁ST S - 1 , ▁we ighed ▁ ▁at ▁take ▁off . ▁ ▁Re aching ▁space ▁ ▁The ▁most ▁commonly ▁used ▁definition ▁of ▁outer ▁space ▁is ▁everything ▁beyond ▁the ▁K á rm án ▁line , ▁which ▁is ▁ ▁above ▁the ▁Earth ' s ▁surface . ▁The ▁United ▁States ▁sometimes ▁defines ▁outer ▁space ▁as ▁everything ▁beyond ▁ ▁in ▁alt itude . ▁ ▁Rock ets ▁are ▁the ▁only ▁currently ▁practical ▁means ▁of ▁reaching ▁space . ▁Con vent ional ▁air plane ▁engines ▁cannot ▁reach ▁space ▁due ▁to ▁the ▁lack ▁of ▁o xygen . ▁Ro cket ▁engines