▁Island . ▁Cop ern ix ▁satellite ▁image ▁ ▁Category : Is lands ▁of ▁the ▁South ▁Sh et land ▁Islands ▁Category : O cean ▁Fish eries ▁– ▁Burg as ▁Co ▁ ▁Category : B ul g aria ▁and ▁the ▁Ant ar ctic <0x0A> </s> ▁A ▁two - stage - to - or bit ▁( T ST O ) ▁or ▁two - stage ▁ro cket ▁launch ▁vehicle ▁is ▁a ▁space craft ▁in ▁which ▁two ▁distinct ▁stages ▁provide ▁prop ulsion ▁consec ut ively ▁in ▁order ▁to ▁achieve ▁orb ital ▁velocity . ▁It ▁is ▁intermediate ▁between ▁a ▁three - stage - to - or bit ▁launch er ▁and ▁a ▁hypoth et ical ▁single - stage - to - or bit ▁( S ST O ) ▁launch er . ▁ ▁At ▁lif to ff ▁the ▁first ▁stage ▁is ▁responsible ▁for ▁acceler ating ▁the ▁vehicle . ▁ ▁At ▁some ▁point ▁the ▁second ▁stage ▁det aches ▁from ▁the ▁first ▁stage ▁and ▁continues ▁to ▁orbit ▁under ▁its ▁own ▁power . ▁ ▁An ▁advantage ▁of ▁such ▁a ▁system ▁over ▁single - stage - to - or bit ▁is ▁that ▁the ▁most ▁of ▁the ▁dry ▁mass ▁of ▁the ▁vehicle ▁is ▁not ▁carried ▁into ▁orbit . ▁This ▁reduces ▁the ▁cost ▁involved ▁in ▁reaching ▁orb ital ▁velocity ▁as ▁much ▁of ▁the ▁structure ▁and ▁engine ▁mass ▁is ▁e ject ed ▁and ▁a ▁larger ▁percentage ▁of ▁the ▁orb ited ▁mass ▁is ▁payload ▁mass . ▁ ▁An ▁advantage ▁over ▁three ▁or ▁more ▁stages ▁is ▁reduction ▁in ▁complexity ▁and ▁fewer ▁separation ▁events , ▁each ▁of ▁which ▁increases ▁cost ▁and