– 1 0   km / s ▁delta - v . ▁These ▁mission ▁delta - vs ▁are ▁typically ▁numer ically ▁integrated ▁on ▁a ▁computer . ▁ ▁Cy cle ▁efficiency ▁All ▁reaction ▁engines ▁lose ▁some ▁energy , ▁mostly ▁as ▁heat . ▁ ▁D ifferent ▁reaction ▁engines ▁have ▁different ▁effic ien cies ▁and ▁losses . ▁For ▁example , ▁ro cket ▁engines ▁can ▁be ▁up ▁to ▁ 6 0 – 7 0 % ▁energy ▁efficient ▁in ▁terms ▁of ▁acceler ating ▁the ▁prop ell ant . ▁The ▁rest ▁is ▁lost ▁as ▁heat ▁and ▁thermal ▁radiation , ▁primarily ▁in ▁the ▁exhaust . ▁ ▁Ober th ▁effect ▁ ▁Re action ▁engines ▁are ▁more ▁energy ▁efficient ▁when ▁they ▁emit ▁their ▁reaction ▁mass ▁when ▁the ▁vehicle ▁is ▁trav elling ▁at ▁high ▁speed . ▁ ▁This ▁is ▁because ▁the ▁useful ▁mechanical ▁energy ▁generated ▁is ▁simply ▁force ▁times ▁distance , ▁and ▁when ▁a ▁thrust ▁force ▁is ▁generated ▁while ▁the ▁vehicle ▁moves , ▁then : ▁ ▁where ▁F ▁is ▁the ▁force ▁and ▁d ▁is ▁the ▁distance ▁moved . ▁ ▁D ivid ing ▁by ▁length ▁of ▁time ▁of ▁motion ▁we ▁get : ▁ ▁Hence : ▁ ▁where ▁P ▁is ▁the ▁useful ▁power ▁and ▁v ▁is ▁the ▁speed . ▁ ▁Hence , ▁v ▁should ▁be ▁as ▁high ▁as ▁possible , ▁and ▁a ▁station ary ▁engine ▁does ▁no ▁useful ▁work . ▁ ▁Types ▁of ▁reaction ▁engines ▁Ro cket - like ▁Ro cket ▁engine ▁I on ▁thr uster ▁ ▁Air bre ath ing ▁Tur bo jet ▁Tur bo fan ▁P ulse jet ▁Ram jet ▁Sc ram jet ▁Li