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gunsandrockets
Guest
"AFAIK, only hydrogen gives you Isp = 900sec, all other propellants are much less efficient and usually not worth the expense." -- Syndroma<br /><br />You are correct.<br /><br />If water was used, as Dobbins suggested, for a nuclear rocket launch vehicle then it would be inferior to chemical rockets. Compared to a LH2/LOX rocket a nuclear thermal rocket using water would have not only inferior ISP, it would have inferior thrust to weight plus the other headaches of nuclear rocket operation.<br /><br />Most concepts of nuclear thermal rockets as launch vehicles use ammonia for propellent. But even in this case the gain in performance over a chemical rocket is considered not high enough to be worth dealing with the difficulties of nuclear rocket operation. However a nuclear rocket does have much promise as an upper stage for a launch vehicle, and in this case it would use Hydrogen propellent for maximum ISP.