United States upper stages for the next decade

United States (U.S.) upper stage development is approaching another crossroads. In the 1970s the decision was made to fly all future payloads on the space shuttle. Work on high performance shuttle upper stages was halted after the Challenger accident, because of heightened safety concerns about liquid stages in the payload bay. The centaur G′ was ultimately developed as the centaur upper stage for use with the Titan IV launch system. In the last two decades upper stage development decisions and requirements were driven by increased payload performance demands.