NASA rolled out a full-scale model of its next generation space shuttle. The 115-foot mock-up of the planned Shuttle-C, an unmanned, cargo-carrying shuttle, was put together in a hanger at Marshall Space Flight Center in Huntsville, Ala., for about $500,000, officials said. The National Aeronautics and Space Administration hopes to get the first funds for a $1.5-billion Shuttle-C development program in its fiscal 1991 budget. As proposed by Marshall engineers, Shuttle-C would be a wingless version of the existing space shuttles. Shuttle-C would weigh less than half as much as the manned orbiters, but could carry payloads three times as heavy. Unlike its manned counterparts, Shuttle-C could not be reused.