Facing mounting pressure to bring industrial competition to a congressionally mandated heavy-lift rocket development program, NASA has tentatively selected a vehicle design featuring solid-fueled, side-mounted boosters that eventually could be replaced with liquid-fueled engines, according to U.S. industry and congressional sources.

NASA Administrator Charles Bolden has approved a design for the Space Launch System (SLS) whose core and upper stages would utilize space shuttle- and Apollo-heritage propulsion systems, respectively, these sources said. For the side-mounted boosters, NASA would continue development of shuttle-derived solid-rocket motors while initiating work on a brand new engine likely fueled by liquid kerosene, sources said.

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