NASA selects new heavy-lift rocket, say sources, Space.com

"Under the plan, awaiting approval by the White House Office of Management and Budget, initial flights of the SLS would utilize the solid-rocket motors, developed by ATK Aerospace Systems of Magna, Utah. ATK is under contract to develop an advanced version of the space shuttle solid-rocket booster under NASA's now-defunct Constellation program. Among the companies that have expressed interested in developing an advanced kerosene-fueled engine are Aerojet of Sacramento, Calif., Space Exploration Technologies (SpaceX) of Hawthorne, Calif., and Pratt & Whitney Rocketdyne of Canoga Park, Calif. This engine might eventually replace the solid-fueled motors on SLS, sources said."