WASHINGTON — The Space Launch System (SLS) heavy-lift rocket will use a modified Delta 4 upper stage provided by Boeing Co. for its first two missions, according to the terms of an eight-year, $175 million contract NASA announced July 23.

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Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...