WASHINGTON — NASA expects to order launches for three Earth science missions by the end of the summer, and United Launch Alliance (ULA) looks like the strongest contender for the job with its medium-lift Delta 2 rocket, an agency official said.

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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...