A hold-down test of Orbital Sciences Corp.’s Antares rocket, a prerequisite for the launch vehicle’s maiden flight, likely will not be completed before April because of ongoing tests and certification work on the vehicle’s launch pad at Wallops Island, Va., a launch 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...