WASHINGTON — Orbital Sciences Corp.’s top lobbyist, Mark Bitterman, is leaving the Dulles, Va.-based satellite and rocket builder for rival Space Exploration Technologies Corp., (SpaceX), according to officials at both companies.

Bitterman, a 19-year-veteran of Orbital Sciences, is stepping down as senior vice president of government relations effective June 17 to join SpaceX’s 10- to 15- person Washington office in mid-July. He will run the Hawthorne, Calif.-based rocket startup’s Capitol Hill activities, these officials said.

“Mark brings a wealth of experience to SpaceX at a time when the company is increasing its profile as the nation’s premier launch provider,” SpaceX spokeswoman Kirstin Brost Grantham said June 16 in an email. “Mark’s knowledge and leadership will strengthen our efforts to educate policy makers on how SpaceX is revolutionizing space transportation while providing value for the taxpayer.”

SpaceX, like Orbital Sciences, is under contract to start making supply runs to the international space station using commercially operated vehicles built with NASA’s financial assistance.