WASHINGTON โ€” Orbital Sciences Corp.โ€™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 SpaceXโ€™s 10- to 15- person Washington office in mid-July. He will run the Hawthorne, Calif.-based rocket startupโ€™s Capitol Hill activities, these officials said.

โ€œMark brings a wealth of experience to SpaceX at a time when the company is increasing its profile as the nationโ€™s premier launch provider,โ€ SpaceX spokeswoman Kirstin Brost Grantham said June 16 in an email. โ€œMarkโ€™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.โ€

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