George Whitesides, chief of staff to NASA Administrator Charles Bolden, is stepping down, according to a U.S. government administration official. Whitesides served on President Barack Obama’s NASA transition team and was one of the president’s first political appointees to the agency.

Whitesides, a former executive director of the National Space Society and adviser to Virgin Galactic, will be replaced starting May 10 by David Radzanowski, a former White House Office of Management and Budget official who joined NASA in 2006, and currently serves as deputy associate administrator for program integration within NASA’s Space Operations Mission Directorate, the official said.