WASHINGTON — Two top executives are leaving the Commercial Spaceflight Federation (CSF), including former astronaut Michael Lopez-Alegria, who joined the Washington-based advocacy group two years ago.

Combined with the imminent departure of Stuart Witt as chairman of the group’s board of directors — the full-time manager and chief executive of the Mojave Air and Space Port will finish his term as chairman in September — the stage is now set for a wholesale turnover of CSF leadership by the end of the year.

“This year will be one of significant transition for CSF, since our President Michael Lopez-Alegria has announced he will be moving on by the end of the year. I’m very proud of what we have all achieved, and am confident that we are turning over a much stronger and more respected organization to a new team of leaders,” Witt said in a June 27 statement to SpaceNews.

Lopez-Alegria’s planned departure was initially confirmed by CSF Executive Director Alex Saltman, who stepped down June 26 to move to California with his family. Sirisha Bandla, CSF’s assistant director, will handle Saltman’s duties until a replacement is announced later this summer.

Federation sources, meanwhile, said the board has identified several promising candidates to replace Lopez-Alegria but expects that he will remain at his post at least through the end of the summer. Reached by phone June 27, Lopez-Alegria told SpaceNews he is still job hunting. “I honestly don’t know when I’m going, or where I’m going,” he said.

The former international space station commander joined the Commercial Spaceflight Federation in March 2012, replacing retired U.S. Navy Rear Adm. Craig Steidle, the former NASA associate administrator for exploration systems whose tenure was cut short by health problems. Steidle was preceded by Bretton Alexander, the former White House Office of Science and Technology Policy staffer who helped found the organization in 2006 but left in 2011 to become business development director for CSF member company Blue Origin.

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...