GovernmentExecutive.com

The heads of NASA's four key mission directorates are being replaced in a management shuffle initiated by the agency's new administrator.

This week, Michael Griffin marked the start of his third month on the job by reassigning a number of key executives, including the leader of NASA's ambitious moon-Mars initiative and its space operations, science and aeronautics directors.

According to news reports, at least 16 more senior officials - and perhaps as many as 50 - could expect in the next few weeks to receive a notice asking them to accept a new assignment or be fired. NASA spokespeople have not disputed the numbers. They said it is not unusual for a new administrator to select his own management team.

Associate Administrator Craig Steidle quit rather than accept an assignment at a NASA field installation. Steidle, a former Navy admiral and procurement specialist, was named exploration chief in January 2004 after President Bush issued a space policy directive to return Americans to the moon by 2020. Steidle will leave the agency June 24 to become vice president of international affairs at the Aerospace Industries Association.

Notices also went to Space Operations Associate Administrator William Readdy, Science Associate Administrator Alphonso Diaz and Aeronautics Associate Administrator Victor Lebacqz.

Readdy, who has overseen NASA's recovery from the Columbia disaster, indicated in a memo to employees that he planned to remain in his post until shuttles return to flight. Beyond that, his future was uncertain. "I will certainly leave this post for a new challenge, possibly within NASA, but perhaps not," he wrote. "I cannot decide now as my attentions must remain focused on our most critical missions at hand."

Lebacqz and Diaz wrote similar memos. Diaz said he plans to retire. Lebacqz said he would serve through an indefinite transition period and had not decided whether to accept reassignment.

During his Senate confirmation process, Griffin made no secret of his dissatisfaction with the pace and price of work on the exploration initiative. One of Griffin's first decisions as administrator was to accelerate the development of a spacecraft that is central to the initiative in order to reduce the number of years between its first flight and the space shuttle's planned retirement in 2010.