Washington ? A former Marine officer who has held engineering and management jobs in three NASA centers is taking over as manager of the space shuttle program as the space agency tries to recover from the Columbia accident.

William W. Parsons, 47-year-old director of NASA’s John C. Stennis Space Center in Mississippi, was named Friday as the new manager of the space shuttle program, succeeding Ronald Dittemore, who acted as NASA’s most prominent spokesman after the loss of Columbia.

Dittemore announced plans to resign on April 23. Officials said there would be a period of transition, with Parsons and Dittemore working together for a time, but Parsons should be in charge by this summer.

Parsons said he approaches his new job “with a bit of trepidation” because it comes during a period of recovery for the program. “This is a big challenge for me and I had to think through it” before accepting the appointment, he said.

Space shuttle Columbia disintegrated while returning to Earth on Feb. 1. All seven astronauts on board were killed. The three remaining space shuttles have been grounded while the accident is investigated. Without the space shuttle fleet, NASA has had to rely on the Russian space program to rotate crew members and send new supplies to the International Space Station .

Parsons said his focus initially will be to take the recommendations of the Columbia Accident Investigation Board and devise a plan to safely start flying the space shuttles again.

The investigating board is expected to complete its report this summer, and NASA has pledged to address each of its recommendations.