Scott J. “Doc” Horowitz, associate administrator for the Exploration Systems Mission Directorate, will leave NASA in October, he announced.

A retired U.S. Air Force colonel who served as commander or pilot on four space shuttle missions, he now leads efforts to develop the new family of spacecraft that will return astronauts to the moon by 2020.

NASA already awarded to Lockheed Martin Corp. [LMT] the contract for the Orion crew exploration vehicle, and NASA soon will award the contract for the Ares lifters that will thrust Orion into orbit.

Horowitz is stepping down for personal reasons, he said, to devote more time to his family. His career plans are not certain. His successor will be named later.

NASA Administrator Michael Griffin praised Horowitz for his leadership in the program to acquire hardware needed to return the United States to space flight. The space shuttle fleet will retire in 2010.