<p>WASHINGTON (AP) - NASA's most prominent voice in the days following the Columbia accident announced Wednesday he is leaving the space agency at the conclusion of the investigation into the loss of the shuttle.</p>
<p>Ron B. Dittemore, a 26-year veteran of NASA who served more than four years as head of the space shuttle program, said he plans to leave as soon as the agency appoints a new program chief and starts an orderly transition of leadership.</p>