Space shuttle Discovery sits on a Kennedy Center launch pad before its last mission, in August of 2001.
NASA has not launched a space shuttle since the Columbia disaster a year and a half ago. After revamping its shuttle program, the agency is preparing to return to space next spring, when the 20-year-old shuttle Discovery is slated to launch a Mercury probe.
Kennedy Space Center officials gave a recent tour of preparations for the mission, including new safety standards. NPR's Richard Harris reports.