Countdown starts

MIAMI – The countdown clock ticked back into action Saturday as NASA tried again to launch Discovery on the first shuttle mission since the loss of Columbia and its crew more than two years ago.

Liftoff from the Kennedy Space Center is scheduled for 10:39 a.m. EDT Tuesday, and mission managers said all seems well. The countdown began at noon Saturday.

“Discovery is in excellent shape,” said Pete Nickolenko, a NASA test director. “We’re tracking no significant issues.”