The crew of the shuttle Discovery, wearing bright orange spacesuits, climbed into the ship's cockpit Thursday for a full-scale practice countdown marking a final milestone before blastoff in just three weeks.

The five-man, all-veteran crew of the first post-Challenger flight - commander Frederick Hauck, co-pilot Richard Covey, George "Pinky" Nelson, David Hilmers and John "Mike" Lounge - began climbing aboard Discovery shortly before 8 a.m. All five were on board and strapped in about 45 minutes later.It was the first time since the Challenger disaster 31 months ago that a crew has climbed aboard an operational space shuttle. The only problem in the otherwise smooth countdown was an annoying echo in the crew's communication gear.

The "terminal countdown demonstration test," or TCDT, is a traditional milestone that gives launch crews a final chance to rehearse countdown procedures before the real thing.

As they climbed aboard, each crewman, wearing a bulky partial pressure suit for the first time since the fourth shuttle flight in 1982, strapped on a backpack containing a parachute, a small collapsible life raft and emergency survival gear.