Discovery's astronauts passed the midpoint of their shuttle shakedown flight Saturday and the ship's commander said the flight proves NASA is "back on track" after Challenger.

The five crewmen will land at Edwards Air Force Base, Calif., Monday and, with the return in mind, two fliers practiced putting on the emergency bailout suits they will wear as the ship glides back through the atmosphere.The bright orange suits were developed as a result of the Challenger disaster, and this was the first time astronauts had donned them in the weightless confines of the shuttle cabin. It was not an easy task but NASA said it took less time than expected.

Commander Frederick Hauck indicated his crew would open a televised news conference from space Sunday at 9:57 a.m. MDT with a three-minute ceremony in memory of the seven astronauts killed when Challenger blew up 73 seconds after launch 32 months ago.

In keeping with the conservative test-flight philosophy of the 26th shuttle mission, the astronauts had another relatively light schedule Saturday. They signed off for the night at 5:15 p.m.

"We decided to put a very light load on the crew in order to be able to handle anything that might come up," said flight director Milton Heflin. But he said the ship has been "performing great."

Aside from rehearsing the landing preparations, the astronauts did a lot of sightseeing, performed more experiments and conducted two science demonstrations on NASA television.