CAPE CANAVERAL -- Discovery's five astronauts enjoyed another quiet but productive day in space today, conducting experiments and beaming down a special birthday greeting to a crew member's wife.

Calling themselves "The Discovery Chorus," the men sang "Happy Birthday" to Kaye Akers, wife of astronaut Tom Akers, who turned 34 Monday. They floated in front of a shuttle TV camera during the short serenade.

Earlier, astronauts Bruce Melnick and Bill Shepherd conducted another test of an experimental system using voice commands to control TV cameras.

Discovery put NASA back in the space flight business when it lifted off Saturday on the first shuttle mission in nearly half a year. The launch ended the fleet's second-longest grounding ever and was topped several hours later by the successful deployment of the sun probe Ulysses.

Ulysses continued to streak through the solar system on its way to Jupiter. The giant planet will provide a gravity assist and push the satellite into an orbit over the sun's unexplored poles.

The $250 million European spacecraft is expected to pass over the sun's south pole in 1994 and the north pole in 1995.

Discovery is scheduled to land Wednesday morning at Edwards Air Force Base, Calif.

The shuttle Atlantis is scheduled to lift off on a secret military mission in early November. NASA officials said they expect the launch to be delayed only a day or so by damage caused by a metal beam that was left inside the shuttle by workers last week.