Vowing "we're ready to fly," the commander of the shuttle Discovery says his crew's launch on the first post-Challenger mission, planned for the last week in September, should be viewed as a test flight to prove modifications and improvements will work as advertised.

NASA managers, meanwhile, planned to submit a launch date recommendation to NASA headquarters in Washington that could be announced later this week, pending results of debate about a hydrogen leak aboard Discovery and inspections of two sluggish valves in the shuttle's engine compartment.Richard Colonna, a top shuttle manager at the Johnson Space Center, said late Monday the valves will be removed for a detailed inspection and that "we haven't resolved anything fully."

But he added: "We don't think we're going to find anything that's going to require us to take any major corrective action."

Veteran shuttle skipper Frederick Hauck, speaking at the crew's formal pre-launch news conference Monday, said he is eager to blast off on his third space mission.

"The last time I saw Discovery on the launch pad, I allowed myself to start getting excited about this flight. When you get out there and see the hardware poised and ready to go, there's a thrill that races through your body."

As for his four crew mates, all shuttle veterans, Hauck said simply: "I think we're a well-trained crew, I think we're ready to fly."

Hauck and his crew - co-pilot Richard Covey, George "Pinky" Nelson, John "Mike" Lounge and David Hilmers - plan to spend about four days in orbit to launch a $100 million NASA communications satellite identical to the one destroyed in the Challenger disaster on Jan. 28, 1986.

"Training for this mission has been a delight," Nelson said. "It's been a long time, and I think at times each of us has been a little impatient that things have gone slowly.

"At this point, speaking for me, we are ready to fly, (but) we understand that there are still a couple of hurdles to get over."