With Discovery back on the ground in apparently good shape, NASA officials are increasingly confident the post-Challenger space agency can meet an ambitious seven-flight 1989 launch schedule.

Engineers are gearing up to haul Atlantis to the launch pad Thursday for blastoff in just six weeks to carry a $530 million Venus probe into space."We've got a lot to do in the next year and in the future," Rear Adm. Richard Truly, associate administrator for space flight, said after Discovery's landing Saturday at Edwards Air Force Base, Calif. "But I think this flight of the shuttle, again, shows what a marvelous and capable vehicle it is. I'm extremely happy with where we are."

Atlantis, already bolted to an external fuel tank and a pair of solid-fuel boosters, is scheduled to blast off April 28 to ferry the Magellan Venus radar mapper into space in a flight marking the first use of a space shuttle to launch an interplanetary spacecraft.

Atlantis is scheduled to be hauled to the firing stand Thursday for final preparations. The "launch window" opens at 2:24 p.m. EDT April 28, but because of the positions of Earth and Venus, along with a variety of other factors, NASA will have just 18 minutes to get Atlantis off the pad.

Truly said Discovery's flight cleared the way for Atlantis' mission and other flights to come.

"After the (first post-Challenger mission), I said one of the greatest things about such a successful flight is that we had to do it again and again," Truly said at a news conference. "And we have done that. This is the third straight very successful flight of the space shuttle.

"Now the fun really begins because before next week is out, the Atlantis will be on the launch pad with Magellan."

The shuttle Columbia is scheduled for launch in July on a classified military mission, but a launch delay is likely because of time needed to complete post-Challenger safety modifications.

"The biggest challenge the program has today is the status of Columbia," Truly said. Whether the shuttle can be ready for a launch try in July or August remains to be seen and in any case, Discovery is scheduled for its next flight Aug. 10 to ferry another military payload into space.

Following that flight, Atlantis takes center stage again, this time to carry the $1.4 billion Galileo Jupiter probe into orbit.

Galileo, equipped with an inertial upper stage booster, will be fired into orbit around Jupiter to study its stormy atmosphere and many moons. In addition, a small probe will be dropped into the planet's atmosphere in an unprecedented voyage of discovery. Atlantis is scheduled to carry Galileo into orbit Oct. 12.

Assuming Columbia makes it off the ground this summer, the veteran shuttle would be scheduled for its next flight Nov. 13.

During that mission, a military communications satellite will be deployed and the crew will retrieve a science satellite left in orbit in 1984 to test the long-term effects of the space environment on a variety of materials.

Discovery is scheduled to close out 1989 with blastoff Dec. 11 to carry the $1.4 billion Hubble Space Telescope into orbit.

The telescope will be the most sensitive optical telescope ever deployed above Earth's obscuring atmosphere, equipped with a 94.5-inch mirror sensitive enough to detect the light of a firefly at 10,000 miles.