Atlantis' astronauts zoomed toward Earth "happy and healthy" Tuesday to end a secret four-day military mission during which they reportedly deployed a radar satellite to spy on the Soviet Union.

The shuttle and its five travelers were on course to ignite re-entry rockets for a fiery hourlong dash through the atmosphere. Landing was scheduled for 4:36 p.m. MST on a dry lakebed at Edwards Air Force Base in California's Mojave Desert.Because of the military nature of the mission, the public wasn't allowed to watch the landing from the base. More than 400,000 spectators were there in October to cheer Discovery's return from the first post-Challenger shuttle flight.

The National Aeronautics and Space Administration and the Air Force Monday broke three days of silence on the Atlantis mission to give a 24-hour notice of the planned landing.

"The crew is doing well and is making preparations for landing," the agencies said in a brief statement. They also said the weather outlook at Edwards was good and that a slow leak detected before launch in a landing gear tire was not a concern for touchdown.

"Things are going super," Rear Adm. Richard Truly, a former astronaut in charge of the space shuttle program, said in an interview. "The crew is happy and healthy. The orbiter has done real well. It's been very clean.

"This was one of our most important missions," Truly said. "It's Atlantis' first flight after the standdown, and now you have two vehicles proven in flight. That's extremely important."

The Atlantis mission was the second shuttle flight since Challenger exploded in January 1986, halting launches for 32 months.

Truly, who was in the Johnson Space Center in Houston Monday, could not comment on specific accomplishments of the military mission.

The flight, under Air Force command, has been veiled in secrecy since Atlantis blasted off Friday morning from Cape Canaveral. The usual air-to-ground conversations of the astronauts were blacked out during the flight.