Atlantis returned safely to Earth on Sunday after dropping off an astronaut on the Russian space station Mir and overcoming mechanical problems that had almost forced an emergency landing.
The shuttle ended its nine-day, 3.8-million mile mission at Edwards Air Force Base, touching down during a spectacular Mojave Desert sunrise.
“Welcome back Atlantis,” Mission Control announced. “Congratulations on successfully delivering Shannon.”
“It sure feels good to be home,” commander Kevin Chilton replied.
For two days, cloudy skies over Florida prevented the shuttle from landing at Kennedy Space Center, which would have saved NASA the $1 million it costs to move the shuttle coast-to-coast.
Still, the shuttle almost had to make an emergency landing Saturday after its planned landing was called off. Two switches indicated that the cargo-bay doors that must be open during orbit had not swung open. The doors must be open to dispel heat from electronic equipment and are closed for landing.
After making a visual check to confirm the latches were open, the crew was ordered to override the automatic system and open the doors manually.
NASA blamed two malfunctioning microswitches for the problem, which almost caused Mission Control to order an emergency landing at a backup site.
There were other mechanical problems. A steering system sprang a hydraulic leak just before the March 22 launch but NASA decided it wouldn’t jeopardize the shuttle, which has two backup systems. Also, three of 38 steering thrusters failed.
At a news conference after Sunday’s landing, shuttle manager Tommy Holloway said he saw no pattern in the mechanical glitches that have troubled the last several missions. Atlantis first flew in 1985.
“So far, I do not find a pattern that would suggest any of these problems are caused by the orbiter getting old,” Holloway said. “I think we just happened to have a couple of things that lined up on this flight … the last couple of flights.”
The mission marked the third docking with Mir and the first spacewalk by U.S. astronauts while the spacecraft was attached to the Russian station.
The last time astronauts performed a spacewalk outside a space station was at Skylab in 1974 - seven years before the first shuttle flight.
The crew delivered biochemist Shannon Lucid and more than two tons of cargo to the Russian outpost and moved 1,200 pounds of equipment from Mir to the shuttle.