After nearly two weeks in orbit, Atlantis and its crew aimed for a Wednesday landing on either coast to clear the way for the military to shoot down a dying spy satellite.
Flight director Bryan Lunney said Tuesday that NASA was under no pressure from the Defense Department to hurry up the touchdown.
He stressed that Mission Control would abide by the usual weather rules and keep the shuttle aloft until Thursday if conditions took an unexpected turn for the worse.
Favorable weather was expected at Cape Canaveral on Wednesday morning as well as at the backup touchdown site in Southern California.
NASA normally does not activate the California landing strip so early, but wants to get Atlantis down if at all possible to give the Navy more time to take aim at the satellite from a warship in the Pacific.
The Pentagon has said there is roughly a weeklong window to shoot down the satellite before it enters Earth's atmosphere with a toxic load of fuel. That window began early this week.
It would be dangerous for Atlantis and its seven-man crew to descend through all the debris generated by the satellite's destruction.
The international space station is orbiting 210 miles up, higher than the satellite and thus safe from any of the expected debris.
Shuttle commander Stephen Frick said he and his co-pilot, Alan Poindexter, are excited about the satellite operation and can't wait to see how it turns out. Both are Navy commanders.
"My first thought when we talk about that is, 'Go Navy,'" Frick said.
Frick and his crew spent nine days at the space station, helping to install Europe's science lab, Columbus.
Except for the undisclosed illness of German astronaut Hans Schlegel, which delayed the lab's hookup, everything went precisely as planned.
After leaving the space station Monday, Atlantis experienced a heating system failure that knocked out four small aft thrusters.
The thrusters are not needed for re-entry, but to prevent any fuel line damage that could hold up Atlantis' next flight, NASA had the pilots point the thrusters toward the sun.
Atlantis' next mission is at the end of August when it flies to the Hubble Space Telescope with a team of repairmen. It will be NASA's last visit to Hubble.
The only other shuttle issue involved a radiator hose in the payload bay that ended up bent before the flight.
It was straightened just before the Feb. 7 launch, but engineers expect it to kink again when the payload bay doors are closed early Wednesday in preparation for landing.
Lunney said there are no safety concerns if that happens.
As for Atlantis' thermal shielding, a late laser inspection Monday found it to be in good shape for the fiery descent through the atmosphere.
"We're going to bring the ship back in as good of condition as we found it," Frick promised.
Atlantis is bringing home astronaut Daniel Tani, who spent four months on the space station.