This story was updated at 2:03 a.m. EST.
CAPE CANAVERAL, Fla. - Astronauts aboard NASA's shuttle Atlantis are converting their spacecraft back into a 100-ton glider today as they gear up for a planned Wednesday landing.
Shuttle commander Stephen Frick and pilot Alan Poindexter will fire Atlantis' thrusters and test vital systems to ensure their spacecraft is ready to once again fly through the Earth's atmosphere.
"We're looking forward to getting home, and we're headed home now," Frick said after Atlantis undocked from the space station early Monday.
Atlantis' seven-astronaut crew is due to land at 9:07 a.m. EST (1407 GMT) on a runway at NASA's Kennedy Space Center in Cape Canaveral, Fla., here to conclude a successful 13-day mission to the International Space Station (ISS). The astronauts delivered the European Space Agency's (ESA) 1.4 billion euro ($2 billion) Columbus laboratory to the ISS and swapped out one member of the station's three-person crew.
"This mission has gone extremely well," said Mike Sarafin, NASA's lead shuttle flight director for Atlantis' spaceflight.
Engineers did tackle a glitch overnight with heaters for four of Atlantis' aft-mounted vernier thrusters used for attitude control. The heaters appeared to have failed, but the glitch does not pose a safety concern for the shuttle crew's landing, NASA officials said. The shuttle has a total of 44 thrusters that make up its reaction control system.
"They are small attitude control jets and they are not used during deorbit maneuvers," said NASA mission commentator Lynette Madison. "There are no power or propellant concerns."
Mission Control radioed the Atlantis astronauts early today with an update on the glitch, adding that the crew may fly some unplanned maneuvers to keep the unheated thrusters from growing too cold.
"Thanks a lot for those words," said Frick, whose crew awoke to the song "Always Look on the Bright Side of Life" from the musical "Spamalot" — a tune chosen especially for him — this morning. "We kind of figured we would be down [vernier jets] from now on but it is good to hear we don't have any power or prop concerns."
Sarafin said the shuttle astronauts and Mission Control accomplished all of their goals despite some major changes, including the unexpected illness of German astronaut Hans Schlegel, of the ESA, that kept him from participating in one of the mission?s three spacewalks and added a day to the spaceflight.
"I couldn't be prouder of them," Sarafin said of the Atlantis crew and flight controllers on Earth. "We learned that we had a good process in place."
Atlantis has four landing opportunities on Feb. 20; two at KSC and two others at a backup runway at California's Edwards Air Force Base. NASA hopes to land Wednesday to give the U.S. military more time to shoot down an ailing spy satellite laden with a half-ton of toxic hydrazine rocket fuel.
"Generally, the weather looks favorable at the Kennedy Space Center," Sarafin said, adding that mission managers were drawing up a landing strategy on Monday.
Engineers were also analyzing imagery from the Atlantis crew's final inspection of their spacecraft's heat shield late to seek out any new damage from micrometeorites or orbital debris during the mission. The orbiter was already cleared of any concerns related to launch debris last week.
Atlantis astronauts will spend time stowing away final bits of cargo and setting up a recumbent seat for their newest crewmember — U.S. astronaut Dan Tani — who is returning to Earth after a four-month flight to the ISS.
Tani joined the station's Expedition 16 crew during NASA?s last shuttle flight in late October and originally hoped to return home in mid-December. But delays to Atlantis' current mission added an extra two months to his orbital trek.
The recumbent seat, which will allow Tani to weather Atlantis' landing in a reclining position, is designed to ease his return to Earth's gravity after months of weightlessness.
"I've been working out on the treadmill quite a bit," Tani said of his preparations, adding that past long-duration crewmembers have found the exercise regime helpful. "Other than that, there's not really a lot much more preparation that I can really do."
Tani's replacement, ESA astronaut Leopold Eyharts of France, launched aboard Atlantis on Feb. 7 and stayed aboard the station to continue the commissioning of the Columbus laboratory until late March.
"I'd like to say that Dan is a great guy," Eyharts said before Tani left the station. "I hope that in a few weeks, we'll be able to do 1/100th of what he is able to do today."
NASA is broadcasting Atlantis' STS-122 mission live on NASA TV. Click here for SPACE.com's shuttle mission coverage and NASA TV feed.