Published: May 25, 2010 4:01 PM EDT
Updated: May 25, 2010 12:53 PM EDT

CAPE CANAVERAL, Fla. (AP) - Atlantis' homeward-bound astronauts paid tribute Tuesday to their space shuttle, close to winding up its final journey after a quarter-century of flight.

Commander Kenneth Ham noted that Atlantis has spent nearly 300 days in orbit over 32 missions, and traveled 120 million miles. He and his crew took along a small U.S. flag that actually flew on Atlantis' first flight. "Atlantis is just a fabulous ship," said Ham's co-pilot, Dominic "Tony" Antonelli.

"If this ends up being space shuttle Atlantis' last flight, we've got an American flag here that we're honored to fly," he said, holding it up and explaining that it flew on Atlantis back in 1985. This is the last flight on the books for Atlantis.

Only two missions remain as NASA's shuttle program winds down, unless the Obama administration agrees to add one more trip for Atlantis. Touchdown is scheduled for 8:48 a.m. EDT Wednesday.

Mission Control warned the crew that rain could interfere, but noted: "We think we've got a pretty good fighting chance." Atlantis has enough supplies to remain in orbit until Saturday.

Flight director Tony Ceccacci said the preliminary results of Monday's survey of Atlantis' heat shield looked good and the shuttle appeared to be in fine shape for re-entry. With just 26 hours officially remaining in their mission, the six astronauts beamed down a video they recorded over the previous few days aboard Atlantis as well as the International Space Station.

"I hope that when she lands successfully - which I'm relying on these guys up front to do - that she'll go somewhere and get the respect she deserves as a ship of exploration," said astronaut Piers Sellers, nodding to the pilots on board. He's flown on Atlantis twice.

The astronauts spent Tuesday getting Atlantis ready to come home after 12 days circling the Earth, and checking the critical flight systems. They're returning from the space station, where they delivered and installed a new Russian compartment, an extra antenna and 12 fresh batteries.

In an interview with the crew, Comedy Central's Stephen Colbert asked if they were double-A batteries. Astronaut Michael Good pointed out they were nickel-hydrogen batteries weighing nearly 400 pounds apiece and that he and his fellow spacewalkers had to work out at the gym in advance.

"But why would you have to work out? I thought nothing weighs anything in space," Colbert said. "Oh no, you figured it out," replied astronaut Garrett Reisman. "Busted!" Colbert shouted. "The whole thing's a fraud. No wonder they're canceling the program. It's all been a sham the entire time."

Given that it's the third-to-last shuttle mission, the TV comedian asked, "You guys putting your resumes together?" Antonelli replied that he's been collecting all the school calendars from the local community college back home in Houston and checking on the schedule for the truck-driving class.

As for Atlantis' future, the shuttle will be prepped for a potential rescue mission for the very last shuttle flight, to be conducted by Endeavour no earlier than November. Assuming no emergencies arise, NASA would like to fly Atlantis anyway, in June 2011.

Space agency officials said they need to know from the White House by June or July whether that's going to be possible. That's how much lead time would be needed to train a crew and flight control team, and prepare the payloads.