After space shuttle Discovery returns from its last mission, NASA workers will start getting it ready for its next voyage — to a museum.

NASA is retiring its shuttle fleet this year, and 21 museums across the country - including Chicago’s Adler Planetarium - are vying for the chance to become a retirement home for one of the iconic space shuttles.

The trouble is, NASA has only three spaceships — Discovery, Atlantis and Endeavour — and the agency has said it intends to offer Discovery to the Smithsonian’s National Air and Space Museum in Washington, D.C. That just leaves Atlantis and Endeavour, both of which are scheduled to fly for one last time this year.

“Chicago has a number of advantages. It’s the major metropolitan area in the Midwestern part of the country,” says Paul Knappenberger, president of the Adler Planetarium. He says it “just seems to make a lot of sense” to put a shuttle in Chicago, where it could be seen by millions of people. He notes that the Adler Planetarium has plans for a dramatic new building to house this prize.

“In one direction, the shuttle would be framed looking out over Lake Michigan with the sky behind it, and the other direction would be the beautiful Chicago skyline,” Knappenberger says.

Chicago is not the only possible place in the Midwest, of course.

Glenn Wright is head of the Tulsa Air and Space Museum, which has a request in to NASA.

“They know we’re qualified, that we could do it, and they’d like to have it in the middle of the United States,” Wright says. “But there’s other places, too, that are asking for it, and we’re just on the list, like everybody else.”

That list includes the Evergreen Aviation & Space Museum in Oregon, currently known for being the home of the world’s largest wooden flying boat, known as the “Spruce Goose.” Curator Stewart Bailey says they’d love to have a space shuttle, too.

“I personally think we’ve got a good offer; however, there are a lot of good museums in the running,” Bailey says. “It’s hard to tell what NASA is thinking.”

“It’s going to be a tough decision,” says Bob Sherouse, who is managing the selection process for NASA. “At this point, I think anything is possible.” For example, Houston wants a shuttle to come home to NASA’s Mission Control, but it has some competition nearby. The Brazos Valley Museum of Natural History in Bryan, Texas, has managed to become “a very serious contender” for a shuttle, according to its executive director, Deborah Cowman.

The museum is collaborating with Texas A&M University in College Station and hopes to build an expanded facility on its campus to showcase a shuttle near the George Bush Presidential Library and Museum.

The former president has endorsed the plan in a video posted on the natural history museum’s website. Local leaders are on board, too.

“I definitely think that we are going to get one of the shuttles,” Cowman says.

But other museums are equally convinced that they have the best proposal.

NASA has said the shuttles must be displayed indoors, so the Museum of Flight in Seattle is already building a huge new exhibit hall with glass walls — all that’s missing is the spaceship.

“Almost everybody that you can find says to me, ‘When are we going to get the shuttle? When are we going to hear about the shuttle?’ ” says Doug King, president of the museum. “It’s become a community event.”

And if his community is passionate, imagine how folks feel in Florida, where the space shuttles have been their pride and joy for three decades.

“Every launch of the space shuttle program left here from Kennedy, and more than half of those came back and landed here,” points out Bill Moore, head of the Kennedy Space Center Visitor Complex. It’s planning a $100 million exhibit that will suspend a shuttle in the air to make it look like it’s in orbit.

It’s only natural that a shuttle would retire to Florida, says Moore, who predicts that if the shuttles all go elsewhere, the local reaction would not be good.

“I think people would be beyond disappointed,” he says. “This would be a very emotional decision, were it not to be placed here.”

Other locations may not have such a long history with the shuttle, but they emphasize different assets.

NASA Administrator Charles Bolden will make the final decision after consulting with his aides, Sherouse says.

“All options are still available and on the table,” he says.

Bolden recently said he will make his announcement of the shuttles’ final destinations on April 12, the 30th anniversary of the first space shuttle flight.

The lucky museums will have to pay about $28.8 million to prepare and transport the shuttles, which could be ready to go about six to nine months after their final missions.