CAPE CANAVERAL, FL (AP).- As the 30th anniversary of the first space shuttle launch draws near, the focus is not so much on the past but the future: Where will the shuttles wind up once the program winds down?

Twenty-one museums and science and visitor centers around the country are vying for one of NASA's three retiring spaceships. They'll find out Tuesday on the 30th anniversary of Columbia's maiden voyage.

Snagging Discovery, Atlantis or Endeavour for display doesn't come cheap. NASA puts the tab at $28.8 million. Consider that a bargain. Early last year, NASA dropped the price from $42 million.

One space shuttle is already spoken for — the Smithsonian Institution is getting Discovery, NASA's oldest and most traveled shuttle that ended its flying career last month. It will go to the National Air and Space Museum's hangar in Virginia and take the place of Enterprise, the shuttle prototype used for tests in the late 1970s.

That frees up Enterprise for another museum, so there will be three other winners — a 1-in-7 chance.

NASA Administrator Charles Bolden Jr., a former shuttle commander, is making the final decision, with input from a committee. He'll announce the winners Tuesday while marking the 30-year anniversary at Kennedy Space Center, NASA's launch and landing site, and the front-runner in the nab-a-shuttle race.

The festivities could end up being delayed if the federal government shuts down.

As the big day looms, shuttle suitors are getting anxious and pulling out all the stops.

Even the prime contender, the Kennedy Space Center Visitor Complex, is jittery despite its "knock your socks off" endorsement from NASA's shuttle launch director. The commercially run tourist site wants to suspend the shuttle over visitors, with the payload bay doors wide open as if in orbit and the robot arm outstretched.

"We're extraordinarily nervous. We don't sleep much these days," Bill Moore, chief operating officer for the visitor complex, said this week. "Three of anything in the world, it's going to get awfully competitive. And three of the shuttles, I think, even raises the bar."

NASA originally had four space shuttles. Challenger was destroyed during liftoff in 1986, and Endeavour was built as a replacement. Then Columbia was lost in 2003.

Columbia was the first to fly on April 12, 1981, 20 years to the day that Soviet cosmonaut Yuri Gagarin became the world's first spaceman. Tuesday will mark the 50th anniversary of his flight.

Endeavour is set to soar late this month, and Atlantis will close out the shuttle program with a summer liftoff.

All this was set in motion in 2004 by President George W. Bush. President Barack Obama stuck to the shuttle-ending agenda, but canceled Bush's moon exploration plans, preferring to have NASA aiming for an asteroid and Mars while private companies take over taxi trips to and from the International Space Station.

Discovery, the first to be retired, should be ready this fall for its piggyback ride atop a modified jumbo jet to Washington. Before it can go on public display, the shuttle has to be drained of toxic fuel and contaminated plumbing removed. NASA also wants to pull out some pieces for analysis, to help in the development of future spaceships. No main engines will be included; they're available separately to museums for merely transportation and handling costs.

Community officials, from mayors to members of Congress, are making their final pitches to score a shuttle, just over two years after the initial call went out. Plans for exhibition halls are getting grander. Online polls are popping up, as well as online petitions. Astronauts are putting in their two cents' worth.

In Houston, home to NASA's astronaut corps and Mission Control, four widows and one widower of the fallen Challenger and Columbia astronauts are speaking out. They'd like shuttles to go to the Space Center Houston tourist stop next door to Johnson Space Center, Kennedy and the Smithsonian.

For the other bidders, "we suggest that NASA share with them some of the invaluable pieces of the shuttle legacy," the astronauts' spouses wrote in a letter to Bolden.

A main engine or other artifact wouldn't equal a shuttle, but the Tulsa Air and Space Museum and Planetarium in Oklahoma still would embrace it. Curator Kim Jones' dream would be to land Enterprise, which made an appearance in Tulsa in 1979.

"We're very hopeful. But yes, we're up against some big guns," Jones acknowledged Wednesday.

Some of the hot contenders: National Museum of the U.S. Air Force in Dayton, Ohio; Intrepid Sea, Air and Space Museum in New York City; Museum of Flight in Seattle; and Adler Planetarium in Chicago.

Officials at each institution are giddy over the extra ticket sales a space shuttle would generate.

"There are so many good choices across the country, so I don't really want any part and I'm not going to make a recommendation," Steven Lindsey, the commander of Discovery's final journey, told The Associated Press from orbit last month.

Lindsey hopes Discovery is displayed so the "entire public can see Discovery as we see her, and as the people who have worked on her at Kennedy Space Center see her."

The skipper of the last shuttle flight, Christopher Ferguson, is rooting for Houston. He'll fly Atlantis into orbit at the end of June on the 135th and final shuttle voyage.

"To me, this is the center of the human spaceflight universe," Ferguson told reporters last month at Johnson Space Center.

The $28.8 million price tag is based on NASA's estimate for transporting a shuttle from Kennedy to a major U.S. airport, atop a modified jumbo jet, and for displaying it indoors in a climate-controlled building. The cost will vary, depending on the locale. Kennedy's visitor complex, for example, is just five miles (8 kilometers) down the road from the shuttle hangar, a short tow trip.

"We're not quite sure how to pick it up over the guard gate," Moore said. "I told somebody today, I tell you what, we'll knock it down and build them a new one. It will still come out cheaper."

Copyright 2011 The Associated Press.