Adler may get Atlantis, Discovery or Endeavour

May 20, 2010 (CHICAGO) Paul Knappenberger said NASA has narrowed it down to 21 planetariums and museums in the U.S. Those institutions are all capable of raising the estimated $28.8 million needed to exhibit one of the retired shuttles correctly and offer the best access to the public.

NASA will not decide on where the shuttles will go until after the active orbiters- Atlantis, Discovery and Endeavour- have each made their final mission. Atlantis is currently on its final mission to the International Space Station. Two flights remain- one each for Discovery, which is scheduled to fly in September, and Endeavour, which would take off in November at the earliest.

Meanwhile, upon its return, Atlantis will be prepped as an emergency responder should something go wrong with either of the other shuttles' last missions.

NASA plans to end its 30-year shuttle program by the end of 2010, at which time American astronauts would hitch rides to the space station from Russia. NASA expects to keep the space station running through 2020.

Learn more about the shuttles:

Discovery

Atlantis

Endeavour

The Associated Press contributed to this report.