NASA has considered the possibility of bringing Hubble back to be exhibited at the Smithsonian, but there are two main reasons why this is not considered feasible.
First, Hubble was specifically designed to function with the space shuttle. Since the shuttle program is expected to be retired in the near future, and Hubble is expected to function at least until 2014, no shuttles will be available to bring it back. Second, shuttle missions have risks, and while everyone would like a museum exhibit, it's not a worthwhile risk to send astronauts out for that sole purpose. The last visit to Hubble is expected to take place via an robotic spacecraft, which will attach a propulsion module to the telescope to guide it through its de-orbit.
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