There is a full-scale shuttle mockup in Houston that had "Explorer" as its name, but it is being re-christened due to an unrelated series of events on Saturday (Oct. 5).
But it may have also been that Explorer wasn't always the intended name for the film's orbiter. The hint to this comes from the movie's soundtrack.
Each of the tracks from composer Steven Price's spatial score are titled to correspond with the scene in "Gravity," which in several cases translates to just the name of the spacecraft. For example, track seven is "I.S.S." and track 13 is "Soyuz."
Track four, which is the music that accompanies Kowalski and Stone as they return to their badly damaged shuttle is not titled "Explorer" but rather "Atlantis."
Atlantis was NASA's final space shuttle to fly in space.