The Tomorrowland Transit Authority will be closed from April 14 through August 19, 2009. This is almost certainly an effect of the Space Mountain refurbishment.
The Tomorrowland Transit Authority will be closed periodically during the renovation of Space Mountain. Exact dates have yet to be announced.
Disney has recently filed a permit to fabricate and install new metal railings for the Tomorrowland Transit Authority attraction. The attraction is rumored to close along side Space Mountain because of it’s integration into that ride’s building.