As part of the refurbishment, updates will be made to the queue, the track (though it will still follow the original layout) and the effects that are projected on the dark ceiling of the attraction, among other things.
This is the most significant refurbishment to Space Mountain in ten years.
In addition to Space Mountain, the popular Tomorrowland Transit Authority (or TTA), also known as the WedWay People Mover, closed today for a refurbishment. The TTA is expected to reopen sometime in the fall. This is no surprise as the TTA runs through Space Mountain, so there really was no way for Disney to keep the TTA open while major work takes place at Space Mountain.
With a major attraction (Space Mountain) and a minor attraction (TTA) now closed at the Magic Kingdom, it will be interesting to see how Disney attempts to deal with the expected increases at other major attractions like Big Thunder Mountain, Splash Mountain and Buzz Lightyear's Space Ranger Spin, which is the only real attraction left in Tomorrowland right now. I don't consider the Tomorrowland Speedway a significant attraction, and don't even ask me about Stitch's Great Escape. Tomorrowland's going to be a barren place this summer.
Hopefully these two refurbishments will go as planned and not go beyond Thanksgiving. We will have to wait and see.
By the way, guests may experience some additional temporary closures at times this summer, especially for the Walt Disney World Railroad as it may have to close to allow heavy equipment in and out of the Space Mountain area.