I don't think that the opening of Mission:Space will have anything to do with the Columbia tragedy. I think that was just an obvious rumor that someone came up with. On the contrary, Columbia was a tragedy, but space exploration will go on, and must go on. It is the best way to honor those who parished.
As for the ride, it has been delayed several times due to technical issues. The latest word that I have heard is that a few people are being randomly selected to go on the ride and give their comments to WDW Imagineering. Supposedly, they have one ride vehicle working at this point and it is being used occasionaly for that.