Here's a secret, sure-fire way to guarantee a ride on Mission:Space.... Wait until August 15.
I can niether confirm nor deny this rumor. General Cast Previews should be soon, but have not occurred yet.
I was followed by two creepy internet people with cameras when I went to ride last week. Not a good sign when soft openings have been announced already as being 2 months away.
Soft-soft-soft openings and cast-only previews are intended to help with training the cast, and if they end up with people camping out in front of the building or harrassing CMs, the surprise operations will almost definitely be cut short of canceled. Concern of overwhelming the newly-trained CMs is what led to by-appointment-only and no-guest Cast Previews for Rock 'n Rollercoaster and Millionaire. Go to Epcot, have fun, if you get to ride Space, Hooray! Think of it as icing, but don't plan a trip around it.