If you want space flight then you are better off with another sim. MSFS has a hard alittude limit which I doubt they will ever change.
Try this sim out if you want realistic space simulation. Be warned however it's very realistic when it comes to the physics of flight and has an extremely steep learning curve. There's a very realistic Space Ship One and White Knight as well as a lot of historic add ons and some science ficiton space craft as well.
I've been flying it for longer than I have MSFS and it's a wonderful sim and best of all it's completely free. You do have to download another free program to get sounds. That can be found at the second link below.
Orbiter Space Flight Simulatorhttp://www.medphys.ucl.ac.uk/~martins/orbit/orbit.htmlOrbiter Soundhttp://orbiter.dansteph.com/