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 Simulator

http://www.medphys.ucl.ac.uk/~martins/orbit/orbit.html

Orbiter Sound

http://orbiter.dansteph.com/

X-Plane does orbital altitudes also.  I do know its far better flying the SR-71 in X-Plane than in MSFS.  I had that baby high enough to loose control surface authority.  I think like 120k.  Lost the engines to.  It is possble to get a blackbird that high with a shallow dive at high altitude and then a sharp pull up at full throttle, you will just keep going up up up until the engines quit and you can no longer manuever. Also, the space shuttle scenario in X-Plane starts you at 80 something miles high just following the de-orbital burn and you have to hand fly the approach.  As yet, Austin Meyer still hasn't modeled the auto-pilot system for his shuttle.  It isn't real hard, just keep the box in the box and you will stay on track.  It even takes you on the zig zag pattern that is actually done to bleed off speed.  Final starts Somewhere over Midway at like 80,000 ft. and approach and landing is Edwards AFB.  Real challenge to keep from becoming a splat because the shuttle's threshold speed is over 200kts, its nearly as heavy as a 737, no power, and a very high wing loading. Lots of fun.