This is one of my favorite things to do in FSX, going up into low orbit, then preforming a manual reentry. Here is a simple
How-To Guide for doing this:

1) Download a Sci-Fi ship, or spacecraft (Go into FSX>Misc do find these)

2) Find a nice open area (i.e. Area 51)

3) take off, only about 20 - 40% power for this.

4) go full-power, then nose up.

5) keep nose between 75 and 85 degrees

6) at about 400k - 600k ft, you will lose control

7) after you lose control activate the autopilot, that will keep you stable for longer

8) lower power, you are now in orbit

9) when you want to get down cut power and slowly descend

10) when you re-enter try to keep the nose down and fire full engines

11) land normally (Or VTOL depending on you spaceship)

and that's it, my current record is 800,000 ft. tell me if you get higher (without slew)