Complex sentence: Mojave Spaceport has been a test site for several teams in the Ansari X Prize, most notably SpaceShipOne, which conducted the first privately funded human sub-orbital flight on June 21,2004.
Split into simpler sentences: Mojave Spaceport has been a test site for several teams in the Ansari X Prize, most notably SpaceShipOne. The "spacecraft" performed the first privately funded human sub-orbital flight on June 21,2004.