Posted for "Neal Garvin" <nrgarvin@comcast.net>:

 The answer is so simple it's ingenious. It has no pressurization system or
 pressure control system as we typically know them.  The spaceship is sealed
 up on the ground (or perhaps at 5000') and the pressure never escapes as the
 OAP drops to nearly zero.  Onboard oxygen tanks supply oxygen to the pilot
 for the short duration flight.
 
 SpaceshipOne is a beautiful example of an ingeniously engineered design that
 is just enough and no more to meet the mission profile. The cockpit door
 doesn't even have a latch. It's just 'stuck" in place with Velcro or
 something and differential cabin pressure holds it shut tight and sealed.
 
 Rutan and his team had a lot of luck with them and they took very
 significant risks. Risks that you or I or most anyone else would not accept
 or allow Boeing or other "government" entities to take relative to our
 public transportation system and vehicles. That's why new commercial
 airliners have hundreds of "CPUs" and multiple redundant systems in them. It
 reduces risk.
 
 Not many people would fly on a 757 who's cabin door was "velcro'd" shut!
 
 

"""
 The Lancair IVPs have a  5 PSI cabin differential.  Airlines have 8 PSI
 differentials.  SpaceShipOne is way up there in altitude, nearly zero
 atmospheric.  Yet he wasn't wearing a pressure suit during the flight.
 Inside an astronaut EVA suit, there's ~10.5 PSI (versus our
 14.5 PSI on terra firma).
 
 So, what is the cabin pressure differential inside SpaceShipOne?
"""