Open to the public if you have some sort of business affiliation (working for a company, or something in the field).
I would imagine that there are parts of it that are invite-only, but the main floor is pretty much open. Hurry though, since I think it's the last day today. It really is a great experience - more fun than Paris or Farnborough since you actually get to sit inside some of the planes (or at least you did last year).
7 billion, one nation, imagination...it's a beautiful day