I was a little surprised (but, as a European, chuffed!) that this is launching on Ariane 5. I would have thought that Falcon 9 would be cheaper, and Atlas V would be preferred as a way of keeping it in-house. I believe they both have the capacity needed. Maybe Falcon 9 wasn't sufficiently proven when the deal was done, and Atlas V was more expensive?
In my head, JWST was a NASA project (James Webb was an early director of NASA, during its formative years). I had completely blanked the fact that it's an international project, sorry!
