Make that 14, 7 each on Challenger and now Columbia. It's really too bad Enterprise was not made in such a way as to be upgradeable to space worthyness, but as I understand it, it wasn't. (In case someone doesn't know, Enterprise was the first shuttle, but it was only used for "drop tests", from the back of the same 747 they use to transport the shuttles back to Kennedy if they have to land elsewhere, usually Edwards. They did this with pilots in Enterprise, flying it back to the dry lake at Edwards.)