DWARDS AIR FORCE BASE – Space shuttle Discovery is tentatively scheduled to leave California on Friday, more than a week after it was diverted to the Mojave Desert in the first shuttle flight since the Columbia accident. Discovery's cross-country ferry to Cape Canaveral, Fla., expected to cost at least $1 million, has been postponed twice – first because of Monday's thunderstorms, then because of problems Wednesday in trying to attach a 10,000-pound aluminum tail cone to the shuttle to eliminate drag during flight.