The postponed launch of the space shuttle Endeavour on Friday was not only disappointing for the thousands of spectators that flocked to the Florida coast to see the historic liftoff; the delay also carries a large price tag, NASA officials say.

"It's the cost of propellant," NASA spokesman Allard Beutel told "We capture most of the propellant back, and recycle it and use it again, but some of it gets boiled off. The propellant is really the cost."

Ground crews had to drain the propellant from the shuttle's massive external fuel tank. Beutel estimates that this de-tanking process costs approximately $500,000. NASA now expects the next launch of Endeavour to occur no earlier than May 8