The same leak which scrubbed last Saturday's launch attempt caused NASA to cancel this second attempt at 1:55 am EDT today.
The launch team halted fueling when the gaseous leak from the hydrogen fuel was detected. They then cycled the vent valve and began to see a smaller amount of leaking hydrogen. They then resumed and stopped the fueling again due to the continued leaking fuel.
The fuel loading of Endeavour's external fuel tank began at 11:06 pm Tuesday night - three hours later than planned - due to strong thunderstorms and lightning at the launch pad and around the space center. Lightning struck at least two areas around the space shuttle.
The seven member crew of mission specialists Christopher Cassidy and David Wolf, pilot Doug Hurley, commander Mark Polansky, and mission specialists Julie Payette, Tom Marshburn and Timothy Kopra, were dressing into their launch and entry suits when the scrub was called.
NASA and Endeavour's crew will now stand down until a possible next launch attempt on the evening of July 11.
NASA in the meantime has to go to work to troubleshoot what is the cause of this leak, and why has it scrubbed three shuttle launch attempts out of the last five tries. The launch team still does not have a firm understanding why this valve leak from the gaseous hydrogen vent connection continues to cause trouble.