Those hoping to end the week by watching the Discovery shuttle launch are out of luck. Though things were on track for a Friday launch just hours ago, a hydrogen gas leak has now delayed the launch until at least Monday, according to NASA.

"NASA shuttle managers have scrubbed today's launch attempt of Discovery's STS-133 mission due to a hydrogen gas leak," NASA tweeted this morning.

"Preliminary schedule is Monday at the earliest," the agency said about a half hour later. Space shuttle managers are scheduled to meet at 11am to discuss the schedule.

Just before 6am this morning, the shuttle team started the three-hour fueling process, which adds about 535,000 gallons of liquid oxygen and hydrogen to the shuttle. About two hours into the process, however, NASA reported that shuttle managers were evaluating "a gaseous hydrogen leak at the Ground Umbilical Center Plate (GUCP) that attaches to the external tank."

The GUCP carries gaseous hydrogen safely away from the shuttle to a flare stack, where it burns off, according to NASA.

Leaks and weather issues have delayed the shuttle launch several times throughout the week. The shuttle was initially scheduled to launch on Monday, but helium and nitrogen leaks in the pressurization portion of space shuttle pushed that to Tuesday. When repairs related to those leaks lasted longer than expected, NASA again delayed the launch to Wednesday. Electrical issues prevented launch on that day, however, while the Cape Canaveral weather marred a Thursday launch.