After a hydrogen leak delayed last Saturday's planned launch of the space shuttle Endeavour, NASA announced this afternoon it has rescheduled its liftoff for Wednesday.

NASA announced on its Web site that the launch now is set for 5:40 a.m. EDT on June 17.

Because of the rescheduled shuttle launch, NASA had to push back the launch of two lunar satellites, the Lunar Reconnaissance Orbiter and the Lunar Crater Observation and Sensing Satellite. The satellites had been set to lift off together aboard an Atlas V rocket on Wednesday. That launch has been pushed back just a single day to Thursday between 5 p.m. and 5:32 p.m.

Saturday's launch of space shuttle Endeavour was called off a little less than seven hours before its planned 7:17 a.m. EDT liftoff Saturday. The launch was cancelled when a leak was detected in the gaseous hydrogen venting system outside the shuttle's external fuel tank.

Endeavour is set to carry a seven-person crew on a 16-day mission to expand the Japanese laboratory housed on the International Space Station.

NASA has called Wednesday's mission one of its most technical ever -- one that will call on the power of three separate robots. The complex mission will include five spacewalks, the use of three robotic arms, two robots working together and one that will actually "walk" across the outside of the space station.

Holly Ridings, lead space station flight director for the Endeavour mission, told Computerworld that as the astronauts begin their work outside the space station, a robotic arm will lift a 4-ton piece of the Japanese complex out of the shuttle's payload bay. This piece, dubbed a "front porch", will be permanently attached to the outside of the Japanese module. It is designed to hold its own payloads, as well as host experiments that need to be conducted in outer space.

Once the station's robotic appendage, called the big arm, extracts the porch from the shuttle, it will be handed off to the space shuttle's own robotic arm. While the shuttle's arm holds the porch, the station's arm will move itself about 50 feet down the length of the space station by basically moving much like a child's Slinky toy.

Ridings explained that either end of the big arm can be used as the base, just as either end can be used as a gripping hand. Once the arm hands off the porch, it's gripper end will swing over and attach to the space station and the end that was originally attached to the station will let go and free itself to be the gripping hand.

Ridings said the robotic arm has several redundancies built into its software so five to seven things would have to go wrong for the arm to lose its grip on the space station and float away into space.

Once the arm has completed what NASA calls its "walkoff," it will reach out and take back the porch and move it into place against the Japanese module. The porch then should automatically attach itself.

The robotic arms are slated to conduct seven similar hand-offs between the two arms during the mission.

Meanwhile, there is a third robotic arm attached to the Japanese module that will be used for the first time next week. The arm, installed at the station in June, 2008, will pick up and move payloads to the porch.