NASA officials postponed the Space Shuttle Discovery launch Wednesday afternoon seven hours before it was scheduled to lift off for the International Space Station (ISS). While the skies over Kennedy Space Center remained clear Wednesday, crews discovered a leak in a liquid hydrogen vent line between the shuttle and an external fuel tank. (See: Space shuttle Discovery to lift off tomorrow)
Discovery's liftoff originally was targeted for 12 February, but concern about its three hydrogen gas valves resulted in four delays. The latest failure was in a different part of the system that already had caused a vexing one-month delay.
Shuttle managers put off the launch until at least Sunday and indicated that Monday might be more likely. The latest delay means Discovery's two-week flight must be shortened and some spacewalks cut out of the mission. That's because Discovery needs to be gone from the space station before a Russian Soyuz rocket blasts off 26 March with a fresh station crew.
If Discovery isn't flying by Tuesday, it will have to wait until April. That almost certainly would bump the succeeding space shuttle missions as well as plans to double the size of the space station crew at the end of May, said Mike Moses, chairman of the mission management team.
Mission Control radioed the news to the three space station residents Wednesday evening. Commander Mike Fincke took it in stride, saying he'd rather see the shuttle this month than next. "But more importantly, we'd rather see it up safely, so we understand," Fincke said.
Other members of the crew include will be Commander Lee Archambault, Pilot Tony Antonelli, Mission Specialists Joseph Acaba, John Phillips, Steve Swanson and Richard Arnold. They're joined by Japan Aerospace Exploration Agency astronaut Koichi Wakata who'll remain on the ISS. NASA does not want a shuttle at the space station at the same time as a newly arrived Soyuz because of the tremendous workload it would put on all the crews.
The gaseous hydrogen began leaking just as the launch team was close to wrapping up the loading of Discovery's external fuel tank for a late-night liftoff. The seven astronauts had yet to board the spaceship.
Launch Director Mike Leinbach explained yesterday "the leak developed on the piping that runs from the fixed service structure, or launch tower, to a valve at the intertank section of the shuttle's external tank".
The agency elaborates: "The pipe moves hydrogen gas away from the shuttle and to a flare stack near the launch pad that burns it away safely. He said there was never any danger to the shuttle while it was being fuelled, but that the leak allowed too much gaseous hydrogen to escape the vent line."
Engineers won't know exactly what's wrong until they are able to reach the area Thursday afternoon. Leinbach said he's "99.9 per cent sure" that the problem is not in the tank itself but in the outside connections, which makes for an easier, quicker repair.
Officials acknowledged it was a huge disappointment, especially coming on the heels of all the earlier delays.
"Let's be honest. We'd rather be launching than scrubbing," Leinbach told reporters. "But our business requires perfection, and our vehicle is not perfect today and so we're going to stand down. We're going to fix the vehicle and fly when it is perfect."
Shuttle managers said they're convinced after extensive testing that the valves in Discovery's engine compartment are safe and won't break like one did during the last shuttle launch in November. These valves - part of the main propulsion system - control the flow of hydrogen gas into the fuel tank in order to maintain proper tank pressure.
Tucked aboard Discovery is 31,000 pounds of framework that holds two folded-up solar wings and a radiator. The space station already has six electricity-producing wings; the two going up will be the last ones and elevate the orbiting outpost to full power.
Four spacewalks had been planned for the shuttle mission. Moses said much of that work could be handed off to the space station crew, after the shuttle leaves, in order to get the solar wings up this month and avoid the logjam that would be created if Discovery has to wait until April.
NASA will consider the mission a success as long as the astronauts can deliver and install the solar wings, drop off a new urine processor for the space station's water-recycling system, and carry out a space station crew member swap.