Discovery Launch A Day Earlier Than Expected; NASA Likely Can Execute Its Five Planned Space Shuttle Missions This Year, On Schedule
Satellites Colliding Raise Risk Of Catastrophic Damage To Space Shuttles, Officials Predict
NASA leaders think they have solved the threat of cracked flow control valves breaking and damaging fuel systems on Space Shuttle Discovery, so those senior officials cleared Discovery to launch at 9:20 p.m. Wednesday on the STS-119 Mission to the International Space Station.
Experts were able to “ensure that valves have a low probability of cracks,” much less problems withbreaking, Bill Gerstenmaier, NASA associate administrator for space programs, said in a press briefing. “We’re fully ready to go fly” in a nighttime launch that should light up Central Florida skies.
Concerns were raised when a flow control valve on Space Shuttle Endeavour was found to have broken off in a mission in November. Apparently, hydrogen fuel moving through the valves at high speed causes vibrations which can fatigue the valve metal. The fear is that if part of a valve cracks off, high fuel pressure will send it shooting through the fuel system like a bullet, leading to a possible fuel line rupture or other disaster.
To ensure that Discovery and other shuttles in future don’t lift off with cracked valves, NASA has a new way of checking them using a magnetic field around the circumference of each valve.
Valves on Discovery had a dozen flights on them, so the valves were pulled. While the three seemed sound using a skimming microscope, using the magnetic field inspection turned up cracking on one of the valves, which was replaced.
NASA experts reasoned it was safe to use these valves, since the space agency never saw sound valves crack and break in just one mission.
Further, even if a valve broke, only a tiny piece likely would break off or liberate, which would be very unlikely to damage the fuel lines plumbing, according to John Shannon, shuttle program manager. “We’ve flown many times with cracks in valves larger than those,” and no pieces have liberated, he said. But to be safe, now NASA isn’t going to fly with any cracked flow control valves.
Likely, on some future mission, a post-flight check will show that cracking began in a valve on that trip, and that will help NASA to redesign the valves so they have less danger of cracking, Gerstenmaier said.
An additional move, to brace elbows in the fuel lines against the impact of a broken valve particle, won’t be attempted on this mission, Shannon said, since that “extra margin” of safety isn’t seen necessary. Elbow bracing might be used on future missions.
Other than that, the shuttle is in good shape to launch, according to Mike Leinbach, launch director.
NASA Flight Schedule
Some questions at the news conference centered on whether NASA can complete all of its remaining scheduled space shuttle flights on the manifest, before the mandatory retirement of the shuttle fleet by Sept. 30 next year that former President Bush mandated and President Obama recently endorsed.
NASA can handle five shuttle flights a year, though that is at the upper limit of what the space agency can support, the officials said.
Gerstenmaier added that a possible additional shuttle flight — to carry the $1.5 billion Alpha Magnetic Spectrometer (AMS) experiment for installation on the space station — can be permitted to slip beyond the Sept. 30 deadline, lifting off as late as the end of December next year.
If that added mission isn’t flown, the AMS will remain uselessly on the ground, the $1.5 billion multi-nation effort wasted.
As for this STS-119 mission, if there were any last-minute glitches, it could be delayed all the way to next Monday, the 16th, and still be able to lift off for the space station, Gerstenmaier said.
Safety Backup For Atlantis
One question still unanswered concerns Space Shuttle Atlantis flying May 12 from Launch Pad 39A at Kennedy Space Center, on a servicing mission to the Hubble Space Telescope.
The question is whether Space Shuttle Endeavour, which must meanwhile be ready to fly to the rescue if Atlantis develops a problem, must be sitting on Launch Pad 39B, or whether Atlantis can be permitted to take off, and Endeavour then would go to Pad 39A.
Assuming no rescue mission is required, Endeavour later in May would lift off from Pad 39A on the STS-127 Mission to the space station.
“We’ve got to decide whether we’re going one single pad, or dual pad” when Atlantis takes off, Gerstenmaier said. A decision must be made soon, he said.
A complication is that the first flight of the Ares I rocket, called Ares I-X, is set for July 11, and the Orion-Ares next-generation U.S. spacecraft system being developed to succeed the shuttles needs to begin taking over facilities that shuttles have used.
Finally, the NASA officials were asked how much new danger has been added to space shuttle flights by deadly debris created when two satellites collided recently: an Iridium Satellies LLC spacecraft and a defunct Russian intel bird. (Please see Space & Missile Defense Report, Monday, Feb. 16, 2009.)
Gerstenmaier said the odds of a catastrophic collision were “still the same” as an earlier estimate: the collision itself raised odds of debris causing catastrophic damage to a shuttle by 6 percent, and other orbiting debris raised the probability of a catastrophic collision further, for an overall 8 percent increase in likelihood of disaster.
However, looked at another way, Shannon saw a one in 318 chance of such as mishap, which he said is comparable to threats facing typical 14-day missions to the space station.
In the Discovery mission lifting off Wednesday, Air Force Col. Lee Archambault will lead the crew of STS-119, and Navy Cdr. Tony Antonelli will serve as the pilot. Mission specialists for the flight will be NASA astronauts Joseph Acaba, John Phillips, Steve Swanson and Richard Arnold, and Japan Aerospace Exploration Agency astronaut Koichi Wakata.
Wakata will remain on the station, replacing Expedition 18 Flight Engineer Sandra Magnus, who returns to Earth with the STS-119 crew. He will serve as a flight engineer for Expeditions 18 and 19, and he will return to Earth on shuttle mission STS-127.
STS-119 is the 28th shuttle mission to the space station. Discovery also will carry the S6 truss segment to the orbital outpost. That will include a solar array that will bring the space station up to full electrical generation capacity.