NASA's is aiming for a May 10 target to launch its next space shuttle flight - the second to fly since the Columbia accident - though much work remains before the mission lifts off, the agency's shuttle chief said Tuesday.
Space shuttle program manager Wayne Hale told reporters that he is "optimistic" NASA's STS-121 shuttle mission will lift off this May based on ongoing work to prepare the Discovery orbiter and its fuel tank for flight.
"As of today I see no reason to say anything other than we're progressing toward May," Hale said during a press conference at NASA's Kennedy Space Center (KSC). "There is a lot of work that needs to be done."
An "aggressive" effort is underway to reach STS-121's current launch window, which runs through May 22, though a significant, time-consuming glitch could push the flight into July, NASA officials said.
Fuel tank checks
Much of the work remaining involves the verification of external tank modifications aimed at preventing potentially harmful chunks of foam from separating during launch and striking the orbiter's heat shield.
According to video from NASA's first post-Columbia accident flight - STS-114 also aboard Discovery - a total of 16 pieces of foam separated from the orbiter's fuel tank during its July 26, 2005 launch, including a large chunk from a protective ramp that was previously believed to be safe, according to a NASA report.
The problem was similar to one which doomed the space shuttle Columbia and its seven-astronaut crew in early 2003. A briefcase-sized piece of foam fell from that orbiter's tank at launch and breached the heat shield along its left wing, allowing hot atmospheric gases to enter the hole during reentry and destroy the craft on Feb. 1, 2003.
Engineers were able to remove about 37 pounds (16 kilograms) of foam in a pair of Protuberance Air Load (PAL) ramps from ET-119 for the STS-121 flight. But engineers are awaiting results from a string of ongoing wind tunnel tests to verify the fix will not compromise fuel tank integrity, since PAL ramps were designed to shield pressure and fuel lines from the air pressures at launch.
Study is also underway to determine how much material can be shaved from ice frost ramps, each covered in about 1.5-pounds (0.6-kilograms) of foam, that run vertically along the external tank, Hale said.
Tim Wilson, NASA's external tank tiger team lead for the agency's Engineering and Safety Center, said his group is watching over the agency's fuel tank preparations.
"Foam will still come off the tank after we've done all these mitigation efforts," Hale stressed, adding that pieces the size of a matchbox or smaller are expected. "We believe the pieces will be small."
If the Discovery's STS-121 launch, commanded by veteran astronaut Steven Lindsey, goes as expected, NASA could launch two additional orbiters later this year, Hale added.
"It does depend on what happens on those flights," Hale said. "I am very optimistic that, if we can fly in May or July, that we can get three flights up in this year."
NASA launch director Michael Leinbach said there other, non-foam related challenges also facing Discovery's STS-121 flight.
Shuttle workers found that main engine seals used for Discovery's three main engines are not as thick as specifications call for. While they passed leak checks, study is ongoing to ensure their flight worthiness, Leinbach said. The seals could be replaced without detaching Discovery's engines, he added.
Engineers also found a small metallic particle on a filter that leads into an engine valve. Analysis has shown it to be too small to clog up any plumbing downstream it shake loose, but shuttle officials are concerned it may provide an ignition source for the volatile liquid oxygen used during launch.
"We've tried to remove the particle and we can't get it out," Leinbach said, adding that engineers have attempted using a bore sight instrument to extract the particle through test ports.
Analysis is ongoing to determine whether the engine will have to be opened up - which could risk even more contamination - for cleaning, or if the particle can be left as is, he added.
Any extensive unplanned change or modification could push Discovery's flight outside of its May launch window into July, where a lift off could occur between July 1 and July 19.
"If we run into a big gotcha, we won't have much time to resolve it," Leinbach said, adding under current plans there are no added contingency days in Discovery's preflight schedule. "Barring the big gotcha in processing, we're confident we can make May."
Next fuel tank on the way
Leinbach said shuttle workers are eager to greet Discovery's external tank, which shipped out Saturday from NASA's Michoud Assembly Facility in New Orleans, Louisiana.
The tank, NASA's first PAL rampless vessel to fly, will arrive at KSC by barge at about 1:00 p.m. EST (1800 GMT) Wednesday.
"We're just really glad to get another piece of flight hardware here and to get on with the mission process," Leinbach said.
- NASA to Ship Shuttle Fuel Tank
- Discovery Astronauts Check Shuttle for Return to Flight Mission
- NASA Nixes Foam Ramp for Next Space Shuttle Flight
- Return to Flight: NASA's Road to STS-121