NASA's is aiming for a May 10 target to launch its next space shuttle flight - the second tofly since the Columbia accident - though much work remains before the missionlifts off, the agency's shuttle chief said Tuesday.
Space shuttleprogram manager Wayne Hale told reporters that he is "optimistic" NASA's STS-121shuttle mission will lift off this May based on ongoingwork to prepare the Discovery orbiter and its fuel tank for flight.
"As oftoday 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). "Thereis a lot of work that needs to be done."
An "aggressive"effort is underway to reach STS-121's current launch window, which runs throughMay 22, though a significant, time-consuming glitch could push the flight intoJuly, NASA officials said.
Much of thework remaining involves the verification of external tank modificationsaimed at preventing potentially harmful chunks of foam from separating during launchand striking the orbiter's heat shield.
Accordingto video from NASA's first post-Columbia accident flight - STS-114 also aboard Discovery -a total of 16pieces of foam separatedfrom the orbiter's fuel tank during its July26, 2005 launch, including a large chunk from a protectiveramp that was previously believed to be safe, according to a NASA report.
The problemwas similar to one which doomed the space shuttle Columbia and itsseven-astronaut crew in early 2003. A briefcase-sized piece of foam fell from thatorbiter'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 thecraft on Feb. 1, 2003.
Engineerswere able to remove about 37 pounds (16 kilograms) of foam in a pair ofProtuberance Air Load (PAL) ramps from ET-119 for the STS-121 flight. Butengineers are awaiting results from a string of ongoing wind tunnel tests toverify the fix will not compromise fuel tank integrity, since PAL ramps weredesigned to shield pressure and fuel lines from the air pressures at launch.
Study isalso underway to determine how much material can be shaved from ice frostramps, each covered in about 1.5-pounds (0.6-kilograms) of foam, that runvertically along the external tank, Hale said.
Tim Wilson,NASA's external tank tiger team lead for the agency's Engineering and SafetyCenter, said his group is watching over the agency's fuel tank preparations.
"Foam willstill come off the tank after we've done all these mitigation efforts," Halestressed, adding that pieces the size of a matchbox or smaller are expected. "Webelieve the pieces will be small."
If theDiscovery's STS-121 launch, commanded by veteran astronaut StevenLindsey, goes as expected, NASA could launch two additional orbiters laterthis year, Hale added.
"It doesdepend on what happens on those flights," Hale said. "I am very optimisticthat, if we can fly in May or July, that we can get three flights up in thisyear."
NASA launchdirector Michael Leinbach said there other, non-foam related challenges alsofacing Discovery's STS-121 flight.
Shuttle workersfound that main engine seals used for Discovery's three main engines are not asthick as specifications call for. While they passed leak checks, study isongoing to ensure their flight worthiness, Leinbach said. The seals could bereplaced without detaching Discovery's engines, he added.
Engineersalso found a small metallic particle on a filter that leads into an enginevalve. Analysis has shown it to be too small to clog up any plumbing downstreamit shake loose, but shuttle officials are concerned it may provide an ignitionsource for the volatile liquid oxygen used during launch.
"We'vetried to remove the particle and we can't get it out," Leinbach said, addingthat engineers have attempted using a bore sight instrument to extract the particlethrough test ports.
Analysis isongoing to determine whether the engine will have to be opened up - which couldrisk even more contamination - for cleaning, or if the particle can be left asis, he added.
Anyextensive unplanned change or modification could push Discovery's flight outsideof its May launch window into July, where a lift off could occur between July 1and July 19.
"If we runinto 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'spreflight schedule. "Barring the big gotcha in processing, we're confident wecan make May."
Nextfuel tank on the way
Leinbachsaid shuttle workers are eager to greet Discovery's external tank, which shippedout 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 1:00p.m. EST (1800 GMT) Wednesday.
"We're justreally glad to get another piece of flight hardware here and to get on with themission 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