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."
Other
challenges
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.
advertisement
