CAPE CANAVERAL -- NASA
engineers think they have pinpointed the cause of dangerous hydrogen leaks that
prompted back-to-back launch scrubs for shuttle Endeavour, and they plan to
conduct a fuel-loading test by the first of July.
Shuttle program managers,
meanwhile, said they think the problem can be repaired in time to proceed with
a launch attempt scheduled
for July 11.
"They have good
confidence that they know what the problem is and how they can fix it,"
Kennedy Space Center spokeswoman Candrea Thomas said Saturday.
Endeavour and its seven
astronauts have to launch no later than July 14 to get to the International
Space Station and complete a complex assembly mission before the arrival of a
robotic Russian space freighter carrying critical supplies.
A delay past July 14 would
push the launch to July 27 and have a significant ripple effect on a station
assembly mission set to launch Aug. 18 on shuttle Discovery.
"Obviously, there
would be a downstream impact," KSC spokesman Allard Beutel said.
Significant leaks of
gaseous hydrogen from a line that vents the substance from the shuttle's
external tank prompted NASA to scrub a June 13 launch attempt, as well as a
second try Wednesday.
Some cryogenic liquid
hydrogen, which is minus 423 degrees Fahrenheit, always "boils off"
-- or changes to a gaseous state -- during fueling.
The vent line maintains
proper pressure levels within the tank by carrying excess gaseous hydrogen to a
flare stack about 1,000 feet from the shuttle. There, the highly flammable
substance is safely burned off.
Thomas said engineers think
a slight misalignment between the line and a carrier plate that connects it to
the external tank is causing an internal Teflon seal to pull out of place,
creating a path for the leaking hydrogen gas.
Engineers think technicians
can fix the misalignment and install an alternative seal that would provide a
tighter fit and stop the leak.
Technicians this weekend
are taking exact measurements of the misalignment. Next week, they will
disassemble the vent line, the carrier plate and a quick disconnect valve that
enables the line to separate from the tank at liftoff.
The plan then calls for
technicians to try to correct the misalignment and install an alternative seal
before a fueling test near the end of the month.
Engineers will load more
than 500,000 gallons of super-cold liquid hydrogen and liquid oxygen into the
shuttle's 15-story external tank.
Leak rates will be
measured, and if they are within engineering specifications, NASA will press
ahead with plans to get back into a countdown posture and make another launch
attempt July 11.
"It's a confidence
test," Beutel said.
The launch-scrubbing leaks
on Endeavour were nearly identical to one that caused a delay for a Discovery
mission in March. That time, however, a swap of seals allowed NASA to load
Discovery's external tank and proceed with a mission to deliver a fourth and
final set of massive American solar wings to the station.
A Russian Progress cargo
carrier is slated for launch July 24 on a station supply mission. The unmanned
freighter can loiter in orbit for five days but must dock at the outpost no
later than July 29.
Endeavour consequently must
launch by July 14 to complete a 16-day mission and leave the station before the
Russian ship arrives.
Seven astronauts aboard
Endeavour plan to deliver the third
and final section of the $1 billion Japanese Kibo science research facility
to the station.
Published under license
from FLORIDA TODAY. Copyright © 2009 FLORIDA TODAY. No portion of this material
may be reproduced in any way without the written consent of FLORIDA TODAY.
advertisement
