CAPE CANAVERAL - NASA's
first shuttle mission since the Columbia
accident will be delayed until July because of fears that ice could shake free
from Discovery's external fuel tank, triggering another deadly disaster.
NASA halted launch
preparations at launch pad 39B on Thursday. Discovery will be hauled back to
the Vehicle Assembly Building
to fix the 15-story fuel tank as early as next week, according to a NASA
official familiar with the decision. NASA will announce the decision today.
The extra time also will
allow NASA to deal with other technical problems that have cropped up recently
at the pad.
"I don't think we're
ready to fly yet," the official said. "Is it disappointing? Yes. But
is it the right thing to do? Yes."
NASA had hoped to launch
Discovery on a test flight to the International Space Station during a 13-day
window that extends from May 22 to June 3. The agency now will target liftoff
during the next available launch period, which extends from about July 14 to
July 31.
NASA engineers this week
completed a review of debris sources on the external fuel tank, which was
redesigned after the Columbia
accident and holds about 500,000 gallons of supercold
propellants.
Three areas remain a
concern, including a 70-foot long liquid oxygen propellant line that runs along
the outside of the tank. Engineers fear that ice could build up near the top of
that line, break free during launch and smash into the orbiter's heat shield.
Columbia and its seven astronauts were lost in 2003 when a
1.6-pound wedge of foam insulation broke free from the shuttle's external tank,
punching a hole in the left wing. The breach enabled hot gas to get inside the
ship during re-entry, and Columbia disintegrated
above Texas.
The foam wedge has been
replaced by a heater system. NASA has modified foam insulation in several other
areas of the tank, including the 17-inch wide propellant pipe. The changes
around the pipeline were designed to keep condensation from pooling and
freezing into large chunks of ice.
Ice dangers persist
Data from a recent
fuel-loading test showed significant amounts of ice still could build up near
the top of the pipeline in humid weather, NASA deputy shuttle program manager
Wayne Hale told reporters last week.
"We will not launch if
we think there is a concern for an unacceptable amount of ice to hit the
orbiter," Hale said.
NASA planned to add a heater
to the propellant line to eliminate the problem, but that modification was not
expected to be ready until the third post-Columbia flight, which is scheduled
for December.
This week, workers at the Michoud plant outside New
Orleans began installing a pipeline heater on the tank
slated for the third flight, although some qualification tests remain, Lockheed
Martin spokesman Marion La Nasa said.
NASA will either install a
pipeline heater on Discovery's tank or replace the tank with another that is
equipped with one of the devices. That work can't be done at the launch pad. It
must be done in the assembly building.
NASA also is wrestling with
other technical problems:
Engine
cutoff sensors
Sensors that serve the same
purpose as an automobile gas gauge did not work during a recent external-tank
fueling test. Engineers still don't understand why the sensors acted erratically,
said Jessica Rye, a Kennedy
Space Center
spokeswoman.
The sensors gauge the amount
of propellant left in the 15-story tank during a shuttle's climb to orbit. They
also are designed to shut down the shuttle's three main engines if they sense
the tank is out of fuel.
A malfunctioning sensor
could trigger a premature engine shutdown in flight, which could force
astronauts to attempt a risky and unprecedented emergency landing at either KSC
or overseas runways.
"We would not launch if
they were not working," Hale said last week.
Heat-shield blankets
During routine launch preps,
hydraulic fluid dripped on launch pad equipment. High winds then blew the oily
fluid onto thermal protection blankets that cover hump-like engine pods on the
tail of the orbiter.
NASA might have to replace
the blankets, a time-consuming job.
The postponement raises
questions about whether NASA can complete two test flights in time to resume
construction of the space station as planned in December.
Daylight launches
The space agency aims to
launch its next two flights during daylight and at times when the external tank
will be jettisoned on the sunlit side of Earth. The idea is to capture clear
pictures of any launch debris and to make sure changes to the external tank were
successful. The windows that opened in May and July meet those requirements.
The next available window
after that is in September, but the scheduled launch of a fresh crew to the
station on a Russian rocket that month could narrow the available shuttle
launch period to a mere five days.
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