UPDATE: Story first posted 2:05 p.m. EDT
CAPE CANAVERAL - NASA flight
controllers scrubbed the planned launch of the space shuttle Discovery today
due to a glitch with the orbiter's external tank.
A
malfunctioning fuel level sensor in the orbiter's external tank forced flight
controllers to call off today's launch attempt of NASA's first shuttle mission
since the Columbia
disaster. The sensor is one of four required inside the external tank that monitor
fuel levels in order to shut down Discovery's main engines before the tank runs
dry.
Launch
officials reported that the external tank glitch occurred during a test of the
fuel sensor system, in which flight controllers direct sensors - which register
'wet' when the tank is full - to register as 'dry.' The faulty sensor failed to
register as 'dry,' launch officials said.
"It
will take some time to determine how long we will have to stand down," NASA
spokesman George Diller said.
Launch
officials have at least two more opportunities to launch Discovery this week.
"NASA
will launch when NASA is ready, and when they know when everything is ready,"
Sen. Bill Nelson (D-Florida) told reporters here. "Spaceflight is a risky
business, but it is an acceptable risk."
The
next launch date for Discovery opens on the afternoon of July 14, with a second
opportunity on July 16. However, should Discovery still remain earthbound after
that, pad engineers will have to remove the fuel reactants inside the orbiter. An approaching storm could also prompt launch
officials to rollback the orbiter to avoid damage from high winds, NASA
officials said, adding that such a situation would cause a longer delay.
There
are still two more weeks in Discovery's July launch window, which closes on
July 31.
Mission managers and
engineers are holding an ongoing technical meeting to discuss and assess the
situation, a spokesman said. NASA will hold a technical briefing for reporters
no earlier than 4:30 p.m. EDT (2030 GMT).
The
shuttle was slated to launch at 3:50:53 p.m. EDT (1950:53 GMT) from Launch Pad
39B here at NASA's Kennedy Space Center (KSC). The STS-114 crew, commanded by
veteran astronaut Eileen Collins, had already begun strapping into Discovery
when flight controllers called off the launch. The astronauts have disembarked
their spacecraft and are returning to their crew quarters.
"We
are disappointed, but we'll fly again on another day," said NASA test director
Jeff Spaulding. "There are a lot of long faces, but we can't let being anxious
interfere with our attention to safety."
The
external tank will have to be drained of its 526,000 pounds of liquid hydrogen
and liquid oxygen propellant before engineers can pin down the anomaly, NASA
officials said, adding that the process will take several hours. Loading the
tank took about three hours earlier today.
NASA
officials plan to conduct shuttle troubleshooting before they begin emptying
Discovery's external tank.
Discovery's
STS-114 flight is NASA's first shuttle launch since 2003 accident that claimed
the lives of seven astronauts and destroyed the space shuttle Columbia during the STS-107 mission. Columbia was destroyed on
Feb. 1, 2003, as it reentered the Earth's atmosphere after a successful science
mission that began 16 days earlier.
But
launch debris from Columbia's external tank
separated at launch and struck Columbia's
left wing leading edge, fatally crippling the spacecraft's vital heat-resistant
skin. During reentry, hot gases entered the hole from that collision and led to
the orbiter's destruction.
Discovery's
external tank has been touted by engineers as one of the safest tanks ever
built for the shuttle program, and was redesigned in the wake of the Columbia accident to
reduce the amount of ice formation on the launch pad, as well as foam shedding during
liftoff.
During
an April fueling test with Discovery's first external tank, flight controllers
detected a sensor glitch which seems similar to that experienced today, though
the shuttle's current tank is a newer version. Discovery switched external
tanks in June. The current tank contains a heater that prevents the formation
of ice on a flexible bellows unit. Shuttle officials have never been able to
pin down the source of that anomaly, nor recreate it in simulations.
If
flight controllers are unable to launch Discovery this month, they could also
opt to push the spaceflight into the next shuttle launch window, which runs
between Sept.9-24.
That
launch window is currently allotted to the Atlantis orbiter and its STS-121
crew, slated to perform NASA's second return to flight mission.
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