http://www.space.com/missionlaunches/050713_rtf_sts114_scrub.html
Sensor Glitch Scrubs Discovery Launch
By Tariq Malik
Staff Writer
posted: 13 July 2005
02:44 pm ET
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.
"It showed a state of low-level fuel, even though we know we aren't
low," NASA spokesman George Diller said. “It will take some time to
determine how long we will have to stand down.”
Launch officials have at least two more opportunities to launch
Discovery this week.
The first flight window opens on the afternoon of July 14, with a second
launch opportunity on July 16. However, should Discovery still remain
earthbound beyond that date, 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.
"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."
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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