July 14, 2005

NASA engineers seek cause of shuttle problem

By Deborah Zabarenko

CAPE CANAVERAL, Fla. (Reuters) - NASA engineers searched on
Thursday for the cause of a fuel-sensor problem that kept space
shuttle Discovery from flying, delaying the first shuttle
mission since the 2003 Columbia accident.

The U.S. space agency called off Wednesday's
much-anticipated launch of Discovery less than three hours
before the scheduled mid-afternoon liftoff. The next attempt
could be on Saturday at the earliest, but first NASA must
figure out why the fuel sensor malfunctioned, and that could
take time.

Engineers' trouble-shooting meetings at Kennedy Space
Center in Florida began early on Thursday, with a closed-door
gathering of mission managers set for midday. Even after that,
a launch timetable may not be clear.

NASA has until July 31 to launch Discovery, a deadline
dictated by its planned rendezvous with the International Space
Station and a new requirement that all shuttle launches take
place during daylight hours.

If Discovery fails to launch this month, the next window of
opportunity begins Sept. 9. Any substantial delay after that
could threaten construction of the orbiting station and perhaps
the long-term plan to return humans to the Moon and eventually
to Mars and beyond.

NASA experts acknowledged that the sensor problem -- which
they described as an intermittent event with no obvious cause
-- represented a difficult challenge.

"It does at this stage remain an unexplained anomaly. It
reminds me of an old truck I owned with an intermittent
electrical problem," said deputy shuttle program manager Wayne
Hale. "Unexplained anomalies are the worst ones."


The faulty sensor is one of four that would cut off the
shuttle's three main engines if at least two showed that
hydrogen fuel was running low. A premature cutoff might damage
the engines, force the shuttle to make an emergency landing or
leave it short of its desired altitude.

Discovery's planned liftoff from Cape Canaveral marks the
first shuttle mission since its sister ship Columbia fell apart
over Texas on Feb. 1, 2003, killing all seven astronauts.

Falling foam from Columbia's external fuel tank had knocked
a hole in its wing at liftoff 16 days before. The shuttle
disintegrated when superheated gases tore into the breach on
re-entry into the Earth's atmosphere.

Delays caused by bad weather and technical problems have
bedeviled shuttle launches in the past. But this mission has
gained wider attention because the fleet of three remaining
shuttles has been grounded since the Columbia disaster.

NASA managers said their readiness to call off Wednesday's
scheduled launch even after Discovery's seven-member crew had
been strapped into the spacecraft reflected a new aversion to
risk in the wake of the Columbia disaster.

In addition to testing new safety measures and experimental
heat-shield repair techniques, Discovery will take much-needed
supplies and equipment to the space station.

The 16-nation space-station project has been on hold since
Columbia crashed because the U.S. shuttles are the only
spacecraft capable of lifting heavy components to orbit.

NASA aims to keep the shuttles flying until 2010 so the
station can be completed. The aging shuttles will then be
retired and replaced by a new generation of spacecraft.

While engineers worked to fix the hydrogen fuel sensor,
Discovery's crew, led by veteran commander Eileen Collins,
remained in Cape Canaveral to continue training flights.

Should the delay extend beyond Saturday, the astronauts
would probably return to Houston, NASA said.