Countdown resumes for space shuttle launch Tuesday

By Irene Klotz

CAPE CANAVERAL, Fla. (Reuters) – NASA restarted its
countdown clocks on Saturday in preparation for a second
attempt to return its space shuttle fleet to flight following
the 2003 Columbia accident.

“We are all eagerly looking forward to a successful
launch,” said NASA test director Pete Nickolenko.

Liftoff of space shuttle Discovery is targeted for 10:39
a.m. (1439 GMT) on Tuesday. The seven-member crew arrived at
Florida’s Kennedy Space Center on Friday for final flight
preparations.

NASA had planned to launch Discovery on July 13 but a
critical fuel sensor failed a routine preflight test and
managers called off the flight.

After more than a week of tests, engineers were unable to
duplicate the glitch but did find some slight problems with how
some parts of the sensor system were electrically grounded.
Technicians made adjustments to three groundings.

Attempts to trace possible electromagnetic interference so
far have not been successful, but NASA plans to continue tests
once the shuttle’s fuel tank is filled with 500,000 gallons
(1.89 million litres) of cryogenic liquid hydrogen and liquid
oxygen on launch day.

“The battery of testing and analysis that we’ve done so far
leads us to believe we are confident that we’ve got good
sensors,” Nickolenko said. “The true proof will be when we
perform the tanking operation for the launch attempt Tuesday
morning.”

The shuttle fleet has been grounded while NASA modified the
ship’s external fuel tank, which investigators determined was
responsible for the Columbia accident.

A piece of foam insulation fell off Columbia’s tank during
launch, striking and damaging the ship’s wing. When the shuttle
tried to return to Earth for landing on Feb. 1, 2003,
atmospheric gases blasted into the hole, tearing the ship
apart. All seven astronauts aboard were killed.

The sensor that failed during NASA’s first launch attempt
this month is one of four identical devices that the shuttle’s
main computers use to determine if the hydrogen fuel tank is
dry.

If two of the four sensors register dry, the computer would
shut down the shuttle’s three main engines to avoid the
potentially catastrophic situation of having the motors run
without fuel.

An engine shutdown before the shuttle reached its intended
orbit, however, could force a risky emergency landing, or leave
Discovery in an orbit too low to reach the International space
Station for docking.

The shuttle is to spend a week at the orbital outpost for
NASA’s first re-supply and servicing missing since before the
Columbia accident.

The main goal of Discovery’s flight is to check that post-
Columbia safety upgrades, including modifications to the
external fuel tank, are successful.

Meteorologists on Saturday predicted a 60 percent chance
weather conditions would be acceptable at launch time on
Tuesday, said shuttle weather officer Kathy Winters.