CAPE
CANAVERAL - NASA faces a number of hurdles in its bid to return the shuttle
fleet to service, but managers are confident Discovery will fly in July.
Now
perched on Kennedy Space Center's launch pad 39B, Discovery is scheduled to
roll back to the Vehicle Assembly Building on Thursday for extra safety
modifications.
The
spaceship will be outfitted with a new external tank and then moved back to the
pad. The ultimate aim is to have Discovery ready for a test flight to the
International Space Station at the opening of a launch window that extends from
July 13 to July 31.
"We
roll back out to the pad in mid-June, and that sets us up fine for the
beginning of the launch window," said Mike Leinbach, a Scottsmoor resident
who leads the shuttle launch team.
"The
only thing that would change that is if we determine that we want to do some
other testing," added Bill Parsons, a Merritt Island resident and NASA's
top shuttle program manager.
Challenges
ahead include passing extra safety inspections and completing work on the
recommendations of the Columbia Accident Investigation Board.
Among
the unresolved issues:
NASA
is delaying Discovery's rollback so technicians can inspect mechanical linkage
that opens the shuttle's main landing gear doors and holds them in place.
A
small crack was found on the linkage on Atlantis' right main landing gear door,
and engineers want to make sure Discovery doesn't have the same problem. The
linkage on Atlantis is being replaced. No cracks were found on Endeavour.
Once
Discovery is back in the 52-story assembly building, technicians will remove
the shuttle orbiter from its external tank and attached solid rocket boosters.
On
June 7, the orbiter will be connected to a tank-booster set NASA had planned to
use on its second post-Columbia flight.
The
new tank is being outfitted with a heater designed to keep ice from building
around a 70-foot propellant line on the outside of the fuel-reservoir.
NASA
managers decided the heater is needed after a dangerous amount of ice formed on
the propellant line on Discovery's current tank when it was filled with
supercold liquid hydrogen and liquid oxygen during a mid-April fuel-loading
test.
Engineers
feared ice could break off during flight and damage the shuttle's heat shield.
A
1.7-pound chunk of external tank foam insulation blasted a six- to 10-inch hole
in Columbia's left wing, allowing hot gas to tear the ship apart during re-entry.
NASA
will decide by early June whether to conduct another tanking test before
clearing Discovery for launch.
An
initial test was done to check out safety changes that have been made to the
tank since the Columbia accident. A second test was carried out last week to
pinpoint the causes of valve and sensor problems that cropped up during the
first test.
Should
NASA decide another is needed, the planned July 13 launch likely would be
delayed a few days, Parsons said.
A
group of experts led by former astronauts Tom Stafford and Richard Covey must
complete an assessment of NASA's work to implement recommendations made by
accident investigators.
NASA
has finished work on seven of 15 return-to-flight recommendations, which range
from fixing the tank to providing astronauts with ways to make emergency
repairs in space.
The
group will meet with shuttle program officials the week of June 6 to review
work done on six of the recommendations. Work on the other two recommendations
-- fixing the tank and hardening the skin of shuttle orbiters -- is expected to
be complete by late June.
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