Space shuttle
engineers have no worries over the planned swap out of the Discovery orbiter's
external tank this month, a major step forward in NASA's first return to flight mission.
"I have
every confidence that the process will go smoothly," said Tim Riley,
integration operations chief for United Space Alliance (USA), NASA's prime
contractor for its shuttle fleet.
Riley's
team and a host of other engineers and technicians are preparing to exchange
Discovery's fuel tank with a replacement equipped with an extra heater to limit
ice
debris hazards to the orbiter during launch.
Discovery's
STS-114 mission, commanded by veteran astronaut Eileen Collins, is slated launch
spaceward from Pad 39B no earlier than July 13 of this year. The orbiter is
NASA's first shuttle to fly since the loss of Columbia and its seven-astronaut crew
during reentry on Feb. 1, 2003.
NASA
officials pushed back Discovery's
launch from a May 22 target to allow time for additional ice debris tests and
the tank change out.
Switching
tanks
It is
actually the orbiter that moves between external tanks, not vice versa, Riley
told SPACE.com.
During the
process, technicians will detach Discovery from its perch alongside its current
154-foot-tall (46-meter-tall) tank, and hoist it over the launch stack towards
a different work bay. There, the external tank for Discovery's follow-up
mission STS-121 aboard Atlantis, is awaiting its new spacecraft.
"Once we
get the [Discovery] back into the bay, it's roughly a five-day process," Riley
said. "It's pretty straightforward then."
Discovery
and its launch stack are expected to cross the 4.2 miles (6.7 kilometers)
separating the launch pad and 52-story VAB next week, NASA officials said
Wednesday. The move will follow a May 20 fueling
test of the current tank, they added.
The tank swap
will mark the eighth time a NASA space shuttle launch stack has been rolled
back into the VAB for a partial or complete disassembly. Technicians most
recently adjusted a shuttle launch stack in 2003, when they destacked the
launch system for the Atlantis orbiter, Riley said. At that time, Atlantis was
expected to carry the STS-114 crew into orbit in March 2003.
Increasing
safety
The driving
force behind Discovery external fuel tank swap is launch and crew safety.
In 2003,
investigators traced Columbia's destruction back to wing damage caused by a
suitcase-sized chunk of foam insulation that separated from the tank's bipod
ramp, where an orbiter connects to a fuel tank, and struck the shuttle during
launch. NASA has since redesigned
shuttle external tanks to replace bipod ramp foam with a heater at the.
But last
month, shuttle managers announced that ice forming on an external tank's bellows
unit, which expands and contracts in response to supercold fuel, could pose a similar
danger to Discovery if it strikes the orbiter during the high speeds of launch.
The new
heater, combined with a drip lip modification to the bellows unit, should limit
that risk, NASA officials said. Heater kits arrived on May 5 for both the
STS-121 launch - which will feed Discovery's main engines in July - and for
ET-120 currently attached to the STS-114 launch stack, they added.
"The heater
is here and they're doing the work on it," said USA spokesperson Tracy Yates.
Despite
Discovery's launch delay, NASA's push to return its shuttle fleet to flight
status is a step forward for the U.S. space program, USA officials said.
"The return
to safe flight brings me great satisfaction in that we faced the adversity of
[Columbia's] tragedy and recovery as a team, and together carried out the
rigorous and responsible plan for getting back into the business of
spaceflight," USA president and CEO Michael McCulley said in an e-mail
interview. "We can now focus our energy and talents on safe, successful
missions."
Shuttle
integration crews may also benefit from the upcoming tank change operation, since
it calls for additional hands-on work with flight hardware, which keeps
technician skills fresh.
"It
certainly has values in that respect," Riley said. "The guys jump at any
chance, whether we're mating or de-mating hardware, to work with an orbiter."
First
things first
Before
Riley and his team can carry out Discovery's external tank swap, they must first
wait for NASA to put the orbiter's current tank through its second fueling test.
Launch managers
hope the May 20 tanking test, which will fill Discovery's external tank with
more than 500,000 gallons (1.9 million liters) of liquid oxygen and liquid
hydrogen fuel, will shed light on sensor and valve questions
raised in the initial April 14 test.
In the
meantime, Riley and other shuttle technicians will prepare for Discovery's
rollback by conducting maintenance on the orbiter lifting swing that hoists shuttles
about the VAB, as well as other equipment used to support the vehicle during
transfer operations.
"I am
extremely eager to see it fly," Riley said of Discovery. "I am even more eager
to see it land [back] here."
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