Many SPACE.com
readers have written letters asking about the white external fuel tanks that
fed NASA's first two orbiter test flights - STS-1
and STS-2 - and whether the paint job added any additional protection against
the type of foam shedding that led to the 2003 Columbia accident.
John
Chapman, NASA's external tank project manager at the Marshall Space Flight
Center (MSFC) in Huntsville, Alabama, said the white paint was initially added
to protect shuttle fuel tanks from the damaging effects of exposure to
ultraviolet rays during extended periods on the launch pad.
While tests
were unfinished as NASA prepared STS-1 for its maiden flight, engineers painted
the first two tanks to be on the safe side, Chapman said.
"Because
you just don't go up to the external tank on the pad with a can of paint and a
roller," Chapman told SPACE.com, adding that he, former shuttle tank
project manager Sandy Coleman and Kennedy Space Center (KSC) director Jim
Kennedy watched Columbia's April 12, 1981 launch
debut from the roof of a Winnebago the trio had driven to KSC with three
other coworkers from MSFC.
Subsequent
tests found that the paint wasn't vital for shuttle launches and it was
abandoned to free up weight - about 600 pounds (272 kilograms) - for additional
payload, NASA officials said.'
The paint
also did not prevent foam from popping free of Columbia's fuel tank during its
first two launches, Chapman added.
Following
the Feb. 1, 2003 loss of Columbia during reentry, which investigators found was
due to heat shield damage caused by tank foam insulation debris at launch, NASA
revisited the white paint approach, as well as a myriad other schemes to reduce
foam shedding.
But adding
additional protection measures, such as a nylon covering or chicken wire mesh,
could not only add another debris source during launch, but also lead to larger
pieces pulling free from anchored spots, Chapman said.
"The
biggest thing for us would be to make sure that anything we do doesn't cause
more harm than good," Chapman said.
Since the
2003 Columbia accident - and NASA's subsequent July-August 2005 STS-114 return to flight mission
in which unacceptably
large chunks of foam were also shed during launch - tank engineers have
focused on reducing the amount of foam insulation on future tanks.
Engineers
are also replacing a set of engine
cut-off sensors inside the next tank to fly, and preparing for large-scale
wind tunnel tests to evaluate the removal of a large
foam ramp that shed unacceptably large pieces of debris during the STS-114
flight.
"We do a
lot of subscale wind tunnel tests, but this will be a closer to a full-size
test," Chapman said of the upcoming checks.
The wind
tunnel tests will aid NASA's second return to flight mission - STS-121aboard
the Discovery orbiter - slated to launch no earlier than July 1.
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