Space Forum / Shuttle / May 2005

06:45 a.m., 05/20/05, Update: Tanking test underway

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Engineers began pumping a half-million gallons of supercold rocket fuel into
the shuttle Discovery's external tank early today to collect more data on
ice formation and to help track down the cause of two problems that cropped
up during a similar test in April.

The three-hour fueling process began at 5:36 a.m. and should be complete by
around 8:30 a.m. At that point, just like in a real countdown, a small team
of engineers will head to the launch pad for a detailed external ice
inspection.

Relatively high humidity was expected today, which will increase the chances
for ice formation on the tank. During the first tanking test April 14,
humidity was relatively low and ice formation was minimal. Engineers were
hopeful today's test would provide additional insights into where ice might
build up on the tank.
Today's test will be run in two stages. The first will end around 1:40 p.m.
with a countdown cutoff at the T-minus 31-second mark. For that run, the
bipod heaters at the bases of the two struts connecting the nose of the
orbiter to the external tank will be turned on to prevent ice buildups.

The shuttle Columbia's destruction was triggered by the loss of foam
insulation around the left-side strut. In the wake of the accident, the foam
in question was removed and the bipod heaters were installed to do the same
thing: Prevent ice formation.

For the second part of today's test run, the countdown will be recycled to
the T-minus 20-minute mark and the heaters will be turned off. The countdown
will resume and continue to the T-minus 31-second mark a second time to find
out if the bipod heaters play any role in how often a hydrogen pressure
relief valve operates. The second countdown cutoff is expected around 3 p.m.

During the April 14 tanking test, the pressure relief valve cycled more
often than expected and engineers want to find out why. Another problem
involved two of four hydrogen depletion sensors in the tank that failed to
operate properly. The sensors are used to make sure the shuttle's main
engines shut down properly after reaching space and all four must be
operational for a countdown to proceed.

It's likely a moot point for Discovery. NASA managers decided earlier to
move the shuttle to a different tank and boosters for its launch attempt in
mid July. The new tank will feature an additional heater to prevent ice
buildups around a flexible propellant line bellows, which prompted concern
during Discovery's initial launch pad processing flow.

In addition, the new tank's engine cutoff sensors presumably will work
properly. But engineers may stage a third tanking test before Discovery's
eventual launch just to make sure.

Engineers were surprised by the problems that came to light in April and
today's test was ordered to collect additional data before moving the
shuttle back to the Vehicle Assembly Building next week.