NASA engineers continue to acquire data on how insulating foam debris
behaves when shed from the Space Shuttle’s external fuel tank during launch.
NASA’s Dryden Flight Research Center at Edwards Air Force Base, Calif., is
conducting a series of flight tests of the debris, known as divots, as part of
the Return to Flight team effort.

The Lifting Insulating Foam Trajectory (LIFT) flight test series at Dryden is
using the research center’s F-15B jet Research Testbed aircraft to test divots at
speeds up to approximately twice the speed of sound (Mach 2).

Small divots pop off the external tank when the Thermal Protection System (TPS)
foam fails. This occurs as a result of decreasing atmospheric pressure combined
with increased heating during Shuttle ascent causing air trapped beneath the TPS
to expand.

“We’re using the unique capabilities of the supersonic F-15B and the aerodynamic
flight test fixture to provide a means to eject these divots from the fixture. We
record them with a high speed digital video system. We’re able to record the
divots in flight at up to 10,000 frames per second,” LIFT project manager Stephen
Corda said.

Aeroscience engineer Ricardo Machin of NASA’s Johnson Space Center, Houston,
said, “The LIFT flight tests will help validate the models used for debris
transport analysis.” “In particular, it’s going to help us understand whether the
divots break up once they come off the external tank, and secondly whether they
will trim and begin to fly, or if they’ll tumble. The difference between trimming
and flying makes a huge difference in the amount of kinetic energy debris can
impart to the Shuttle,” Machin said.

The LIFT flight test required two new capabilities: an in-flight foam divot
ejection system, and a high-speed video system to track and record the
trajectories of the divots in flight. Both capabilities were developed by Dryden
engineers in just over two months.

Dryden’s LIFT team designed, fabricated, and ground-tested four different divot
ejection systems, completing 70 ground tests to determine and refine the best
approach. They designed and procured the very high-speed digital video equipment,
including development of a system to synchronize the cameras with the divot
ejection system, and they developed videography analysis techniques to quantify
divot trajectories.

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