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.
For information about NASA’s Return to Flight efforts on the Web, visit:
http://www.nasa.gov/returntoflight