History

Text Size

Dryden Gave a LIFT for Shuttle's Return To Flight
10.28.11
 
F-15B flight research test bed carries shuttle thermal insulation panels on its underbelly flight text fixture. NASA Dryden's workhorse F-15B flight research test bed carried the shuttle thermal insulation panels on its underbelly flight text fixture during the Lifting Insulating Foam Trajectory flight test project in 2005. The tests gathered critical data on how divots of the foam behaved after they broke off the shuttle's external tank. (NASA / Jim Ross)

As part of NASA’s Return to Flight effort following the loss of the space shuttle Columbia and its crew during mission STS-107 on Feb. 1, 2003, NASA’s Johnson Space Center approached NASA's Dryden Flight Research Center for help in modeling thermal protection system foam loss from the shuttle’s external fuel tank.

The Columbia Accident Investigation Board, convened following that vehicle’s breakup during re-entry, found that the primary cause of the tragedy was a breach in the shuttle’s thermal protection system resulting from a piece of insulating foam that separated from the external tank’s left bipod ramp area.

Panels on the F-15B's flight test fixture show five divots of TPS foam were successfully ejected during the LIFT experiment.A close-up of the panels on the F-15B's flight test fixture shows five divots of TPS foam were successfully ejected during the LIFT experiment flight #2, the first flight with TPS foam that was used as insulation on the space shuttles' external tanks. (NASA / Tony Landis) The detached piece of foam struck the shuttle’s left wing near its leading edge, in the vicinity of the lower half of Reinforced Carbon Panel number eight. The foam strike occurred about 81 seconds after launch, punching an estimated 10-inch diameter hole in the panel. This damage went undiscovered throughout the mission.

During the shuttle’s fiery re-entry, the hole allowed the super-heated air surrounding the vehicle, called plasma, to penetrate through the gap in the thermal protection panel. The plasma melted the orbiter’s aluminum wing structure to the point of sufficient structural failure to cause an aerodynamic loss of control as it descended thhrough the upper reaches of the atmosphere, resulting in the breakup of Columbia. Heartbreak rolled across the nation and the world as a second space shuttle crew was lost.

Following the accident, Dryden geared up to provide flight data on foam loss requested by NASA engineers at the Johnson Space Center. Called the Lifting Insulating Foam Trajectory (LIFT) project, this effort utilized the center's F-15B Research Testbed aircraft to acquire data on how insulating foam debris or "divots" behaved when the small pieces were shed from the shuttle's external fuel tank during launch.

The unique capabilities of NASA’s supersonic F-15B Research test bed aircraft enabled it to garner the LIFT data in a real flight environment at altitudes up to 50,000 ft. and at speeds up to Mach 2. The project continued NASA Dryden’s shuttle program support of testing shuttle insulating materials begun with F-104 and F-15 test bed aircraft early in the program.

Though the fatal piece of foam that broke off the bipod ramp area of STS-107’s external tank was significantly larger, small-scale foam loss called divoting, or “popcorning,” had occurred throughout the entire space shuttle program. Immediately after the loss of Columbia, all foam-shedding issues took front-and-center attention in the shuttle program’s return to flight effort.

Panels on the F-15B's flight test fixture have five divots of TPS foam that were successfully ejected during the LIFT experiment .A post-flight inspection of the panels on the F-15B's flight test fixture shows five divots of TPS foam were successfully ejected during the LIFT experiment flight #2, the first flight with TPS foam used for insulation on the space shuttles' external tanks. (NASA / Tony Landis) Divoting, as with most forms of shuttle foam loss, occurred when the foam’s adhesive failed. This happened as a result of decreasing atmospheric pressure combined with increased heating during Shuttle ascents, causing air trapped in or beneath the insulating foam to expand.

The LIFT flight tests on NASA’s F-15B required two new capabilities: an in-flight foam divot ejection system and a high-speed video system to track and record the paths of the divots in flight. Both capabilities were developed rapidly by Dryden engineers in just over two months.

Dryden's LIFT team designed, built and ground-tested four different divot ejection systems, completing 70 ground tests to determine and refine the best approach to use.

In addition, NASA Dryden engineers designed a digital video synchronization system used in the tests that linked the high-speed cameras with the divot ejection system. They also developed video analysis techniques to help track the foam.

Two primary questions were to be answered by the LIFT tests: understanding whether the divots broke up once they came off the external tank, and secondly, whether they trimmed and began to fly, or if they tumbled instead. The difference between trimming (flying) or tumbling made a huge difference in the amount of kinetic energy that a foam divot could impart to the shuttle, as tumbling pieces exerted more energy than trimmed divots, posing a greater risk of damage.

Following the rapid LIFT system design phase, ground test and flight test hardware construction and validation, Dryden successfully flight-tested the LIFT system on the F-15B, providing the much-needed divot trajectory test data.

Analysis of the high-speed video data showed that of the 36 successful supersonic foam divot ejections, all of the divots trimmed. This data helped engineers at Johnson validate the models that they used for debris transport analysis.

NASA' s Space Shuttle Systems Engineering and Integration office at the Johnson Space Center in Houston, Texas, funded the LIFT flight tests.
 
 
Gray Creech
NASA Dryden Flight Research Center