DRYDEN F-15B SUPPORTS SHUTTLE EXTERNAL TANK INSULATION TESTS January 28, 1999 Release: 99-01 Printer Friendly Version
Flight tests at the NASA Dryden Flight Research Center, Edwards, Calif., recently demonstrated that a new type of insulation foam used on the Space Shuttle's giant external tank remains intact under some of the dynamic environments seen during the initial stage of the Shuttle's ascent.
Mimicking a Space Shuttle launch profile, an F-15B research aircraft based at NASA Dryden flew a series of missions to evaluate the dynamic response characteristics of the new insulation material. The Shuttle External Tank Experiment involved six research flights over a two-week period by Dryden's F-15B in partnership with NASA's Marshall Space Flight Center, Huntsville, Ala., and the Michoud Assembly Facility near New Orleans, La.
"This experiment was a perfect example of the versatility of the F-15B and its Flight Test Fixture," said Dave Richwine, Dryden's F-15B project manager. "It shows how we can customize our capability for any particular experiment's requirements."
The experiment was part of an effort to determine why small particles of spray-on foam insulation flaked off of the inter-tank section of the external fuel tank on Space Shuttle mission STS-87 as the Shuttle ascended. The new lightweight insulation material was developed to comply with an EPA mandate to reduce ozone-depleting chemicals released into the atmosphere. Although such flaking or erosion of the insulation off the external tank posed no safety hazard to the Shuttle or its crew, engineers wanted to determine its cause to prevent future maintenance and operational problems. The flights aboard Dryden's F-15B were just one of many tests to which the new insulation material is being subjected.
Initial results of the flight tests at Dryden, which were designed to replicate the pressure environment the Shuttle encounters in the first 65 seconds after launch, indicate the new foam survived the tests in perfect shape, with no evidence of flaking or erosion found.
For the tests on Dryden's F-15B, test panels covered with the foam insulation were mounted on the left side of the Flight Test Fixture that is carried underneath the aircraft's center fuselage. Six different panel configurations were flown one on each flight. Five of the panels were covered with the insulation now used on the sidewalls of the Shuttle's external tank, while one was covered with an alternate formulation of slightly higher density that is used on the dome atop the tank. While several panels were left in wavy as-sprayed configurations, others were finely machined to duplicate the thrust panel rib structure of the thrust panels where the solid rocket boosters are attached to the new "super-lightweight" external tanks now flown on Shuttle missions. Four panels had the ribs aligned with the airflow, while two others had the ribs mounted vertically in order to simulate the complex airflow around the Shuttle and its external tank during its ascent.
On each flight, Dryden research pilot Dana Purifoy flew the F-15B through a series of side-to-side yaw maneuvers beginning at 7,300 feet altitude. He then increased speed and altitude in a stair-step approach, finally zooming up to 61,000 feet at speeds of up to Mach 1.5 (1.5 times the speed of sound) before descending for landing.
"It was important that the F-15B could match part of our (shuttle launch) profile, and it does a fantastic job of doing that," said aerodynamicist Roy Steinbock of Lockheed-Martin Michoud Space Systems, staff engineer on the experiment.
"Our main goal was to try to match the dynamic pressure history (that the external tank encounters during a shuttle launch). The Dryden F-15B can match the high-altitude, low-pressure environment that the Shuttle encounters, and can test a multitude of Mach numbers in (one) flight. That's something we cannot do anywhere else--we can't replicate that in a wind tunnel."
"Marshall's objectives included flying at Mach 1.5, reaching 60,000 feet and completing six research flights in two weeks," added Richwine. "We were proud to be able to meet Marshall's performance and schedule objectives for this experiment."
"The successful completion of the tests at Dryden, along with wind tunnel testing at the Arnold Engineering Development Center in Tullohoma, Tenn., hot gas testing at Marshall and a multitude of other tests, has given us additional data to further improve the foam insulation on the Space Shuttle's External Tank," said Parker Counts, Marshall's Space Shuttle External Tank program manager. "This was a fine example of the team work between NASA centers and other government agencies."
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