Posted on 02/03/2003 4:43:52 PM PST by Wolfstar
Edited on 04/29/2004 2:02:01 AM PDT by Jim Robinson. [history]
Released Monday morning, a high-speed NASA engineering film shows a piece of debris falling from the large external tank on the space shuttle Columbia's liftoff and hitting the orbiter's left wing. Bear in mind that these are extreme close-ups of a high-speed event. In the top couple of photos, you see only the top of the broken-off piece. Most of it is in the shadows. Depending on which clip you see and how slowly it is run, to the uninitiated person's eye, it can look either like the debris strikes the wing hard enough to pulverize the debris, or the debris strikes a glancing blow and bounces off in the direction of the main and booster engine exhaust.
(Excerpt) Read more at cnn.com ...
Sure hope you are all talking about Dolly Parton, and not the "other" Dolly. :O)
On the other hand, all this data I have read leads me to believe that they really had not nailed this problem down and were guessing at the cause.
I have taken many courses in an art called systematic troubleshooting, and I do not believe that enough data is there to determine a insulation strike cause and effect.
Wind tunnel data might prove this theory and other tests can be performed to verify it, but I think it is something else entirely. I think it may be just as likely that they hit some space debris, and have been hitting the stuff all along. Micrometeorites, bolts, nuts and metal objects that are way too small to track reliably.
True, but did you see the report on the inspection after flight STS-87, posted by Jael. Note the small part quoted below.
They also stated that when that occured, there was a relative wind of Mach 2 to Mach 4 (Wow).
THE MAIN THING TO REMEMBER IS THAT WITH THIS MUCH DAMAGE TO THE TILES, THE FLIGHT STILL RETURNED SUCCESSFULLY.
"Three hundred and eight hits were counted during the inspection, one-hundred and thirty two (132) were greater than one inch. Some of the hits measured fifteen (15) inches long with depths measuring up to one and one-half (1 1/2) inches. Considering that the depth of the tile is two (2) inches, a 75% penetration depth had been reached."
Now I remember where I have seen you before.
BINGO!!!!
The main reason for this assumption is that this tank and this insulation has been flown time and time again since STS-87. No unusual tile damage was reported from this effect. I cannot draw a conclusion on this data alone. I would like to see wind tunnel tests which we are quite capable of doing and I am sure it is in the works. That is why they wanted to try the insulation hypothesis and test it for voracity.
NEWS RELEASE
United States Air Force
Air Force Materiel Command
Office of Public Affairs
Arnold Engineering Development Center
100 Kindel Drive
Arnold AFB, TN 37389-2213
(931) 454-5586
http://www.arnold.af.mil
Writer: Danette Duncan
Date: March 19, 1999
Release # 99-041
Photo # none
AEDC Performs Shuttle Materials Test for NASA/Lockheed Martin
ARNOLD AFB, Tenn.—Arnold Engineering Development Center is assisting the National Aeronautics Space Administration with improvements in existing Space Shuttle materials.
According to NASA, during several previous Space Shuttle flights, including the shuttle launched Nov. 29, 1998, the shuttle external tank experienced a significant loss of foam from the intertank. The material lost caused damage to the thermal protection high-temperature tiles on the lower surface of the shuttle orbiter. The loss of external tank foam material and subsequent damage to reentry tiles is a concern because it causes tile replacement costs to significantly increase, however, it is not a flight safety issue. As a result, NASA-Marshall Space Flight Center selected AEDC to perform flight hardware materials tests on the shuttle’s external tank panels in the center’s von Karman Facility Supersonic Tunnel A. The purpose was to establish the cause of failure for the tank thermal protection materials at specified simulated flight conditions. "NASA chose AEDC due to its technical expertise and historical program successes," Steve Holmes, a NASA-MSFC technical coordinator, said.
The Lockheed Martin-manufactured non-reusable external tank, the largest element of the Space Shuttle, fuels the shuttle orbiter during powered flight and is comprised of three components—a liquid oxygen tank, a liquid hydrogen tank and an intertank assembly that connects the two propellant tanks. At the full capacity of 528,600 gallons of propellant, the external tank weighs 1.6 million pounds. The tank is covered with a multi-layered, spray-on foam insulation that provides thermal insulation for the tank against the extreme internal and external temperatures generated during prelaunch, launch and flight.
Wayne Hawkins, Sverdrup project engineer, explained the foam system is exposed to multiple forces, causing difficulty in determining the actual failure of the thermal protection system. "Multiple forces act on the foam system," Hawkins said. "The environmental factors include thermal protection system cell expansion, aerodynamic loading, highly variable local flow conditions, oscillating shocks, vibration, temperature and main external tank substrate flexure."
Although NASA and other facilities have performed a number of tests in an attempt to define the underlying root cause of this foam loss, they were not successful. At one time, the center’s 4-foot and 16-foot transonic aerodynamic wind tunnels were possibilities for the test, but Tunnel A’s ability to closely duplicate flight conditions and control both ambient pressure and test sample immersion time made it the facility of choice. Tunnel A is a continuous flow-variable density wind tunnel with an automatically driven flexible-plate nozzle and a 40- by 40-inch test section and can cover the Mach number range of 1.5 to 5.5.
"The ideal success for the test is the generation of foam loss on a consistent basis with simulated flight conditions," Hawkins said.
Although the AEDC Tunnel A tests did not replicate the in-flight failures, they did provide detailed measurements to better understand the flight environment and fundamental failure mode. From these tests, NASA determined the failure is caused principally by foam cell expansion due to external heating at approximately Mach 4 combined with pressure change and aerodynamic shear. Specialized miniature shear gages and other instrumentation were installed during the test to measure these forces. The customer and sponsor were pleased with the AEDC test results. "No other facility can test with articles/models as large as AEDC with conditions that can match flight," Holmes said.
They actually have(and did have) enough data now to analyze what happened during that strike as I outlined in #295. They also have enough data to know what would happen if the silica is removed from the Nomex. The Nomex burns right off followed by whatever is underneath. Once there's a hole, it grows until the process driving it's growth ceases, or the hole results in a catastrophic failure. A catestrophic failure happened here and the only big driving force for it was the frictional and momentum forces occuring during the deceleration of reentry.
According to NASA, they do that anyway on every flight.
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