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Tile damage from the tank...its happend before

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From the NASA Page:During the STS-87 mission, there was a change made on the external tank. Because of NASA's goal to use environmentally friendly roducts, a new method of "foaming" the external tank had been used for this mission and the STS-86 mission. It is suspected that large amounts of foam separated from the external tank and impacted the orbiter. This caused significant damage to the protective tiles of the orbiter. Foam cause damage to a ceramic tile?! That seems unlikely, however, when that foam is combined with a flight velocity between speeds of MACH two to MACH four, it becomes a projectile with incredible damage potential. The big question? At what phase of the flight did it happen and what changes need to be made to correct this for future missions? I will explain the entire process.

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Good Find,Another example of why we need to keep asking questions.basically what I have learned is they spray a different thickness on different parts of the ET's.STS-87 had an ET-89 which Had a delivery date of 6/26/1997 and an on-dock date of 7/15/1997. STS-87 flew on 11/19/1997, which was alos Columbia and it sustained extensive tile damage during launch according to Michoud.Thanks, Braun, you have reinforced my beliefs with this additional info. MichoudMichoudMichoudFix the ET's and we can go fly again. :-)Braun, you did read my other threads didn't you?Edit:Same Article: at what this guy said:Greg Katnik 12/1997 (Engineer at Kennedy Space Center)" The tiles do a fantastic job of repelling heat, however they are very fragile and susceptible to impact damage."Further down, the questions that he asked:Now the big question -- why? The evidence of this conclusionhas now been forwarded to Marshall Space Flight Center (MSFC)because this is the design center for the external tank. MSFC willpursue the cause of damage. Here are some descriptions of someof the possible causes:POSSIBILITY 1The primer that bonds the tank foam to the metalsub-stream was defective and did not set properly. Thiswas eliminated as a cause because the photographyindicated that the areas of foam loss (divots) did notprotrude all the way down to the primer.POSSIBILITY 2The aerodynamics of the roll to "heads up." The STS-87mission was the first time this maneuver had ever beencompleted.POSSIBILITY 3The STS-86 mission revealed a similar damage patternbut to a much lesser degree than STS-87. The STS-86tile damage was accepted ruled as an unexplainedanomaly because it was a night launch and did notprovide the opportunity for the photographic evidence theSTS-87 mission did. A review of the records of theSTS-86 records revealed that a change to the type offoam was used on the external tank. This event issignificant because the pattern of damage on this flightwas similar to STS-87 but to a much lesser degree. Thereason for the change in the type of foam is due to thedesire of NASA to use "environmentally friendly"materials in the space program. Freon was used in theproduction of the previous foam. This method waseliminated in favor of foam that did not require freon forits production. MSFC is investigating the considerationthat some characteristics of the new foam may not beknown for the ascent environment.POSSIBILITY 4Another consideration is cryogenic loading, specificallyhydrogen (-423 degrees Fahrenheit) and oxygen (-297degrees Fahrenheit). These extreme temperatures causethe external tank to shrink up to six (6) linear incheswhile it is on the pad prior to launch. Even though thismay not seem much when compared to the circumferenceof the external tank, six inches of shrinkage issignificant.This is where the investigation stands at this point in time. As youcan imagine, this investigative process has required many hoursand the skills of many men and women dedicated to the safety ofthe shuttle program. The key point I want to emphasize is thePROCESS OF INVESTIGATION, which is coordinated amongstmany people and considers all possibilities. This investigation hasused photography, telemetry, radar coverage during the launch,aerodynamic modeling, laboratory analysis and many moretechnical areas of expertise.As this investigation continues, I am very comfortable that thequestions will be answered and the solutions applied. In fact,some of the solutions are already in progress. At present the foamon the sides of the tank is being sanded down to the nominalminimum thickness. This removes the outer surface, which istougher than the foam core, and lessens the amount of foam thatcan separate and hit the orbiter.****************************************Well, It seems they were aware of this problem, huh?Good for NASA, but it didn't work, IMHO, whatever changes they made still continued to occurr.We are darn lucky that other shuttles have not been lost due to this.Regards,Joe

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