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Columbia,: It was so obvious to a layperson, but not to those "inf
(James Oberg) wrote: We're also seeing that the NASA analysis of tile threat was correct -- foam hitting tiles didn't hurt and was unlikely ever to do so. The spillover of this experience to foam-hitting-RCC was the flaw, as I see it, and here (I'm writing up a longer piece) the culture failed. But tiles? Bang on 'em, scrape them, knock some off -- they take a lickin' and they kept on tickin', and seduced space officials into thinking that RCC would act the same way -- and they NEVER, EVER did tests to check out this convenient analogy. Wait a minute. Your interpretation of the managment thinking may be correct. It probably was the RCC this time. But regarding the tiles the question of early boundary-layer transition came up last months. I`m unfamiliar with hypersonic transition. But in subsonic there is a range of Reynolds nummbers inside them the occurence of transition is only predictable by statistics. It seems the shuttle in early re-entry is in such a range: http://www.newsmax.com/archives/arti...7/194414.shtml The first known aerodynamic shift occurred on mission STS-28 in 1989 and was studied carefully by Gibson, an aeronautical engineer who helped investigate the Challenger disaster and redesign shuttle's solid rocket boosters. The Challenger exploded on liftoff in 1986, killing its seven-member crew. Gibson was also commander during four shuttle missions and piloted a fifth mission. Gibson told UPI he found the surface of Columbia's wings was two-to-four times rougher than the wings of the three other shuttles -- Atlantis, Discovery and Endeavour -- and that Columbia's left wing was 50 percent rougher than its right. He suspected the roughness caused the 1989 shift and another in 1995. NASA engineers did not pay much attention to Gibson's concern in 1989, he said, finding another cause for the shift. Other experts told UPI, however, that such roughness could trigger a premature aerodynamic shift, leading to additional heating and drag. The transition (here called shift) is not only related to the mean roughness but could be triggered by very small flow obstacles in specific distance to each other. Like inducing an oscilation by some wavelenght. The transition occurs as an accumulation of small vortices over some lenght to the whole turbulent layer. In the case of the shuttle a single damaged tile will never be a problem. But what if a streamline crosses several damaged (super-rough) places? It seems whether the transition occurs is not only a matter of how many damages we have but their location to each other too. It could cause an burn through in an un-damaged downstream area: http://www.chron.com/cs/CDA/story.hts/space/1790143 Foam or ice damage to the wing can cause turbulent airflow earlier than normal in a shuttle's re-entry to Earth's atmosphere, wrote Dennis Bushnell of NASA's Langley Center. This can produce friction at the hottest point in the shuttle's flight. "If the flow is turbulent at peak heating, the heat shield would/could burn through the wheel well doors (even with undamaged tiles)," he wrote, based on his research for the shuttle's original flight certification in 1980. http://www.orlandosentinel.com/news/...cssboundary170 31703mar17,0,669319.story A Columbia flight in 1995 underwent the earliest-known boundary-layer transition at Mach 19, or roughly 13,000 mph. That's approximately the speed the orbiter was traveling Feb. 1 as it began to break up. That was one of four times Columbia is known to have experienced early transition. During another instance, in 1989, a few of its protective silica tiles partially melted on the dive through the atmosphere. The following seems me to refer to a later super-sonic flight regime where heat is less the issue then the now higher stagnation pressu http://www.floridatoday.com/columbia...ry2A44731A.htm "One tile here and one tile there does not affect anything; you get some local turbulence," said Greg Sakala, a former NASA shuttle program engineer. "You get in too deep . . . it does not take much to get a loss of laminar flow, which could create a lot of turbulence. Then you get what they call burbling, which would start ripping tiles off behind like that zipper effect they keep talking about. Then the skin heats up." "You might not cause burn through, but you could cause enough turbulence to create drag that overcomes the shuttle's ability to compensate," Sakala said. To sum up this has not much to do with Columbia. But the danger of tile damage in further missions should not be downplayed. ## CrossPoint v3.12d R ## |
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Columbia,: It was so obvious to a layperson, but not to those "inf
In article ,
Mary Shafer wrote: See "Space Shuttle Hypersonic Aerodynamic and Aerothermodynamic Flight Research and the Comparison to Ground Test Results", Kenneth W. Iliff and Mary F. Shafer, NASA TM-4499, June, 1993. One should usually doubt a poster's claims when she cites herself for support of her own opinion. On the other hand, the usual Usenet poster's self-citation is rarely this well-founded . . . :-) -- Herb Schaltegger, Esq. Chief Counsel, Human O-Ring Society "I was promised flying cars! Where are the flying cars?!" ~ Avery Brooks |
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Columbia,: It was so obvious to a layperson, but not to those "inf
In article ,
"Kent Betts" writes: According to one CAIB witness, Columbia never made the transition to the turbulent flow regime. It was one of the early thermo or aero dynamicists. I haven't seen that yet. Unless they were looking at certain specific sensors, most of which are, I believe no longer installed, I'm not so sure that they'd be able to tell easily. Under normal conditions that's true, but a leading-edge (RCC) irregularity could trigger a transition early. -- Pete Stickney A strong conviction that something must be done is the parent of many bad measures. -- Daniel Webster |
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Columbia,: It was so obvious to a layperson, but not to those "inf
The forces were more blow torch than wind tunnel?
"Kent Betts" wrote in message ... According to one CAIB witness, Columbia never made the transition to the turbulent flow regime. It was one of the early thermo or aero dynamicists. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 80,000 Newsgroups - 16 Different Servers! =----- |
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