On 06 Jul 2003 15:42:00 +0200, wrote:

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, a

Hoot is wrong. The first near-instantaneous boundary layer
transition, and resulting perturbation, was observed on STS-1. It was
also seen on STS-2 and 3 and thoroughly documented.

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.

I haven't seen the numbers from the right wing or the other Orbiters,
but the left wing was rougher than expected, about 0.085 in. maximum,
at the landing gear door.

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.

I can point you to pre-1989 reports stating that the
near-instantaneous BLT was caused by windward surface roughness.

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:

Catalycity is probably as significant as BLT, though.

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.

You will note that ref. 34, which addresses BLT, was published in
1983. 1983 is well before 1989.

Mary

--
Mary Shafer Retired aerospace research engineer

"Turn to kill, not to engage." LCDR Willie Driscoll, USN