Jeff Findley wrote:
"ed kyle" wrote in message
oups.com...
wrote:
In the e-mail Sunday to shuttle engineers and managers, Hale said
vertical cracks in the external tank's "protuberance air load," or
PAL, ramp extended deep into the foam insulation and appear to have
been caused by contraction and expansion as the tank was being filled
with supercooled liquid hydrogen and oxygen.

Could this have something to do with the use of Aluminum-Lithium
tanks? Aluminum-Lithium tanks began flying just a few years ago,
replacing the previous all-Aluminum.

I seriously doubt it.

Jeff

I remain to be convinced one way or the other, but I
did find the following unsettling tidbit. NASA replaced
the original 2219 Aluminum alloy with 2195 Aluminum-
Lithium beginning with STS-98.

"http://www.ingentaconnect.com/content/asm/jmep/1998/00000007/00000005/art00015"

- Ed Kyle