I am following the shuttle program from STS-1
I don't remember any foam shedding problems throughout the 80s, even most of the 90's. According to my memory recollection: when freons were banned, NASA got an exception (the manufacturer used freon to manufacture the foam covering for the external tank), but NASA chose to be "environmentally correct" and instructed the manufacturer to replace the freon with something else, which they did. Only after that foam shedding became an issue.
Can someone verify or contradict all this?
Wrong (or partially right) on two accounts :
1) There were debris right from the start, and STS-1 crew reported them. But the problem in foam application were so frequent, contrary to what you think to assume, that they were considered variance more than problem.
2) the CFC started to be replaced from around 1995 on. Replacing CFC-11, Nasa certified HCFC 141b for use in the Shuttle Program. The "green" HCFC is used in all the machine sprayed areas of the tank. For all the remaining hand-made areas, they indeed stick to CFC.
HCFC was first used for STS-79, in 1996, and then expanded with STS-86.
So debris have nothing, or little, to do with the "green" HCFC replacing the CFC. The thing is just that media and fans talked more and more about the debris problem, and it came more and more to the public's knowledge. Perhaps also, the top executives at NASA realised that there was a real issue here and they could not ignore it longer (though, as we saw with STS 127, nothing has really changed today, even with all the improvement they made).
Shedding foam is just a consequence of the aerodynamic pressures the tank is exposed to during atmospheric flight... although sometimes stuff gets shaken loose after the atmosphere is next to nil.
Foam shedding on flights is pretty common. It just wasn't recognized as a real threat until STS-107.
STS-27 and another past flight that I can't recall ow were particularly bad. Check out the pictures of STS-27's belly during landing, damn lucky that one didn't result in a LOC.
vertical
STS-27's damage was not caused by ET foam. Insulation from the right SRB nose cone caused all the damage.
Quote from: Greggy_D on July 17, 2009, 09:04:32 PM
STS-27's damage was not caused by ET foam. Insulation from the right SRB nose cone caused all the damage.
Correct. Read Astro Mike Mullane's "Riding Rockets" and you'll see the story <g>. Sorry for the shameless plug.
/Admin
...but a good book ;)