Hello all,
Last week (on 9/13) Delbert posted a thread as to the nature of the apparant change in color in the Shuttle's External Fuel Tank. I had trouble finding any info. so I submitted a question to the folks at Nasa - and they responded.
Here is a quote of their response (it just goes to show, it doesn't hurt to ask):
The ET is thermally protected with a nominal one inch CPR-488 spray-on foam
insulation, and charring ablators (MA-25S and SLA-220) to withstand
localized high heating during ascent. The thermal protection system weighs
approximately 4,823 pounds. The insulation was protected by a white-colored fire retardant latex (FRL) coating for the first two flights (STS-1 and
STS-2), but has been left bare on subsequent flights to save 595 pounds and [approx] $15,000." (From: Jenkins, Dennis R. SPACE SHUTTLE: THE HISTORY OF THE NATIONAL SPACE TRANSPORTATION SYSTEM. Voyogeur Press, 2001. p.241)
The $15,000 is most likely 1984 dollars so it would be considerably more
expensive now. The major thing, though, was the weight savings. For every pound save on the outside more payload can be carried.
Thank you for your interest in the Space Program.
See ya, VINCE