Reply #10: It's more complicated than that

[ThoughtCriminal]

The Freon issue got big play on right-wing blogs that wanted to blame ... frum roll... Bill Clinton via the "Tree-Hugging" EPA.

The foam loss has been a problem since the first flights and average of about 40(?) tiles in the first 50 flights. There was an increase in foam hit after the switch from freon propellants, but it was thought that that problem was solved (sound familiar). At that time it was not considered a safety problem, but a cost problem from repairs.

Even more significant, the foam that damaged Columbia's wing is believed to have come from a part of the external tank that was still using the freon based propellant (I'm still looking for a solid link on this).

It's a nasty problem that goes back to a poor compromised design. 1) The configurartion places the shuttle next to, instead of above the tank, so it is vulnerable to any debris coming off it. 2) It was only after they settled on a design that they figured out that ice on the tank would be a problem (look at film of a Saturn 5 launch) so the tank had to be insulalted. 3) they can't put insulaltion inside the tank because it would contaminate the fuel. 4) Adding a outer shell would probably add enough mass so that the shuttle could not carry any payload.