All these freaking foam problems. Why can't they just cover the foam with a second tank or something?

Question

It doesn't have to be a pressure vessel so the metal can be thinner and lighter.

Answer 1

Its not a bad idea--except it won't work. Here's whhy: the external fuel tank is composed of a lightweight aluminum/lithium aloy just 3mm thick (a bit over 1/8 inch). And still weighs about 55,000 pounds (that tank is BIG--over 150 feet long and over 25 feet in diameter). So you couldn't make an outer shell much lighter. There's just not enough reserve for the system to pay that kind of weight penalty--not and get into space with any payload.

Answer 2

The foam is used as an insulator, and as such does a very good job. More metal would not only add lots of weight, but would not insulate properly.

I am sure that engineers have been busy trying to improve the foam adhesive, as well as looking into other improvements.

By the way, weight is a very important issue. Every ounce is counted and calculated into thrust amounts with very little extra room. I can't imagine what a 300 ft tank of even thin aluminum would weigh, but enough that the shuttle would never have enough thrust to get to orbit.

The foam loss on this flight happened after 2 minutes, which the engineers are not too concerned about.

Answer 3

The foam tiles are used to protect the inner skin of the space shuttle from the extreme heat at reentry. If you covered the foam tiles with metal, the metal would just burn off and leave the foam tiles beneath. They don't have anything as resistant to the heat as the foam tiles to cover the foam tiles with.

Answer 4

Foam is the lightest kind of insulation. Liquid hydrogen and oxygen are really cold so the tank needs to be well insulated.

Answer 5

but it'll add more weight to the overall shuttle "stack" so it would be impractical...