08.27.03

Things I Have Learned About Foam From the Columbia Accident Investigation Board Report

Insulating foam falls off of the external tank on every Shuttle mission, usually in popcorn-size pieces.

No one knows why foam falls off the tank.

On about 10% of missions, foam falls off of the left bipod ramp, part of the Y-shaped structure that holds the Orbiter's nose to the external fuel tank.

No one knows why this happens, either.

Pieces of foam that fall off of the bipod ramp are the largest bits of flight debris ever seen during launch. Some are the size of a suitcase.

When foam falls off of the bipod ramp, it is always from the left side, never the right.

Not a clue why.

Several mechanisms have been proposed for foam loss. They have elaborate names like cryopumping, cryoinjection, and explosive expansion of trapped blowing agent. All of them posit some kind of bubble of gas rapidly expanding and shearing foam off of its substrate.

None of them matches observed data.

The orbiter is not supposed to be hit by any debris during launch. The reinforced carbon panels on the Shuttle's wing are only required to withstand a minimal impact. By luck and good engineering, they are much, much stronger than the Shuttle design says they need to be.

The orbiter design does not anticipate anything ever falling off of the tank.

A piece of foam traveling at 550 miles per hour can punch right through a reinforced carbon panel.

Foam falls off of the external tank on every Shuttle mission.

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