Shuttle Columbia and Foam Strike

[bcullman]

for the report, engineers shot pieces of foam out of a cannon at 500mph and proved that foan traveling that fast could indeed create damage that would cuase a catastophic failure of the shuttle.

But would the foam really strike at that speed? the moment the foam seperated from the shuttle it began decelerating, sure. But being only recently attached to the shuttle, it still had forward momentum - wouldn’t that make the resulting impact happen at a much lower speed?

[scr4]

I believe they determined the impact speed from the film footage, so it should be pretty accurate. At such high speeds, anything not bolted down to the shuttle will decelerate very quickly due to air resistance, especially something light and irregularly shaped like a chunk of foam.

[friedo]

But the shuttle is also accelerating very fast. How long did it take between the time the foam broke off and when it struck the wing?

[rsa]

The answer can be found in a sidebar on page 60 of the official Columbia Accident Investigation Board report. (Warning: 10 MB PDF. MSNC has the report broken into sections; this quote is from Chapter 3.)

“How could a lightweight piece of foam travel so fast and hit
the wing at 545 miles per hour?”

Just prior to separating from the External Tank, the foam was
traveling with the Shuttle stack at about 1,568 mph (2,300
feet per second). Visual evidence shows that the foam debris
impacted the wing approximately 0.161 seconds after
separating from the External Tank. In that time, the velocity
of the foam debris slowed from 1,568 mph to about 1,022
mph (1,500 feet per second). Therefore, the Orbiter hit the
foam with a relative velocity of about 545 mph (800 feet per
second). In essence, the foam debris slowed down and the
Orbiter did not, so the Orbiter ran into the foam. The foam
slowed down rapidly because such low-density objects have
low ballistic coefficients, which means their speed rapidly
decreases when they lose their means of propulsion.

[rsa]

Here is the MSNBC link which has the report available by chapter if you have a slow internet connection.