Albert D. "Bud" Wheelon - Pioneer: 1929-2013

[thcrozier]

Rogers Commission

And this:


MR. LUND: Yes. The machine forms the other seating surface that would occur in a rocket motor.

What this said was that at 100 degrees, as that head came back to its original position, I'm sorry, not to its original position, but to within 5/1,000ths of its original position, still maintaining the squeeze, that at a high temperature, at 100 degrees, the O-ring came right back.

It followed the machine right up. At 75 degrees, it took several seconds to recover. And, as we went lower in temperature, it took much longer to recover.

DR. WHEELON: That's pretty nonlinear. How do you account for that?

MR. LUND: It is the modulus of the rubber. Those polymers do that.

DR. FEYNMAN: The rubber - ordinarily in materials, like steel or something when you squash it, you are compressing the molecules together and they simply expand back. When you stretch a piece of rubber, the reason that it responds is because of dynamic motion. It is trying to shake molecules and pull something; like, you take a long chain across a room, which has a lot of tennis balls bouncing in it. The chain will be "ponged" by the balls and pulled together. If the balls are slowed up, and low temperature means slowed up, then there is much less ponging and much less pulling back together, and the same way responding.

I used the expansion. But you can do the same thing with compression. If you compress it out of shape, it goes back into shape because of thermal notion, really, not because of spring. And when the thermal temperatures change, it goes back very, very much lower.

It is very characteristic of materials of this kind, that have this enormous effect. Temperature has such enormous effect.

DR. COVERT: Does it follow the square root?

DR. FEYNMAN: No. It's E to the minus A over T. It is exponentially. So, at 32 degrees on the scale, you probably wouldn't be able to measure the time. It would be too late to wait for the hour, or whatever.

MR. LUND: Now, keep in mind that resiliency is not the only issue. But you have the pressure load coming in and the pressurization of the motor kicking that O-ring up and saying go with me.

So this is one factor.
(Viewgraph.) [Ref. 2/14-12]

DR. FEYNMAN: But if there is a gap left, is there really any pressure remaining to push?


v4part6: Official Transcript, NASA History Office
http://history.nasa.gov/rogersrep/v4part6.htm#1


This exchange always makes me uncomfortable as it becomes apparent that O-Ring resiliency with respect to temperature was understood - how incredibly sensitive it was to temperature in the designed use was known, but that knowledge was ignored in practice.