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NASA's Foam Test Offers Lesson in Kinetic Energy

Posted by michael on from the school-of-hard-knocks dept.

Puneet submitted a followup story on the foam test that NASA conducted to get an idea of what sort of damage could be caused by foam falling off the shuttle fuel tank at launch. As it turns out: a lot.

6 of 503 comments (clear)

  1. Relative velocity? by dschuetz · · Score: 5, Interesting

    I've been wondering this from the beginning of the foam investigations and tests...

    They've talked about firing foam samples at wing mockups at hundreds/thousands of miles an hour, 'cause (I think) the Shuttle was flying at that speed when it was hit. But wasn't the foam also flying at that speed? Shouldn't the actual velocity of the foam hitting the wing edge be fairly minimal?

    Or are they assuming that the wind drag on the foam chunk would reduce its absoute speed significantly, thus increasing the relative speed with which it hit the wing?

    In other words, did the foam fall off and drop, low speed, into the wing, or did the foam flake off and stop dead in the air, then the shuttle ran into it at a huge velocity?

  2. Scary Stuff by OrangeGoo · · Score: 5, Interesting

    It's frightening that such a light-weight piece of foam can doom a fantastically complex and brilliant piece of machinery like the shuttle, not to mention the crew on board who are far more complex and brilliant - and the loss of whom is so much more painful. But it's not really a surprise. I mean, if a penny can kill - and it certainly can - then so can a big block of foam, even if it doesn't weigh much.

    Unfortunately, dangers such as these are just a part of space flight. It's never going to go away: as someone else posted earlier, birds can bring down planes and that's a mature technology. If space flight ever becomes routine, it will still be filled with dangers - the question is whether or not people are willing to take the risk. From a scientific perspective, we're very, very lucky that so many astronauts are willing to take it to advance our understanding of the world and the universe.

    Still, it's really hard to see that shuttle crew lost to a piece of foam. Or a piece of rubber (Challenger). It strikes me as odd that on something as monstrously complicated as the shuttle, the only two complete failures were due to relatively simple components. It also strikes me as a major accomplishment. Anyway...

  3. Intuitive sense of physics by fname · · Score: 5, Interesting

    Well, there are a couple things at play here:

    1) Materials are stronger at higher strain rates; essentially, the foam can probably remain elastic to much higher stresses when it is being deformed quickly, in a case such as this. To know more, you would want to do a series of high-strain rate tests on the foam to measure it's basic properties. In hindsight, choosing a foam with poor high-strain-rate performance should have been a requirement.

    2) The piece of foam they fired was so big that it probably acted as a constriant; essentially, a piece of foam being confined laaterally will have greater apparent strength than one that is not. When a very small piece of foam is fired, this effect would not be present. Scale is important, beyond just increased mass causing increased damage.

    It seems so obvious now, but I hadn't thought of these things before. Ideally, NASA would've conducted tests long ago with many sizes of foam hitting many parts of the shuttle, instead of abandoning the tests after seemingly benign results, in addition to basic experiments-- tests of the confined and unconfined foam.

  4. Analysis of the evidence by AlpineR · · Score: 5, Interesting
    While the Columbia was in orbit, the Boeing engineers made a presentation to NASA about their prior tests of how much damage the foam might do. Edward Tufte has analyzed the slides and illustrated how not to present scientfic data. Basically, the actual foam chunk was far larger than anything they had used in testing. But poor wording and misleading statements obscured that important point.

    Tufte also examined the Challenger evidence in his excellent book Visual Explanations.

    AlpineR

  5. How could they miss this? by Anonymous Coward · · Score: 5, Interesting
    I mean, tornados can punch 2x4s through concrete walls, and embed a piece of straw into a tree, and their winds maybe are 300 mph tops.


    So a 1.7lb chunk of foam going 500 mph would do SERIOUS damage. Come on! I mean, what kind of physicists are they hiring that can't wrap their brains around this?


    500mph = 804,672 m/h = 224 m/s

    1.7lb = 0.77kg

    from 1/2mv^2, we get...

    0.5*0.77kg*(224 m/s)^2 = 19,000 joules of energy!


    From a website on the power of explosives...

    TNT releases 2.72x10^6 J/kg

    So...

    g of TNT = (19,000 J/ (2.72x10^6 J/kg) )*1000g/kg = 7g ~ 0.25 Oz

    The size of a large blasting cap.


    Now, if you asked Nasa if setting off a blasting cap on the shuttle wing would be good or bad, well, I'd think they'd give you an incredulous look and call the FBI on you for being a terrorist and asking suspicious questions.


    This back of the envelop calculation MAY be off somewhat. But any engineer who sat down and said "Does this make sense" could have done it on an envelop as a sanity check.


    Now, knowing that foam hitting the wing is like setting off a blasting cap on it, perhaps people will realize the dangers of light things traveling very fast...


    Hmmm, I wonder how much energy a feather traveling at 0.5C would release...

  6. Foam misconception by confused+one · · Score: 5, Interesting
    I keep seeing people refer to this stuff in comparison to a nerf ball. This is way off !!!

    The tank is coated in a hard foam similar to the polyurethane foam used in insulation.

    Do a little experiment yourself here (warning: not for little children : ) Go to the hardware store and find a can of "Great Stuff" foam insulation spray. It's used to fill the holes in walls around pipes.

    Now, lay out a plastic trash bag, and empty the entire can onto the bag -- (warning: the stuff expands as it hardens; so, start in the middle of the bag).

    Once it hardens, take a look at the result. This is similar stuff, not quite as nice as what they use on the shuttle of course... Also, keep in mind that an entire can of "Good Stuff" is only 12oz. (3/4 lb). You'd need over two cans of the stuff to make a piece the size they're talking about.

    Think about that hitting you doing 500 mph...