NASA's Foam Test Offers Lesson in Kinetic Energy 503
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.
is it time to ban nerf guns then ... (Score:5, Funny)
Re:is it time to ban nerf guns then ... (Score:5, Funny)
Definatly works for NASA.
Uh... (Score:5, Funny)
Should I be worried?
Re:Uh... (Score:5, Funny)
(If it was, tell me where you got your shelf.)
Re:Uh... (Score:2)
Re:Uh... (Score:3, Funny)
And then there's the rotation of the galaxy. I hope all these people who claim to have set world speed records were travelling in the right direction at the right time of year.
Re:Uh... (Score:3, Insightful)
Re:Uh... (Score:4, Interesting)
Even though the foam was traveling at an extremely high velocity, wouldn't the relative velocity between it and the shuttle wing been quite low? Because, after all, until a few seconds before the strike, they'd been accelerating in the same direction as part of the same vehicle. Unless the acceleration rate was continuing at a substantial measure, I don't see how the total velocity of the foam off the tank would matter any more than the total velocity of the foam off your shelf.
Definitely not a physics major, am I? But could someone with a talent for dumbing things down explain this so I can understand it?
Not really... (Score:4, Informative)
Re:Uh... (Score:5, Interesting)
It's the 1000 MPH relative wind that produced the huge change in speed between the wing and the foam. The shuttle was accelerating upward somewhere around 3-4 G, and there's the 1 G due to gravity, but those are small accelerations compared to the wind resistance.
Re:Uh... (Score:3, Informative)
It was the shuttle's 1000 MPH speed relative to the ground that caused a 1000 MPH apparent wind relative to the shuttle, which blew the foam so that it was traveling 500 MPH relative to the shuttle. OK, clear?
Re:Uh... (Score:3, Insightful)
Re:Uh... (Score:3, Funny)
My shelf came from Home Depot.
...Later that day...
"Hi, welcome to Home Depot, can I help you find anything?"
Uh, yeah, I'm looking for supersonic home organization solutions. Do you have anything with rounded toe edge boards?
Some how I just can't realate... (Score:5, Funny)
Basic Physics (Score:4, Insightful)
I'm surprised that the impact was ever taken so lightly. Paint chips drill holes into satellites and birds take down planes, any impact, given the forces involved with such vehicles has the potential to be catastrophic.
Re:Basic Physics (Score:2)
Re:Basic Physics (Score:5, Informative)
It's not really force/acceleration that's important, it's kinetic energy and momentum:
Kinetic Energy = 0.5 * mass * (velocity^2)
Momentum = mass * velocity
So a 1g spec of dirt travelling at 20,000mph has the same momentum as a 1KG block travelling at 20mph - something best avoided!
Re:Basic Physics (Score:5, Insightful)
Not only that, but the 1g spec of dirt has a much smaller surface area than the block, therefore excerting a huge weight per surface area. And that's what punches a hole through you.
Re:Basic Physics (Score:3, Informative)
Nope. By the time they realized that something *MIGHT* be wrong, they were already in the wrong orbit for ISS. There wasn't enough delta-v available to get to ISS.
Re:Basic Physics (Score:3, Interesting)
come to think of it, it might be worthwhile to provide special suits for this kind of thing. EVA suits are big, bulky things designed for extended work outside the vehicle, and are therefore expensive to launch and require lots of space to store.
Since human skin is plenty strong enough to hold people together for short periods under vaccum conditions (sci-fi movies not withstanding), I'll bet it would
Re:Basic Physics (Score:2, Insightful)
How are kinetic energy and momentum more relevant than force? It all depends on how you do the analysis. The total kinetic energy is irrelevant - only the amount of energy transferred to the wing is important. Quoting e=0.5mv^2 looks good in the article because it highlights the importance of velocity, but saying that energy is important and force isn't is ridiculous, because in this scenario the two quantities are com
Re:Basic Physics (Score:3, Informative)
And that same 1KG block would have to be travelling at 632MPH to have the same kinetic energy!
K = 1/2m*v^2
K = 0.5 * 1g * 20000mph^2
K = 200000000
Therefore:
200000000=0.5 * 1000 * mph^2
40000 = mph^2
mph = sqrt(40000)
mph = 632.4555
Momentum increases artithmetically with velocity where as kinetic energy increase geometrically with velocity.
Re:Basic Physics (Score:5, Insightful)
At one point in the article they actually say that the force was equivalent to catching a basketball thrown at 500 mph. OF COURSE IT IS. It is equivalent to catching ANYTHING thrown at 500 mph which weighs about 1.7 pounds. The only real difference is elasticity(which is almost irrelevant at that velocity) and surface area of impact(the same amount of force to a much smaller area).
Reminds me of the old trick question you use to catch kids: "What weighs more: a kilogram of bricks or a kilogram of feathers?"
Re:Basic Physics (Score:5, Informative)
If a kilogram of bricks is put on a scale beside a kilogram of feathers on a scale, the readout from the two scales (aka, the weight) will be equal.
The metric system isn't silly with respect to mass and weight, it keeps them seperate. Kilograms are a unit of mass, and get used day to day because they more accurately reflect the common man's need for such a unit. People are generally interested in buying an AMOUNT of a material, instead of an AMOUNT THAT EXERTS A CERTAIN FORCE. Weight, on the other hand, is expressed in Newtons, and is generally used for scientific or engineering applications.
For example, if I bought a kilogram of sugar on the moon, I would be getting the same amount of sugar as if I had bought a kilogram of sugar on Earth. A pound of sugar on the moon would be five to six times as many granules of sugar as a pound of sugar on Earth, however.
I don't mean to sound like I'm flaming here or anything, but the popular confusion of mass and weight, especially in the Imperial unit system, really bothers me.
'Volkswagen Beetle' math, please. (Score:5, Interesting)
I wonder how many Volkswagen Beetles that is?
Re:Basic Physics (Score:5, Insightful)
I think foam hitting the shuttle not doing any damage was a classic case of wishful thinking. Good engineers like this are exactly the people not suppose to do that kind of thinking.
Mistake was made but I think a lot will be learnt from it. If you look at some of the future shuttle designs you can see they already place the shuttle on top (in front depends how you look at it) so anything coming off doesn't hit the shuttle. This was a major design flaw having the shuttle in that position to the tanks and they know it.
Re:Basic Physics (Score:5, Interesting)
Because of this, I think the engineers were lulled into thinking "Well, it happened before and it didn't cause any damage, why whould anything change now"
Tragically, their apathy about the whole situation cost the lives of 7 really smart and talented people.
In the future when we build the next generation shuttle, they integrate some better sensors that would detect that kind of damage.
Re:Basic Physics vs Intuition (Score:5, Insightful)
I would think that the line of thinking was, when the foam separated, it was moving at the same speed as the shuttle itself. Since the shuttle, at time of impact was at 50,000+ feet, the force of air drag on the foam would be negligible and the piece of foam would approximately maintain its speed.
I seem to remember that it is about 30 feet from the bipod to where the foam struck the orbiter's leading edge, so assuming that the foam travels at approximately the same velocity as when it came off and the shuttle was accellerating at 2.5 Gs, it would take about 1.4 seconds for the foam to hit the leading edge. Using these assumptions, the velocity of the foam at impact, relative to the leading edge, would be 110 ft/sec or roughly 75 mph.
This doesn't sound too bad - after all, it's foam. Getting hit by a Nerf football that has been thrown hard by somebody close by stings, but it won't break bones or even come close to breaking the skin. If you don't think it could do more than bruise you, then it would be hard to accept that the carbon-carbon leading edge of the orbiter could be damaged.
I think that this was the level of intuitive analysis that was done. Unfortunately, it wasn't backed up by any kind of quantitative analysis using known facts (such as estimating the speed of the impact from the film and checking it against the intuitive speed of impact) to test whether or not there were grounds for concern.
myke
You haven't thought of everything (Score:5, Insightful)
1) Aerodynamic drag at 50,000 feet is hardly "negligible". Drag is proportional to local atmospheric density times the square of the velocity. Atmospheric density at 50,000 feet is 15% that at sea level. Therefore the drag at that altitude is equal to the drag at sea level at 39% of the speed. In other words (pick a number) 500 mph at 50,000 feet causes the same drag as 195 mph at sea level.
2) Therefore, not only was the space shuttle ACcelerating, but the foam was DEcelerating - probably a LOT - but the point is, it needs to be taken into consideration.
3) The foam coating the fuel tank is HARDLY the same as that a nerf ball is made of. It is much more substantial.
4) As I understand it, the piece of foam that broke off was very likely coated with ice. I think if you got hit by a piece of ice travelling 75 mph (much less at an even higher speed), you would most certainly be injured, and so would the leading edge.
5) Prior strikes were grazing blows on the surface of the wing. We are postulating a direct hit on the leading edge of the wing, made up of very brittle carbon fiber composite.
All that said, in the end I don't blame those on the scene as much as those responsible for the crappy concept as a whole. Hopefully I would have thought of the case of a direct strike on the leading edge, and hopefully I would have woken up to danger (albeit maybe too late) when a piece of the shuttle was OBSERVED to part company while in orbit, but my true ire is reserved for whoever is responsible for the design concept as a whole. If the fuel tank was coated with crappy insulation that frequently broke off in chunks during launch, that in itself doesn't constitute a hazard. But as soon as you mount a manned space vehicle directly in the path of the debris, that is just unforgiveably negligible.
Re:Basic Physics (Score:4, Insightful)
The fact is that some engineers thought that it might be a problem. And from what I have heard they also had computer simulations showing that the impact could have caused damage. So what happened?
The publicity for this would suggest that as a whole NASA just didn't figure that this foam hit was a problem. The problem I see is that their minority opinions didn't float up along with the majority report. This is very human, either managment wanted to or was under pressure to give a definative statement or else the engineers with the dissenting view points decided they weren't sure enough of their positions to take a stand.
But why should any engineer have to be sure about their analysis? They are dealing with a limited amount of data with a large number of unknown variables. So perhaps the minority engineers figured that they were just really making an educated guess, but then so were the majority engineers. What basis would they have for disagreement, so if a conclusion was asked for then it makes sense to go with the conclusions of the majority, very simple and in most cases most of the time it will give you a good result. But they had the resources and time to continue to analyze this and it would make sense to continue to do so if a real worst case scenario had emerged.
Seems to be that this type of bad decision making
is what needs to be addressed at NASA. Yes, the foam needs to be fixed, but it wasn't like the O-Ring problem in the Challenger accident when the weather conditions caused a catastrophic failure of the seal. Rather this was a catastrophe that unfolded over many years and culminated when a NASA spokesman told reporters that the falling foam was not a problem.
This foam accident had happened before and could have been fixed, before the columbia even flew. But like the drunk that decides that they have driven home before without a problem so why should tonight be any different, they largely decided to rely upon experience. But this is not the type of problem where experience can be used. This wasn't even really engineering, they were being asked to solve a mystery.
Analysis by consensus with a single conclusion was a bad idea in this situation. If you are going to take a vote and then report the result as a conclusion, then that is a fundamental mistake. Like asking a roomful of people if God really exists. The majority might say yes or no, but won't you still want a few people praying just in case.
If the initial analysis of the foam strike had included the minority opinions then NASA management could have directed more resources towards the analysis, they would have gotten the military to take a picture of the wing and then perhaps had the astronauts do and EVA to take a look and then perhaps launched the Discovery for a rescue mission and this could have had a very happy ending. If the initial analysis had included any indication that the conclusions were not certain, then it seems likely and obvious that these additional steps would have been taken. In fact the military had already been put on standby to take some pictures of the affected area, but it wasn't to be.
So, it isn't clear to me if the engineers were truly at fault here or if it was the management process that was in place. Certainly engineers could have expressed certainty in their concerns, but why express certainty when there is none? Seems to me the problem here was that the engineers were asked to reach a conclusion and they did. They clearly did not have enough evidence to be certain of what effect the hit would have on the shuttle. Unless another timeline comes to light, I have to conclude that the faulty analysis came from the management of the engineering group or from the nature of the directive that that group received. This is what should be addressed, anomali
Re:Basic Physics (Score:2, Informative)
Otherwise flying through heavy snow/rain would down every aircraft on earth.
Tom
Re:Basic Physics (Score:4, Informative)
Really? As I recall, the SI system didn't exist when Newton developed his equations.
Also, as long as you use the proper constants, what's the difference if you use kilograms, meters, and seconds; or slugs, feet, and seconds?
Flecks of paint are dangerous, too. (Score:5, Interesting)
Glasses with tape (Score:5, Funny)
It is pretty obvious that these guys are geeks yes?
__
Cheap reseller hosting [cheap-web-...ing.com.au] Action figures dragon [mibglobal.com.au]
Re:Glasses with tape (Score:2, Funny)
Geeks or kindergartners, sure.
Re:Glasses with tape (Score:3)
Bad picture? (Score:3, Interesting)
Did they print the wrong picture? The article implies a great deal of damage but all I can see in the picture is the foam object getting destroyed. The wing itself looks completely fine.
Re:Bad picture? (Score:4, Informative)
This guy is a rocket scientist? (Score:3, Funny)
This guy is a rocket scientist? I guess that's one stereotype debunked.
Re:This guy is a rocket scientist? (Score:5, Informative)
So will people *PLEASE* quit insulting rocket scientists.
Re:This guy is a rocket scientist? (Score:2)
Relative velocity? (Score:5, Interesting)
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?
Re:Relative velocity? (Score:3, Insightful)
Re:Relative velocity? (Score:5, Informative)
You are probably somewhat right, the velocity of impact is something like the speed of the shuttles ascent - speed of the foams ascent. However to maintain a 500 MPH ascent requires a considerable amount of constant energy. The foam probably decelerated much quicker than you are thinking.
Re:Relative velocity? (Score:3, Interesting)
Re:Relative velocity? (Score:3, Insightful)
Argh, of course. Yeah. So if the "white blur" moves 10 feet in a single 1/60 second frame, then it's moving, what, 600 feet per second (or something around 400 MPH). Factor in uncertainty for the size of the blur (because, after all, it's blurred), and you get a nice clean velocity range.
I shoulda thought of this, too.
Here's the real issue. (Score:5, Interesting)
1) When the insulation piece fell off it was essentially encased in solid ice, which is a pretty hard material to start with.
2) At the time the insulation fell off, the space shuttle was travelling a couple thousand miles per hour already. That could (in theory) add to the impact force on the wing.
NASA should have tested the insulation foam encased in ice fired at physical simulation of the shuttle leading edge, in my opinion.
Re:Here's the real issue. (Score:5, Insightful)
How much ice exactly? There's no way of knowing. They do know how much foam fell off. If they test using just foam, they know the minimum amount of damage done for sure. If they add a guestimated amount of ice, they haven't proven anything.
At the time the insulation fell off, the space shuttle was travelling a couple thousand miles per hour already. That could (in theory) add to the impact force on the wing.
It's irrelevant how fast the shuttle was travelling. Only the speed of the foam relative to the wing matters (i.e. when bloan by a thousand mph wind). Presumably they measured this from the video they had.
Re:Here's the real issue. (Score:2, Interesting)
Also the Ice thing is just a possibility, Only if air (which contains water vapour) gets in between the foam and whatever cool part it was covering will ice form.If that was the case, Nasa has bigger problems to worry about.
Re:Here's the real issue. (Score:2)
Re:Here's the real issue. (Score:3, Informative)
The exact values can be found in public record if you choose to look
The foam was moving 500 mph relative to the wing
Intuition (Score:4, Insightful)
No kidding. How could they think a piece of foam shot at over 500 mph would bounce off harmlessly? Nearly everyone knows a penny dropped off the Empire State Building can kill someone- this foam (which is heavier, and is going faster than the penny would be going) would most certainly do damage.
Penny's can't kill. (Score:5, Insightful)
And the empire state building is wedge shaped, with ledges ever couple of stories. There's no way for a penny to even make it to the ground.
Also, it's not the fact that the foam was going 500 mph hour, it's the fact that the shuttle was.
Re:Intuition (Score:5, Funny)
It's intuitively correct, but I should warn that the physics of sleeker objects like cellphones are quite different, judging from the one dropped on me while descending a staircase last Memorial Day. Fortunately for me it was a glancing blow -- the phone shattered after deflecting from my head. Apparently a cellphone in freefall is not accompanied by an apology, but I took satisfaction enough in the destruction of the phone.
Astounding... (Score:5, Insightful)
Re:Astounding... (Score:2)
You must not work for the government. EVERYTHING operates at a glacial speed.
It takes a month of meetings to decide on a course of action, two months to do any purchasing required, then another month to assemble the stuff that was bought.. then actually do the job that the meetings decided they should do.
You may think I'm kidding, but I'm not.
In fact unless I've already lost track of the passage of time
Don't forget - this wing was *stronger*... (Score:5, Insightful)
From the article:
The next round of tests in Texas could add weight to the growing consensus about the cause of the accident. Last week's tests used wing panels from the Enterprise, a test vehicle that never flew in space. That craft's leading edge panels were made from fiberglass because the Enterprise never had to face the heat of re-entry.
Foam testing will resume on Thursday with the first effort to fire a chunk of foam at the actual material used on the leading edge of the shuttle's wing. The material, reinforced carbon-carbon taken from the shuttle Discovery, is substantially weaker and less flexible than fiberglass.
A lesson in kinetics indeed. Perhaps it was a micro-meteorite or junk, but based on this data I'd say they've solved it.
NASA: Kinetic jerks (Score:2)
are you kidding... (Score:3, Insightful)
is he serious?? performing a 5 second equation before telling the shuttle to come back could have predicted and prevented this tragedy. i'm glad it's hitting home for him now...too bad he completley forgot his rudimentary physics a few months ago. this is just another in a long line of examples of NASA engineers not being up to par with basic math. (what...yards != meters???)
Scary Stuff (Score:5, Interesting)
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...
Birds? (Score:3, Interesting)
I know they test-fire birds at the fuselage, but if a bird hits the wing (or rather, if the wing hits a bird) it could cause problems.
They can find ways to ensure that foam doesn't come loose like this in the future, but I don't think they can eliminate the possibility of overflying birds.
Re:Birds? (Score:2)
Re:Birds? (Score:2)
Re:Birds? (Score:2)
Oh no! (Score:3, Funny)
Intuition vs. Calculation? (Score:2, Interesting)
If it's such a simple formula and the facts
Basic grasp of Physics not needed at NASA (Score:5, Insightful)
The second most frightening part of the story is that these tests were performed on a mock-up wing taken from the Enterprise (which has never flown) and is made out of fiberglass, a stronger (but much more heat labile) material than the carbon-carbon stuff the leading edge of the actual wing was made from. I wonder how nasty the results will be once they use the real material that failed.
BFL
Re:Basic grasp of Physics not needed at NASA (Score:4, Insightful)
Re:Basic grasp of Physics not needed at NASA (Score:3, Informative)
Re:Basic grasp of Physics not needed at NASA (Score:3, Insightful)
Wow, and THEY'RE rocket scientists... (Score:3, Funny)
Next we'll have terrorists near the shuttle launch with slingshots...
Intuitive sense of physics (Score:5, Interesting)
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.
Re:Intuitive sense of physics (Score:3, Insightful)
You propose tests based on your knowledge of what events might occur. That's why they shoot birds into jet engines and cockpit windows. I guarantee that they also eit
What is it with these Hubbard people? (Score:4, Funny)
Considering a Tornado .. (Score:3, Interesting)
And even then an F6 on the Fujita scale which is completely inconceivable (if the F5 is the finger of God, this is the "2-stroke 250cc dirt bike of God") would have wind speeds of 319+ MPH
Re:Considering a Tornado .. (Score:4, Interesting)
And that was merely to protect the weaker heat shielding on the conical part of the spacecraft. The blunt end heat shield was protected by the Service Module until shortly before re-entry. The ice generating fuel tanks were also below the space craft, instead of partially above it. One of the problems with the Shuttle design is that much of the heat shielding is exposed during lifoff. I suppose some variation of the BPC could have been designed for the leading edges of the wings, but there certainly would have been a weight penalty, and the Shuttle is a heavy bird to begin with.
This is a problem that is going to have to be solved if a production re-usable spacecraft is ever to happen. We might not be at the stage of materials science to do it yet, though.
Analysis of the evidence (Score:5, Interesting)
Tufte also examined the Challenger evidence in his excellent book Visual Explanations [amazon.com].
AlpineR
tornadoes and straw (Score:2, Interesting)
test videos available online (Score:5, Informative)
The videos are here [streamos.com] (where the panel visibly ripples after the impact) and here [streamos.com].
The accompanying slide presentation [caib.us] has the details: the 1.7 pound foam block was fired at 531 mph and, where it struck a T-seal between two panels, displaced them and caused a 4/10 inch gap. This fake wing was made of fiberglass, but given the results, a test with actual shuttle wing material from the Space Shuttle Discovery is planned for today.
Here are some of the headlines [google.com] from news.google.com [google.com]:
Shuttle Wing Under Gun [newsday.com]
Investigator Amazed by Shuttle Foam Force [yahoo.com]
Foam theory faces pivotal test [chron.com]
Tests Show Foam Causing Wing of Shuttle to Deform [washingtonpost.com]
Foam chunk was shuttle's undoing, tests indicate [globeandmail.com]
How was the test done? (Score:2)
From how far away was it shot? How cold was the wing section? What was the ambient air pressure?
What was the foam shot out of??!?
How could they miss this? (Score:5, Interesting)
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...
Re:How could they miss this? (Score:2)
I don't get the 500 miles per hour number (Score:4, Interesting)
What bothers me is the 500 miles per hour number. It's irrelevant how fast the foam was moving relative to the ground, only how fast it was going relative to the shuttle wing. And since this liftoff was very non-realativistic, we can use classical kinematics:
This foam was attached to the tank at lift-off, right? That means it was going the same speed as the shuttle at that instant it broke off. THAT means that RELATIVE TO THE SHUTTLE, it accelerated from zero to 500 mph (AGAIN, ELATIVE TO THE SHUTTLE) in the space of 200 ft or so. Well, using the kinematics equation:
Vf^2 - Vi^2 = 2ad
with:
d = (worst case for most acceleration) = shuttle length = 200 ft,
Vi=0
Vf = 500 mph = 733 ft/sec
gives
acceleration = a = (Vf^2 - Vi^2)/2d = 733^2/(.0379 * 2)= 7088245 ft/sec^2 = 220000 times the acceleration due to gravity!
Check my numbers, please, but that seems a little high to be caused by braking due to air resistance.
Re:I don't get the 500 miles per hour number (Score:3, Informative)
But regardless, I believe the 500 mph was measured by looking at how far the foam moved between frames of video, relative to the shuttle.
I don't think it was calculated from an acceleration.
Re:I don't get the 500 miles per hour number (Score:3, Informative)
But gravity is not the only force involved. The shuttle was moving up at 1000 miles an hour.... through the air and the wind. When the foam broke away, it immediately became subject to wind resistance, and slowed down due to wind. A 2 pound piece of foam in 1000 mile an hour wind can change velocity quite a lot in 200 feet. It was able to slow down (relative to the ground/wind) by 500 miles an hour due strictly to wind resistance.
The math is left as an excercise for the v
Re:I don't get the 500 miles per hour number (Score:5, Informative)
Re:I don't get the 500 miles per hour number (Score:3, Insightful)
Vf^2 - Vi^2 = 2ad
This formula assumes constant deceleration. However, aerodynamic drag (and hence deceleration) is proportional to the square of the velocity.
Duh or Aha? (Score:2)
Keep this in mind next time you hear about a "Duh" experiment. Scientists routinely test even the most "obvious" of assertions, because every so often those "obvious assertions" are actually wrong.
Don't be morbid (Score:2, Insightful)
Leave the engineering issues to engineers and scientists. The general public doesn't give a rat's ass about kinetic energy or materials science, they just use it as an excuse to re-live the tragedy over and over.
Why are people suprised? (Score:2, Insightful)
Considering how much damage something as small as a paint fleck can do [nasa.gov], at high speeds, a 1.5 pound chunk of anything can be dangerous.
We need shuttle alternatives. (Score:3, Insightful)
This illustrates why it may be a good idea to put some money into research of an alternative to the shuttle program. The shuttle program will always face dangers of this type, considering the speeds/forces involved in getting the shuttle into orbit.
Perhaps a program where a spacecraft could actually take off like an airplane and be piloted out of the atmosphere. Even if a large burst of propulsion was needed to get it out of the atmosphere: it would be pulling less G's since it would already be moving with good speed, it would have to do so for less time, and there possibly wouldn't be external systems needed to do it (booster rocket and foam...).
If the official consensus ends up being that the foam caused this, perhaps it will be an impetus for change.
Foam misconception (Score:5, Interesting)
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...
They should have realized. (Score:4, Insightful)
These stories of ice covered foam remind me of something...
In one of the NRC labs in Ottawa, they have a "chicken gun" that fires broiler chickens at high velocity into mock ups of aircraft windshields. It is probably an urban legend, but I heard a story that some British engineers decided to duplicate the experiment, and were horrified to find that the chicken smashed a hole clear through the windshield mockup and buried itself in the far wall. They emailed their Canadian colleages to ask what they were doing wrong. The reply was simple: "thaw the chickens first."
But seriously, as the velocities increase, so does the danger. I once saw a picture of the windshield on another orbiter that had been struck by a tiny fleck of paint from an old booster. It looked like it had been struck with a bullet, and had the paint fleck been slightly larger, NASA would have had yet another catastrophic end to a shuttle mission.
If we ever develop a really good propulsion system that can approach light speed, we had better invent deflector shields along with it. As you hit relativisitic speeds, anything you collide with releases energy proportional to an equivalent sized hydrogen bomb. Even molecules become dangerous, and a dust speck would blow a good sized hole in your spacecraft.
Re:They should have realized. (Score:5, Informative)
What's really funny (and what provides an additional clue that this is an urban legend that's been around the block a few times) is that in most versions of the legend, it is a group of American engineers who have to clue in their foreign counterparts (their nationality varies too) that they have to thaw the birds first. If there's one universal in comedy, though, it's making fun of foreigners.
Proof? Experiments?*shrug* NASA says Whatever... (Score:5, Interesting)
"In fact, he said, the force was equivalent to catching a basketball thrown at 500 miles per hour."
THEN
although the experiment "moves us a lot closer to saying that foam can do this kind of damage," it did not rule out other possible causes of the hole in the wing, including small meteorites and debris in space.
What is it about this being a peice of foam that they still can't cop to this being most likely.
If I saw you throw a basketball at my car at 500mph, I would likely stop looking for the "real" cause of the dent!
Even after the experiment and the basic lesson in physics, they still won't say "Yeah, we are keeping our minds open to any new evidence, but right now it appears that this foam strike was the a major factor in the accident."
THERE IS NOTHING WRONG WITH SAYING "Yes, we think this is what caused the damage" If it was instead the basketball that indeed hit the shuttle, the debate about what caused the damage would be wrapping up.
I say major factor, becuase I personally have theorized on
Below is the text of my former post on this idea-
'Under the conditions of a normal return to earth, the shuttle flies on autopilot until it is traveling more slowly than the speed of sound. But pilots train to take the shuttle all the way down in case the autopilot malfunctions, and so it is possible one of the pilots was trying to take control of the yawing craft in its final moments. 'It is relatively easy for the autopilot to be turned off by accident, which in fact happened just minutes before the problems with the Columbia started to become apparent. In the recovered segment of flight deck video of the waning minutes of the flight released by NASA, Colonel Husband is heard to exclaim, "Oh, shoot," and to tell mission control that "we bumped the stick earlier," briefly disengaging the autopilot. He quickly and calmly corrected the error'
What this all leads me to is this, and I have not seen this suggested in anything I have read as an important concern: Is it possible that this accidental disengaging of the autopilot CONTRIBUTED to the loss of the Shuttle? Although the pilots are trained to fly the Shuttle without the Autopilot, if they were unaware that it was turned off then the "minute" adjustments that either one would make would be missed. All accounts I have seen suggest that the slightest details on the approach make HUGE differences in the results. Add to this the fact that it has been reported that the Autopilot, when on, was acting to correct the flight path anomalies caused by the damage outside. If the autopilot is off, then what other consequences were being experienced?
Is it possible that this with the likely outside damage and other factors may have COMBINED have caused the loss of the Shuttle where any issue ALONE would have not? With all the speculation I have seen in the media, I am not sure this is any less of a possibility...
BTW, I personally am not trying to lay blame on the astronauts themselves. Much like a Cruise Control that starts to mysteriously disengage on a vehicle, I would not be surprised if the Autopilot may have "sensed" a disengage as simple as moving the stick, and the pilots assumed that one of them must have done it."
Why won't they address this simple question? (Score:5, Insightful)
The Shuttle's main tank is a huge cryogenic storage cylinder. It is cold, very cold. So cold that they have to insulate it. So cold that atmospheric air will form a sheet of ice on its outsides. So cold that ice formation is monitored before launch. Why won't they talk about this?
The leading portion of an aircraft body and wing is where ice will accumulate in flight. It can collect in amounts large enough to make the aircraft unaerodynamic. Amounts large enough to fall off in chunks. Why won't they talk about this?
The material seen impacting the Shuttle wing has been described as "grayish-white". Ice just happens to be this same color. What color was the insulation? Was it grayish-white too? I doubt it! If the insulation were the same color, how could they visually check against ice formation before launch?
A pound of feathers versus a pound of lead (Score:3, Interesting)
Folks, a small weight moving fast packs a lot of punch. Even foam/feathers/pillows.
Ice? (Score:3, Insightful)
I don't know how fast the air friction melts this, but wouldn't foam laden with ice be even worse?
Environmentalism destroyed the shuttle? (Score:5, Informative)
Management triumphs over Engineering, again. (Score:3, Insightful)
It's looking more and more like there was a management decision to accept foam impacts despite the engineers of the shuttle specifying that nothing should impact the shuttle.
Previous reports indicated NASA management argued that the impacts were OK since nothing bad happend from past impacts,and because it was "just foam". Some of the same articles stated that the engineering design docs stated no impacts were acceptable.
The challenger disaster was for sure due to managers deciding to launch against the strong advice of the engineers not to launch.
This current article's quote of the NASA Ames person (who has been in management for awhile now as someone has already pointed out) surely is suggestive of the problem. It indicates his surprise that the physics don't match his inuitive expectation. Maybe that's a root of the problem. People with some science background in a non-relevent field who move on to a management role are relying on their own intuition over that of those that are doing the actual engineering in the relevent field.
For sure if they were going to accept the impacts then they had a responsibility to put the resources into experts carefully analyzing what the outcome would be for all the possible impact area's and times. That would allow a scientifically informed decision.
Instead there was an intuitivly informed decision.