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Post by drewid on Nov 22, 2009 12:56:21 GMT -4
Yes and no, it can't be simplified like that, a boundary needs to be defined for a specific purpose.
An analogy,
Say you are approaching a particular river. The ground starts firm, then gets soft, then marshy, then turns into wet mud, then shallow silty water a couple of inches deep, then running water ankle deep, then slow flowing water a couple of feet deep, then fast flowing water a couple of fathoms deep.
Where does the river start? It depends who is asking and for what purpose. A structural engineer wanting to build a bridge might say the river starts before the marsh, an angler might say it starts where he can stand to catch fish, for a boat pilot the river could be said to start from the depth it becomes navigable. They are all correct.
"Traditionally" the rings have been said to extend to ten radii, but this isn't a particularly useful boundary for discussing the TLI orbit. The radiation that far out isn't intense enough to be worth considering as a possible threat, which is a point of the discussion.
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Bob B.
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Post by Bob B. on Nov 22, 2009 13:04:33 GMT -4
I will also point out that Apollo 11 was traveling in a sunward direction, where the Earth's magnetic field is compressed by the solar wind. The VARB don't extend as far in that direction as they do in the opposite direction. The maximum number of 10 radii doesn't apply in this case.
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Post by fm on Nov 22, 2009 13:19:35 GMT -4
Ok, regarding the question of bremsstrahlung, I may have found an answer to my own question: Degradation by High Energy Radiation Phenolic resins and phenolic resin molding compounds may be of considerable interest for use in electrical components in nuclear power equipment and high voltage accelerators, components of equipment for handling radioactive materials, electrical and structural elements of space vehicles and as protective coatings in nuclear power plants. In these applications high thermal resistance is required apart from resistance to high energy radiation. When high energy radiation, including g- and x-rays, neutrons, electrons, protons and deuterons, passes through matter, a strong interaction either with the nucleus or with the orbital electrons occurs, leading to dissipation of a large fraction of the incidental energy. The final result of such interaction in polymeric materials is the formation of ions and radicals followed by rupture of the chemical bonds. At the same time, new bonds are formed, followed by cross-linking and degradation at different rates. The difference in the corresponding rate constants determines the resistance to high energy radiation. The rates of degradation are much lower for polymers containing aromatic rings because of resonance stabilization of the transient species. In general, rigid molecular structures, i. e. thermosettings, are more resistant than flexible thermoplastic and elastomeric structures. According to this figure, phenolic resins reinforced by glass- or asbestos fibers can be regarded as very radiation resistant synthetic materials. Non-filled phenolic resins have a relatively low radiation resistance. The oxygen content of phenolic resins has a considerably negative effect on the radiation resistance. www.niir.org/books/book/zb,,12f_a_0_0_a/Phenolic+Resins+Technology+Handbook/index.html So I have to admit, I think at this point the CM was shielded for bremsstrahlung
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Post by drewid on Nov 22, 2009 16:05:05 GMT -4
Also worth noting, the CM outer welded skin is specified as 0.190" ( 4.826mm ) of aluminium. In addition there are the lining insulation materials, which as noted are radiation resistant, and include more aluminium in honeycomb, phenolic resins, stainless steel and so on. and then the inner skin of the crew compartments, (as well as various metal faced control panels and equipment) and then the suits. That's a lot of thickness of various metals for a particle to get through
For example here are the approximate particle ranges in solid aluminum. Energy 1 MeV , electron 01.5mm , proton ~ nil Energy 3 MeV , electron 05.6mm , proton ~ nil Energy 10 MeV, electron 18.5mm , proton0.6mm Energy 30 MeV, electron no flux , proton03.7mm Energy 100 MeV , electron no flux , proton37.0mm
As you can see it's not really worth considering any electrons with an energy level of <3MeV, and any protons with an energy level of < ~40MeV since they aren't going to even get through the outer hull, let alone the rest of the materials.
If we produce a diagram showing the belts out to the 10 radii x 3 radii sizes it's actually somewhat misleading. Any HBer seeing the diagram would run around waving their hands in the air and yelling "Lookit radiation, they wuz in it fur hours!", but the bottom line is that the radiation out there is low level and couldn't get through a bean tin, and wouldn't do any physical damage if it did hit you.
One suitable boundary to depict could be at the point where radiation levels get dangerous outside the craft, as long as the shielding is fully explained. It would also be possible to depict when the radiation levels inside the craft go past a certain point, perhaps the 100 MeV level with a 20,000 particle per second per cm flux, but the scale of the belts shown would be very small since they only spent about five minutes at that level, and HBers would call it cheating, even though it's a perfectly valid description of what happened.
edited for clarity
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Post by Jason Thompson on Nov 22, 2009 16:55:13 GMT -4
Since my name is written clearly on every post I make, would you mind at least trying to get it right? This is the first time you have mentioned height from top to bottom. I amaware of the significance of the height of belts, but my point still stands: the diameter is less relevant if the craft is coasting above or below them. No reason he should, since he superimposed the trajectory of the spacecraft on some actual maps of the belts. In essence, he has already answered your question, but evidently not in a way you choose to take the time to understand. Notwithstanding your later admission that you consider the spacecraft adequately shielded, thank you for showing conclusively that you did not actually read the page of information you were presented with.
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Post by gillianren on Nov 22, 2009 17:08:27 GMT -4
Since this analogy (which I think is at least as clear as the river one) seems to have gotten lost in the press, I'm going to present it again in the hopes that it will do some good. ETA: Okay, try this. I came up with it while explaining the concept to my boyfriend, my own personal gauge of "what normal people know and understand." Let's say someone has put up a line of sprayers, and you're planning to walk under them. Now, the way they're set up, there's a place where you get kind of vaguely sprinkled upon, and the waterfall gradually gets heavier until you're just being "rained" on, then ebbs again. How long did you spend under the sprayer? Are you going to start from where the breeze is blowing occasional random droplets on you? When you walk directly under the beginning of the spray? When you're in the real, heavy part of the spray? What counts?
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Post by JayUtah on Nov 22, 2009 17:28:09 GMT -4
...Which I thought I sourced much earlier.NASA or third-party source? As for everyone throwing a hissy fit about boundaries and what not. What happened to common sense around here?Common sense (i.e., intuition) has little to do with this. You have suggested that the Apollo astronauts were "in the Van Allen belts" for far longer than is generally accepted and thus were subjected to a much greater dose of radiation than has been reported. If you had any argument to debunk, that may be what we're doing. Instead we're having to spoon-feed you the information necessary to determine what, if anything, your argument really means. You won't defend it and you won't provide the information required for anyone else to refute it. You're just making noise. The belts have always been defined up to at most 10 radii, right?Wrong. "The belts" have been described in a number of ways, many of which you've seen in this thread. Not all the ways in which the belts have been described (e.g., flux isolines) are directly relevant to your specific questions. Your trying to debunk an argument so use the worst case scenario.What argument would that be: the naked, unsupported assertion that the astronauts were "in the belts" longer than claimed? When you actually provide that argument, maybe there would be something to debunk. So I would assume you all would use the 10 radii as the utmost boundary regardless if the craft is still in the VAB or not, at that point. Is that clear enough?No it isn't. You're trying to paint an invisible line in space and say that inside of it live the Van Allen belts and outside of it is perfectly normal, quiescent space. That doesn't work, and we've explained why until we're blue in the face. If you take the dimensions of the Van Allen belts at the point at which the charged particle is just barely detectable, you can have one set of measurements. But that's utterly irrelevant to the question of radiation exposure, which is really what you're trying to answer. If you want dimensions in nautical miles, statute miles, furlongs, or Earth radii, you will have to determine at what level of exposure that isosurface is to be measured. And if that level of exposure is going to correlate to a biologically-significant level of radiation exposure inside a spacecraft, you will have to show and justify it. Simply picking out isolines on a drawing does not justify that "the boundary" is where you say it is for the purposes behind your questions. You may not simply handwave past that. We can wait till AP-9/AE-9 is officially released by the end of the year and base everything on that.Why does that matter? You don't understand and won't use the current models. More distraction and handwaving. And furthermore, the issue I am also raising is how large the belt is from top to bottom.At what intensity? You still haven't wrapped your mind around the notion that the trapped radiation environment doesn't have clearly-defined boundaries because it represents a phenomenon that is naturally highly variable as one moves through space. I addressed this earlier.No, you expressed extreme ignorance and unfounded skepticism over it earlier. No one is responsible for spoon-feeding you past every example of your ignorance. If you can't be bothered to learn even the basics of this science then you'll have to be content with the answer prepared for layman: "The conspiracy theories are nonsense." (James Van Allen) Scientist von Braun in his 1960 book...More decades-old hogwash. Why is it that you can only make headway when you cite stuff that was published in uncertainty right after this phenomenon was discovered? Sheesh, you whine that we'll have to wait for revision 9 of the standard models, yet you won't pay attention to anything that was done after 1961. I would like to know which materials in particular were used to prevent Bremsstrahlung.Steel, aluminum, fibrous thermal insulation, and various resins. You seem to think now that Bremsstrahlung is the new killer form of radation, even though you didn't know about it until last week. What is the wavelength of Bremsstrahlung produced in aluminum and how far does it penetrate aluminum for common shielding thicknesses?
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Nov 22, 2009 23:08:48 GMT -4
I've revised my article to include Apollo 11's return trajectory. Scroll down to just after the first color coded VARB exposure map; the second map is the flight path at reentry. On the return, Apollo 11 had an even greater inclination and velocity than at TLI -- it misses the VARB by an even wider margin. Apollo 11's Translunar Trajectory (Revised)
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Post by Cavorite on Nov 23, 2009 1:23:06 GMT -4
Allow me to add my voice to the chorus of appreciation.
Yet another example of how interesting this sort of detailed explanation can be even if it is underappreciated by the catalyst for its creation.
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Post by fm on Nov 23, 2009 6:06:06 GMT -4
I've revised my article to include Apollo 11's return trajectory. Scroll down to just after the first color coded VARB exposure map; the second map is the flight path at reentry. On the return, Apollo 11 had an even greater inclination and velocity than at TLI -- it misses the VARB by an even wider margin. Apollo 11's Translunar Trajectory (Revised)Well like I said, I couldnt imagine the trip to and fro being the same
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Post by Kiwi on Nov 23, 2009 7:43:39 GMT -4
I've revised my article to include Apollo 11's return trajectory. Scroll down to just after the first color coded VARB exposure map; the second map is the flight path at reentry. On the return, Apollo 11 had an even greater inclination and velocity than at TLI -- it misses the VARB by an even wider margin. Bob, that illustration could cause confusion because it shows the spacecraft reaching earth on the moon-side, whereas splashdown occurred on the opposite side of the earth, the one facing away from the moon. Could the path be extended to an approximate splashdown point? AS17-148-22727 was taken on Apollo 17's outward journey from a little below an extension of the Tropic of Capricorn, and I wonder if it is useful to illustrate the path taken to avoid the most intense parts of the VABs. It shows the earth from Antarctica up to the Middle East. Was this outward path at a southerly latitude an exception?
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Post by Kiwi on Nov 23, 2009 8:04:37 GMT -4
Fm, it seems you're scraping the bottom of the barrel. What's next? You're going to complain that the orbits haven't be[en] carved in Swiss chocolate and delivered to your door by liveried elves? One other thing that seems to be proved in this thread is that JayUtah comes up with some of his best lines when his patience has been stretched way past the breaking point of more ordinary mortals. That one is right up with another which is nine pages into Radiation for turbonium: You paint a totally wrong picture of space as a wholly unknown entity full of the physical equivalent of krakens and sea serpents, the existence and nature of which cannot be known except by throwing monkeys to them. Pure handwaving.
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Post by gee on Nov 23, 2009 11:25:30 GMT -4
Hi Just joined after finding this site a few days ago While i've never doubted Man has walked on the Moon, this thread and in particular Bob B's work has been not only educational (I never realy thought about the Van Allen Belt) but quite fun as well (i got the idea after the Doughnut)
Any way great site and a great bunch of people, i hope i can contribute in the future ( if you ever need to know the correct way to make a martini to help debunk a HB then I'll be there)
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Bob B.
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Post by Bob B. on Nov 23, 2009 12:27:42 GMT -4
Bob, that illustration could cause confusion because it shows the spacecraft reaching earth on the moon-side, whereas splashdown occurred on the opposite side of the earth, the one facing away from the moon. Could the path be extended to an approximate splashdown point? I can't show what I need to show if I did that. As I explaining earlier in the article... "Unlike the previous illustrations, which attempted to accurately depict what the orbit looked like from various perspectives, the above does not represent any specific viewing angle. The radial movement of the spacecraft is depicted in a flattened out profile view. Motion tangential to Earth's surface is in the third dimension not visible."It isn't a view per se, it is a graph of distance above/below the geomagnetic plane versus distance from Earth in the geomagnetic plane. It is what it is, I can't change it. If I were to draw the trajectory wrapping around Earth, I would lose the ability to show the data I need to show. I guess you can think of the view as a moving cross-section. What you see is the position of the spacecraft projected onto a plane that contains the center of Earth and Apollo 11 and is normal to the geomagnetic plane. Of course, as Apollo 11 moves, this plane moves along with it. The trajectory wraps around Earth, but it does so in the dimension that is in and out of your computer screen. If this latter descriptions makes more sense, perhaps I should rewrite that part of the article to make it more clear. Opinions, anyone?
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Post by echnaton on Nov 23, 2009 12:29:21 GMT -4
Hi Just joined after finding this site a few days ago While i've never doubted Man has walked on the Moon, this thread and in particular Bob B's work has been not only educational (I never realy thought about the Van Allen Belt) but quite fun as well (i got the idea after the Doughnut) Any way great site and a great bunch of people, i hope i can contribute in the future ( if you ever need to know the correct way to make a martini to help debunk a HB then I'll be there) Welcome to the board. Some topics are interesting, such as the Apollo program. Some topics are downright essential, such as how to make a great martini. Perhaps you can combine these subjects by devising a Van Allen Belt martini? Enquiring minds want to know.
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