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Wich is the best Radiation Hull or Shield we can build for a spacecraft?
In article , (Steve Harris ) writes:
wrote in message ... Yes. Complicated stuff. What you end up with is a "sandwich shielding", a set of layers, each with a specific function. We do it already. When you want to shield against fast neutrons, you need a sandwich of moderator-neutron_absorber_gamma absorber. You can think up more complex configurations. Yes. And you need a sandwich for spallation neutrons which are 20% of the radiation in some cases, and which come off of 30 or 40 heavy ion species at a very wide range of energies. No simple answers to any of this. On doing a little research I find that much of the needed data and analysis hasn't even been collected or done. Its not that bad. Most if not all of the information required exists, you just need to put it together into a design. COMMENT Nope you underestimate this. Truely. There are monte carlo quantum codes for heavy ion radiation transport in solid matter. There is much more than just this. Heavy ions, protons, ultra-relativistic electrons, gammas, neutrons and all possible mixes. How much you'll find in the open literature, that's another story. But that's just the beginning. You have to know the input flux of heavy ions not only in interplanetary space, but also on the Martian surface, where the atmosphere has greatly screwed things up and changed the character of the radiation (more neutrons!) but not blocked very many rads. We know this muchy, but we know too little of the character of radiation on the Martian surface to model effects on humans that well, yet. It's a major question on future Mars robotic missions. Then you have the problem that heavy ion biological effects are the most poorly studied of all known radiation effects, and here they're a major player. Only if you shield very poorly. The reason heavy ion biological effects are the most poorly studied, is because heavy ions are the easiest to block. It is only when their kinetic energy, per nucleon, exceeds their binding energy (again, per nucleon), that spallation effects become a bitch. But you don't encounter many heavy ions in this range. For every phase you have that 3-element neutron sheild design, but you have to do it THREE times, and in three separate ways. Not really. A neutron shield is a neutron shield. One which is designed for the highest energy neutrons you expect to face is good for all the rest, as well. The problem with neutron shields is that there is really no way to make them compact. You need sufficient thickness for moderation. So, basically, you've to plan on sufficient thickness to stop the fast protons, followed by a sufficient thickness, from this point, to moderate the neutrons. And the you've to absorb the thermal neutrons and provide sufficient thickness, from this point, to absorb most of the resulting gammas. That's quite bulky. Mati Meron | "When you argue with a fool, | chances are he is doing just the same" |
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Wich is the best Radiation Hull or Shield we can build for a spacecraft?
Personally, I was thinking from the NASA Ames Summer Study 1975, wherein the
participants were charged to build a permament Space City. This can correlate to building the initial Martian, or Lunar, Settlement. One of the problems The Summer Study faced was the issue of Radiation in the Colony Station. The participants solved it through use of a six feet thick shield, consisting of lunar regolith, between the double hulls. A reduced version could be used in the interplanetary spacecraft. Unfortunately, the regolith is deadweight mass, and requires fuel to transport it between Earth and Mars (as well as vice versa). Comments? -- Leonard C Robinson "The Historian Remembers, and speculates on what might have been. "The Visionary Remembers, and speculates on what may yet be." |
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Wich is the best Radiation Hull or Shield we can build for a spacecraft?
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Wich is the best Radiation Hull or Shield we can build for a spacecraft?
In article , (Steve Harris ) writes:
wrote in message ... Then you have the problem that heavy ion biological effects are the most poorly studied of all known radiation effects, and here they're a major player. Only if you shield very poorly. The reason heavy ion biological effects are the most poorly studied, is because heavy ions are the easiest to block. It is only when their kinetic energy, per nucleon, exceeds their binding energy (again, per nucleon), that spallation effects become a bitch. But you don't encounter many heavy ions in this range. COMMENT: You do in interplanetary space and on the Martian surface---that's the whole point. The fraction of hadron radiation in space goes down as some power loaw, but it's not absolute fractions that are important as energy fluxes (fluences). For (extra galactic) cosmic rays (which will cause more radiation than a quiet sun), in order to look at all significant biological dosing, you have to integrate all the way up from channels of 10 MeV per nucleon to 100 GeV per nucleon. You got some confusion here. There are protons in all possible energies. There is little if any evidence for any significant amount of heavy ions at hig energy (heavy ion is an ion with *Z 1*). Proton at 1000 Gev has an energy of 1000 GeV pre nucleon. This *does not* mean that you've heavy ions at high energies. All above binding energy. As I said, 20% of your total radiation dose on the Martian surface is spallation neutrons. Certainly since all protons above 10 MeV or so will give you spallation. Nothing to do with "heavy ions". For every phase you have that 3-element neutron sheild design, but you have to do it THREE times, and in three separate ways. Not really. A neutron shield is a neutron shield. One which is designed for the highest energy neutrons you expect to face is good for all the rest, as well. The problem with neutron shields is that there is really no way to make them compact. You need sufficient thickness for moderation. So, basically, you've to plan on sufficient thickness to stop the fast protons, followed by a sufficient thickness, from this point, to moderate the neutrons. And the you've to absorb the thermal neutrons and provide sufficient thickness, from this point, to absorb most of the resulting gammas. That's quite bulky. COMMENT: Reread my message. You need three neutron sheilds because you need to make them out of three different sets of materials, and they need to do the job against two different radiation environments. No you don't yyou need a primary shield which is thick enough to stop all (or nearly all) charged particles). Then you need a moderation layer thick enough to slow all neutrons in generated within the first layer (or neutrons incoming into the first layer) to thermal or near thermal velocities. Then you need something to absorb these neutrons and absorb the gammas generated by the neutron absorption. Mati Meron | "When you argue with a fool, | chances are he is doing just the same" |
#6
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Wich is the best Radiation Hull or Shield we can build for a spacecraft?
wrote in message ...
In article , (Steve Harris ) writes: wrote in message ... Then you have the problem that heavy ion biological effects are the most poorly studied of all known radiation effects, and here they're a major player. Only if you shield very poorly. The reason heavy ion biological effects are the most poorly studied, is because heavy ions are the easiest to block. It is only when their kinetic energy, per nucleon, exceeds their binding energy (again, per nucleon), that spallation effects become a bitch. But you don't encounter many heavy ions in this range. COMMENT: You do in interplanetary space and on the Martian surface---that's the whole point. The fraction of hadron radiation in space goes down as some power loaw, but it's not absolute fractions that are important as energy fluxes (fluences). For (extra galactic) cosmic rays (which will cause more radiation than a quiet sun), in order to look at all significant biological dosing, you have to integrate all the way up from channels of 10 MeV per nucleon to 100 GeV per nucleon. You got some confusion here. There are protons in all possible energies. There is little if any evidence for any significant amount of heavy ions at hig energy (heavy ion is an ion with *Z 1*). Proton at 1000 Gev has an energy of 1000 GeV pre nucleon. This *does not* mean that you've heavy ions at high energies. Not my confusion. Need for you to read up on the subject, since you're way out of date. 98% of extragalactic cosmics are H and He, but the remaining 2% (which is better than our own solar system for metalicity) are ions all the way up the periodic table, at any energy you like (and as far up as has been measured). Mostly below Z=30, as expected, but also going higher. Relative abundances for even elements look a lot like what we're used to. All evidence for the supernova shock origin theory. http://www.wkap.nl/prod/a/ISBN_0-7923-7196-8_29.PDF Certainly since all protons above 10 MeV or so will give you spallation. Nothing to do with "heavy ions". Heavy ions are important to the extent you have to do your shielding with other than hydrogen. If you're sheilded with a big ball of frozen H2 on the voyage out, heavy ions are your most important source of neutrons. COMMENT: Reread my message. You need three neutron sheilds because you need to make them out of three different sets of materials, and they need to do the job against two different radiation environments. No you don't yyou need a primary shield which is thick enough to stop all (or nearly all) charged particles). Then you need a moderation layer thick enough to slow all neutrons in generated within the first layer (or neutrons incoming into the first layer) to thermal or near thermal velocities. Then you need something to absorb these neutrons and absorb the gammas generated by the neutron absorption. Yes, and since you have three different sets of materials available to do some of these jobs. The moderator will be of different thicknesses depending on how much neutron radiation has to be dealt with, which is a function of radiation type atmosphere interactions, and type of primary sheild (how much hydrogen). If you are in space this will be a lot of hydrogen, so your moderator has to deal with only those neutrons produced by heavy elements in the primary sheild, and neutrons produced by high Z cosmics in the primary sheild. But on the Martian surface things are very different, and you have neutrons produced by a primary sheild of sand, and in the atmosphere before that. Neutrons which may need to be moderated, but with only sand absorption after that. Remember, with enough sand you not only don't need a gamma sheild (certainly you dont' need to carry down from orbit whatever you used in space),you also don't even need a dedicated neutron absorber, and won't use it any more than one is used in modern power plants. You don't really think there's a layer of gadolinium or cadmium in powerplants, do you? Similarly, there's no point in carrying carrying gadolinium down to the Martian surface, either, except possibly in the small quantities necessary to protect the lander capsule during the initial "foxhole digging" or "concrete making" phase of the surface stay. SBH |
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Wich is the best Radiation Hull or Shield we can build for a spacecraft?
I can see the answer to my question depends in part upon if you are in
a spacecraft somewhere in between Earth / Mars orbits, or on some part or other of the Moon, or on some part or other of Mars. My question is, what directions does this radiation come in from; and if you're on some body, what cyclical variation do you see? The case for shielding sounds pretty good; but if I were there, I wouldn't yet know where best to put it. Thanks -- Martha Adams |
#8
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Wich is the best Radiation Hull or Shield we can build for a spacecraft?
In article ,
Martha H Adams wrote: My question is, what directions does this radiation come in from; and if you're on some body, what cyclical variation do you see? Galactic cosmic rays essentially come in from all directions uniformly; their paths are randomized by interaction with the galactic magnetic field. The only significant variation in intensity is due to solar activity: there are fewer of them near solar maximum, presumably because the stronger solar wind and its associated magnetic fields have some tendency to fend them off from the inner solar system. The case for shielding sounds pretty good; but if I were there, I wouldn't yet know where best to put it. All over. The only direction in which you don't need shielding is down, if you are on a planetary surface. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#9
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Wich is the best Radiation Hull or Shield we can build for a spacecraft?
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#10
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Wich is the best Radiation Hull or Shield we can build for aspacecraft?
In article , says...
In article , Martha H Adams wrote: My question is, what directions does this radiation come in from; and if you're on some body, what cyclical variation do you see? Galactic cosmic rays essentially come in from all directions uniformly; their paths are randomized by interaction with the galactic magnetic field. The only significant variation in intensity is due to solar activity: there are fewer of them near solar maximum, presumably because the stronger solar wind and its associated magnetic fields have some tendency to fend them off from the inner solar system. The case for shielding sounds pretty good; but if I were there, I wouldn't yet know where best to put it. All over. The only direction in which you don't need shielding is down, if you are on a planetary surface. So then this configuration might be sufficient? http://www3.telus.net/webshrinker/wow/marsshot.jpg |
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