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Space Forum / Space Flight / October 2003Heat Sink Heat Shields
henry@spsystems.net (Henry Spencer) wrote in message news:<HLsH2G.3In@spsystems.net>... > In article <c0e0a1dd.0309231321.3f3bff42@posting.google.com>, > John Carmack <johnc@idsoftware.com> wrote: > >If you are willing to trade mass for it, copper heat shields have been > >shown to work, and they would be cheap and easy to fabricate... > A good point. Heat-sink heatshields have been out of fashion for a long > time because of their mass, but they're the only flight-proven TPS that's > both durable and fully reusable. (It's hard to imagine anything much more > durable than a thick slab of solid metal...) Several questions... *What re-entry vehicles demonstrated copper heat shields? *How thick is "a thick slab of solid metal"? Aerospace definitions of "thick slab" probably differ from, say, shipbuilding definitions of "thick slab." *For water-cooled heat shields, what percentage of the re-entry vehicle's mass is typically needed as cooling water? Mike Miller, Materials Engineer >> A good point. Heat-sink heatshields have been out of fashion for a long >> time because of their mass, but they're the only flight-proven TPS that's >> both durable and fully reusable. (It's hard to imagine anything much more >> durable than a thick slab of solid metal...) > >*What re-entry vehicles demonstrated copper heat shields? Early ICBM and IRBM warheads. The suborbital Mercury capsules also had heat-sink heatshields, but using beryllium instead of copper. >*How thick is "a thick slab of solid metal"? I don't have numbers handy, but think 10-20cm. Slab, not sheet. >*For water-cooled heat shields, what percentage of the re-entry >vehicle's mass is typically needed as cooling water? Only a couple of percent, I think, but here my memory is quite vague. (Again, references aren't handy.)  SignatureMOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer first ground-station pass 1651, all nominal! | henry@spsystems.net In the table below I multiply the specific heat by the melting point to get a figure of merit I call "HeatSink Joules/Kg" (should really have subtracted some starting temp like 20 C). Note that a heatsink also has to have a high conductivity, which rules out titanium. Beryllium looks far better than the others. Copper is very conductive, but it stores less heat than anything else on this list. Is there any chance that the the US ICBMs with "copper heatsinks" could have really been copper coated beryllium? Maybe they coated it to reduce the danger of handling beryllium? I have never seen details of ICBMs with heatsinks or transpiration. I don't know of any non-military transpiration flights and suspect there are none. Beryllium has flown on at least John Glen's suborbital Mercury flight. So for sure it can be done. In my simulations a Beryllium heatsink looks like a fine reusable heat shield for reentry from a 5 km/sec rotovator/space-tether. I am simulating a 4 meter diameter capsule that weighs 4,000 Kg. For this a heatsink of around 5% of the mass would be enough for suborbital and around 15% for orbital. You can calculated the thickness from the density below and the 4 meter diameter. I would use a suborbital sized heatsink and water/transpiration to handle the extra heat in the case of missing the LEO tether on the way down and having to do a full orbital speed reentry. Material Conductivity Density Specific Melting HeatSink Heat Point W/m-C kg/m3 J/kg-C C Joules/Kg Beryllium 175 1,859 1885 1278 2,409,030 Titanium 16 4,507 544 1668 907,392 Iron 80 7,874 449 1538 690,562 Lithium 85 535 3582 181 648,342 Aluminum 220 2,707 896 660 591,360 Tungsten 180 19,350 134 3422 458,548 Copper 386 8,954 380 1085 412,300 Ice Melting 333,000 Heating Water 100 C * 4184 J/Kg-C 418,400 100 C Water to Steam 2,500,000 Ice to Steam 3,251,400 If steam used in transpiration x4 13,005,600 Charing Ablative Char radiation / vaporization / Transpiration very good The only bad thing about a charing ablative is that it is not testable/reusable. Beryllium Strong, very light, resistant to oxidization like aluminum high melting point, very high specific heat Used in aerospace One of the lightest metals Stronger than steel pound for pound Brittle Something like $160/lb or $350/Kg. About this all through 1990s. So could afford for reusable vehicle. Berylliosis Breathing fumes or dust, or getting them on open cut. DOE has worker standards. Machining can expose worker to risk. Solid it is not a health hazard. In 1998 US consumed 240 tons and exported 60 tons. Brush Wellman Inc is only US ore processor. Has 60 years reserve. Primary processor for world. Some sources for some of the above info: http://www.arkthermal.com/metals2.doc. Conductivity, Density, Melting Point: http://www.webelements.com/ Specific heats: http://www.allmeasures.com/Formulae/static/formulae/specific_heat_cap acity_300K/ -- Vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vincent Cate Space Tether Enthusiast vince@offshore.ai http://spacetethers.com/ Anguilla, East Caribbean http://offshore.ai/vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You have to take life as it happens, but you should try to make it happen the way you want to take it. - German Proverb >In the table below I multiply the specific heat by the >melting point to get a figure of merit I call "HeatSink Joules/Kg"... >Note that a heatsink also has to have a high conductivity... Conductivity is very important, because the heatsink surface must not melt. Copper wins big there, and a bunch of otherwise-attractive metals flunk completely. High-temperature oxidation resistance is also significant. According to the old books, copper and beryllium are the only heatsink materials that looked useful. >Is there any chance that the the US ICBMs with "copper heatsinks" >could have really been copper coated beryllium? Nope, straight copper. Heavy, yes, but cheap, easily fabricated, and mechanically durable. (Whereas beryllium, although light, is costly, very difficult to work with, and brittle.) Remember that those warhead designs were done in desperate haste, to get *something* operational ASAP. My reading of the history (from limited information, mind you) is that they might well have gone to beryllium for a second-generation design, except that they went to ablators instead. >Beryllium has flown on at least John Glen's suborbital Mercury >flight. So for sure it can be done. Glenn never made a suborbital Mercury flight. Shepard and Grissom flew on Mercury's original beryllium heatsink heatshield. The ablative design was ready in time for the orbital flights, and was deemed superior. (I think they did qualify the heatsink design for orbital flight, at least on paper.) >Beryllium ... > Used in aerospace Even aerospace use is declining, due to practical hassles and competition from carbon composites. > Stronger than steel pound for pound > Brittle The brittleness is not only a problem for the final structure, but greatly complicates machining etc. It's inherent in the crystal structure and is not fixable (this was studied in great depth), although with considerable difficulty you can make beryllium that is ductile in two dimensions and only brittle in the third. The brittleness makes the practical strength much less than theoretical values in most applications, because you must design very conservatively to avoid local stress concentrations that would be of no importance with a more ductile metal. Its one big advantage is something that actually isn't in your list: stiffness. Not how much load it will take before breaking, but how much it will resist flexing under lesser loads. In particular, specific stiffness -- stiffness per kilogram -- does not vary a lot between metals, except that beryllium is way out in front of everything else. Until carbon composites came along, that is. > Berylliosis > Breathing fumes or dust, or getting them on open cut. > DOE has worker standards. Machining can expose worker to risk. And that too complicates working with it. Wild idea of the week: I wonder if you could take a leaf from Apollo's book, and make a heatsink heatshield out of hexagonal beryllium rods in a copper or stainless-steel honeycomb? The honeycomb would take mechanical loads and hold the beryllium together, eliminating brittleness issues, while the beryllium handled most of the heat. One book, interestingly enough, mentions the idea of adding expendable (perhaps liquid) coolant behind a heatsink heatshield, but says the idea was not pursued, because straight heatsinks seemed adequate for satellite applications, while nothing short of ablators would do for the most demanding warhead flight profiles. SignatureMOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer first ground-station pass 1651, all nominal! | henry@spsystems.net >> In the table below I multiply the specific heat by the >> melting point to get a figure of merit I call "HeatSink Joules/Kg"... [quoted text clipped - 5 lines] > significant. According to the old books, copper and beryllium are the > only heatsink materials that looked useful. Diamond oxidises, like copper and beryllium, but it has 6 times the thermal conductivity of copper. And a much higher melting point. Expensive though... SignaturePeter Fairbrother >> Conductivity is very important, because the heatsink surface must not >> melt. Copper wins big there, and a bunch of otherwise-attractive metals [quoted text clipped - 3 lines] >Diamond oxidises, like copper and beryllium, but it has 6 times the thermal >conductivity of copper. And a much higher melting point. Diamond doesn't really have a melting point. If you get it hot enough, it reverts to graphite -- diamond is only metastable. The process starts as low as 1000degC. And in an oxygen-containing atmosphere, the oxidation rate becomes significant even before that. Copper and beryllium oxidize, yes, but the result is a durable surface layer of solid oxide. But diamond oxidizes to CO2... SignatureMOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer first ground-station pass 1651, all nominal! | henry@spsystems.net >>> Conductivity is very important, because the heatsink surface must not >>> melt. Copper wins big there, and a bunch of otherwise-attractive metals [quoted text clipped - 12 lines] >result is a durable surface layer of solid oxide. But diamond oxidizes >to CO2... Talking of composites, however, one might face a carbon or diamond heatsink in tungsten (completely sealed, to exclude oxygen). If C or diamond are good candidates, surely avoiding oxidization is not that hard... Also, something I a noticed is that the temps you're peaking at with these materials indicate that precooling down to say 100K might make a significant performance difference with a lot of potential heatsinks. I am not intimately familiar with the low temp performance of all the materials in question, in particular beryllium and diamond. -george william herbert gherbert@retro.com >>>In the table below I multiply the specific heat by the >>>melting point to get a figure of merit I call "HeatSink Joules/Kg"... [quoted text clipped - 10 lines] > > Expensive though... Diamond burns, is a somewhat more accurate statement. A lot of jewelers have found that out the hard way when trying to cast rings around a diamond inset. There isn't a large separation between solid diamond and carbon dioxide in certain operational environments. > Its one big advantage is something that actually isn't in your list: > stiffness. Not how much load it will take before breaking, but how much > it will resist flexing under lesser loads. In particular, specific > stiffness -- stiffness per kilogram -- does not vary a lot between metals, > except that beryllium is way out in front of everything else. Until > carbon composites came along, that is. Some heavy metals exceed beryllium for stiffness. Beryllium has a 44MSi stiffness (vs 29-30 for steel, 16ish for titanium, 10 for aluminum), but tungsten is up to 58Msi, and I think rhenium and osmium are stiffer. Of course, there's that whole density angle that makes beryllium so special for its stiffness. > One book, interestingly enough, mentions the idea of adding expendable > (perhaps liquid) coolant behind a heatsink heatshield, Mr. Spencer, if you ever do get to a place where you have reference books handy, I'd love to see more precise estimates for the mass fraction of water in transpiration cooling. If I understood the exchange between you and Mr. Carmack, were you saying that if you were willing to accept the higher mass and made a Cu or Al transpiration heat shield thicker, you could use larger, more manageable pore sizes? Would the larger pores reduce the insulation efficiency of the vented steam outside the shield? Mike Miller, Materials Engineer >Mr. Spencer, if you ever do get to a place where you have reference >books handy, I'd love to see more precise estimates for the mass >fraction of water in transpiration cooling. Took a bit longer than expected :-), but I do have a number or two. Parker's "Materials for missiles and spacecraft", specifically Steurer's chapter on thermal-protection materials, has a table of effective thermal capacities, from which I excerpt a few relevant numbers (I think these are in Btu/lb): Heat sink, Cu 180 Heat sink, Be 1105 Convective cooling, water 1000 Convective cooling, hydrogen 8500 Transpiration, water 2500 Transpiration, hydrogen 12000 Ablation, glass-reinf. plastics 2000-3000 He cautions that these numbers should be taken with a large grain of salt, because there are many variables and the results differ depending on the test method used. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > Transpiration, water 2500 > Transpiration, hydrogen 12000 That doesn't look right. I though water had a much higher specific heat and heat of vaporization than any other common substances. And that cryogens such as hydrogen had an extremely low heat of vaporization. If that's supposed to be room temperature hydrogen gas, rather than liquid hydrogen, then you don't even get the benefit of the heat of vaporization. SignatureKeith F. Lynch - kfl@keithlynch.net - http://keithlynch.net/ I always welcome replies to my e-mail, postings, and web pages, but unsolicited bulk e-mail (spam) is not acceptable. Please do not send me HTML, "rich text," or attachments, as all such email is discarded unread. >> Transpiration, water 2500 >> Transpiration, hydrogen 12000 [quoted text clipped - 3 lines] >And that cryogens such as hydrogen had an extremely low heat of >vaporization. Water's specific heat is very high, but only as solid or liquid, and in practice the useful range is the liquid range, about 100K. The specific heat of steam is only slightly higher than that of hydrogen gas. Hydrogen stored as liquid has to be warmed about 250K before it gets to the *start* of the water range, and it soaks up an awful lot of heat along the way. Some of its other properties also make it a better transpiration coolant, e.g. as a gas, a given mass of it is about 9x the volume of the same mass of steam, so it fends off the incoming hot air rather better. A more correct statement is that water isn't as bad as you would think, given its high molecular mass and high freezing point, because of that high specific heat and very high heat of vaporization. And then there are the practical advantages of high density, simple storage, and low cost. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > >Is there any chance that the the US ICBMs with "copper heatsinks" > >could have really been copper coated beryllium? > > Nope, straight copper. Heavy, yes, but cheap, easily fabricated, and > mechanically durable. (Whereas beryllium, although light, is costly, > very difficult to work with, and brittle.) Do you know what sort of trajectories they fly? Like do they come in at a very high angle? If I simulate 7.7 km/sec coming in at 45 degrees it generates like 1/8th the total heat of coming in at 0 degrees. This could explain how they could get by with copper and I can't for a human capsule with L/D of 0.4 and CD of 1. Of course the G load is not human friendly at like 120 Gs. :-) That is probably even more Gs than you want your nukes to have to deal with. > Glenn never made a suborbital Mercury flight. Shepard and Grissom flew on > Mercury's original beryllium heatsink heatshield. Thanks. > Its one big advantage is something that actually isn't in your list: > stiffness. But for a heatsink this does not seem like a feature I was looking for. For other things, sure. > Wild idea of the week: I wonder if you could take a leaf from Apollo's > book, and make a heatsink heatshield out of hexagonal beryllium rods in a > copper or stainless-steel honeycomb? The honeycomb would take mechanical > loads and hold the beryllium together, eliminating brittleness issues, > while the beryllium handled most of the heat. It seems like something could be done. Do you know how much trouble the brittleness issue was for Mercury? > One book, interestingly enough, mentions the idea of adding expendable > (perhaps liquid) coolant behind a heatsink heatshield, but says the idea > was not pursued, because straight heatsinks seemed adequate for satellite > applications, while nothing short of ablators would do for the most > demanding warhead flight profiles. It seems like this becomes a good idea when you use water and then use the steam for transpiration/film-cooling. Also, when you are making a reusable vehicle you may not be as willing to use ablation. You could at least fly your heatsink/transpiration capsule any number of times before you put people on it. -- Vince >> Nope, straight copper. Heavy, yes, but cheap, easily fabricated, and >> mechanically durable... > >Do you know what sort of trajectories they fly? Like do they come in >at a very high angle? Don't know what the numbers would have been like for those. Steeper than a manned reentry, but not too severe, as I know there was concern about warhead vulnerability from decelerating too high up, and that one reason for interest in ablators was to give more flexibility in trajectory. Note that they did use a relatively wide, flat shape to reduce ballistic coefficient (less mass per unit frontal area). >If I simulate 7.7 km/sec coming in at 45 degrees >it generates like 1/8th the total heat of coming in at 0 degrees. >This could explain how they could get by with copper and I can't for >a human capsule with L/D of 0.4 and CD of 1. Of course the G load >is not human friendly at like 120 Gs. :-) That is probably even >more Gs than you want your nukes to have to deal with. Not sure about that -- it's actually surprisingly easy to make most things (other than people) tolerate quite high Gs. >> Wild idea of the week: I wonder if you could take a leaf from Apollo's >> book, and make a heatsink heatshield out of hexagonal beryllium rods in a >> copper or stainless-steel honeycomb? ... > >It seems like something could be done. Do you know how much trouble >the brittleness issue was for Mercury? Not specifically. I know that manufacturing Mercury's beryllium heatshields was a significant problem and there were doubts for a while about whether it could be solved well enough, but I don't know exactly what the difficulties were. My guess would be that brittleness was the main issue, but I don't know that for sure. >...when you are making a >reusable vehicle you may not be as willing to use ablation. You could >at least fly your heatsink/transpiration capsule any number of times >before you put people on it. Indeed so. Ablators have the same problem as other one-shot hardware: even if the heatshield is a quick-change easily replaceable part, there is still the need to be very sure that a newly-manufactured one will do the job properly, *without* being able to test it. SignatureMOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer first ground-station pass 1651, all nominal! | henry@spsystems.net I wrote: >>It seems like something could be done. Do you know how much trouble >>the brittleness issue was for Mercury? > >Not specifically. I know that manufacturing Mercury's beryllium >heatshields was a significant problem and there were doubts for a while >about whether it could be solved well enough... Ely's "Return from Space" (which was published in 1966 but clearly written before Mercury was very well defined) says that beryllium was abandoned for early ICBM heatshields because of the prohibitive difficulty and cost of fabricating large shapes out of a costly, brittle, toxic metal. (He says that even copper presented significant fabrication problems at the sizes involved.) SignatureMOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer first ground-station pass 1651, all nominal! | henry@spsystems.net > Ely's "Return from Space" (which was published in 1966 but clearly written > before Mercury was very well defined) says that beryllium was abandoned [quoted text clipped - 3 lines] > (He says that even copper presented significant fabrication problems at > the sizes involved.) On page 128 of "Re-entry and Planetary Entry Physics and Technology - II" by W. H. T. Loh, 1968, a graph indicates that the reentry time time for ICBM is just over 0.1 min, while IRBM is around 0.2 min and Apollo is just under 10 min. In my simulator, this kind of steep reentry reduces the total heat by something like a factor of 8 compared to a shallow human tolerable one. It also has higher heating rates, so copper's higher conductivity could be important. With the lower total heat, you don't really need beryllium. So it now makes sense to me that they used copper and not beryllium for some ICBMs. However, for a manned reusable suborbital vehicle designed to rendezvous with a rotovator (something I am interested in) beryllium still seems very interesting. If the problem is just cost/difficulty of fabrication, and they managed it for Mercury, then it could be reasonable for a reusable vehicle which can amortize the costs over many flights. -- Vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vincent Cate Space Tether Enthusiast vince@offshore.ai http://spacetethers.com/ Anguilla, East Caribbean http://offshore.ai/vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You have to take life as it happens, but you should try to make it happen the way you want to take it. - German Proverb >On page 128 of "Re-entry and Planetary Entry Physics and Technology - >II" by W. H. T. Loh, 1968, a graph indicates that the reentry time [quoted text clipped - 4 lines] >heating rates, so copper's higher conductivity could be important. >With the lower total heat, you don't really need beryllium... Careful, that may be a reentry time for an ablative RV. Ely notes that a heatsink RV's maximum heating rate was limited by thermal conductivity, so it generally needed a lower ballistic coefficient and a shallower trajectory, which would give longer reentry times -- the greater total heat load simply had to be accepted. >...beryllium >still seems very interesting. If the problem is just cost/difficulty >of fabrication, and they managed it for Mercury, then it could be >reasonable for a reusable vehicle which can amortize the costs over >many flights. Cost/difficulty of fabrication seems to be the biggie, as best I can tell. It looks to me like heroic efforts just barely got the beryllium design shippable in time for Mercury. And the three guys :-) who knew how to do it are probably retired or dead now... That said, for a reusable vehicle it's definitely an interesting approach. Especially if you can do something clever to make it more mechanically robust and less sensitive to the beryllium fabricator's skill (and to the possible aging of the material under repeated thermal and mechanical cycling). I would worry a bit about maintenance impact of a highly toxic heatshield material, but that may well be manageable. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net I read that Lawrence Livermore has invented a heat-conducting graphite foam. http://www.ornl.gov/news/pulse/pulse_v103_02.pdf I wonder if this stuff could be used to create a "radiator" behind a thinner, lighter heatshield to conduct reentry heat into the relatively cool wake of the spacecraft. Patrick > > Ely's "Return from Space" (which was published in 1966 but clearly written > > before Mercury was very well defined) says that beryllium was abandoned [quoted text clipped - 32 lines] > You have to take life as it happens, but you should try to make it > happen the way you want to take it. - German Proverb > Ely's "Return from Space" (which was published in 1966 but clearly > written before Mercury was very well defined) says that beryllium > was abandoned for early ICBM heatshields because of the prohibitive > difficulty and cost of fabricating large shapes out of a costly, > brittle, toxic metal. Surely metallurgy has improved a lot in the past forty years. Anyhow, why couldn't it be cast (rather than machined) in any shape you like? SignatureKeith F. Lynch - kfl@keithlynch.net - http://keithlynch.net/ I always welcome replies to my e-mail, postings, and web pages, but unsolicited bulk e-mail (spam) is not acceptable. Please do not send me HTML, "rich text," or attachments, as all such email is discarded unread. >> ...beryllium >> was abandoned for early ICBM heatshields because of the prohibitive >> difficulty and cost of fabricating large shapes out of a costly, >> brittle, toxic metal. > >Surely metallurgy has improved a lot in the past forty years. Not a lot, in this area. There's only so much that can be done to make beryllium more tractable. (People tried hard to make ductile beryllium, completely without success -- its brittleness is quite fundamental.) And one area that has changed, big time, is rules about working with hazardous materials, especially grossly hazardous ones like beryllium. The safety requirements are a lot stricter than they used to be. >Anyhow, >why couldn't it be cast (rather than machined) in any shape you like? Some metals can be cast practically, some can't. Beryllium has quite a high melting point and is quite chemically active, which leads to the obvious problem of just what you make your casting molds out of. There may be other problems as well. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > And one area that has changed, big time, is rules about working with > hazardous materials, especially grossly hazardous ones like beryllium. > The safety requirements are a lot stricter than they used to be. You're making me nervous. About twenty years ago, *I* worked with beryllium. Should I start panicking? At least I refrained from checking to see if it really does taste sweet. I wonder what became of whoever discovered that it does. And about how anyone knows that cyanide smells like bitter almonds. SignatureKeith F. Lynch - kfl@keithlynch.net - http://keithlynch.net/ I always welcome replies to my e-mail, postings, and web pages, but unsolicited bulk e-mail (spam) is not acceptable. Please do not send me HTML, "rich text," or attachments, as all such email is discarded unread. > > And one area that has changed, big time, is rules about working with > > hazardous materials, especially grossly hazardous ones like beryllium. [quoted text clipped - 6 lines] > sweet. I wonder what became of whoever discovered that it does. > And about how anyone knows that cyanide smells like bitter almonds. I seem to remember Asimov saying that chemists, as a group, had shorter life spans than other scientists. He surmised it was because of all the exposure to toxic stuff. Well there is the old story where an new optical shop guy was given a project to polish a berrylium mirror... He found a nice small room that he could seal up well to avoid temp changes,air currents, dust ect... He died not long after just from that....so the story goes take care Bll > You're making me nervous. About twenty years ago, *I* worked with > beryllium. Should I start panicking? I don't think so - you would have shown symptoms earlier. AFAIK, only inhaling dust particles containing Beryllium is dangerous, because it causes fibrosis of the lung. It's probably similar to a lot of other things in this regard (e.g., mercury) - eating it is much safer than breathing it. Jan >> And one area that has changed, big time, is rules about working with >> hazardous materials, especially grossly hazardous ones like beryllium. [quoted text clipped - 5 lines] > At least I refrained from checking to see if it really does taste > sweet. I wonder what became of whoever discovered that it does. I never heard that... [looks] Hmm. Apparently its compounds tasted sweet, hence its original name (glucinium). You never know, some of them might be okay. Having read about the effects of Be, I wouldn't want to test that hypothesis, mind. > And about how anyone knows that cyanide smells like bitter almonds. I'm fairly sure it's safe to know how cyanide smells, so long as you don't examine it *too* closely :-) There's been enough people who killed themselves with it, or were killed by it, and the discoverer of the body reportyed a noticeable smell... Signature-Andrew Gray shimgray@bigfoot.com >> And one area that has changed, big time, is rules about working with >> hazardous materials, especially grossly hazardous ones like beryllium. >> The safety requirements are a lot stricter than they used to be. > >You're making me nervous. About twenty years ago, *I* worked with >beryllium. Should I start panicking? I think not. As far as I know, the major health effects of beryllium are all reasonably prompt. If it didn't kill you then, lingering problems are unlikely. >At least I refrained from checking to see if it really does taste >sweet. I wonder what became of whoever discovered that it does. >And about how anyone knows that cyanide smells like bitter almonds. Early chemists had a habit of tasting things. This may not be unconnected to their high mortality rate... SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > I think not. As far as I know, the major health effects of beryllium are > all reasonably prompt. If it didn't kill you then, lingering problems > are unlikely. Actually, beryllium is sneaky that way: "What is Beryllium Disease (Berylliosis)? Beryllium disease primarily affects the lungs. The disease occurs when people inhale beryllium dust or fumes. Skin disease with poor wound healing and rash or wart-like bumps can also occur. A person can develop beryllium disease even after being away from the beryllium industry for many years." http://www.nationaljewish.org/medfacts/beryllium_medfact.html You know, I've had 2 replies in this thread commenting on the formability of beryllium in heat shields, and they were both eaten. I'm having a similar problem on sci.military.moderated with my replies to the "stillsuit" thread. Have I done something to offend The Herbert? :) Mike Miller, Materials Engineer >> And one area that has changed, big time, is rules about working with >> hazardous materials, especially grossly hazardous ones like beryllium. [quoted text clipped - 6 lines] > sweet. I wonder what became of whoever discovered that it does. > And about how anyone knows that cyanide smells like bitter almonds. Nothing. It starts to smell of bitter almonds somewhere near 1 ppm for most humans. Its lethal somewhere around 100 ppm IIRC and humans can be in 10ppm environment for a realtively long time (hours) and only get mild effects like nausea and headaches. So lots of oppourturnity to smell it and not suffer any real consequences. Not that you should go out and try to be exposed to cyanids - except possibly your daily intake of B12. SignatureSander +++ Out of cheese error +++ > In my simulations a Beryllium heatsink looks like a fine reusable > heat shield for reentry from a 5 km/sec rotovator/space-tether. Beryllium is far less practical than water (hint: imagine your vehicle has just reentered and is sitting on the runway attached to this white-hot/~1200C heatsink.) Note that the Soyuz capsule drops its heatshield at altitude- one of the reason that it does that is to reduce the heatsoak problem; and that's not even a heatsink design and hence has much less energy left in it. By way of contrast, if you use water for the heatsink, the hot steam can be vented, so by the time you are on the ground, your vehicle has enormously less thermal energy. Maybe if you were building nuclear weapons would you seriously want to consider a solid heatsink made from Beryllium. However nuclear weapons are not generally reusable, and that's why they use beryllium. > -- Vince >> In my simulations a Beryllium heatsink looks like a fine reusable >> heat shield for reentry from a 5 km/sec rotovator/space-tether. > > Beryllium is far less practical than water (hint: imagine your vehicle > has just reentered and is sitting on the runway attached to this > white-hot/~1200C heatsink.) It's going to be cooling fast after it passes under mach 5 or so. Signaturehttp://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling. ---------------------------+-------------------------+-------------------------- If it can't be expressed in figures, it is not science, it is opinion. -- Robert A Heinlein. I got a new book and learned some more. First I have added 2 lines for ablatives to the most interesting parts of the table earlier in this thread: Material Conductivity Density Specific Melting HeatSink Heat Point W/m-C kg/m3 J/kg-C C Joules/Kg Beryllium 175 1,859 1885 1278 2,409,030 Aluminum 220 2,707 896 660 591,360 Copper 386 8,954 380 1085 412,300 If steam used in transpiration x4 13,005,600 Phenolic-nylon Charing Ablative 15,000+ BTU/lb (p. 127) 34,890,000 Apollo Total heat/heat shield weight (p. 133) 13,886,220 The book says that for Apollo to have used Beryllium, the heatsink would have to have been about half the total mass (page 120). With the ablative they show the heat-shield weight as 1300 lbs out of a total of 9500 lbs or 13.7%. It has 5,970 BTU/lb as the total heat / heat shield weight which I converted to 13,886,220 Joules/Kg. No doubt there is some margin there. It is dated 1968 (i.e. before landing on the moon) so there is some chance some Apollo numbers changed after ths book came out. The book is "Re-entry and Planetary Entry Physics and Technology - II / Advanced Concepts, Experiments, Guidance-Control and Technology" By W. H. T. Loh There is also a volume I, but II has been more interesting so far. My attempts to simulate the Apollo reentry are not working well so far. The book describes the Apollo computer's guidance logic during reentry but my simulator does not have that. I may try to put the logic in just so I can get some validation of my simulator. If I scale the heat I get at 7.7 km/sec to 11.3 km/sec I get close to their numbers. The kinetic energy goes up with the square of velocity, this would be about 2.15 times the heat (we are assuming the same fraction of the heat goes into the capsule, which is only an approximation). If you take 2.15 times the heat I get for a 7.7 km/sec reentry you are about at the heat the book says for Apollo reentry. So my similator may be close to reality on reentry heat!!!!! -- Vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vincent Cate Space Tether Enthusiast vince@offshore.ai http://spacetethers.com/ Anguilla, East Caribbean http://offshore.ai/vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You have to take life as it happens, but you should try to make it happen the way you want to take it. - German Proverb |
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