From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.tech Subject: Re: Heat Sink Heat Shields References: <5dcb47db.0310011151.51d744ce@posting.google.com> NNTP-Posting-Host: 209.88.68.33 Message-ID: <9186edb5.0310012120.758e3a2a@posting.google.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" (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_300 K/ -- 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