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*To*: starship-design@lists.uoregon.edu*Subject*: starship-design: Hull Materials*From*: TLG.van.der.Linden@tip.nl (Timothy van der Linden)*Date*: Fri, 14 Nov 1997 12:25:20 +0100*Reply-To*: TLG.van.der.Linden@tip.nl (Timothy van der Linden)*Sender*: owner-starship-design@lists.uoregon.edu

Hi Lee, >I don't remember the specifics on Kelly's sail, but most proposals for >solar/laser/microwave sails are only 100 micrometers thick at best. I still >think most protons, etc. will just blow right through the sail without even >impacting much of anything, especially if it isn't a solid sail, and there >is no reason why it should be solid. With not solid, you mean meshlike? That indeed would decrease the problem significantly. Protons, unlike photons can/will loose their energy partially when they encounter matter. If the formula I use is valid and my calculations are right then a proton will loose 7.5MeV in a solid lithium layer of 100 micrometer. Let me do some calculus to estimate the equilibrium temperature of the sail. 10 protons per cubic cm, sail velocity 1.2E10 cm/s Number of protons per square cm per second: 1.2E11 Number of protons per square meter per second: 1.2E15 Power per square meter: 1.2E15*7.5E6*1.6E-19=1440 Watt/m^2 Sail has 2 sides to radiate the energy away, so that makes 720 Watt/m^2 That gives an equilibrium temperature of 335 Kelvin or 62 Celcius. (Litium melts at 180 Celcius.) A reverse calculation tells me that a 600 micron thick solid litium shield will melt assuming 10 protons per cubic cm at 0.4c. So indeed the problem may be less than I at first thought. Let's just hope that this number of 10 protons per cubic cm is a maximum. Timothy

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