# Re: starship-design: Hull Materials

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In a message dated 11/14/97 5:26:19 AM, TLG.van.der.Linden@tip.nl wrote:

>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? --

Yup.

>--That indeed would decrease the problem
>significantly.

Yeah!

>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.

Thats probably high.  Last i heard they were expecting it would be well under
1 p per cm cubed.  Thats why the ramscoop looked like such a lost cause.

>Timothy

Kelly

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