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Re: Sail Questions

To Lee,

>>>Umm, monofilament diamond?
>>I'm not sure what this is, is this a suggestion or a question?
>Kind of both, since we can't exactly make it yet, but it is strong and light
>enough to do the job. Monofilament carbon is closer to our reach and almost
>as strong. Materials science is progressing swiftly, who knows what will

But how many of such wires would you need per square metre? You must assume
a pull-pressure of at least 1 bar (1E5 Pascal). I wonder if a 100 nm layer
could hold such a pressure.

>>We weren't going to use...
>It doesn't really matter whether you are talking a straight solar sail or a
>beam pushed sail (the Lightness Number (Ln) is the ratio of its acceleration
>by light pressure to the star's gravitational acceleration. In other words,
>you still have to worry about mass. As you pointed out, you could keep
>increasing beam density to compensate, but there is a point where you can't
>go any farther.

Do you know numbers for this breakdown energy-pressure? I've tried finding
some, but did not succeed.

>If you don't pay attention to weight ALL the time, you end up wasting lots
>of potential payload.

Yes, I'm aware of that, but I don't see how some 100 km foil-disc is going
to pull the starship without being teared apart.

>>Assuming the we have a sail made of a mesh with 2 mm-2 cm holes, I don't
>>think that would matter much.
>Probably not, but your holes need to be closer to 0.12 um for infrared and
>even smaller for visible or UV. The higher the frequency of the radiation
>you use, the smaller the aperature of the laser you are using for
>propulsion. I earlier posted the result of the calculations for a yellow
>light laser, it was 400 km across at the aperature. Obviously, UV would be
>much better! Also, you need to remember that laser intensity will decline as
>the inverse square of the distance from the source. I've seen somebody's
>posted calculations of beam power requirements, but I think they are too low.

But until now most of us were talking about using micro-waves.

>>You are talking about loss of area, what kind of an area are you talking
>>about? Does this also count for aluminium?

What I meant was for aluminium rods (say 1 cm cross-section). Are these
dust-particles also making completely cut trough holes in such rods?

>I was only pointing out that the only figures I've seen for erosion were for
>ridiculously low speeds, there would be a significantly higher amount for
>higher velocities.

0.2 c isn't ridiculously low. (unless you compare them with 0.999c)