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# Re: Sail Questions

```To Less,

>>The problem is how do you attach a 1000 ton starship to it.
>
>Umm, monofilament diamond?

I'm not sure what this is, is this a suggestion or a question?

>>Since I'm thinking of a quite solid sail build of aluminium or something
>>like that, I'm not worried much about corrosion, even small debris will just
>>make some holes in it without doing much more damage.
>
>You just blew your ship mass to power ratios out of the water. Solar sails
>are described by their Lightness Number, the sail you seem to be describing
>will not leave anything for payload.

That only depends on the density of the radiation. We weren't going to use
Solar sails but just sails. While solar density non variable (at a fixed
distance) we can change the momentum density of our own beam. In theory we
could do with a small sail (upto the limit where the radiation pressure
would ionize it away).

>>>What is the drag coefficent of such a sail in the ICM?
>>
>>Is ICM the same as ISM?
>
>The Interstellar Medium (ISM) consists of HI and HII regions which are
>comparitively dense and Intercloud Medium (ICM) which are not. The Solar
>System is curently on the edge of an ICM where there is comparitively little
>matter.

Ah, but if we know that we are at the edge of an ICM, can we than determine
what the shape of this ICM is? In knowing this does Tau Ceti or Alpha
Centauri lie in such a cloud too?

>>>At
>>>what speed does the acceleration balance drag? Is this before or after the
>>>sail is shredded?
>>
>
>A 10 ly journey at 0.2 c would result in the loss of 1/500 of the area of
>the sail by impact with dust grain sized particles. I don't know of anyone
>who has calculated beyond that speed for sails. IF there are larger
>particles present in the ISM, the word catastrophic comes into mind...

Assuming the we have a sail made of a mesh with 2 mm-2 cm holes, I don't
think that would matter much.
You are talking about loss of area, what kind of an area are you talking
about? Does this also count for aluminium?

>>Only at very high c, probably far beyond 0.99c. I don't see any reason why
>>the sail would brake if the pressure is equally divided.
>
>Assuming that whatever erosion there is occurs uniformly

Yes, and assuming the sail is equally strong (no material flaws).

Tim

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