Re: starship-design: Yikes!

[TLG.van.der.Linden@tip.nl (Timothy van der Linden)]

To Ken and others:

>>We both forgot the Logarithm! (did you lure me into that?)
>>This really makes the mass-ratios dramatic for low efficiencies...
>>(This also clarifies my doubts about the apparent low ratios.)
>
>Yes, that's my mistake.  So now, for a 10% efficiency, you need a sail/ship\
>ratio of 10^26!!  Yikes and a half.  Did someone say they could turn beamed
>power into electricity at a 90% or better conversion?  So all we need is a
>way to turn electricity into a perfect beam with a 60% efficiency.  Otherwise
>we'll have to sign off on this idea...

Electricity is not something you want if you're talking about 1E19 Watt in
such a small area, the magnetic field alone would crumple the ship and sail
(a wild guess).

Furthermore, efficiencies less that 99% are not what we can handle if our
radiative area is too small (smaller than 100 square kilometers for losses
of 1E15 Watt).

When we talk about an engine, we usually like to have it rather small,
however it is likely that this is not possible. There's a big chance that we
need many small engines or one huge engine.
Actually a mirror is the best engine, it has a large radiative surface and a
high efficiency. Of course we are ignoring the beamingstation which now has
to cope with all the trouble. Luckely the beaming station can be bulky
without needing exponentially more energy.

This, may actually be a reason to forget any engine and to only think about
sail designs.

>Damn logarithm.

Damn physics... ;)

Timothy