starship-design: Beamed power

["Kevin 'Tex' Houston" <hous0042@tc.umn.edu>]

Zenon Kulpa wrote:

> My worry about the instability of the "payload-up-front" design
> did not concern the sail. The sail will still work like the parachute,
> but it will not be pulling the payload directly, only push the end
> of a long truss with payload at its other end:
> 
> Warning: ASCII art follows (use a fixed font to view)
> -----------------------------------------------------
> 
>          ...  sail                  ...
>           |                           \  shrouds to the sail
>           |                            \
> payload   |                             \
>           |                              \        <---
>   ####    |       pulling truss           \       <---  beam
>  #####==================<==================#      <---  from
>   ####    |                               /       <---  Earth
>           |                              /        <---
>           |                             /
>           |                            /
>           |                           /  shrouds to the sail
>          ...  sail                  ...
> 
> As a result, the pulling truss (with the heavy payload at the other end)
> will be unstable, with the tendency of the payload end
> to veer to the sides.
> 

I like this idea for a "shielding sail"  That is, a small sail used to
protect the crew quarters from the beam.

I still think we should use tension members (instead of compression) to
support the payload (along with it's associated shielding sail)


> The tugs shepherding the sail will be needed in any case,
> especially if the whole construction should be able to make
> sideways manoeuvres to follow the jiggling (or spiraling) beam.
> 

I don't think sideways manuevers will be possible (or desirable) the
beam should  be a straight line connecting the two suns.  If any
sideways motion of the beam occurs, it will be either too fast (jitter)
or will take us away from the system.

The number one problem with a beamed system is what to do if the power
cuts out.  All I can think is that the crew will have to stay the course
and hope that earth gets things straightened out before the ship impacts
the target system's sun.


> Concerning the shielding/drag problem:
> > From: TLG.van.der.Linden@tip.nl (Timothy van der Linden)
> >
> > Zenon worried:
> >   That seems an important observation.
> >   My guess is that even more restrictive on the sail speed
> >   would be the physical damage inflicted on the sail by the
> >   interstellar medium (even the hydrogen atoms, but also other debris,
> >   like dust). You cannot shield the entire sail...
> >
> > My suggestion was to use part of the beam to blow clear the path.
> > We may re-route a part of the beam to a more divergent beam
> > which will push the few atoms in our way to the side.
> >
> Or make the sail partially transparent.
> 

perhaps a dual frequency beam would work.

A main power beam in the microwave band (for example) and a lower power
path clearing one in the visible or UV band.  The main sail could then
have holes in it that are smaller than the microwave frequency, which
would allow the higher frequency band to pass through.  The higher band
wouldn't even need to be on all the time.  it could be pulsed or
gradually decreased in power as the trip progressed.

> But these solutions further increase the beam power losses,
> comparable to (or possibly larger than) those caused by the drag.
> So it will not be the solution for the drag problem,
> but possibly for the shielding problem.
> 
> I wonder how much energy in the beam will be needed to sweep clear
> the space before the ship from dust and how big are the particles
> that can be sweeped fast enough this way?
> Note however, that the gas & fine dust pushed by that
> "shielding beam" before the ship will accumulate into
> a "shock wave" than can possibly destroy/pulverize
> the larger debris way ahead of the ship. (*)
> Certainly, if it will work efficiently enough for large velocities
> of the ship, it will solve the problem of shielding nicely.
> 
> (*) Hope it will dissipate before reaching the target system
>     and wiping out the life or whatever from some planet(s) there...
> 

Perhaps a lower powered beam could be sent ahead by several months/years
-- 
Kevin "Tex" Houston 		http://umn.edu/~hous0042/index.html
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"Whoever undertakes to set himself up as a judge of Truth and
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