[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: starship-design: Beamed Power (was: Perihelion Maneuver)

L. Parker wrote:

>There is/was a design for an extremely simple, MECHANICAL laser (trick 
>optics) that could be easily mass produced. It incorporated it's own 
>collector as part of the emitter and produced a collimated beam of 
>incoherent (white) light.

This design will not produce a beam collimated enough to focus
on a small spot a considerable distance away.  The laws of optics
won't allow it.  The problem is that the Sun is not a point light
source (nothing is).  The spread on the emitted beam will always
be at least the angular size of the Sun at the distance the
collector is at (it will have an additional spread due to
diffraction limits).

For instance, a solar optic mirror/lens mechanism in orbit around
Earth will always have a conical spread of .5 degrees or more,
no matter how clever it's done.  At a distance of 1AU, this
means spreading to the size of the Sun.

I know what you're thinking--let's put the things further away
from the Sun, then!  Unfortunately, this gets you nowhere.
If you go 10 times further from the Sun, the spread does
indeed go down to .05 degrees.  This means that for any
given distance from the collector/emitter, the spot is
1/100 the size.  However, since you're 10 times further
from the Sun, you're also collecting 1/100 the amount
of sunlight!

>Technically, this isn't a laser, but it is darn 
>close and because of the potential of mass producing them by the millions, 
>you COULD build an array of them packed shoulder to shoulder 1,000 km 

Packing these things shoulder to shoulder doesn't really get you
anywhere.  Because they can't be put in phase with each other,
you can't get any benefit from phased array emissions to focus
the beam further.

>In essence, all it is doing is focusing 1,000 km of solar energy into a 
>spot out to a considerable distance. True, since it isn't coherent, 
>intereference will cause the beam to spread faster than a real laser, but 
>the potential efficiency was limited only by the reflectivity of the 
>material used to make the collector/emitter. It could go as high as 95 
>percent. It vastly increases the acceleration envelope of a solar sail. It 
>also has some interesting potential for industry.

It does have the potential to help out interplanetary solar sails,
but simply doesn't have the range needed to be helpful for
interstellar travel.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
\=\)-----(/=/  ...Yokatta go-buji de..." - Karigari Hiroshi