The REAL obstacle to SPSS

> [mailto:ssi_list@... On
> Behalf Of Fred
>
> How hard is it to refocus a square-kilometer power
> beam into a
> ten-square-meter weapon beam?
>
> Harder than you apparently think. Please study the
> SPS proposal in a
> bit more detail. It almost seems as though you
> might be visualizing the
> "focusing" of this microwave beam as being somehow
> analogous to the
> focusing of a beam of light with lenses or mirrors,
> resulting in
> concentrations. The actual technology proposed
> involves a phased-array
> transmitting antenna about a mile across. The most
> that can be achieved
> in an ideal world is a beam which is imperfectly
> parallel.
>
while correct (and arthur laters explains this in much
better detail), you can in fact somewhat focus a
phased array into various spots beams whose phase and
amplitude can be changed on the fly. While not as
well versed in the physics as Arthur, I am currently
working on 2 commsats that do exactly that, Terrastar
and ICO. Albeit, these are on the order of between
12-18 meter phased-array antennae and the focus area
is something on the order of the state of New Jersey,
the physics of it all should scale upwards.

Interesting aside, DARPA is currently has out a study
for a 100 meter unfurlable phased antennae that IIRC
is due for launch around 2011 or 2012. While not the
1 km wanted for SPS, they are moving closer...

Ryan Z