[Laser] Re:: heliograph vs. laser indeed!

[Chuck Hast]

On 6/17/07, Charles Pooley <ckpooley at sbcglobal.net> wrote:
>
> F1AVY wrote:
>
> >I have checked your relation wavelength / aperture ratio as beam angle that
> >seemed to me too optimistic.
> >In the moon laser ranging at CERGA in France the telescope is a 1,5 m one in
> >diameter and 20 m focal lens.
> >The best beam it produces is 0,64 arc second or (2pi / 1296000) x 0,64 =
> >0,000003 radiant or 3 microradians.
>   --------------------
>   With extremely high resolution atmospheric distortion becomes dominant in limiting achievable resolution.  Especially when the atmosphere is in front of the telescope.  In the spacecraft situation, there is a vacuum in front of the telescope and only a tiny fraction of the light path at the end of the trip to earth involves air.  The only effect from that will be twinkling, as with looking at a star.
>   ---------------------------------------------------------------------
>
> >If I apply your calculation for a 1 micron wave length laser, 1000 nm / 150
> >cm will give 0,6 microradians that is very best but I think the laser
> >emitting area and its initial divergence are also active parameters.
>   ---------
>   The laser emmiting area does not count.  What counts is if the beam is coherent, and even for laser diodes it is.  So the light (after use of optics) acts as if coming from a point source within the laser medium.  This is why in CD drives, the spot diameter is actually only a lettle larger than a wavelength.  The tracks on CD are 1.1 micron apart if I remember correctly.
>   ---------------------------------------------------------------------
>
> >I found your laser link on the "microlaunchers" site at :
> >http://www.microlaunchers.com/7407site/L3/laser/laser-link.html
> >It is a very ambitious project !
>   ----
>   Thank you.  Tell your friends.  I'm trying to get this out to as wide a population as possible.  So maybe 1 in 1000 or 10,000 might be motivated enough to join (due to ITAR regs, US citizens only--not my idea or preference).
>
Perhaps if like minded technical people in other countries want to get
involved, they can start their own micro launcher groups, I have been
following this of late, I did not realize that ITAR had you screwed to
the wall, but perhaps other groups starting up in other countries might
be the way to do it.


>   If you can think of ways to "get the message out", I'd like to hear.
>   ------------------------------------------------------------------------------
>
> >The aiming stability with the earth cressant tracking will be a real
> >challenge !
>
>   Astronomical grade CCDs, a little software, and a quite non-vibrating spacecraft should make this achievable.
>
>   It has only to be barely possible at first, then (hopefully) a community of interested participants will drive the performance (the "evolutionary pathway" I've been mentioning)
>
>   Microlaunchers is more about creating a new community than just a rocket.  It's an attempt to see in space exploration an analog to what happened with the PC.
>
>   Charles Pooley
>
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-- 
Chuck Hast  -- KP4DJT --
To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going
out and having to identify your bits and pieces in the midst of torn
and twisted metal."