[Laser] moon repeater

[Steve Bailey]

I suppose one could lobby NASA to explode a large package of glass
micro-spheres [the kind used in highway centerline paint] over the lunar
surface.    -ka1rxx
----- Original Message -----
From: <TWOSIG@aol.com>
To: <laser@mailman.qth.net>
Sent: Monday, December 15, 2003 8:09 PM
Subject: Re: [Laser] moon repeater


> I like the thinking that my weird ideas generated.  I don't know a whole
lot,
> but I have two comments on the excerpt I copied below.
>
> On using the Apollo retro reflectors, please forgive me if my memory is
> faulty, but I think that a web site on the Lunar range experiment at the
McDonald
> observatory in west Texas described the experiment.  In it, a high energy
> compressed laser pulse is sent through a one meter diameter telescope at
the tar
> get.  The light pulse expands from one meter to about two kilometers.  The
> retroreflector panel is about area of a disk a half meter in diameter, and
reflects
> almost all of the incident light in a beam that returns to the earth with
an
> expansion to an area of about 20 kilometers.  The photons of the beam are
> collected in a 1 meter telescope (I don't remember if it is the same one,
or
> another.)  The point of this description was that they collected one
photon from
> most of the pulses.  They then ran a statistical analysis on when the
photons
> were received to use it it as a distance measuring device, which by now
has an
> accuracy of about one or two inches.   Also as I remember there are three
Apollo
> retro-reflectors and another one that I think is French made on a Russian
> probe.  They have been tracking not only the orbit of the Moon, but its
"rocking"
> as well.   Cool stuff.
>
> For a communication from the Moon to be received on the Earth, the beam
will
> need to be more powerful when it leaves the Moon than the above system.
If
> you send a beam from Earth to the retroreflectors, you will need a much
narrower
> beam or a lot more power.  If a lower power beam is sent to the Moon, it
will
> need to be tightly columated to have a similar energy.  I guess that some
> astronomers (amateur or not) would know what kind of telescope would be
needed.
>   On the down side, I think that any beam from the retroreflectors would
come
> back to the Earth in a beam 20 kilometers around its origin.  EME for
> neighbors.
>
>  That brings me to the other point about retroreflectors.  If a beam comes
> from the Earth, it does not matter how much the Moon rocks from side to
side.
> The return beam will be back toward the line of origin with some
additional
> expansion.  A retroreflector will need no more than two degrees of
expansion.
> Practically, I think that one degree will be plenty.  The typical STOP
sign is a
> lot more beam expansion.
>
> Someone else suggested that the natural reflectivity of the moon is about
5%.
>  I think the number is more like 2 - 3 %.
>
> As much as I like the I like the idea of a passive reflector, I am afraid
> that it will need to be too big for the first decade of a lunar base.
>
>
>
> James
> N5GUI
>
>
>
>
> I think most kinds of retro-reflective paint have a
> backscatter spread of about 5 to 10 degrees? That
> might be great for covering the whole earth as seen
> from the moon (2 degrees) without wasting an excessive
> amount of the energy.
> Even though the moon keeps one side always toward the
> earth, it liberates a bit during the month by a few
> degrees (6 or 7). So an extra margin on top of that 2
> degree "earth width" would take that into
> consideration as well. Also with the added benefit of
> being much less critical in alignment when being set
> up, compared to say, a plane mirror type reflector.
>
> I was wondering if anyone has tried using the Apollo
> retroreflectors with low power lasers in combination
> with the 20 hz QRSS type modulation? Since that seems
> to be the cutting edge of weak signal tech these days.
> Even though it would only be usefull for hearing your
> own signals i suppose.
>
> Tim
> toasty256@yahoo.com
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