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Re: Fw: Mars? Why not P3x in moon orbit...?

   Hi Tony,
     I am aware of the Moon's liberation and realise that the antenna needs
to be
steerable but it only has to move around on a monthly cycle and so low
powered (low geared) actuators could do that and the "aiming system could
simply be a camera such as the SCOPE camera which could be mounted on the
side of the antenna and provide earth images "for all" as well as the
feedback to the control system to keep the antenna aimed at Earth.

    My first thought was, "how much gain is practicle?" Considering the cost
and difficulty of landing an "OSCAR" on the Moon, it would seem to me to be
best value to have the highest practical gain antenna steered towards Earth.

    Earth has a diameter of about 12732 km which means that from the Moon at
an average distance of about 385000 km the Earth subtends an angle of about
1.9 degrees. If we were to consider the half power beam with of the lunar
antenna should be about 1.5 degrees (stations who want to comunicate close
to Moon rise or Moon set need a good view of the horizon which most of us
don't have anyway and so a reasonable compromise might be to need more
preformance in these situations - atmospheric losses would be worse in those
situations anyway) then we could benifit from about 42.7 db (my first guess
was a bit high).

For 2400 MHz this would be a 5.4 m dish.

For 5800 MHz this would be a 2.2 m dish.

For 10400 MHz this would be a 1.25 m dish.

    An interesting way of using a 5.4 m dish would be to have a mult band
feed so we could experiment with the higher gains of the higher frequency
bands when the Moon was high over head. Might be a good way of downloading
images etc.?

    Just a few thoughts to think about from another non-expert on the

Murray Peterson

----- Original Message -----
From: "Tony Langdon" <tlang@freeway.apana.org.au>
To: <amsat-bb@AMSAT.Org>
Sent: Sunday, September 02, 2001 11:21 PM
Subject: Re: Fw: [amsat-bb] Mars? Why not P3x in moon orbit...?

> Hello Murray!

> Trouble is an antenna with this much gain would need to be steerable, to
> compensate for the Moon's libration.  A fixed antenna would need a
beamwidth of
> 10 degrees or so, otherwise squint would be a serious problem.
> Tony, VK3JED

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