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



>From: William Leijenaar <pe1rah@yahoo.com>
>Hello,
>
>In the AMSAT-DL magazine I red about the idea to send
>an OSCAR into orbit around Mars. In my oppinion it is
>not really AMATEUR RADIO anymore because there are
>only few big stations that can use this oscar hehe.
>
>The idea is still interresting. When it is possible to
>send an OSCAR to Mars then the Moon will also be
>possible !! An station on the Lunar surface will not
>be easy. The problem is to land up there, and
>temperatures can be hot or cold for long periods of
>time. 
>
>An better idea would be an OSCAR in an orbit around
>the moon with its antennas pointed towards the earth.
>This satellite would be very interresting, even for
>radio amateurs :-) I don't know about the path losses
>but I think this will be not an huge problem when use
>high gain antenna's. When using only an 23cm/13cm
>transponder then the satellite and antennas can be
>small. The satellite would be light and only an little
>engine would be needed.   
>
>Maybe it can also be possible to make the orbit
>eliptical with its apogeum towards the earth ! Then
>the satellite would be visible for long time and only
>very short behind the moon.
>
>I would like to discussed these ideas and like to know
>what you think of it...
>
>73 de PE1RAH, William Leijenaar.

William,

You peaked my interest so I ran the space loss equation for the moon:
L = 32.45 + 20*Log(F) + 20*Log(R),
where F = MHz
and R = km

Well Rmoon = 359,000 km at perigee and 406,000 km at apogee, so lets chose
386,000 km as an avg.
F = 1269:
L = 32.45 + 20Log(1269) + 20Log(386,000)
L = 32.45 + 62 + 111.7
L = 206.18 dB 

F = 2400:
L = 32.45 + 67.6 + 111.7
L = 211.75 dB

So great...so what?  Well lets compare this with AO-40 at apogee:
Rap = 59,000 km
F = 1269:
L = 32.45 + 62 + 95.4
L = 189.87 dB

F = 2400:
L = 32.45 + 67.6 + 95.4
L = 195.45 dB

So on 1269 MHz the lunar orbiting s/c signal would be 206.18-189.87 = 16.3
dB weaker, 
and on 2400 MHz it woud be 211.75-195.45 = 16.3 dB weaker as well  ...did
you think it would be other?

So if this lunar s/c had the same radios and antennas as AO-40, you would
need antennas with 16.3 dB more gain!  Or lots more power into the same
antennas.  If you are using a 3-foot dish on 2400 you would need a dish six
times the diameter...18-foot!  Lets say you use 25w and 20 dBi gain on
mode-L, now...If you used 100w, you would need at least a 12-foot dish!
BTW that last one will do eme!

Well I guess the s/c would need to use a bit bigger dish and more power to
bring the ground station down a bit.  Still it looks to me that it would
take (small) eme "class" stations to work it!

Hey, If they launch it I'm ready to work it...maybe next year.

Ed


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