Re: [amsat-bb] Info about OSCAR on Moon surface

[Phil Karn <karn@xxxxxxxxxxxxxxx>]

>So then the next idea is an OSCAR on the moon itself. Or in other words and 
>moonlander with OSCAR on board :-)

If this list had a FAQ, this would be entry #1.

In short, the moon is an absolutely *terrible* place for a
communications relay intended to link users on earth.

1. It is very far away, about 400,000 km. That's over 10 times the
   distance to geostationary orbit, so the path loss would be 20+ dB
   greater than GEO, and something like 46 dB worse than LEO. That's
   only 1% of the received signal power for the same transmitter in
   geostationary orbit, and only 0.0025% for the same transmitter in
   low earth orbit.

   Check out the (excellent) movie "The Dish". There was a good reason
   for using such a large antenna.

   And the round trip propagation delay is about 2.7 seconds, which
   makes casual conversation very difficult (just listen to some of
   the Apollo tapes).

2. The moon's surface is very difficult to reach. Not only is the
   total delta-V required for a soft lunar landing actually greater
   than that for a mission to the surface of Mars, but the technical
   sophistication (not to mention propulsion reliability) needed to
   guide a lander to the surface in one piece is far beyond anything
   AMSAT has ever done.

3. It gets dark there for 2 weeks at a time. Not only won't you have
   any power from your solar arrays, you won't have any way to keep
   warm. Apollo 11's solar-powered surface experiment package lasted
   only a few weeks.  The later ones were nuclear powered. That's not
   an option for us.

There are only two good reasons to send a radio relay to the
moon. First, as a relay for some other lunar mission. Second, to
perform radio astronomy using the moon as an RF shield from the
earth. Such a mission would be most easily done in lunar orbit, not on
the surface. Just such a mission was done in the late 1960s.

Phil

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