[Laser] How much power? Ideed!

[Art]

Hi Charles,

I think 4 Km footprint on the Earth is a problem. That's just to 
small to hit reliably. Libration makes that small footprint nearly 
impossible, unless your aiming platform on Earth and the one on the 
Moon have fast response times and can lock on a star to constantly 
correct for the libration.

Does a 10 milliradian wide beam end up being 4 Km when it reaches the 
Earth? That sounds small.

When we listen to EME, the libration is fast enough to modulte a 
carrier in the 10's of Hz range, so both platforms would have to be 
pretty 'fast' to correct for the libration.

You might store energy, so it can be used after the Moon base is in 
the dark as well.

I notice your sig file says you are involved with microlaunchers. Is 
this part of a plan to put a laser on the Moon?? I remember someone 
in AMSAT was talking about putting a comm center on the Moon. It 
would be a transponder, allowing 133/432 Mhz Oscar class stations to 
be able to QSO (single yagi and 100 watts on both ends). I think they 
had plans for a laser beacon as well. Are you part of that plan or do 
you have any other information about it?

Thanks,

Art






>I did not suggest that you could see a 5 mW laser shining from the Moon with
>the naked eye...
>
>   For Microlaunchers I have been using as a transmitter starting 
> point 30 mw at 650 nm, that being a round number 10e17 photons/sec.
>
>   A 7 cm or slightly larger optic can make a 2 arcsec beamwidth (10 
> microradians), so a data transmission would land on a 4 km dia spot 
> on earth and be about 5th magnitude.
>   Earth image and an uplink location transmission at, perhaps 780 nm.
>
>   For practical reasons (like getting solar power to run it) this 
> would be coming from the daylight side of the moon to a spot on the 
> nightside, so spotting it would rely on a bandpass filter at the 
> receiver end, a narrow field of view, and use of the modulation.
>
>   I haven't done an adequate analysis of this situation yet, but I 
> think it can work.
>
>   Charles Pooley  KD6HKU, Microlaunchers
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