[Laser] comments about Moon pictures

[laser@mailman.qth.net]

I hope I didn't come across as throwing cold water on the idea (although, 
after rereading my message, I'm afraid I did come across a little more 
negatively than I intended).  

I like the rover idea.  I really like the rover idea.  I'm quite surprised that no one
has tried to put a rover on the moon.  I mean, NASA has been having quite a bit
of success with their rovers on Mars, and it would be significantly easier to have
a rover on the Moon [1] [2].

[1] I'm aware that the Soviets did have a lunar rover at some point in the
late 1960s/early 1970s, but that was pretty ancient technology, and there 
just wasn't the opportunity for downlink those signals directly.

[2] One of the problems with a Mars rover is the signal propagation time.
It can take many hours to uplink a command sequence, have the rover perform
it, and then report back.  The Moon is MUCH closer, so the signal propagation
delays are a lot smaller.

I'm not sure that allowing commands to be uplinked to it would be a good idea.
However, it shouldn't be too hard to allow a command sequence to be forwarded,
via the internet to the project administrators, who could approve it after reviewing
it for safety, and then upload it to the rover.  At that point, the rover would execute 
the command sequence, perform any picture taking or other data analysis (Lunar 
soil analysis?  Lunar surface photography?  Lunar geology?), and down link the 
data via a laser transmitter directly to the people on the ground.

The comments about viewing the Earth from a "quarter" moon make some sense.
While this would limit the amount of the Earth that would be visible, it may make the
terrain stand out more, especially along the terminator.

The issue of solar power is still one that's a little troubling to me.  On the one hand,
solar power would significantly simplify some of the design aspects to the craft.
However, on the other hand, it might be really useful to have the laser transmission
coming from the dark part of the moon since this would minimize the amount of
reflected light that would contribute noise to the signal.  

One option would be to supply the rover with rechargable batteries which could
be charged while the craft is in sunlight, and would supply the rover while it's on
the dark side.  The problem with this is that it increases the mass of the rover
significantly, especially for a battery pack which could keep the transmitter 
operating for two weeks at a time, while decreasing the reliability of the craft,
since rechargable batteries are some of the less reliable items on spacecraft.

Fuel cells aren't really an option, due to the limited lifetime available due to limited
fuel supplies.  The way NASA handles this type of problem for deep space or 
interplanetary probes to the distant planets where solar cells aren't an option is
by using RTGs (RadioIsotope Thermoelectric Generators).  Unfortunately, these
devices, which use a bit of radioactive material, tend to draw severely negative
publicity.

One of the tradeoffs involved in selecting the power system for the craft involves
the power of the laser.  From the earlier calculations, a one watt laser may be
really marginal, at least for reasonable data rates.  One option might be to 
increase the laser transmitter power to something approaching 100 watts.  This
would represent a 20 db increase in the transmitted power, and would make
the receiving equipment cheaper (smaller lenses, use of higher noise (cheaper) 
photodetectors, higher data rates possible, etc.).  Of course, a higher transmitter 
power necessitates a larger power source on the craft, as well as creating 
concerns about waste heat dissipation.  Fortunately, heat may not be a problem 
while operating from the dark areas of the Moon.

Maybe a compromise might be to have limited rechargable batteries that could
run the transmitter for a few days a month when it's in the dark area.  In any case,
it might be an interesting design (although one that's probably better conducted
in a more appropriate reflector).

As for the treaties, I think most of them are designed to prevent contamination or
commercial exploitation of the Moon.  Teaching science is fine, but ripping large
sections of the Moon up for mining operations isn't.  Nor is spreading reflective
powder to form space billboards.  Then again, will leaving tire tracks over the
Moon violate any of these laws?  Or, will some third world country make a protest,
just to be doing some sabre rattling?

As for Project Echo, I'm a little too young to remember it (I'm 44.), although I have
seen the shuttle visually, as well as quite a number of other satellites.  

Aha!

Has any one proposed a laser data downlink from the International Space Station?
That might be a step easier than the Moon system, and might be a good training
exercise for more difficult systems.  I know that there is amateur radio equipment
on the space station, so why not a direct laser downlink?

Ok, I hope I came across as a little less negatively this time.

Dave
WA4QAL

-----Original Message-----

From: TWOSIG@aol.com
Date: Mon, 23 Feb 2004 22:57:42 EST
To: laser@mailman.qth.net
Subject: [Laser] comments about Moon pictures
Reply-To: laser@mailman.qth.net

If I had had the benefit of all the comments about my idea for sending 
pictures of the Earth down from the Moon, I would probably have suggested either a 
rover that would take pictures of the Lunar lanscape as it moved along or a 
camera overlooking an amateur radio station inside a permanent lunar base.  

The idea is to have something interesting comming down, by laser, that would 
attract others to be looking up at the laser beam.  Need the "receivers" to be 
cheap enough encourage many to use their own.  Commercial services that can 
be bought and "sponsored" activities that are on line will have better pictures 
and much more professional scientific research.  It may be possible to learn 
as much science by looking at the work of others, as by doing your own 
experiments.  I think you can only learn to have passion for science by participating.

Dave, WA4QAL commented about solar cells on the Moon working only half the 
time and the visible side of the Moon is in full darkness when the Earth is full 
illuminated.  I think that he is suggesting that the best viewing of the 
Earth is when it is "full".  I disagree.  When the Moon is full, it may be a 
romantic sight to the naked eye, but in a telescope I think the detail is a lot 
better when it is less than half lit.  I also think that seeing a real time 
picture of the Earth in a phase that compliments the phase of the Moon would be 
interesting to lots of Tekkies.  I figured that the advantage of solar panels 
would overcome the background sunlight.  

Taking pictures on the Moon and teaching science on the Earth is exactly the 
kind of thing that international treaties are trying to encourage.  If you 
want to throw boulders down onto cities you don't like.... Now that will bring 
out more than just the lawyers.  

I thought that Echo was a marvelous success.  I watched it many nights.  The 
facts that it was pushed arround by sunlight, and that the air is not as thin 
as some people thought it would be up there, well that just made it a more 
interesting experiment.  I assume that it also convenced investors to support 
active communications satellites.

I think I said something before about retro-reflectors in orbit.  It would be 
better if the return beam width was greater.  The true geo-synchronous orbits 
are too valuable to tinkerers like us to be allowed to use.  But the 
mechanics of orbits is such that a satellite can be "hung" in a small patch of sky for 
a few hours below the geosynchronous altitude.  Above the geosynchronous 
altitude has some more potential.  Circular vs eliptical.... too far off topic for 
now.

Thanks to all.

James
N5GUI