[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Repeater on the Moon

> 1) Just surviving the extreme heat and cold

Mainly a matter of designing the hardware to withstand a fairly wide 
range of temperatures and repeated cycling.  Component selection, 
mainly, since the hot and cold periods are so long that shielding the 
hardware is not practical.  Plus mechanical design that take 
expansion/contraction and thermal creep of connectors and structural 
elements (metal does not return to exactly the same shape it expanded 
from when it contracts) -- this will be perhaps the second biggest part 
of the challenge, and testing in a simulated environment will be the 
only way to catch some subtleties of it.

> 2) the Several week long period of total darkness (no power)

Not sure if there is any way of getting around this.  We might have to 
just let it shut down over the lunar night.  Batteries aren't practical 
to run a 100W+ transponder or two for two weeks with no solar power, 
not at the kind of target payload weight we'd need to look at.  If 
there's some way to exploit thermal differentials and operate in a 
reduced power mode, it might be possible to get some sort of operation 
(possibly telemetry/command only) during the lunar night, but I'm not 
optimistic that anything but daylight operation would be possible.  
There's just no way to carry enough energy capacity to last that long 
without sunlight, without making the payload far too heavy.

> 3) Pointing the gain antennas.

This might be an easy one.  How accurately does the antenna need to be 
pointed?  The earth doesn't move much in the lunar sky, mainly from 
eccentricity/libration effects, and all of these motions are 
predictable at least to some extent.  It's probably worthwhile putting 
in some az/el control of the high-gain antenna into the command system, 
if nothing else but fine tuning, but your high-gain antenna is going to 
be pointed pretty close to the earth at all times.  Depending on what 
the pattern of the antenna is, it might be sufficient to position it so 
the center of its pattern is aimed at the center of the earth's 
relative motion -- this would reduce the power demand from steering the 
high-gain to track the earth and would keep the gain antenna more or 
less correctly pointed if (i.e. when) the az/el motors fail.

> 4) getting it there!  (a few trillion dollars)...

This is obviously the biggest part of the job.  A ride to low earth 
orbit costs about $10,000 a pound (NASA's figures, other space agencies 
are roughly comparable) and that's a CHEAP launch.  Lunar transit alone 
would be probably an order of magnitude more than that, lunar orbit 
somewhat more, and a soft lunar landing and deployment, well, figure at 
least several million dollars PER POUND.  To be worth launching, this 
would have to be a project that would have at least a couple of years 
lifetime, working reliably every lunar day, and provide enough gain to 
make EME voice QSO's on sideband practical for people with fairly 
average UHF or microwave stations.  (It isn't at this point -- the only 
mode I know of that's practical on EME right now is CW.)  This is what 
makes the concept a fairly daunting project -- it would make AO-40 look 
like a walk in the park by comparison.  If we can pull it off, it might 
be the single biggest PR coup for ham radio ever, but it's a major 
project, no two ways about it.

The ONLY way we could get this payload to the lunar surface would be to 
ride on someone else's mission, and pay whoever gives us a ride out 
there and some means of getting the payload deployed and oriented 
correctly.  The only type of mission I know of that would be able to do 
that would be a manned lunar mission, unless this payload is extremely 
small and can piggyback on an unmanned lunar lander ..

"Many that live deserve death. And some that die deserve
life. Can you give it to them? Then do not be too eager to deal out
death in judgement. Even the very wise cannot see all ends." -- Gandalf

           --... ...-- -.. . -. ..... ...- -...
                   Bruce Bostwick N5VB

Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org