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

Re: Oscar-Zero anyone?

>  >Ok, I'll bite ;-)  I  know this is hypothetical, but how is this going to be
>>powered?  If solar panels you've got to remember that the length of the
>>"day" on the moon is about one month. Half of that is "daytime", and half
>>"nighttime"  If you want continuous service you'll need *considerable*
>>battery power to last the lunar night.
>I'd say:  Just accept the fact that it would work only two weeks out 
>of four...

Well, there are a lot of other problems with equipment living on the 
lunar surface.  The monthly thermal cycling is the worst part -- 
there were a few RTG-powered experiments in Apollo ALSEP's that 
lasted for some time, but eventually the transitions from +200 to 
-200 F just kill the equipment.  The only Apollo surface experiment 
that lasted any real length of time was the lunar ranging experiment 
at the Apollo 11 site, and it's a passive retroreflector.  Active 
electronics get baked during the lunar day, with surface reflection 
and re-radiation from hot soil and rocks, and frozen during the lunar 
night, with no solar exposure at all and conductive heat losses to 
the surface as it cools.  Spacecraft in orbit don't have to deal with 
long cold soaks or high ambient thermal input nearly that much -- as 
you can see from telemetry on a lot of the LEO satellites, the 
temperature doesn't change too dramatically since they make a 
complete orbit in a couple of hours or so.  AO-40 is even better off, 
because its eclipse periods aren't much longer than a LEO and it has 
the long apogee period where it can reach a good solid thermal 

Batteries won't hold up too well on the lunar surface either -- you 
may be able to find a battery chemistry that doesn't like those large 
long-period temperature excursions, but I doubt it.  You might get a 
few good charge/discharge cycles out of them, but in the long run 
their efficiency is going to drop below the point of any real 
usefulness.  You will also see a great deal of thermal creep in the 
joints connecting the solar cells in the panels, which will 
eventually cause failure of the panels, and solar cells start to lose 
efficiency when they are heated.

Then there are path losses -- this would not be a system usable with 
an HT and a ducky, or even a handheld Yagi.  You would need a 
tracking antenna mount or some other way of pointing at the moon, 
some decent transmitter power (which rules out a handheld antenna 
unless you don't mind RF burns), and a fairly seriously narrow beam 
antenna -- maybe not quite as much as you'd need for passive EME, but 
still quite a lot -- and it would probably need to be SSB/CW with a 
fairly wide passband.  It would probably need to be crossband with 
144 or 432 up and 432 or 1296 down, to save space required by 
duplexers, and this would involve UHF and microwave local oscillators 
and amplifiers designed to withstand years of thermal cycling and 
remain stable.

None of this is cheap, and we haven't even started to talk about 
getting it there -- anyone remember the Surveyor missions?  That's 
about the level of ambition we're talking about here, and remember 
the Surveyors didn't last one lunar night, and one of them was DOA to 
begin with.  Getting a transponder into Earth orbit is hard enough, 
and going beyond that to lunar free-return trajectory, then to lunar 
orbit, then to soft landing descent, and delivering it to the lunar 
surface in once piece and still working, is orders of magnitude 

Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org