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

Re: Repeater on the Moon



I will begin by stipulating that very few things are truly impossible, given
sufficient commitment of time, energy, guile, cunning, creativity, politics,
and money. (But a faster-than-light starship is probably impossible unless we
invent new physics.)

So the appropriate question is:  

Is a lunar repeater the BEST use of the worldwide amateur radio community's
limited resources? 

What is the purpose of the proposed moon repeater? There is the technical
challenge of building the thing, which will be attractive to some in the
hardware builders community, and the technical challenge of operating through
a moon based repeater, which will be attractive to the operators community
(although they already have passive moonbounce to excite the technical
juices). Is the purpose to be able to earn an "I worked the moon" award,
suitable for framing? 

If on the other hand, the purpose is to provide maximum communication service
to hams on the ground, for DX country hunting, for wideband data exchange, and
possibly for public service and emergency communications, then a high Earth
orbit satellite seems more reasonable than going all the way out to the moon.


The moon looks large in the night sky, but imagine that the Earth is a soccer
ball, the moon would be about the size of an orange and it would be TWENTY
FEET (6 meters) away from the soccer ball Earth. The geosynchronous orbit
would be roughly the size of a hula-hoop centered on the soccer ball. AO-40's
apogee would be 40 inches (1 meter) from the soccer ball. The space shuttle
and ISS would orbit about 1/4 inch (0.6 centimeters) above the surface of the
soccer ball. The moon is really really far away compared to most satellites.
When Apollo 8 fired the third stage engines to leave Earth orbit and head for
the moon, December 21, 1968, that truly was "One Giant Leap For Mankind", much
more than Neil Armstrong climbing down a ladder 7 months latter.

Let's move AO-40 out to lunar distance, hypothetically, an increase in range
of roughly 6 times. The path loss increases by LOG10(6^2) or about 16 db. Can
your present AO-40 receiver setup stand a 16 db loss over what you get when
AO-40 is at apogee? You will need to improve the uplink signal by 16 db also.
This is not impossible but it will reduce the number of hams who can get into
the game by some factor. Amsat is currently having trouble raising money for
an AO-40 follow-on elliptical orbit satellite. How do we get money from the
ham community to put a repeater on the moon?
 
The next question then is how do you get it to the moon? Three alternatives
are possible:

1. Piggyback on a manned mission: China is the only country even talking about
a manned mission to the moon. They have yet to launch an astronaut into Earth
orbit but that is expected "real soon now". They have talked about going to
the moon sometime around 2010, though that seems to me to be pushing it. They
would need an Apollo-style commitment. Perhaps they are working in secret on
such a massive program, just as President Kennedy committed the US to a lunar
landing before we had placed a man in Earth orbit. I wish them well, it would
provide the kick in the butt that NASA sorely needs right now. To piggyback a
ham payload you would need to get on good terms with the management of the
Chinese program. There are also technology transfer issues from the US
government involved in shipping any hardware or technical documents to China.
This red tape can kill a project as surely as a failed launch vehicle. More
likely the apparatus would be designed and built by students at a Chinese
university, with perhaps a little prodding and guidance from worldwide Amsat
groups.

2. Piggyback on unmanned mission: Europe and Japan have made some noises about
unmanned lunar missions. Payload delivered to the surface will be very tight,
they may not have room for anything but essential science instruments. Success
all depends again on cultivating the right relationship with the people in
charge.
 
3. Build your own lander: The Surveyor missions of the 1960's are probably the
minimum hardware required of a moon lander. The Ranger project tried to land
balsa wood encased instruments but none survived the impact, neither did the
$20 million NASA Mars microprobes survive impact. You would need to build a
liquid fueled propulsion system more complex than AO-40, with throttle
controlled braking engines and thrusters for attitude control during descent
and you need to program a modern software version of the old lunar lander
computer game from 30 years ago. You only get one chance to get it right.
Given our recent history with propulsion on AO-40, is anybody up for trying
this?

Thermal problems on the moon are severe, the temperature cycling kills
electronics. If you dig down one meter into the soil the temperature is much
more stable but digging into the ground also introduces complications. Using
Radioisotope Thermoelectric Generators made from Plutonium 238 carries so much
political baggage that if any part of the project is truly impossible, this
would be it. For NASA projects using plutonium power sources, the sign-off
chain goes all the way up to the President. Plutonium is pretty dammed
expensive also. It would certainly be a good way to bring attention to Amsat,
with the anti-nuke protesters at the launch site we're sure to get lots of
press. I don't really see us getting a license from the DOE to handle
plutonium, but if you want to approach them about it then have a go at it.
Just please don't mention Amsat by name, lest we get unwanted attention from
the three-letter government agencies toward our little organization.
Incidently the little heater capsules carried by Mars Pathfinder generate 1
watt of heat, no electricity. 

Aspiring lunarnauts (lunatics?) will certainly want to look at these books: 

The Lunar Sourcebook : a user's guide to the moon 
edited by Grant H. Heiken, David T. Vaniman, Bevan M. French. ISBN 0521334446
(may be out of print?)

The Lunar Base Handbook : an introduction to lunar base design, development,
and operations, 
edited by Peter Eckart ; with contributions by Buzz Aldrin ISBN 0072401710
 
The Once and Future Moon. Spudis, Paul D. ISBN 1560986344 

I hope that there will be a permanent manned lunar base before I become QRT
from this Earth. I hope that some successor to SAREX and ARISS will be present
there, it will probably be quite popular with the lunar colonists as an
informal link to the home planet. But in the present world, if you want
worldwide DX ham contacts by satellite, a high altitude earth orbit satellite
seems the most cost effective choice. The technical problems of a lunar
mission are severe but the political problems could be even worse. No big
surprise there!

Nothing posted on amsat-bb has or will ever stifle anyone from going ahead and
working on it. This is Amsat, you don't need permission from your boss, just
go ahead and do it.

Dan Schultz N8FGV



----
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



AMSAT Top AMSAT Home