Today's outlandish ham radio idea: plop a repeater on the surface of the moon.
This came up during a discussion on Twitter, of course. The main challenge would, of course, be getting to the moon. Also, the repeater would be have to significantly larger than a satellite repeater because it would have to have a significantly higher power budget. Path loss from the earth to the moon (one way) is between 190 and 200 decibels, so a transmitter power of at least a couple hundred watts would be desired, more than can be handled in your typical cubesat.
In order to power this device, a substantial solar array will be needed, and the lander will have be developed to self-deploy the array on landing. The station's antennas will also need some way to track the earth, as we'd want to use relatively highly directional antennas for best results. Presumably all the signals will be coming from the earth, and so an antenna whose beamwidth is only slightly wider than the earth's apparent size from the moon's surface (how big is that, anyway?) would make sense. At the very least the deployment system has to find the earth initially; since the moon is tidally locked once you've found it it shouldn't move a whole lot, but I think libration movement probably exceeds one earth diameter when seen from the moon's surface and so active tracking would probably be a net gain.
This is, of course, completely impractical, but it would be fun. And probably very expensive. And the EME people would probably complain to high heaven if we ever did it.
This came up during a discussion on Twitter, of course. The main challenge would, of course, be getting to the moon. Also, the repeater would be have to significantly larger than a satellite repeater because it would have to have a significantly higher power budget. Path loss from the earth to the moon (one way) is between 190 and 200 decibels, so a transmitter power of at least a couple hundred watts would be desired, more than can be handled in your typical cubesat.
In order to power this device, a substantial solar array will be needed, and the lander will have be developed to self-deploy the array on landing. The station's antennas will also need some way to track the earth, as we'd want to use relatively highly directional antennas for best results. Presumably all the signals will be coming from the earth, and so an antenna whose beamwidth is only slightly wider than the earth's apparent size from the moon's surface (how big is that, anyway?) would make sense. At the very least the deployment system has to find the earth initially; since the moon is tidally locked once you've found it it shouldn't move a whole lot, but I think libration movement probably exceeds one earth diameter when seen from the moon's surface and so active tracking would probably be a net gain.
This is, of course, completely impractical, but it would be fun. And probably very expensive. And the EME people would probably complain to high heaven if we ever did it.
I was contemplating a repeater on the moon a while back myself and created a Wiki for compiling some of my notes, resources I found online, and possibly input from others if anyone else was interested in a similar idea.
ReplyDeletehttp://moonrepeater.com/
Checking some of the reference links at the bottom of that first page, it appears this has been talked about quite a bit through history. Back with the earlier plans on it, it was back in the day when a nuclear generator could have been utilized... hehe, the good ole days... now we'll have to make do with solar power.
In the 60s we thought about how to do the impossible. Over the years we now first think things are impossible to do.
ReplyDeleteI don't know how to technically place a repeater on the moon. I do know how to raise money and would be excited to put the vehicle together necessary to start funding such a venture.
Contemplate how in a year so dark with bad news how inspiring on a worldwide level this can be.
Don't think NASA, rather private enterprise.
Loren Shirk, K7LRS, Chandler, AZ
480.252.1056
may not need a tracking system once the repeater is pointed in the right direction because the same side of the moon always faces the earth
ReplyDeleteCarson ac0bu
@Carson: well, that's true, but not really. If you watch the little animated GIF I included in the blog article, you'll see demonstrated the phenomenon called "libration". While the moon is tidally locked so that, more or less, the same side faces the earth, in practice there's a significant "wobble" in this, and this might create enough variation that tracking would be desirable. I commented on this in the original post.
ReplyDeleteThe history of Ham Radio and unmanned space vehicles is long, remarkable and successful.
ReplyDeleteLoren, I know how to do this, and agree that it would be inspiring. I've been consulting with one of the Google Lunar X-Prize teams for sometime now, and we, like Dan, at Lunar Pioneer have been working on this for thirty years. (Not real seriously, obviously, but the times have had to be right. Most folks don't remember the Golden Gate was built at the height of the Depression, by the people in San Francisco and Oakland, all by themselves?)
While the Lunar Pioneers, the heart of which has been cussing and discussing this for decades, have our own plans for the Moon, we've been happy to share what we know (and what we think we know) about the Moon with that GLXp team. The most remarkable part of that experience that stands out for me was the look of utter surprise these boys had when we calmly suggested avoiding Lunar Orbit Insertion, altogether. They just thought that was part of the game. Fact is, of course, our first landers and those of the Soviets were 125 hour slow trips to the leading edge of the Moon in its orbit, slowing only from 2500 meters per second beginning as little 70 miles up.
Etc.
Fact is the hard part is endurance through thermal coefficients during a two week day and then the damn cold of a two week night. Fortunately, the materials and designs are well along since our first landings in 1967.
Libration shouldn't be a problem. But we might be doing the whole world of cosmology a favor if brought along a Laser Range Reflector, and target Sinus Medii, near the remains of Surveyor 4 a few miles or less from Surveyor 6.
Read up on the Apache APOLLO program, in New Mexico, where they are spinning up increasing accuracy in the Laser Range Reflectors left behind by Luna 21, Apollo 11, 14 and especially Apollo 15, counting the results in photons.
(Imagine, as we have, a beacon that could be seen by the naked eye from Earth. We have, and it can be done with far less difficulty than we originally thought.)
Kelly,
ReplyDeleteYou're more well read on the subject of the mechanics of successfully operating a repeater from the moon than I, including wobble and such. I guess the only point I was trying to bring out was that any tracking system may well be fairly simple and therefore doable without many magic tricks.
Keep up the good work
Carson ac0bu
I think it could be much more interesting to start by putting a probe with a beacon on board working at 28 MHz. For many reasons.
ReplyDeleteFirst they would not need a critical orientation of the antennae, installed on both the probe and on land.
The probe could simply be dropped on the moon, and the orientation would not be critical.
On the other hand would allow the study of the influence of the ionosphere, which is hardly known today their behavior. I seem to remember only the first teams wore lunik Hf.
And we just have information about their results.
Anyone could monitor the signals. The effective areas for the antenna at low frequencies, and working in Cw, serious signs of hearing were comfortable especially at night and minimum of solar cycle, which is very interesting and exciting and worth studying.
Logically interrunpir would need some system for emissions since it seems that there are plans to place radio telescopes of Hf in our satellite.
So should carry a X-band receiver remote control for example.
Thank.
fdiaz_montano@hotmail.com