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At 09:04 AM 12/5/2006 +0000, Graham Shirville wrote:

Uum but if the moonbase is at the south pole then it wont even be line of site to the earth for >50% of the time.

Hence this idea of three satellites in elliptical lunar orbit

http://science.nasa.gov/headlines/y2006/30nov_highorbit.htm?list140623

Or maybe it would be cheaper/simpler just to have a nice big telescopic tower to see over the horizon or even some lunar repeaters on nearby hilltops which have been delivered and placed by unmanned rovers which would help with base to mobile comms on the lunar surface and have moon<-> earth comms capability as well.

Sounds like they really need some ham "experts" to work on these issues:)

cheers

Graham G3VZV

The article I read mentioned that the base was destined for a location "near: the southern pole which received 100% sunlight throughout the lunar month...but that doesnot imply 100% earthview (very astute observation by Graham). From that I would surmise that solar power is considered (plus it avoids the deep cold temps of lunar night).

All the discussion so far "assumes" a fixed pointed antenna pointed toward earth. I would suggest that with the kind of infrastructure a manned base implies, that a steared dish is reasonable. Thus it can be larger than 5 WL and just compensate for apparent earth movement (libration, etc.). In my private reply to Pat, I suggested that the digital signal (aka CC-rider ACP) might have a contant pilot carrier for locking a tracking system (and AFC as well). This would imply at least three command stations located on earth.

The over Moon-horizon issue is a good one. For NASA comms they may use orbiting relay sats like used for the Mars rovers. But it would be prudent to have direct comms, as well. So either the remote hill-top dish linked back to the Moon-Base as suggested...or just accept that direct comms is only available for part of the lunar month that earth is visible (not an acceptible choice for NASA but certainly one for hams). I think ham radio on the Lunar orbiting sats is a long shot...forget it.

In the artists rendition I viewed, it showed manned rovers. So, in time, there would be the means for setting up a remote Moon ham station. Justification would likely be the same as ARISS (emergency back-up + personal comms for Lunarnauts).

Hope I am arround to see this happen (c. 2020). 73's Ed - KL7UW ========================================= BP40iq, Nikiski, AK http://www.qsl.net/al7eb 50-144-222*-432-927-1296-2304*/2400-3456* -10368-24192* MHz *Under construction USA Rep. for Dubus Magazine: [email protected] =========================================

Bruce etal:

At 09:45 AM 12/6/2006 -0600, Bruce Bostwick wrote:

There are definitely a lot more Part 15 radiators on 2.4 GHz than there were 10 years ago. How much of an issue they pose in terms of raising the noise floor of your receiver depends on where you are and how well your antenna rejects off-axis signals.

---snipped---

I can't see any other way terrestrial 2.4 GHz signals would make a

difference

one way or the other except in terms of raising the noise floor of your receiver's LNA.

It will make a big difference if the signal level is below the noise.

Space loss from the Moon is: L = 32.4 + 20LogF + 20LogD, F=MHz and D=km D = 356,400km at perigee, = 406,700km a apogee 1296: L=205.7 to 206.8 dB 2400: L=211.0 to 212.2 dB 3456: L=214.2 to 215.4 dB 5760: L=218.6 to 219.8 dB 10368: L=223.8 to 224.9 dB actual difference in space loss from perigee to apogee is 1.15 dB (some round-off error in list above).

So what does this mean? Next step is calculating SNR: We'll do it for F=2400 MHz S/N = Ps - Pn Pn = 10Logk + 10LogTe + 10LogB, Te = system noise temp, K and B = bandwidth, Hz Pn = -198.6 + 10Log150 + 10Log2500 Pn = -142.9 dBm (the receiver noise floor)

Ps = Pt + Gt + Gr - L, Pt power transmitted in dBm, Gt = Tx ant gain, dBi, Gr = Rx ant gain, dBi Lets say the tx dish is 8-foot and receive dish is 4-foot, and the Moon Tx output is 10w (+40dBm) Gt = 34.2 dBi, Gr = 28.2 dBi Ps = 40 + 34.2 + 28.2 - 212.2 dB Ps = -109.8 dBm

S/N = -109.8 - (-142.9) = 33.1 dB A nice strong signal on SSB

If Te is compromised to 500K, and we use 2-foot dishes (G=22.2 dBi) then we get an S/N = 18 dB. I guess that is still OK but a lot less strong.

try the numbers for 5670 MHz. BTW all this math is from pp 13-2 and 13-3 of the Satellite Experimenters Handbook, 2nd Ed. by Davidoff.

As far as engineering the transponder itself .. the two biggest problems of putting a transponder on the moon (1, getting it there and deploying it properly, and 2, keeping it powered up through the lunar night to survive the cold soak) get a lot simpler if there's a spacecraft already going there that you can hitch a ride on (at however many $M a pound!), astronauts (i.e. trained eyes and hands) there to set it up, and an external source of power to keep it running without sunlight. It starts to get maybe sort of practical if you squint real hard, once those two problems are solved. Not *really* practical in the sense of being affordable on an AMSAT-type budget, but getting an order of magnitude or so closer at least .. :) .. enough so that if NASA can be sold on it as an emergency communications backup (with the caveat that this means it could be taken over in the event of a station emergency), it might just become feasible.

This thread was based on NASA's announcing plans for a manned Moon Base, so there is your ride, and personnel to deploy the station. The site was described as always in the sunlight (never sees dark) so solar power is good. Never dark means it is not so cold! NASA probably has the same concerns as we do.

The libration problem does get tricky, because the transponder's antenna either has to have a wide enough main lobe that Earth stays in it most or all of the time (the exact percentage being a very critical engineering tradeoff), or there's some tracking mechanism to steer the antenna for a tighter beam, which gets into the additional failure modes of moving parts as well as the control system to steer the antenna (and ways in which that can get out of sync with the Earth's motion causing intermittent LOS and requiring Earthside control ops commands to get it lined back up!), also a critical engineering tradeoff. Which of those two solutions is better is for better minds than mine to decide, but those are the choices antenna- wise ..

With a manned base I would offer that a tracking antenna is practical. Perhaps it could be made piggy-back to NASA's comm system? Of course there is always electronically steered arrays. Perhaps a quad of dishes pointed to cover the 10-degree area of lunar sky the earth moves thru? Then only a 4-way coax switch to track. The 8-foot dish on the Moon has a 3.65 degree bw at 2400 MHz.

In any case, what I am trying to say is this is just a matter of looking at the engineering parameters and coming up with the solution. The ride/power/maintenance issues are the significant ones...and they may be solved by 2020 when Moon Base One is established.

I actually suspect that by then that 10-GHz will be reasonable as an downlink frequency with uplink on 5-GHz. Play with the numbers.

73's Ed - KL7UW ========================================= BP40iq, Nikiski, AK http://www.qsl.net/al7eb 50-144-222*-432-927-1296-2304*/2400-3456* -10368-24192* MHz *Under construction USA Rep. for Dubus Magazine: [email protected] =========================================

Jason White wrote:

The thread on a lunar based transponder has me wondering.. How were the comms with the Apollo missions done? What frequencies/modes? Did amateurs and utility listeners of the time copy much of anything from the moon while man was there? Did they have these same problems or did the fact that Eagle was in orbit solve them?

Uhhh, both. :-)

Digging (real deep) through the links to the books for sale, videos, and what-not on this website will yield tons of information -- I found a complete diagram of the frequencies used, etc... way down in the links.

Wish I'd have bookmarked that one... but it was just a one-time web-spelunking for fun.

http://www.honeysucklecreek.net/

I've heard the crackly "That's one small step.." recordings, and it sort of sounds like SSB, but I had never really thought about it before. Now that I think about it, copying that signal would probably have been the rarest utility DX ever!

Not too bad, really -- just a lot of stations on the ground to deal with the rotation of the earth and the fallibility of the hardware of the day.

The site above has a whole lot of the story of that day's comms, including recordings of the back-channel comms between Houston and the tracking stations. Nifty site.

Nate WY0X

----- Original Message ----- From: "Edward R. Cole" [email protected] To: "Jason White" [email protected]; [email protected] Sent: Saturday, December 09, 2006 9:37 AM Subject: [amsat-bb] Re: Lunar Architecture Moon Base

Edward R. Cole wrote:

< snip >

My boss set up a ten foot comm dish in his front yard and using a diode mixer with a signal generator as LO, detected the 2-GHz carrier of the orbiter as it circled the Moon. It was fascinating to hear the signal and the Doppler shift as it orbited and lost signal for about 20-min as the orbiter went behind the Moon. That was too small and poor a receiver to recover modulation, so we did not hear any voice.

73's Ed - KL7UW

Hi Ed, KL7UW

Was your boss using or not a low noise preamplifier in front of the diode mixer ?

Tanks and 73" de

i8CVS Domenico