Hi > On Sep 29, 2021, at 12:53 PM, Lux, Jim <[email protected]> wrote: > > On 9/29/21 9:10 AM, Bob kb8tq wrote: >> Hi >> >> Road building and graders sort of implies moving large amounts of “stuff” >> onto the lunar surface. While a “road to nowhere” on earth might happen, >> I’d bet you only build one on the moon to connect inhabited installations >> to other full blown (inhabited or not) sites of some sort. >> >> Unless I’ve been dozing off yet again, that sort of intensity is well past >> the >> 10 year or even “several decades” threshold. Would I bet on a date? Nope … >> Yes this overlooks the construction phase of the first installation. I’d >> assume >> “old school” techniques would do fine for that. >> >> If the “whatever” is going on the far side, some sort of redundant coms >> would be a requirement. I can’t see putting folks there without a really >> good way to stay in contact with them. Having a system is not “optional”. >> It’s only a question of what sort of system. These days digital with a time >> stream …. yup …. > > Those desires (Apollo had no far side comms, but in today's risk averse > climate, I can't imagine not having nailed up 24/7 connectivity with the > astronauts) are met nicely by a relay at L2. Or by a sufficient number of > orbiters. You'll see a lot of references to the Near Rectilinear Halo Orbits > (NRHO) which are highly elliptical. Those are "sort of" nice (kind of like a > Molniya in concept), but driven more by "what can we do with launch vehicles > available today, e.g. SLS" .. as opposed to, say, 3 orbiters at a mid height > orbit, which gives much shorter link length from surface to orbiter (so you > don't need as much power or as big an antenna). The field of view from a > lower orbiter is also smaller, so potentially, it doesn't have to handle as > many simultaneous users. NRHO, being highly elliptical-ish (it's not > actually an ellipse, it's a variant of the family of halo orbits from L2 to > L1) - so the range varies a LOT, as does the relative motion in the sky. Long > range, low Doppler, slow motion if you need to track a gain antenna when > you're at apolune, and short range, high doppler, and really fast angular > rates at perilune. > > >> >> The same math that makes it expensive to get things to the surface can >> make it slightly less expensive to put it in lunar orbit. If you can do a >> task >> (like comms) either way .. cheaper usually wins out in the end. Yes, there >> are a *lot* of grubby details to dig into before you really would know if >> in orbit comes out the winner. I’d still bet it does. > > > > Not just getting mass into orbit vs surface, but the environments in orbit > are far more benign (unless you're buried on the surface). > > In space, you don't have the 2 weeks of sun, 2 weeks of night problem, which > drives all kinds of design issues (surface temps between -100 to +100C or > wider, for instance). > > >> >> Do you put clocks on the moon? I think it’s a pretty good bet that the >> sort of science that you would want to do early on needs them. Having >> a couple masers up there well before the road graders arrive seems >> very likely. Just how you link up all the bits and pieces …. eventually >> we’ll see. > > I'm not so sure. You've got a fairly clean propagation path from orbit to > surface (unlike Earth), so you can record an orbiting reference signal along > with your science data, and reconcile in post processing. Yes, the beacon is > moving, just like in GNSS, but there is well developed software to deal with > that (GIPSYx) in some sense. > > If you need spectacularly good phase noise, then a maser might be required as > part of your science measurement, but I don't know that you'd need it for > timekeeping.
My thinking was that radio astronomy / VLBI sort of stuff is something folks get interested in. There are some advantages to a lunar location (more so one on the far side). Enough interest and maybe there’s funding. Clock specs could / might be similar to an earth based station. Yes, there’s more than a little bit of handwaving there. A lot depends on just what is being done and how it is be done. Maybe we’ll have TCXO’s that drive VLBI in 40 years time :) ….( I sorta doubt that will happen. ) Bob > > > > >> >> Bob >> t >>> On Sep 29, 2021, at 11:40 AM, Lux, Jim <[email protected]> wrote: >>> >>> On 9/29/21 8:13 AM, Joseph B. Fitzgerald wrote: >>>> By the time we get to road building, a pretty robust communications system >>>> will be in place. Given the synchronization requirements of modern >>>> digital networks, accurate time will be available just as it is in >>>> terrestrial cell phone networks. >>> >>> Actually, I wouldn't assume this, at least in the next 10 years. There are >>> national security and commercial forces at play on Earth that lead to >>> robust PNT being available. At the Moon, not so much. No need to do >>> midcourse targeting of ICBMs for precision munitions delivery (one reason >>> for original GPS). And there's nothing saying that one would move existing >>> cell phone networks (and their timing/frequency requirements) to the Moon >>> (the density of cells vs users, for instance). >>> >>> Pretty much everyone starts out thinking "we'll just take COTS system X to >>> the Moon" (be it WiFi, WiMax, Cell phones, or whatever). The justification >>> is usually that you'll reduce development costs because you have an >>> existing base of designs and parts. >>> >>> However, you'll find that there are inevitably, some aspects of being in >>> Space or at the Moon that "break" some assumption of the existing protocol. >>> And that's before you get into the need to build this stuff with something >>> that can tolerate single event effects, both transient and permanent. So >>> all of a sudden, you're not "taking existing commercial parts and flying >>> them", so now you're doing some new design, which might drive you to >>> simpler approaches (since they're cheaper). >>> >>> The other problem is that for the foreseeable future, the Moon won't be an >>> environment where you can design protocols and features for a 1 or 2 year >>> life like we do for cellphones, with refreshes of technology as needed. >>> It's incredibly expensive to put things on the Moon (and even if Elon's >>> wildest dreams come to reality, it's still going to be expensive - it's >>> just a mass fraction issue) So you won't have nearly the rapid evolution we >>> do with terrestrial systems, or, if we do, there will need to be >>> significant backward compatibility. We won't be able to do the Apple >>> approach of "Well, the app doesn't support that old iOS any more, buy a new >>> iPad" >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] -- To unsubscribe send >>> an email to [email protected] >>> To unsubscribe, go to and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] -- To unsubscribe send an >> email to [email protected] >> To unsubscribe, go to and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
