[time-nuts] Re: constructing a moon base

[Lux, Jim]

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.




>
> Bob
> t
>> On Sep 29, 2021, at 11:40 AM, Lux, Jim <jim at luxfamily.com> 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"
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