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 <[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.
