date:20210929

Alec Teal writes:

> So you suspect/expect around the time frequency changes started 
> happening, clocks became crap?

Well, it gets complicated fast there, but yes, that's pretty much
where the shit inescapably hit the fan.

Previous to that, most CPU's were clocked with a small PLL chip
which multiplied a 14.318MHz X-tal to whatever was needed.

"Not good, not terrible" is probably a fair summary.

But there are two different things at work here:  On one hand
the choice of Xtals:  To keep the jitter on the multiplied
clock low, the Xtal had to be better and better.  (This is
something the "extreme overclocking" people totally fail to
consider when doing their high-school physics experiments.)

But on the other hand, the CPU architecture must offer
/something/ to the kernel to keep time with, and that's what
Intel utterly fiasco'ed because of their windows focus.

The entire ACPI-solves-that, ACPI-without-gliches-solves-that,
reading-ACPI-is-faster-now saga was just sheer incompetence.

But the ACPI running at 14.318 MHz is inadequate for most modern
kernels in the first place, and that gets us into the TSC-counts-cycles,
TSC-counts-cycles-without-overflow-issues,
TSC-counts-cycles-onlyfor-this-core, TSC-pretends-the-core-is-
always-running-at-the-same-speed saga, which was also caused by
Intels idiocy.

Admittedly, there are good and sane explanations why this is
a hard problem to solve, but competent people solved in in
other architectures decades before Intel botched it.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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[time-nuts] Re: When did computer clocks get so bad?

Hi

If your wrist watch is holding 3 seconds per year without some sort of external 
correction,  that’s pretty amazing …. 10 seconds a month is doing well.

Bob

> On Sep 29, 2021, at 2:35 PM, Alec Teal  wrote:
> 
> Hi there,
> 
> I have a question and I cannot think of anyone better to ask, for a project 
> we need to time some things which are connected to a computer, using NTP and 
> later using a GPS over bluetooth serial ports, we have discovered that 
> computer clocks are terrible
> 
> If you remove a linear drift (for example assuming it ticks at 1.00026 
> seconds per second) it gets less terrible, and Linux can do this but it is 
> clear that the computer clock doesn't expose this coefficient to the OS to 
> let it compensate, it must be found (eg through NTP) - any ideas why?
> 
> 
> But more concretely, my watch is actually pretty good, it's off by < 3 
> seconds and hasn't been set probably this year (I don't tend to bother with 
> DST stuff, not for any reason just never get round to it) - when I was 
> growing up and even now wall-clocks are not so terrible that I have to fix 
> them (or NTP does with computers) very routinely.
> 
> My theory is that super cheap crappy quartz clocks are now used in things 
> which can be reasonably expected to be online most of the time, and thus use 
> NTP - my watch cannot (and probably has temperature correction too? Given the 
> varied temps it is exposed to) any truth to this?
> 
> This is a very open ended question I understand, but if clocks were as 
> terrible as I've found every computer and thing I've checked recently, why 
> don't I remember setting wall clocks easily once a week?
> 
> 
> Alec
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[time-nuts] Re: When did computer clocks get so bad?

2021-09-29 Thread ed breya

I assume you're talking about the RTC chip that runs off the CMOS BIOS 
memory settings battery, to keep time whether the computer is on or off. 
These are as you suspect, typically cheap items that get the basic job 
done. You may be able to find better grade ones. It also depends on 
whether the timing crystal is built into the IC, or a separate piece. In 
this case, you could fairly easily hack in a reference that's as good as 
you want. Usually it's a 32.768 kHz "watch" type resonator, and 
disconnecting one end and hooking in an external source will drive it 
instead. If you provide the same nominal frequency, that's much more 
accurate and stable, can run the RTC under all conditions, and is always 
on, then it should keep time as good as your reference.


Ed
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[time-nuts] Re: When did computer clocks get so bad?

2021-09-29 Thread Dana Whitlow

Alec,

I seem to perceive that PC clocks have gotten quite a bit better since
their early days.  What do others think?

Dana

On Wed, Sep 29, 2021 at 3:10 PM Alec Teal 
wrote:

> Hi there,
>
> I have a question and I cannot think of anyone better to ask, for a
> project we need to time some things which are connected to a computer,
> using NTP and later using a GPS over bluetooth serial ports, we have
> discovered that computer clocks are terrible
>
> If you remove a linear drift (for example assuming it ticks at 1.00026
> seconds per second) it gets less terrible, and Linux can do this but it
> is clear that the computer clock doesn't expose this coefficient to the
> OS to let it compensate, it must be found (eg through NTP) - any ideas why?
>
>
> But more concretely, my watch is actually pretty good, it's off by < 3
> seconds and hasn't been set probably this year (I don't tend to bother
> with DST stuff, not for any reason just never get round to it) - when I
> was growing up and even now wall-clocks are not so terrible that I have
> to fix them (or NTP does with computers) very routinely.
>
> My theory is that super cheap crappy quartz clocks are now used in
> things which can be reasonably expected to be online most of the time,
> and thus use NTP - my watch cannot (and probably has temperature
> correction too? Given the varied temps it is exposed to) any truth to this?
>
> This is a very open ended question I understand, but if clocks were as
> terrible as I've found every computer and thing I've checked recently,
> why don't I remember setting wall clocks easily once a week?
>
>
> Alec
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[time-nuts] Re: When did computer clocks get so bad?

Alec Teal writes:

> My theory is that super cheap crappy quartz clocks are now used in 
> things which can be reasonably expected to be online most of the time, 

There are multiple answers to your question.

The funny one is:  When they set fire to a prototype motherboard
at Intel Architecture Labs.

Unfortunately that is not my story to tell.

But for the PC-ecosystem, that really is the answer:

When Intel had to start modulating clock-frequency in order to not
set things on fire.

Their execution was far from stellar, because they had their eyes
only on Windows, which for all intents and purposes had no timekeeping
worth anything at the time.

By now they have it relatively under control, and due to the very
steep PLL multipliers high end kit actually have comparatively
good XTALS in order to keep the jitter within spec.

For the Internet of Shit segment, the answer is it was never any
good to begin with.

Since these embedded chips generally are incredibly robust with
respect to timing, the xtal on the BOM is the cheapest that will
meet spec.

The one saving grace is external high-speed interfaces like USB-3
and 10G ethernet:  You need good-ish xtals before it even works.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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[time-nuts] When did computer clocks get so bad?

2021-09-29 Thread Alec Teal


Hi there,

I have a question and I cannot think of anyone better to ask, for a 
project we need to time some things which are connected to a computer, 
using NTP and later using a GPS over bluetooth serial ports, we have 
discovered that computer clocks are terrible


If you remove a linear drift (for example assuming it ticks at 1.00026 
seconds per second) it gets less terrible, and Linux can do this but it 
is clear that the computer clock doesn't expose this coefficient to the 
OS to let it compensate, it must be found (eg through NTP) - any ideas why?



But more concretely, my watch is actually pretty good, it's off by < 3 
seconds and hasn't been set probably this year (I don't tend to bother 
with DST stuff, not for any reason just never get round to it) - when I 
was growing up and even now wall-clocks are not so terrible that I have 
to fix them (or NTP does with computers) very routinely.


My theory is that super cheap crappy quartz clocks are now used in 
things which can be reasonably expected to be online most of the time, 
and thus use NTP - my watch cannot (and probably has temperature 
correction too? Given the varied temps it is exposed to) any truth to this?


This is a very open ended question I understand, but if clocks were as 
terrible as I've found every computer and thing I've checked recently, 
why don't I remember setting wall clocks easily once a week?



Alec
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[time-nuts] Re: constructing a moon base

Hi

Indeed the grader and the remote installation both may be “people-less” much
of the time. The “stuff” in those installations (that are big enough to require 
real roads between them) is going to take some significant lift capacity. 

Does the road go in ahead of the first installation? Seems unlikely …

More or less:

“Let’s do a space telescope on the moon”. You build up a device or more likely
a set of devices. They get tossed into orbit and eventually land. By some means
they plug into each other. The site comes to life and does its thing. Is it 10M 
in 
diameter or a hundred?… who knows. No road or significant pre-construction 
needed either way. Lift capacity … yup. Are folks involved on site at any 
point? 
Back to those grubby details …. Are there masers? … who knows. 

In terms of a continuously operating site, this “drop in pre package”  is (at 
least 
to me) going to happen much earlier than sites with a road network between 
them.  
Is even this a decade or many decades out …. unclear right now.

Do folks drive repair trucks on the roads or do robots? Not clear, but both 
would 
be supporting a pretty significant bunch of stuff for roads to make sense. Some 
sort
of 4/6/8 WD rover that does not require a road (but maybe can’t carry a lot) 
could 
get simple stuff done. 

Bob

> On Sep 29, 2021, at 2:19 PM, Poul-Henning Kamp  wrote:
> 
> 
> Bob kb8tq writes:
> 
>> 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. 
> 
> It's funny how peoples thinking about this is still firmly cast in
> a 1950'ies NASA/science-fiction mindset.
> 
> People really do not grasp how much work robots can do.
> 
> One place I really see this is when people look at my lawnmower robot
> and go "There's no /way/ that can handle 5000 m² of lawn..."
> 
> But the thing is: If a human did it on a garden-tractor once a week,
> we'd want it done quickly, so lots of power, wide cutting board and
> so on.
> 
> But the robot has 168 times as much time[1] for the same job, so
> it does not even need one percent of the power of the garden-tractor,
> in particular because it does not have to lug 100 kg of human &
> associated creature-comforts around.
> 
> If we need a road on the moon, we will launch robots and let them
> get on with the job, and they'll be done way ahead of when we arrive,
> probably not even leaving us a few really largish boulders to blow up.
> 
> In other words: The grader on the moon will at most be a meter wide.
> 
> Poul-Henning
> 
> 
> [1] The quoted capacity for lawn-mower robots is for 24hx7d, but
> in general you should not let it work while dark, for the sake
> of the other inhabitants in your lawn:  Porcupines etc.
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
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[time-nuts] Re: constructing a moon base


On 9/29/21 11:19 AM, Poul-Henning Kamp wrote:


Bob kb8tq writes:


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.

It's funny how peoples thinking about this is still firmly cast in
a 1950'ies NASA/science-fiction mindset.

People really do not grasp how much work robots can do.

One place I really see this is when people look at my lawnmower robot
and go "There's no /way/ that can handle 5000 m² of lawn..."

But the thing is: If a human did it on a garden-tractor once a week,
we'd want it done quickly, so lots of power, wide cutting board and
so on.

But the robot has 168 times as much time[1] for the same job, so
it does not even need one percent of the power of the garden-tractor,
in particular because it does not have to lug 100 kg of human &
associated creature-comforts around.

If we need a road on the moon, we will launch robots and let them
get on with the job, and they'll be done way ahead of when we arrive,
probably not even leaving us a few really largish boulders to blow up.

In other words: The grader on the moon will at most be a meter wide.


We are getting astray from time- nuts here...

BUT

You probably want to be bigger than a meter - thermal management is 
easier with larger (surface area to volume ratio), and if you're solar 
powered, you need more solar panel area.  However, the "grading width" 
might be a meter, just the vehicle around it might be significantly 
bigger. It's not like a Bobcat skid steer where you're trying to fit it 
down the side of your house through a 1 meter gap.


Bigger also probably has advantages mechanically - mechanical tolerance 
requirements tend to go as a fraction of the size, so bigger boxes have 
looser tolerances in absolute terms. When you're moving around in an 
environment of electrostatically charged, incredibly abrasive dust, this 
helps.


If you're flying a reactor for power (which would be nice to get through 
the cold night), then there's also an advantage to going bigger. The 
"overhead" for a reactor (shielding, etc.) is highly nonlinear with 
respect to output power. A 100 kW reactor isn't a lot bigger than a 100 
W reactor.


There is, also, serious research into doing stuff like sintering or 
melting the regolith, which, as one can imagine, is a power intensive 
activity.  Civil Engineering on the Moon is an interesting topic, but 
way off topic for this list.



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[time-nuts] Re: constructing a moon base


On 9/29/21 10:24 AM, Bob kb8tq wrote:

Hi


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



Far Side radio observatories, particularly for frequencies blocked or 
distorted by Earth's ionosphere are of great interest for two things:


Cosmology wise - looking at very old deeply red shifted (z=50) Hydrogen 
emissions (1420 MHz) that have been shifted down to 18 MHz - this is 
from before there were stars, much less galaxies. One of the things 
you'd be interested in is how smooth the background radiation is over 
frequency. You're probably familiar with COBE that showed the lumpy 3K 
remnants of the big bang - what astronomers would like to know is that 
if you remove the spatial variability, what does the background look like.


Exoplanets - Earth (and Jupiter, Saturn, etc.) all have aurora, 
resulting from the interaction of solar wind with the strong magnetic 
fields. These AKR (Auroral Kilometric Radiation) are down around 1 MHz 
and are not radiated isotropically (they tend to follow the field 
lines).  The existence of a magnetic field is considered to be "life 
friendly" in that it reduces the charged particle flux on the surface, 
so there is interest in detecting such emissions from nearby "life 
possible" planets, of which dozens have been identified (right distance 
from parent star, right mass, etc.)  - say, within 10 parsecs of Earth.


For both of these applications, you need a large array (maybe 10s of 
km), but not enormous (1000s of km).  You don't need the angular 
resolution of a larger extent.  A fairly conventional "send all the 
signals to a common point and digitize them with a common clock" works 
fine at these frequencies.  A terrestrial equivalent is the OVRO-LWA in 
California, or the MWA in Australia, as well as various starts at the 
Square Kilometer Array (SKA) and the big LOFAR array. All of those are 
higher frequency (above 30 MHz or so) because the "seeing" down low is 
so bad from the ionosphere.



There have been proposals (and actual experiments) with VLBI between 
Orbiter (at the Moon, I think) and Earth, but those were limited in 
scale (essentially demonstrations that it could be done).  It's not 
clear that we *need* (or more properly, that we should spend money on) 
the resolution of higher frequency Space/Earth VLBI (that is, existing 
VLBI on Earth does well enough).  Of course, I guarantee that there are 
at least half a dozen astronomers who will say that 300,000km baselines 
are positively essential, because if they can't do their science, then 
civilization is lost.  (perhaps a bit hyperbolic).


What everyone is eagerly awaiting is the new Astrophysics Decadal Study 
from the National Academies, which describes the "big questions" and 
"what's needed", and gives some sort of ranking of importance to the 
science community.  There is some hope that when this comes out (mid 
October is the rumor) that there will be a recommendation for a "probe 
class" (= ~$1B) mission to build a radio telescope on the far side of 
the Moon.


With that lead in, I give you FARSIDE

https://www.colorado.edu/project/lunar-farside/

The final report (which went to the National Academies): 
https://www.colorado.edu/project/lunar-farside/sites/default/files/attached-files/farside_finalrpt-2019-nov8.pdf


https://www.space.com/farside-moon-radio-astronomy-mission-concept.html 
in the "popular press" - it's also been in a variety of other magazines 
(Popular Science, etc.)




and a nice lecture by Gregg Hallinan, one of the PIs

https://kiss.caltech.edu/lectures/2020_Hallinan.html

https://www.youtube.com/watch?v=Zr0Pq7bFD2Q


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[time-nuts] Re: constructing a moon base

Bob kb8tq writes:

> 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. 

It's funny how peoples thinking about this is still firmly cast in
a 1950'ies NASA/science-fiction mindset.

People really do not grasp how much work robots can do.

One place I really see this is when people look at my lawnmower robot
and go "There's no /way/ that can handle 5000 m² of lawn..."

But the thing is: If a human did it on a garden-tractor once a week,
we'd want it done quickly, so lots of power, wide cutting board and
so on.

But the robot has 168 times as much time[1] for the same job, so
it does not even need one percent of the power of the garden-tractor,
in particular because it does not have to lug 100 kg of human &
associated creature-comforts around.

If we need a road on the moon, we will launch robots and let them
get on with the job, and they'll be done way ahead of when we arrive,
probably not even leaving us a few really largish boulders to blow up.

In other words: The grader on the moon will at most be a meter wide.

Poul-Henning

[1] The quoted capacity for lawn-mower robots is for 24hx7d, but
in general you should not let it work while dark, for the sake
of the other inhabitants in your lawn:  Porcupines etc.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
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[time-nuts] Re: constructing a moon base

Hi

> On Sep 29, 2021, at 12:53 PM, Lux, Jim  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  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

[time-nuts] Re: constructing a moon base

On 9/29/21 9:10 AM, Bob kb8tq wrote:

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 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

[time-nuts] Re: constructing a moon base

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 ….

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. 

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. 

Bob

> On Sep 29, 2021, at 11:40 AM, Lux, Jim  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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[time-nuts] Re: constructing a moon base


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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[time-nuts] Re: constructing a moon base

2021-09-29 Thread Jeremy Nichols

What will be the effect of the lunar ‘mascons’ on orbital time and position
satellites? As I recall from Apollo, the effects were significant in
hitting the targeted landing place—but the orbits were much lower, which
increases the effect of each mascon.



On Wed, Sep 29, 2021 at 7:54 AM Bob kb8tq  wrote:

> Hi
>
> My *guess* (and it’s only a guess) is that before you get to the “road
> building”
> phase, there will already be at least a basic set of satellites providing
> coverage
> for the moon. However much they cost today, they will be way cheaper then.
> They also would be useful for a wide range of activities.
>
> Does that mean full GNSS on the moon? Who knows ….. It does mean that part
> of the com / time transfer stuff could be offloaded.
>
> Bob
>
>
> > On Sep 29, 2021, at 10:30 AM, Chris Howard  wrote:
> >
> > My employment involves the design and manufacturing of construction
> equipment.
> >
> > I had a conversation today about what will be needed for
> time/positioning when GPS is not in sight, like road-building on the far
> side of the moon.
> > The context was timestamp coordination between multiple data sources in
> the vehicle environment, ntpd, and similar things.
> >
> > No GPS probably means cesium on the road grader?
>
> --
Jeremy Nichols
Sent from my iPad 6.
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[time-nuts] Re: constructing a moon base


On 9/29/21 7:30 AM, Chris Howard wrote:
My employment involves the design and manufacturing of construction 
equipment.


I had a conversation today about what will be needed for 
time/positioning when GPS is not in sight, like road-building on the 
far side of the moon.
The context was timestamp coordination between multiple data sources 
in the vehicle environment, ntpd, and similar things.


No GPS probably means cesium on the road grader? 



You might want to talk to Professors Scott Palo and Penny Axelrad at 
Univ Colorado Boulder - they're doing a project with JPL to do Lunar PNT 
using CSACs and LimeMicro SDRs


https://www.colorado.edu/aerospace/scott-palo

https://www.colorado.edu/aerospace/penina-axelrad


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[time-nuts] Re: constructing a moon base

2021-09-29 Thread Joseph B. Fitzgerald

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.

-Joe Fitzgerald

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[time-nuts] Re: constructing a moon base

Hi

My *guess* (and it’s only a guess) is that before you get to the “road 
building” 
phase, there will already be at least a basic set of satellites providing 
coverage
for the moon. However much they cost today, they will be way cheaper then.
They also would be useful for a wide range of activities. 

Does that mean full GNSS on the moon? Who knows ….. It does mean that part
of the com / time transfer stuff could be offloaded. 

Bob

> On Sep 29, 2021, at 10:30 AM, Chris Howard  wrote:
> 
> My employment involves the design and manufacturing of construction equipment.
> 
> I had a conversation today about what will be needed for time/positioning 
> when GPS is not in sight, like road-building on the far side of the moon.
> The context was timestamp coordination between multiple data sources in the 
> vehicle environment, ntpd, and similar things.
> 
> No GPS probably means cesium on the road grader?
> 
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[time-nuts] Re: constructing a moon base

2021-09-29 Thread Marek Doršic

Communication and navigation satellites around the Moon are already under 
consideration by ESA...

https://insidegnss.com/galileo-update-esas-paul-verhoef-outlines-top-priorities/
 


   .md

> On 29 Sep 2021, at 16:37, Andy Talbot  wrote:
> 
> When things get that big they could put a series of location satellites
> around the Moon, so it has its own ... err... not GPS, but MPS perhaps?
> 
> Andy
> www.g4jnt.com
> 
> 
> 
> On Wed, 29 Sept 2021 at 15:31, Chris Howard  wrote:
> 
>> My employment involves the design and manufacturing of construction
>> equipment.
>> 
>> I had a conversation today about what will be needed for
>> time/positioning when GPS is not in sight, like road-building on the far
>> side of the moon.
>> The context was timestamp coordination between multiple data sources in
>> the vehicle environment, ntpd, and similar things.
>> 
>> No GPS probably means cesium on the road grader?
>> 
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>> 
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[time-nuts] Re: constructing a moon base


On 9/29/21 7:30 AM, Chris Howard wrote:
My employment involves the design and manufacturing of construction 
equipment.


I had a conversation today about what will be needed for 
time/positioning when GPS is not in sight, like road-building on the 
far side of the moon.
The context was timestamp coordination between multiple data sources 
in the vehicle environment, ntpd, and similar things.


No GPS probably means cesium on the road grader? 



There's been a lot of research on PNT (Position, Nav, Timing) for lunar 
applications over the last 20 or so years. Google "Lunar PNT" as a start.


Typically, the proposed approaches use fixed monuments (pseudolites) 
which are disciplined by reference to some orbiting source, and then 
your moving things use fairly conventional GPS-like strategies.  There 
are the same discussions about two way vs one way, smart receivers vs 
smart transmitters, etc. that were all hashed out in the early days of GPS.


A complication on the Moon is that the visible horizon is pretty close 
(~2km for something a couple meters high), so the fixed stations need to 
be relatively close together. In a "road building" scenario, you can 
push the survey net forward as you build the roads, just as with 
conventional surveying.  I will note that we built the transcontinental 
railroad in the US, as well as most roads, with conventional surveying, 
and it works just the same on the Moon.   So "relative position" is 
something you don't need clocks for (in general).  It's when it comes to 
timing that satellites are handy for time transfer.


If you're on the near-side of the Moon, then you can receive Earth GNSS 
signals with a suitably large antenna. Or, if you're creating a system 
from scratch, you can set up a ground based transmitter to allow fairly 
small antennas (10s of cm) at the Moon - after all, a fairly small 
antenna (3m) on Earth will illuminate the Moon and surroundings within 
its beamwidth (1/2 -1 degree, depending on frequency), so you don't need 
much Tx power (and Tx power on Earth is a LOT cheaper than in space or 
the Moon).  I seem to recall 50-100 Watts is more than enough, with a 3m 
dish, at X-band (7 GHz) to get nanosecond timing at the Moon with an 
Omni receive antenna.


The challenge with "position" at the Moon using GNSS is that the 
geometry is terrible.  The Moon is 300,000 km away, so the GNSS 
constellation is < 10 degrees across. Talk about Geometric Dilution of 
Precision (GDOP).  That's why most schemes have some orbiter(s) to get 
the geometry better, and then periodically update the clocks on the 
orbiters with reference to an Earth source.  So that puts a constraint 
on the Allan Deviation of the orbiting clock, because it has to ride 
through the hour or so when it's out of view.


Anyway, lots of interesting stuff.  I've been involved with this at work 
for at least 10 years, so feel free to ask questions.


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[time-nuts] Re: constructing a moon base