Interplanetary timekeeping

I bring this up every few years just to see if things have changed...

The task of managing the Spirit/Opportunity sciens adn engineering teams
included making work schedule changes to accommodate the differences in
duration of terrestrial and Martian days. Early in the project, this was
quite a challenge, as documented in a Nova special a few years ago.

Has this contributed anything useful to the prospect of establishing
standards for interplantary timekeeping? If humans ever move to other
worlds, especially the asteroids, this could become a significant issue,
both in practical issues like workforce management and novel matters like
the compounding of commercial interest on loans.

There are some terrestrial precedents related to international recognition
of contract expiration dates and the like, but the very dynamic differences
between local timekeeping among the Earth, Mars and the asteroids might lead
to some considerable confusion and perhaps even threats to health and
safety.

It might or might not be too early to put serious thought into this -- I
have no idea how long it might take to set the relevant standards.


Jim McCauley

Jim McCauley jematfriidotnet wrote:
There are some terrestrial precedents related to international recognition
of contract expiration dates and the like, but the very dynamic differences
between local timekeeping among the Earth, Mars and the asteroids might lead
to some considerable confusion and perhaps even threats to health and
safety.

I expect contracts would simply expand from the usual:

"This contract is governed by the laws of the state of abc"

to add:

... "based on Universal Coordinated Time on the planet Earth".

international contracts that cover many timezones have already had to deal
with this issue.

It might or might not be too early to put serious thought into this -- I
have no idea how long it might take to set the relevant standards.

How long has UTC been in place?

Glen Overby

Glen Overby wrote:
Jim McCauley jematfriidotnet wrote:
There are some terrestrial precedents related to international recognition
of contract expiration dates and the like, but the very dynamic differences
between local timekeeping among the Earth, Mars and the asteroids might lead
to some considerable confusion and perhaps even threats to health and
safety.

I expect contracts would simply expand from the usual:

"This contract is governed by the laws of the state of abc"

to add:

... "based on Universal Coordinated Time on the planet Earth".

international contracts that cover many timezones have already had to deal
with this issue.

It might or might not be too early to put serious thought into this -- I
have no idea how long it might take to set the relevant standards.

How long has UTC been in place?


Do we get to take it's predecessor(s) like Greenwhich standard into
account? Yes, this is a trick question.

Glen Overby

In article ,
Jim McCauley jematfriidotnet wrote:
Has this contributed anything useful to the prospect of establishing
standards for interplantary timekeeping? If humans ever move to other
worlds, especially the asteroids, this could become a significant issue,
both in practical issues like workforce management and novel matters like
the compounding of commercial interest on loans.

Mars is actually a rather special case, and probably *isn't* an indication
of difficulties elsewhere later. It's quite unusual in having a day
that's close enough to Earth's that humans can reasonably use it, and a
day/night cycle that's important enough that you can't just ignore it.

Most other solar-system bodies have days that are either too short or too
long to tempt people to match their schedules. People living there will
keep Earth time, and just treat the local light/dark cycle as a separate
issue.

Only when the cycle is quite close to Earth's do problems arise, because
then there are substantial periods -- weeks long, in the case of Mars --
when you lose a lot of local daylight to sleep time. Then, you probably
*do* want to have people match the local cycle... although whether that
means their clocks are on local time is actually a separate question.

In any case, almost certainly, Earth time would remain the standard for
technical work, legal purposes, etc.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

... "based on Universal Coordinated Time on the planet Earth".
international contracts that cover many timezones have already had to deal
with this issue.

Coming up with something unambiguous isn't really the interesting
part.

Where it could get fun is what are the various time periods you pick.
Law and custom is full of "you have 30 days to return it", "this is a
10 week class", "this report is due every Monday", etc, etc. Will
some of those migrate to "3 million seconds" (or 3 megaseconds)? Will
the Martians just use earth days for everything (I'm guessing not,
since you'd need to consult your watch to figure out whether it is the
same day as when you went to bed or not)? Will Martians talk sols to
each other, but days when conducting business with Earthlings?

Henry Spencer wrote:

In article ,
Jim McCauley jematfriidotnet wrote:

Has this contributed anything useful to the prospect of establishing
standards for interplantary timekeeping? If humans ever move to other
worlds, especially the asteroids, this could become a significant issue,
both in practical issues like workforce management and novel matters like
the compounding of commercial interest on loans.

Mars is actually a rather special case, and probably *isn't* an indication
of difficulties elsewhere later. It's quite unusual in having a day
that's close enough to Earth's that humans can reasonably use it, and a
day/night cycle that's important enough that you can't just ignore it.

Most other solar-system bodies have days that are either too short or too
long to tempt people to match their schedules. People living there will
keep Earth time, and just treat the local light/dark cycle as a separate
issue.

Only when the cycle is quite close to Earth's do problems arise, because
then there are substantial periods -- weeks long, in the case of Mars --
when you lose a lot of local daylight to sleep time. Then, you probably
*do* want to have people match the local cycle... although whether that
means their clocks are on local time is actually a separate question.

In any case, almost certainly, Earth time would remain the standard for
technical work, legal purposes, etc.

My guess is that Martians will probably do with time something similar
to what Yankees are doing with every other unit. They use inches but
they use as the definition of an inch 2.54 cm. Martian will probably
have martian time with a definition based on Earth time and have a key
on their pocket calculator to convert to UTC.


Alain Fournier

JRS: In article , dated Wed, 3 May
2006 16:47:59 remote, seen in news:sci.space.policy, Glen Overby
posted :

I expect contracts would simply expand from the usual:

"This contract is governed by the laws of the state of abc"

to add:

... "based on Universal Coordinated Time on the planet Earth".

international contracts that cover many timezones have already had to deal
with this issue.

It should specify whether that UTC is based on received time signals
from Earth (i.e. delayed by speed-of-light lag) or on exchange of
signals with Earth and averaging (which seems right for a Newtonian
universe).



Contracts involving time generally have one or more places of
fulfilment; for example to accept a load at Kourou by a given Kourou
time and deliver it to an agent at Phobos Port by a given Phobos time.

A "civilised" place will have its own local time in general use; that
time may or may not be UTC, however propagated. An "uncivilised" place
will have no local time of its own, and either will use the time of an
adjacent "civilised" place or will use UTC.

Contracts should normally use the local time of each place of fulfilment
for that fulfilment, because it is more appropriate for the
comparatively small number of hauliers or distributed contractors to
keep track of varieties of time than for the individual localised
customer to do so.

The local time of a location on a large body may vary with location; in
that case the contract needs to specify either a "truly local" time
(e.g. UTC+1/UTC+2 for Paris) or a "body overall" time used on the body
(e.g. GMT/UTC for Earth, but possibly OMMT (Olympia Mons Mean Time) for
Mars.


One might look at the position with respect to "ten-day" cruises across
the Western Pacific - does it mean ten cycles of sunlight, or that the
finishing date is ten more than the starting date? If the Date Line is
crossed an odd number of times, there is a difference.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - w. FAQish topics, links, acronyms
PAS EXE etc : URL:http://www.merlyn.demon.co.uk/programs/ - see 00index.htm
Dates - miscdate.htm moredate.htm js-dates.htm pas-time.htm critdate.htm etc.

Jim McCauley wrote:


I bring this up every few years just to see if things have changed...

The task of managing the Spirit/Opportunity sciens adn engineering
teams
included making work schedule changes to accommodate the differences in

duration of terrestrial and Martian days. Early in the project, this
was
quite a challenge, as documented in a Nova special a few years ago.

Has this contributed anything useful to the prospect of establishing
standards for interplantary timekeeping? If humans ever move to other
worlds, especially the asteroids, this could become a significant
issue, both in practical issues like workforce management and novel matters
like the compounding of commercial interest on loans.

Computer tasks will probably be affected even more so than workforce
management. It seems inevitable that there will be some sort of an
interplanetary Internet (Extranet?), and its time servers (and most other
types of networked servers) are going to have a heck of a task managing
both time differences and different signal delays for packets going
to/from different planet destinations and even from different crafts being
on various distances from Earth.

Cheers,
D.





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Henry Spencer wrote:
In article ,
Jim McCauley jematfriidotnet wrote:
Has this contributed anything useful to the prospect of establishing
standards for interplantary timekeeping?

In any case, almost certainly, Earth time would remain the standard for
technical work, legal purposes, etc.

For (very) detailed technical work, Earth time is not a good choice.
The main problem is that the Earth's orbit is elliptical, meaning the
Earth moves in and out of the Sun's gravity well, and moves at
differing speeds, affecting the rate of clocks. For Earth or
near-Earth applications this has no relevence, since all clocks speed
up and slow down together. But compared to clocks far away from the
Sun, the Earth clocks run slow for part of the year, then run fast for
the rest of the year.

Also, clocks in different places run at different average rates, due to
both the local gravity and the position in the Sun's gravity well. For
example, a (hypothetical) clock at the solar system barycenter loses
15.5 ns/day compared to a clock on the Earth's surface. This is
noticable for Paris vs Boulder, important for GPS, and will be a big
deal when we have time standards on other planets.

So scientists concerned with accurate timing on places other than Earth
have already defined two timescales that take these effects into
account. The first, Barycentric Dynamical Time, runs at the average
Earth rate, but corrects for orbital effects. The second, Barycentric
Coordinate Time, is time as it would be measured by a clock at the
solar system barycenter (and hence runs at a different rate, as well).
Both of these timescales are computed from the actual, physical clocks
we measure here on Earth. (Once we have good atomic clocks on other
planets, we will be able to measure these corrections rather than
compute them, but scientists would be *VERY* suprised if the
corrections differ from the theory for the small velocities and low
gravity fields of the solar system.)

So for technical work, one of the existing barycentric time scales
probably makes the most sense. For legal work, the many existing time
scales can all be translated to each other, so it's probably only
important to be specific about which one is used.

However, another place contracts will need to be more specific is when
they say A must happen before B. If the time between A and B is less
than the light travel time, the order is ambiguous (different observers
may see them in different order). This is pretty negligable and
routinely ignored on Earth, but could be very noticable between
planets. One solution might be to specify that A must happen before B,
as observed by some specified observer.

Lou Scheffer

"Henry Spencer" wrote in message
...
In article ,
Most other solar-system bodies have days that are either too short or too
long to tempt people to match their schedules. People living there will
keep Earth time, and just treat the local light/dark cycle as a separate
issue.

Assuming that we ever settle an asteroids, timekeeping on them might prove
to be truly weird, especially if the development model goes like this:

For radiation protection, build a shell (probably spherical) of reinforced
(with graphene, perhaps) ice around the asteroid. (This only works for
asteroids with local, mineable ice and a simple axis of rotation. Old comet
cores, maybe.) Fill the interior of the shell with breathable gases. The
deployment of the shell will cause a reduction in the rotation rate of the
asteroid, of course.

As the colony population grows and more ice is mined, build another, larger
shell around the original. Seal the new shell and gradually dismantle the
old shell, recycling the ice for deployment in the next larger shell. Keep
doing this until it is no longer economically feasible to continue --
assuming that it is even feasible to start!

Anyway, as each new shell is deployed, the length of your day changes. How
quickly it changes depends on the construction schedule This might require
some flexibility on the part of the inhabitants :-)


Jim McCauley