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time and clocks...

Posted by: Ekkehard Augustin - Tue Mar 29, 2005 5:28 pm
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Post time and clocks...   Posted on: Tue Mar 29, 2005 5:28 pm
Mostly single places are considered here - a vehicle, a station in orbit or a station or landing site at a planet. Time and clocks are no problem at all beacuse of this.

But communication between planets really is a problem if there is no synchronization neither recalculation of time.This can be seeen by a look at the Mars Exploration Rovers Site at the homepage of NASA. The date is expressed by Sols because the martian year is nearly twice the earthian year. The martian day is around half an hour longer than the earthian day which is another good reason to distiguish it from the earthian day by using another name for it.

During flight of an unmanned probe from Earth to Mars this is no problem and not required. And the Apollos were that a short time at the moon that it couldn't become any problem.

But what if manned vehciles are flying to Mars again and again? A sudden switch from earthian year and day to martian year and day might cause health problems (disturbation of biological rythm and clock, jet lag-like problems to sleep etc.) not only but handling problems too that can have severe impacts on safety.

Computers have internaly unchanged and unchangeable time and clock but they have to display a clock to their useres and the displayed time has to be changed when they all are landed on Mars.

The urgency of the question will increase if one day in the far future there will be traffic throughout the whole solar system: Earth to Mars, Mars to Earth, Mars to moon, moon to Earth, moon to Mars, Earth to moon, Mars to asteroid belt, asteroid belt to Earth, Earth to Venus (high atmosphere) Venus to Mars, Mars to Titan, Titan to Ganymede, Ganymede to Mars etc. etc. etc..

Such traffic will or would require coordination and control like air traffic on Earth - because of providing timetables and horarios at least. Such a negotiation would be too difficult and problematic if there were no standard time used which allways is identical throughout the solar system and which doesnÄ't force its use at each planet - it would indicate wrong time at most planets.

What could be a reasonable standard time for the whole solar system? Regardless of the fact that I described a situation one centura or several centuries in the future?



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Post    Posted on: Tue Mar 29, 2005 10:45 pm
Earth time should remain the standard. Human biology works well on that time system. If we have to pick some standard, why not Earth?
As to space lag, it will not be a problem because of the long transit times. You will slowly acclimate to Mars time during the many weeks it takes to get there.


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Post    Posted on: Wed Mar 30, 2005 10:14 am
My question for a solar system wide valid standard time was related to problems of coordination and organization mainly - but the biological aspect seems to be very important as I recognize this moment.

The biological processes of earthian life is controlled by constant change from dalight to darkness and revers. All is optimized to periods of 24 hours and 365 days (with the four seans of the year). The bodies of humans and animals as well as plants are obeying to really the earthian periods. If they have to survive at a planet now that has different periods this might cause lacks of ressources that have to be provided during daylight - half an hour difference compared to the earthian day may be sufficient because of cumulation over months (the lacks sum up to 15 hours after one month and more than 6 days after 10 months). This too is valid concerning the year and its seasons.

All this may be assisted by computers - but these then have to be able to operate by different times, clocks or periods in dialogs and displays. To avoid the complexity of multiple recalculations from earthian time to martian time to lunar time to titanian time to callistean time to asteroidal time ... one solar system standard time would be a good measure. This standard time shouldn't be any planet's time but something different that could be related to stars, constellation of planets or processes at the sun perhaps (what could be added to the list?) - something like that.

Somewhere I read of a similar proposal concerning artificial gravity - the proposal was to reduce artficial gravity slightly after departure from Earth while approaching to Mars and to increase artificial gravity slightly after departure from Mars while approaching Earth. Concerning time there should be a signicificantly different concept because time is of a more general meaning and has infrastructural aspects.



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Post    Posted on: Wed Mar 30, 2005 2:14 pm
Most people’s biological clock does not run at exactly 24 hours a day, but it gets reset every day by the Earth’s day/night cycle. A 30 minute difference on Mars would be no problem, people would not even notice the difference. There will be a big problem on the Moon though. I would assume that on Mars people would use local Mars time and everywhere else, including in flight, they would coordinated universal time (UTC). It may be an arbitrary choice, but so is any other standard. Maybe for interstellar travel a more standardized time would be needed, sort of like UTC without the leap seconds, but here locally in our own solar system regular UTC is the best choice, IMO.


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Post    Posted on: Wed Mar 30, 2005 2:42 pm
[quote="campbelp2002"]Most people’s biological clock does not run at exactly 24 hours a day, but it gets reset every day by the Earth’s day/night cycle. quote]

I think I saw a study carried out on people's sleep patterns somewhere that showed without external stimuli their rest and active periods caused the day to be stretched resulting in a gradual slip out of synchronisation. Perhaps humans would be better suited to Martian days (more evidence that we are descended from Martian microbes no doubt :) ).

As for using a universal time throughout the solar system, why not use GMT like we do on earth and reference all local time differences to it. Why complicate things by introducing another way to count time?

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Post    Posted on: Wed Mar 30, 2005 2:51 pm
The question is most interesting first during flights in the sense of changing the place a human or animal is at and second for someone or something negotiated with central control, coordination and guiding throught the whole system - like central control agencies for airflight on Earth. Such a agency for space flights throughout the whole solar systems would be faced to capacity problems if it would have to handle several different going clocks - Mars, moon, several asteroids (perhaps), Titan, Callisto ... - in parallel.

Transportation entrepreneurs doing business at and between several planets will be faced to that situation too.



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EDIT: It's right the biological clocks sets back itself when required. But the stomach for example doesn't. The period of getting hunger will never be set back and is independent from the biological clock to a high degree as far as I know. At Earth this period of getting hunger will be optimized to the earthian day I suppose. If that is right than problems may be caused by the different length of the martian day by cumulation at least. To me it seems that here alot has to be worked out. But please leave THIS thread to the QUESTION OF TIME AND CLOCKS.


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Post    Posted on: Mon Apr 04, 2005 12:51 pm
campbelp2002 wrote:
Earth time should remain the standard. Human biology works well on that time system. If we have to pick some standard, why not Earth?
As to space lag, it will not be a problem because of the long transit times. You will slowly acclimate to Mars time during the many weeks it takes to get there.


The problem with convincing people to go there in the first place is the long transit time. Get it down to a week or less, and you can convince passengers to travel (it won't seem quite as much like a life sentence).

But yes, GMT (or Zulu, if you're in the military) is and likely will remain the standard time -- if it ain't broke, why try to fix it?

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Post    Posted on: Mon Apr 04, 2005 1:16 pm
At least one time standard would have advantages compared to GMT - the rotation period of the sun.

GMT depends on observations of the sun seen from Earth. It's not our real time because the velocity of the apparent movement of the sun isn't constant but it's the base of the average solar time which is the time we are really using.

So at Earth verification is possible always. The real measurement of time is done by caesium atoms - in Germany at least these atoms are used by the Physikalische Bundesanstalt (Federal Physical Agency) in Braunschweig. But still the measurement is translated into GMT and MEST or MET and has a relation to the sun. The sun could be used for checks and adjustments.

That's not possible at other planets and in free space. Additional atomic clocks could be used there but because of other rotation periods the sun cannot be used for adjustments. And the differences in gravity as well as in velocity conditions are causing slight deviations from earthian clocks. Not long ago I saw a documentation in TV shwoing that the very slight deviations have practical impacts on navigation systems in cars.

But the rotation period of sun is observable everywhere throught the whole solar systems by telescopes. Flares and spots can be used for this purpose. And this rotation is more constant than the velocity of the movement of sun observed at Earth.

Most of the normal average people may demend the sun to measure time - regardless of where they are and wether they may have to use a telescope. The image of the sun with her flares and spots may be projected to a screen if demanded. Often time really is estimated by looking to the sun - when you stripped of your clock from your arm for example.

This way system-wide the time would measured by the identical indicator.



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Post    Posted on: Mon Apr 04, 2005 2:43 pm
Ekkehard Augustin wrote:
Additional atomic clocks could be used there but because of other rotation periods the sun cannot be used for adjustments.
Coordinated Universal Time is already an atomic clock time. It has leap seconds added every so often to reflect the Earth's slowing rotation rate. That is why I suggested,
campbelp2002 wrote:
Maybe for interstellar travel a more standardized time would be needed, sort of like UTC without the leap seconds

However for use in the Solar system where interplanetary radio communication is easy, I don't see why all planets can't synchronize with Earth every so often the same way the different atomic clocks around the world do now. That would be far simpler than inventing a new time standard and then having to remember that the new interplanetary time is X number of seconds different than UTC because there have been X leap seconds since interplanetary time was established. That kind of unnecessary complexity would only serve to make navigation errors more likely.


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Post    Posted on: Mon Apr 04, 2005 3:05 pm
The idea behind using the rotation period of the sun simply is observability. Atomic clocks only can be observed by special agencies like the german Physikalsiche Bundesanstalt in Braunschweig whereas the sun can be observed by everyone if a telescope is provided. this is not that difficult.

And an atomic clock can be damaged easyly and randomly.

The adjustment for Earth's slowing rotation rate by leap seconds doesn't meet the requirements of adjustments to several significant different rotation periods of other planets. Concerning interplanetary travels, trips and traffics the usual situation will be that the pilot or crew of a vehicle or a controlling authority supervising the whole solar system between Sun and Pluto will have to handle several time systems in parallel. This will be so because the needs of average people must be met who are travelling interplanetary and causing or doing interplanetary traffic. ...



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Post    Posted on: Mon Apr 04, 2005 3:18 pm
Ekkehard Augustin wrote:
Atomic clocks only can be observed by special agencies like the german Physikalsiche Bundesanstalt in Braunschweig whereas the sun can be observed by everyone if a telescope is provided. this is not that difficult.
No longer! Atomic clocks are small portable devices that are routinely taken on commercial airliners as carry on luggage. A transit telescope capable of accurate enough measurements is a many ton permanently mounted device. And even this telescope is far less accurate than the atomic clock.
(EDIT) OK some atomic clocks are large, but not all.
http://www.units.muohio.edu/dragonfly/t ... rate.htmlx
(ANOTHER EDIT) Each GPS satellite has SEVERAL atomic clocks on board!
http://tycho.usno.navy.mil/gpstt.html


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Post    Posted on: Tue Apr 05, 2005 7:24 am
I haven't been talking about the size or weight of atomic clocks - I have been talking about observing them, watch them. It's easy to look at them and to read the time - but that's not the point here because they can be showing th wrong time if a part or an element of them is working wrong. Regardless of what it is.

Atomic clocks are expensive - too expensive to have one of my own privately. telescopes are cheap compared to them and it is not required to have a telescope of my own. The could be public telescopes sending images to the households and so on - to send images of collapses of Caesium atoms is very very more difficult. By the telescopes everyone could see the rotation of sun indicated by the movement of spots and flares whereas at least nearly noone can see the collapses of Caesium atoms.

In between I have worked out a (more) systematical description of what I am talking about since my last post yesterday. I will provide it by an additional post later in this thread.



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Post    Posted on: Tue Apr 05, 2005 12:48 pm
Ekkehard Augustin wrote:
Atomic clocks are expensive - too expensive to have one of my own privately.


Not much more expensive than a high-powered, ultra-accurate Keck-style telescope.

Ekkehard Augustin wrote:
telescopes are cheap compared to them and it is not required to have a telescope of my own. The could be public telescopes sending images to the households and so on - to send images of collapses of Caesium atoms is very very more difficult.


And how do you think these work? And they aren't that expensive, either.

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Post    Posted on: Tue Apr 05, 2005 1:44 pm
I dont understand why there needs to be a standard time everywhere, we manage fine on Earth with lots of different local times. Do what people do now, adjust your watch when you get of the spacecraft to what ever is local time. Even if day lengths are different from planet to planet watches could be made to compensate for this.

Commercial airlines run international flights across many time zones OK without having a different way of measuring time, why would this be a problem for spaceflight?

Any system is likely to evolve over time so its likely to be relative to GMT as that is the most commonly used.

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Post    Posted on: Tue Apr 05, 2005 2:34 pm
Today there are highly accurate clocks that are easy to read and use. You may call them time standards instead of atomic clocks, but they are all far easier to read and more accurate than any astronomical observation (especially sunspots which grow and vanish and rotate at variable speeds in the fluid surface of the sun). Reading these clocks does not require looking at “collapses of Caesium atoms”, the clock’s electronics does that for you. You look at an electronic display and just read the numbers. These clocks are calibrated not against astronomical observations but against giant laboratory atomic clocks using radio signals. The same signals can be sent to Mars or space craft in flight just like they are now sent to users around the world and GPS satellites in orbit. If you are worried about “an element of them is working wrong”, then do what GPS satellites do now, have several clocks and check them against each other and against radio time signals from Earth.


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