[JumpCrisscross]

> Do we humans have plans in the pipeline for a universal time standard we can use wherever we are?

This fundamentally cannot exist. Any "universal" system would drift for observers on different planets. Having different times in New York and New Delhi isn't the worst right now; doing a calendar look-up for the time on Mars isn't as neat. But given we won't have real-time communication, it isn't as big of a problem either.

[gonehome]

Somewhat comically J.C.R Licklider's first proposal for what became the internet was titled the Intergalactic Computer Network. He later said he did this because when the project is inevitably downsized it would at least cover the earth.

Interplanetary internet designs and peering are interesting problems to think about though.

https://en.wikipedia.org/wiki/Intergalactic_Computer_Network

[oso2k]

There are real, standardized protocols [0] for this sort of thing, now. Early in my career, when I worked at JPL/NASA, I did a bit of work to test these protocols on Linux in a simulated Network of spacecraft. Fun stuff!

[0] https://en.wikipedia.org/wiki/CCSDS_File_Delivery_Protocol

[jakeinspace]

What a coincidence, I'm working on the core flight system project right now, which includes an implementation of CCSDS File Delivery Protocol. You might be happy to know that project is still very much alive within NASA (you were probably already aware).

[oso2k]

Haha. Great to hear that work still lives! I hope you’re not using the (horrible in retrospect) stuff I wrote 15 years ago that worked on 2.0-2.6 kernels. I remember porting the network kernel driver from 2.0-2.2 manual build system to implementing a (really basic) Makefile that worked with 2.0-2.6.0ish kernels (which were newer at the time). I knew Scott Burleigh was still innovating CCSDS and other protocols at JPL, and, IIRC the work I had done had also been delivered to Ames and ESA for test lab use. I had some other work to create protocol dissectors for Ethereal (before the name change to WireShark). WireShark now includes built in dissectors for CCSDS, CFDP and others.

[justinclift]

Fairly off topic ;), but any idea if SQLite is used on any of the rovers, spacecraft, etc?

Mostly from idle curiosity. Was wondering a few days ago and guessing "probably yes", but no idea who to ask.

So, taking the opportunity (heh) now. :)

[oso2k]

The small parts of the Mars Rovers (MER) I worked on or worked with didn’t use SQLite. It was too early in SQLite’s history for it to be used on MER. MER also used VxWorks which probably didn’t have a lot in the way of POSIX support at the time. I remember other devs telling me the fun they had supporting 1553 bus on “such a new RTOS”.

Wikipedia say MSL used VxWorks as well.

I’d have to ask a buddy still doing Mission Ops Support at JPL but I’d think the answer is no SQLite on MER or MSL missions. The OSes were fairly custom, non-POSIX builds. The ESA folks might have tried though on their missions.

[justinclift]

No worries. Been meaning to investigate VxWorks at some point, mostly from an interest in embedded devices (for specific wearables concepts). This will be another thing to add for that list. :)

[planteen]

Not a Mars spacecraft, but SQLite has definitely been used on some CubeSat missions in LEO. I know because I'm the one who did it. :-)

[oso2k]

Was it a commercial or government CubeSat?

[justinclift]

Cool. :)

[jakeinspace]

I don't know about rovers, but some smaller spacecraft (mainly satellites) use mysql, as well as postgres. Disclaimer: I'm not the right person to ask.

[gcb0]

What does it use for time? The spec mentions time in a lot of places, but never defines it. There is even a field to communicate light-time but no mention of how to synchronize anything. I guess this runs on top of another protocol that solves it? Any idea what it is?

[oso2k]

So, it’s been a while since I’ve dived in [0], but “time” as a dependency has been, what I would call, “engineered out of the system”. Instead, there’s concepts of (local) timers, Store-And-Forward Overlays, retries, communication opportunities and the overall realization that time is relative and synchronized time can be difficult at a protocol level when link-level distances are always changing (by miles to billions of miles at a time per communication opportunity).

[0] https://public.ccsds.org/Pubs/720x1g3.pdf

[timerol]

A more recent protocol based on similar thinking is IPFS: https://en.wikipedia.org/wiki/InterPlanetary_File_System

[omeid2]

> doing a calendar look-up for the time on Mars isn't as neat

This is actually not that a big deal, in many countries, like Afghanistan and Iran, people observe 3 different calendars for different purposes and they all drift from each other! That is, 1st Jan (Georgian) is not always 24th Jaddi/Dey (Afghan/Iranian - Solar) nor 7th of 7th Jumada i-ula (Lunar/Islamic)..

So people use calendars that look like this for each day: https://en.wikipedia.org/wiki/Rumi_calendar#/media/File:1911...

[saagarjha]

That only works if days are the same length, no?

[omeid2]

Nope, Gregorian Calendar and Solar calendar don't have exactly same days (although it is very small), and thus the different leap years.

Martian days being around 37 min longer, you might need more leap days though.

[hinkley]

Leap days are caused by one revolution not being a whole number of rotations.

The weird thing with Mars would be that if you contact someone at 5pm local today it might not be okay to call them at the same time tomorrow, because they would clock in 37 minutes later.

[omeid2]

> Leap days are caused by one revolution not being a whole number of rotations.

Right, a whole 24 hours ;)

> if you contact someone at 5pm local today it might not be okay to call them at the same time tomorrow, because they would clock in 37 minutes later.

That is assuming that people on mars will have 24hr and 37 min clocks instead of 24hr.

The only thing that will be different on Mars would be that the sunrise will change 37 minutes everyday. Weird indeed.

[hinkley]

Living on Mars in the next 100 years is already going to be hard enough emotionally, biochemically, and thermodynamically, without having a work schedule that changes by 37 minutes every day.

Everything about it, including the great distance, or perhaps especially the great distance says that Earthers will have to make the affordances. I expect anyone on Mars who didn't come through the ranks of the Armed Forces (and half of the ones who did), and any medical, psychological, or political scientist brought in as an advisor, are all going to give a big ol' "Fuck You" to anyone who suggests otherwise.

[yingw787]

I know that system clock drift can be bounded to milliseconds using an atomic clock or GPS receiver, but I didn't know whether we could overcome synchronization difficulties when speed-of-light differences are significant. I thought we could package some coordinate reference system, directional travel metadata (I'm traveling 0.000002c this way), and current system clock time, and synchronize that way.

Fantasy use case: Asteroid mining and traffic control. If you want to boost prepared asteroids to an orbit closer to Mars and you had a space station / spaceships to watch out for, different mining companies might want a clock protocol, a request buffer, and a map instead of synchronously planning, timing, and verifying each and every asteroid orbit change in a central location ("What do you mean you were using Earth time and not correcting for relativity??").

[etaoins]

There is Barycentric Coordinate Time which is the time from a hypothetical clock at rest at the centre of mass of the Solar System. This is easier to calculate across spacecraft than an Earth-centric time would be. However, because it's outside of Earth's gravity well it ticks slightly faster than Earth time.

[tim333]

If it was at rest at the centre of mass of the Solar System wouldn't it be in the sun's gravity well?

Edit - I looked it up - it's "a clock that performs exactly the same movements as the Solar system but is outside the system's gravity well."

[Retric]

While true it’s still trivial to do such calculations and then output in GMT or whatever. In theory such calculations can get really messy, but atomic clocks are still not accurate enough to make a huge range of minor issues important.

For example we are not just in the sun’s and earth’s gravity field but also the other planets as well. So, with enough precision you would need to account for their locations.

[ramses0]

If you ever get the chance go to the Royal Observatory in Greenwich, which has a great explanation of the difficulties (and values) associated with timekeeping:

https://en.wikipedia.org/wiki/Royal_Observatory,_Greenwich#O...

[sagartewari01]

It doesn't appear to be impossible.

Setup a transmitter at earth which emits a signal at uniform intervals containing current time (seconds since kanye west's marriage). An observer can then deduce current time if it knows where it is. I don't think relativistic dilation would effect this method.

With multiple such emitters synchronized with each other, one might even be able to 'triangulate' the current time. (I haven't worked out any details)

[hopfscotch]

You can't synchronize the stations because simultaneity does not exist due to relativity. There will always be reference frames where one station signals before another.

[Terr_]

I'm not sure what you're trying to say here.

We've known since the Viking landers of the 70s that clocks on Mars don't run the same as on Earth, and that's not even accounting for the speed-effects as the Earth keeps "lapping" Mars on their respective race around the sun.

[bunderbunder]

I'm not sure I see what you'd be gaining there, though. You'd be, at great expense, trading one basket of headaches - clocks not staying in sync - for another one: one second measuring a different length of time on each planet.

[sagartewari01]

Yes but then earth's one second would become the standard. This method is supposed to synchronize events between stations. We can always use atomic clocks for local uses.

[artursapek]

Would the Y2K bug then be the possibility of Kanye and Kim getting divorced?

[laumars]

> This fundamentally cannot exist. Any "universal" system would drift for observers on different planets.

I hear this argument a lot for why we cannot have a universal time standard but it's a weird cyclic argument because it suggests the measurement of time has to be constant while acknowledging that time is relative. So why can't we have a measurement that is also relative?

For example it could be n "ticks" where mass and speed is at a predefined value and allow for decimal points to account for people travelling faster (for example). This means people's life expectancy (for example) could not be measured in "ticks" because "ticks" is used for time synchronisation rather than measuring the passage of time and those who are only interested in the passage of time can use local time zones just like we do now with UTC for keeping equipment synchronised but local time zones for scheduling our human lives.

[jrhurst]

Speed relative to what?

[laumars]

Fair point, I overlooked that problem. You might get away with using the centre of the galaxy as a point of reference?

To be honest I'm really not qualified to be making these sorts of comments so I'm going to back away from the keyboard and if there's any merit to the idea at all (which there probably isn't) then someone else who understands this stuff better can chime in.

[relativitypro]

Proper time is an invariant that could be used for this... still corrections apply (as you suggest, for the two observers).

https://en.m.wikipedia.org/wiki/Proper_time

[weberc2]

You can factor the drift into the time expression or you can simply agree to use earth time or Martian time or any other time. No fundamental need to base time units on Mars on Martian astronomy.

[hackbinary]

I thought a second was a SI base unit: (from Wikipedia)

The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency {\displaystyle \Delta \nu _{\text{Cs}}} {\displaystyle \Delta \nu _{\text{Cs}}}, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1.

[mdavidn]

Yes, but that frequency depends on the caesium-133's frame of reference. In a deep gravity well or at "high" speed, caesium-133 emits at a lower frequency relative to caesium-133 in deep space moving at "low" speed.

[jldugger]

This is true, but does not compensate for relativistic time dilation.

[matt4077]

I believe they are referring to the relativistic drift experienced when comparing two observers moving with high relative speed.

[djsumdog]

I forget how this was accounted for in Kim Stanley Robin's famous Mars trilogy (highly recommend; best Sci-Fi book I've ever read). I think Earth and Mars were so far apart with time delays and everything else that Martian days/years took on a meaning of their own.

[CydeWeys]

They won't drift if the observers correct for their corresponding known differences. E.g. we know the orbital speed of the planets, so plug those into general relativity and you would know how fast your local time is moving vs time on another planet, and can thus compensate.