Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The Last POWER1 CPU on Mars Is Dead

talospace.com

Post reply on HN
Print view View original

31–40 of 145 posts

Re: The Last POWER1 CPU on Mars Is Dead

#31

Post by relativitypro »

JumpCrisscross wrote: post #9
yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

> 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 e…

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

Re: The Last POWER1 CPU on Mars Is Dead

#32

Post by teraflop »

wlesieutre wrote: post #18
dahfizz wrote: post #8

Earlier quoted context omitted.

I don't really see the problem with standardizing on 'seconds since the epoch' for any interplanetary communication and having clients convert to something more meaningful to humans. Any other "universal" time format will be just as meaningless when days and seasons are all different lengths.

At a certain point of accuracy you run into issues with this - seconds don't pass at the same rate due to relativistic effects (both speed and gravitational). An example we already deal with is GPS satellites orbiting Earth. Their clocks tick a little bit slower on account of how fast they're orbiting, and tick a bit faster on account of being further up Earth's gravity well. The gravitational effect is stronger, and…

I don't think the relativistic effects would be a problem in practice. You can synchronize clocks on other planets to the UTC or TAI reference time, which are already specified in terms of the Earth's reference frame.

Because of relativity, clocks on other planets would very slowly drift relative to UTC on Earth. But the drift is on the order of a few parts per billion (see e.g. [1]) which is comparable to what you'd expect anyway, even from a very high-quality temperature-controlled crystal oscillator. So it doesn't add any new clock synchronization difficulties that you wouldn't have anyway.

For the most demanding applications -- the ones that require atomic clocks -- you would still need to take relativity into account. You can either measure time passing at the local rate (in cases where you need to know locally elapsed time to high precision) or you can measure UTC, which allows you to assign a consistent ordering to events on different planets. But for most ordinary purposes, the distinction is irrelevant.

[1]: https://space.stackexchange.com/questions/33590/time-dilatio...

Re: The Last POWER1 CPU on Mars Is Dead

#33

Post by yingw787 »

JumpCrisscross wrote: post #9
yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

> 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 e…

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??").

Re: The Last POWER1 CPU on Mars Is Dead

#34

Post by echlebek »

twodave wrote: post #24
yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

Well the problem is a "second" is just a unit of rotation of the Earth on its axis. So you'd either need to use some other reference material than a rotating body in space or else use some arbitrary one (like Earth, since that's where we are from!) and choose a reference date (why not use one we're all familiar with? I know! We could use the UNIX epoch!). Even if you did this, your universal time would just be a sync…

That's actually not true if you're using SI units for seconds.

"The SI unit of time is the second (s): The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom."

I'm not a physicist, but I think that's a universal definition - the rate of the periods should be constant everywhere in the universe.

So universal seconds are actually very easy to nail down. Dates are always a little more troublesome. Perhaps seconds since the start of the big bang would be a possibility.

Re: The Last POWER1 CPU on Mars Is Dead

#35

Post by JohnJamesRambo »

Aardwolf wrote: post #4
saagarjha wrote: post #3

There are still Power chips (based on PowerPC 750) on Curiosity; it's just POWER1 that's dead: > That's not the end of Power ISA chips on Mars, though: Curiosity, which is running a pair of RAD750s (one main and one backup, plus two SPARC accessory CPUs), is still in operation at 2,319 Mars solar days and ticking.

> it's just POWER1 that's dead Is it certain that the chip is not still getting some power and running something?

Do POWER1 cpus dream of martian electronic sheep?

Re: The Last POWER1 CPU on Mars Is Dead

#36

Post by jerf »

kharms wrote: post #10
yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

How would such a standard handle time dilation?

Most likely by declaring a standard reference frame and encoding standards for indicating amount of drift from it, tolerance of drift, and standards for how to update against it. A particularly forward-looking standard would encode information about the standard frame used within it, so we could switch from Sol-standard to galactic standard to cluster standard.

Universal time is, of course, impossible in a relativistic universe, but (no sarcasm) that doesn't prevent us from trying, and getting to "close enough to work with for reasonable amounts of effort". Just as only a small portion of the world works on UTC directly right now, this time standard would be something computers would translate for people. Traveling at 80% the speed of light away from Earth in Earth's frame means you wouldn't want to directly use the resulting definition of a Standard Second for human time, but computers would be able to work with it.

Re: The Last POWER1 CPU on Mars Is Dead

#37

Post by merubin75 »

d33 wrote: post #2

So, in other words, the machine's still alive, but has no backup CPU?

"Opportunity likely experienced a low-power fault, a mission clock fault and an up-loss timer fault. The team is continuing to listen for the rover over a broad range of times, frequencies and polarizations using the Deep Space Network (DSN) Radio Science Receiver. The team has begun mission clock fault recovery commanding 'in the blind,' in the hopes of catching the rover during an awake period, as their strategy of last resort."

Source: NASA mission update for sols 5340-5346 (Jan. 31-Feb. 6, 2019) https://mars.nasa.gov/mer/mission/rover-status/opportunity/r...

Re: The Last POWER1 CPU on Mars Is Dead

#38

Post by mattkrause »

dooglius wrote: post #15
yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

There is BCT [0] which corrects for gravitational time dilation on Earth relative to the solar system, but I'm not aware of anything on a universal scale. It seems conceptually difficult to do synchronization if the communication round trip time, bounded below by the speed of light, is significant. [0] https://en.wikipedia.org/wiki/Barycentric_Coordinate_Time

I think NTP uses some statistical tricks to get better synchronization than you'd expect over slow, laggy internet links. Possibly something like that could work.

Re: The Last POWER1 CPU on Mars Is Dead

#39

Post by swebs »

wlesieutre wrote: post #18
dahfizz wrote: post #8

Earlier quoted context omitted.

I don't really see the problem with standardizing on 'seconds since the epoch' for any interplanetary communication and having clients convert to something more meaningful to humans. Any other "universal" time format will be just as meaningless when days and seasons are all different lengths.

At a certain point of accuracy you run into issues with this - seconds don't pass at the same rate due to relativistic effects (both speed and gravitational). An example we already deal with is GPS satellites orbiting Earth. Their clocks tick a little bit slower on account of how fast they're orbiting, and tick a bit faster on account of being further up Earth's gravity well. The gravitational effect is stronger, and…

>"Seconds according to who?"

According to a very accurate pulsar, of course.

https://en.wikipedia.org/wiki/Pulsar#Precise_clocks

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

Re: The Last POWER1 CPU on Mars Is Dead

#40

Post by DannyB2 »

yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

According to relativity, you cannot get two different observers to agree on any kind of universal time, or even the order in which two events occurred.

Observer A says that event X happened before Y.

Observer B says that event Y happened before X.

And they're both right from their POV.

Post reply on HN