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Anyone has insights on how data in such volumes can be transferred from Mars to Earth in the absence of a direct link? Do the intermediate nodes have gigabytes of available storage to emit data to the next available node once it becomes visible ?

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Reddit had AMA with engineers from this mission, IIRC last week. They provided good info on different aspects including how they were able to get video over low bandwith connection, including various mission site link for more info. You might want to check out AMA for your question.

Edit: added following links

This Q&A about storage https://www.reddit.com/r/IAmA/comments/lpzbzo/were_scientist...

These Q&A about data rate https://www.reddit.com/r/IAmA/comments/lpzbzo/were_scientist...

https://www.reddit.com/r/IAmA/comments/lpzbzo/were_scientist...

This Q&A about RTG (operational life) https://www.reddit.com/r/IAmA/comments/lpzbzo/were_scientist...

Do you have a link to this AMA?

https://www.reddit.com/r/IAmA/comments/lpzbzo/were_scientist...

https://old.reddit.com/r/IAmA/comments/lpzbzo/were_scientist...

Others have posted links to the Reddit thread overall, but I think this is the specific question being referred to:

https://old.reddit.com/r/IAmA/comments/lpzbzo/were_scientist...

EDIT: Apparently the rover has an antenna that can directly communicate with Earth at 10 bits per second! That's obviously not useful for pictures or anything, but it's an amazing capability for emergency comms.

Very low bandwidth, very low power, very long distance comms are really cool. The limiting factor tends to be the clock frequency precision - if you have precise enough clocks at both ends, there isn't anywhere in the universe you couldn't communicate with, as long as you're happy to go slow enough.

Given self-clocking signalling[1] exists, why is clock frequency precision the limiting factor?

I would imagine signal-to-noise would be the limiting factor, ie how strong is your transmitter and how sensitive is your receiver.

[1]: https://en.wikipedia.org/wiki/Self-clocking_signal

It is possible to send a signal weaker than the noise floor. The maximum information you can send is defined by shannon's channel capacity formula, which clearly says a signal can be weaker than the noise.

If you use a self-clocking signal, then effectively the information you are sending consists of both the clock timings and the information you're really trying to send. If your channel capacity is very low, you will find there is no channel capacity for even the clocking information, let alone the information you really want to send.

Noise, by definition, doesn't have a qualifying characteristic. It just means "all signals we're not interested in". That means your ability to filter out noise is strongly dependent on having pre-existing knowledge about the shape of the signal you're interested in.

Self-clocking signals are useful when the ambient noise level is low with respect to the signal, but if your signal is just "these two droplets in an ocean" you will not be able to filter out enough of the signal to detect the edges of the original signal.

Having a very reliable clock frequency means you can apply a very exact filter to lock on to the signal you want, thereby making the transmission less sensitive to interference from other radio signals. Just having a sensitive receiver isn't enough, because a sensitive receiver will also pick up more of the other radio signals.

Wrong clock, gotcha. For some reason I didn't think of the carrier signal generator when I read the word "clock".

It all makes sense now, thanks!

> there isn't anywhere in the universe you couldn't communicate with

Right, assuming you are emitting infinite amount of photons, there are no obstructions, black holes and you ignore universe expansion and GR which can make your precise enough clocks go out of sync.

"Precise enough clocks" includes handling GR and other non-destructive effects along the whole light path I assume. :)

That's one big ask :)

> emitting infinite amount of photons

I think that the double slit experiment shows that this isn't an issue... Since we are summing with all other noise in the universe, it doesn't matter exactly which photons came from my transmitter, if any at all, but the total count will still (probabilistically) reflect the the we're after...

On long distances you are talking about receiving single photons. And while we may view it as probabilistic, it will either interact with our equipment or it won't. If it doesn't, communication failed.

But yes, I wondered about that when writing my comment. Certainly photons are more than just "bullets" that are getting more and more sparse. So I got curious and it seems[1] that in context on our detector you can indeed put hard bounds on where the photon may be received. As far as I understand it, based mostly on the abstract, I do not really grasp it.

But ignoring the paper, I think I get your point. If photon has any chance of reaching the target (even lower than virtual particle spawning) and even if you don't know the future of the Universe (other photons hitting detector), you can use some complex encoding so that observing certain (allegedly otherwise unlikely) patterns allows you to say you received some message with some probability (which is what communication always is). If you have synced clocks. Simultaneity is relative though so there's also that.

1. https://arxiv.org/pdf/0903.3712.pdf

PS. I seem snarky today, sorry about that, I'm happy to learn if I'm misunderstanding something.

From my layman's understanding, it's relayed via the orbiters.

There are a few orbiters around Mars. NASA appears to have an arrangement with the ESA to upload data from the rovers to the ESA's orbiters, depending on whose orbiters are within line of sight at any given time. Then the orbiter sends the information back to Earth, which are received by NASA's Deep Space Network

During the time when line of sight between Earth and Mars is blocked by Sol, there isn't any communication.

May interest you: https://mars.nasa.gov/mars2020/spacecraft/rover/communicatio...

It never ceases to impress me that we have the ability to do this sort of stuff. A couple thousand years ago, the height of technology was shooting something from a few hundred metres away with a bow and arrow, now we are landing machines on another planet and transmitting data back and forth through the solar system. Incredible.

Incredible for me, too. The power of building the civilization, one generation after another, and of working together, sharing the knowledge.

But according to Ancient Aliens, the large stone Pyramids were built by aliens, but the TV cameras recording the show's hosts, with CCDs, and likely 10nm chips inside, were built by humans.

In all seriousness, it's impressive what knowledge sharing and cooperation achieves.

[Ancient Aliens] Ah but the cameras and chips are only possible -because- the aliens built the pyramids and inspired humans technologically and a mere 4450 years later, voila! CCDs and computer chips!

Well, given the fact that we still know relatively little about most of the observable universe (dark matter & energy), I don't think you can completely rule out the several unlikely hypotheses. For example, that earlier civilizations instead of electricity used a completely different form of energy - and that basically directed their development into a completely different direction, not leaving many material artefacts. I don't believe this actually happened, but a part of me knows that I can't be 100% sure it didn't.

It is highly unlikely that the cameras being used to produce Ancient Aliens are CCDs unless they are also using ancient camera tech. Most likely, the camera's image sensors are CMOS. 3 chip CCDs reached their pinnacle as 90s/early 00s tech. CCDs can only sense one color, so they put three of them behind an RGB splitter.

A couple of thousand years ago is the peak of the Romans, so you're way off on your 'height' of technology at that time.

Using bows and arrows as an example when you've got wonders of pretty advanced engineering like the Parthenon, plus they also had ballistae, chariots and catapults, so not the peak at all.

Not only that, but even the bows were more advanced, composite bows much more powerful than simple ones made of wood.

The most complex machine of the Roman era was perhaps a water organ. (I would guess that for long historical periods the most complex machines were keyboard-controlled musical instruments.)

Oh see you did it now - opened up a vacuum about ancient tech.

I'll start: https://en.wikipedia.org/wiki/Aeolipile

Great link, thanks for sharing! This has the makings of an excellent thread – please do continue sharing cool stuff!! :o)

(The question as to how - and why or why not - we could go from the Aeolipile to full blown steam engines, I've always found fascinating ...

... what other things / proceses / materials / frame of mind made the steam engine possible vs. this.

What made for an industrial revolution in the 1800's vs. the 1st century AD).-

One thing that severly hampered the romans was their number system.

Makes sense that it would ...

A couple of thousand years ago, humans built massive engineering projects, including the Pyramids, massive irrigation and earthwork systems, and tunnels, and bridges, domesticated wild animals, produced metals - including steel - out nothing but wood, water, and low grade ore, etc, etc.

They did not have internal combustion engines, or electricity, or the ability to machine parts to high tolerances, but ancient engineers cared deeply about efficiently transforming mechanical energy from one form to another.

Vint Cerf has been working with NASA for over a decade on a design for interplanetary internet. I work at Google and he shared a story about how the earlier rovers had radios that were overheating at higher bandwidth transmissions. A smart engineer noted that they had an X band radio on the rover and still had one in an orbiter around Mars. The rover could transmit at 128mbps over xband to the orbitter, which in turn had large antennas to transmit back to earth at 128mbps. I assume Perseverance supports more bandwidth but it may be limited by whatever equipment we have in orbit around Mars.

https://www.quantamagazine.org/vint-cerfs-plan-for-building-...

They added dedicated storage in the rover itself to store phots and videos. So for example they can compress the video files before transmitting. I've hear they use ffmpeg for this purpose. There are 4 orbiting satellites that can relay any data sent to it.

Perseverance sends the data to various orbiters (satellites already in orbit around Mars) during overflights (time windows when the orbiter is in range of the rover) and those orbiters then send (relay) the data to Earth via the Deep Space Network (satellite dishes on Earth).

See https://www.quantamagazine.org/vint-cerfs-plan-for- building-an-internet-in-space-20201021/ for some details on projects related to this. IIRC it's store and forward.

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