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Voyager 1 stops communicating with Earth

cnn.com

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Re: Voyager 1 stops communicating with Earth

#581

Post by thih9 »

apitman wrote: post #544
guenthert wrote: post #482

Earlier quoted context omitted.

> even though there was no computer on Earth at the time fast enough to decode it I'm not sure what is meant by that. Not fast enough to decode in real time? There is/was no need to do that. The transmissions would have gone to tape in any case. Here is a link describing how to decode such a tape : https://destevez.net/2021/09/decoding-voyager-1/

I called it a legend deliberately. One of the things I love about this anecdote is that it makes less sense the older and more experienced I get. It was told to me 12 years ago as a young, starry-eyed junior developer by my supervisor who had a PhD in RF research, while we were working on what we considered to be a world-changing wireless technology at a startup in San Francisco (it wasn't). Who knows how many of the…

When I read the earlier comment, seeing “tech legend” didn’t make me assume that the story would be false. Grandparent’s clarification was helpful for me.

Re: Voyager 1 stops communicating with Earth

#582

Post by thih9 »

apitman wrote: post #308

One of my favorite tech legends is that apparently Voyager 1 launched with a Viterbi encoder, even though there was no computer on Earth at the time fast enough to decode it. After a number of years Moore's Law caught up and they remotely switched over to Viterbi for more efficient transmissions.

Note, this is false. Details: https://news.ycombinator.com/item?id=38655026

Re: Voyager 1 stops communicating with Earth

#583

Post by jsrcout »

dredmorbius wrote: post #182

Among my increasingly prized possessions is an original copy of Nasa's "Voyager Encounters Jupiter* report, detailing mission findings, and featuring some of the image highlights. Internet Archive, bless them, have this online: https://archive.org/details/NASA_NTRS_Archive_19800025809/mo... >

I have the same one, from way back in like 7th grade! Someone from NASA gave a talk about the agency's work including planetary science and Voyager at our school. They also did a memorable demo involving heating a handheld Space Shuttle thermal tile with a blowtorch :-)

The booklet on Jupiter was outstanding. I had it pretty much memorized.

Re: Voyager 1 stops communicating with Earth

#584

Post by slenk »

murkt wrote: post #578
slenk wrote: post #559

Earlier quoted context omitted.

Yes, but WHY can it only write at 8x?

As explained in the nearby comments in more details, it needs more time to heat up a spot on the disk, than to see a reflection from said spot.

I missed that, thank you

Re: Voyager 1 stops communicating with Earth

#585

Post by kqr »

NohatCoder wrote: post #549
apitman wrote: post #308

One of my favorite tech legends is that apparently Voyager 1 launched with a Viterbi encoder, even though there was no computer on Earth at the time fast enough to decode it. After a number of years Moore's Law caught up and they remotely switched over to Viterbi for more efficient transmissions.

This is about error correction. The probes add a redundant convolutional code to their signal. Decoding this is easy as long as the error rate is low, a computer program can simply guess what bits have flipped. The issue becomes harder with a higher error rate, and a Viterbi decoder is computationally expensive, but can correct higher error rates than other constructions. Since the signal strength degrades with dista…

> a Viterbi decoder is computationally expensive, but can correct higher error rates than other constructions.

Higher than others at the time, or higher than turbo codes or low-density parity checks?

Re: Voyager 1 stops communicating with Earth

#586

Post by kqr »

TorKlingberg wrote: post #495
hunter2_ wrote: post #352

Earlier quoted context omitted.

The notion that encoding/transmitting could be simpler than decoding/receiving is interesting. It reminds me of the way optical drives for many years could write at, say, 48x but read at 8x, such that the majority of time spent was the verification step (if enabled) rather than the burn step. Just speculating, I assume it's because of things like error correction, filtering out noise/degradation. Producing the extra…

Others have noted you got the CD-R speeds wrong, but sometimes sending is indeed easier than receiving. I used to work on radio signal processing for phones, and we'd spend far more of both DSP cycles and engineering effort on the receive side. Transmission is basically just implementing a standardized algorithm, but on the receive side you can do all kinds of clever things to extract signal from the noise and distor…

> Video codecs like h264 or VP9 are the opposite: Decoding is just following an algorithm, but an encoder can save bits by spending more effort searching for patterns in the data.

This is a more general point about the duality of compact encoding (compressing data to the lowest number of bits e.g. for storage) and redundant encoding (expanding data to allow error detection when transmitted across a noisy medium.)

Re: Voyager 1 stops communicating with Earth

#587

Post by mcv »

ben_w wrote: post #569
mcv wrote: post #519

Earlier quoted context omitted.

Can you use it to transmit actual sound? Would it be possible to use this for short-range communication in space? Or is this only a very theoretical kind of sound?

Given the supersonic flow, one directional communication only. Given the impedance mismatch[0], even the parts of the solar system outside Kármán lines where the interplanetary medium can support pressure levels equivalent to normal speaking (including low Earth orbit), I'm told human ears can't respond to that pressure change properly. Sensors can be built to pick it up, but that may not be in scope for your questio…

I wouldn't expect human ears to be able to pick it up, because human ears would have far more serious problems just being exposed to the vacuum of space. But if it's possible to make sensors that can detect this sound, and devices that can generate it, and communication between the two would be accurate and really this fast, well, that would certainly be interesting.

Not sure if it would actually be useful, because I'm sure radio waves would be much more practical, but sound in space is a fascinating idea.

Re: Voyager 1 stops communicating with Earth

#588

Post by fasterik »

kjkjadksj wrote: post #556
mlrtime wrote: post #516

Earlier quoted context omitted.

I disagree, I think it's the opposite. Men have lofty dreams, they're also realists. How can you realistically get a man on Mars? Use all their talents to work with a government? Or use it to create enough capital to do it yourself (And piss off some people at the same time for fun)?

Why do you even want to put a human on mars? What would you have them do that you can’t do with a probe or robot?. Its extremely risky to put people in space with our present technology. Even if nothing goes “wrong” they are dealing with microgravity and radiation. We aren’t adapted for it at all.

There are a few reasons. You could say that putting humans on Mars has intrinsic value. In other words, "because it's cool". The other main argument for putting humans on Mars is that the grand projects of humanity push our technology forward. Putting humans on Mars requires solving a larger class of problems than sending probes does. The first space race accelerated the development of rocketry, integrated circuits, computers, satellite communications, and materials science. There's reason to believe that sending humans to Mars will cause similar advances in our capabilities, possibly in novel ways that we can't anticipate. A third argument is existential risk. If something catastrophic happens on Earth, there is some probability that having independent colonies on other planets would prevent extinction of the species. This is definitely true in the long term if we truly master the technology of surviving and thriving in space, but it's less realistic in the near term.

That said, I don't think Musk and others working on this problem are taking the challenges of creating a colony on Mars seriously. We know very little about the long-term effects on the human body, reproductive cycle, and psychology. If they're serious about this, one of their top priorities should be funding research to create isolated self-sustaining human colonies closer to Earth as a proof of concept. If we can't survive for decades at the bottom of the ocean or on the moon, we probably can't survive for decades on Mars. We would also need high confidence that generations of humans born on Mars wouldn't accumulate severe genetic damage and birth defects. This is a whole research program in itself that we're nowhere close to solving.

Re: Voyager 1 stops communicating with Earth

#589

Post by nullhole »

@dang - could you change the title of this? It is factually wrong. The spacecraft is still communicating with Earth.

This gives information (and may be a better link anyway):

"Engineers Working to Resolve Issue With Voyager 1 Computer" (Dec. 12, 2023)

https://blogs.nasa.gov/sunspot/2023/12/12/engineers-working-...

Re: Voyager 1 stops communicating with Earth

#590

Post by saalweachter »

johnwalkr wrote: post #236
WalterBright wrote: post #200

Criminy. Why aren't we launching more of these probes? With Musk's cheap rockets, we could launch a fleet of them.

The trajectory was a once-in-a-lifetime opportunity based on the dynamics of our solar system, and surely the relevant experts will take advantage of the next similar opportunities. It's also almost a miracle that the probes have lasted this long. They used analogue electronics and if they launched ten years later, they would have more modern electronics and would probably have failed by now. And it's not possible to…

> And it's not possible to simply argue to use older designs to last longer in a new mission, because you would give up multiple orders of magnitude of data collection.

Why not both?

The heavy parts of the probe, then or now, were presumably not the electronics themselves so much as the physical structure, the power system, etc etc.

If you were designing a probe to last fifty, a hundred years, why not include series of fallbacks of the electronics to simpler and more basic systems, so that you could still get something out of it, after the primary state-of-the-art electronics fail?

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