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Voyager 1 stops communicating with Earth

cnn.com

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Re: Voyager 1 stops communicating with Earth

#411

Post by kqr »

nemo44x wrote: post #316
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.

I don’t know how well it holds today but for some time it was known that running certain computations on existing hardware would take longer than waiting for new hardware and running when available.

I don't know about that, but there was also the idea that optimising the code would take longer than waiting for hardware to catch up – this was known as "the free lunch".

Re: Voyager 1 stops communicating with Earth

#412

Post by simonjgreen »

hunter2_ wrote: post #352
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.

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…

You have this backwards. In your example it would have been 48x read and 8x write.

Re: Voyager 1 stops communicating with Earth

#413

Post by wongarsu »

Tommstein wrote: post #328
japhyr wrote: post #175

My favorite graph of all time is the one that demonstrate Voyager 1 had left the solar system. I was a high school math and science teacher at the time, and I spent the whole day sharing this graph with students. It was so much fun watching everyone's faces and seeing the moment they realized what it really meant. https://phys.org/news/2012-10-voyager-left-solar.html

The Voyagers leaving the solar system is so popular that they've done it like 10 times!

And in another 300 years or so they will leave the solar system again when they reach the Oort cloud, and in another 30000 years or so they will finally leave the solar system for the last time when they leave the Oort cloud

Re: Voyager 1 stops communicating with Earth

#414

Post by isolli »

paxys wrote: post #340
zamfi wrote: post #315

Earlier quoted context omitted.

You do it every day! The Earth itself moves faster than Voyager -- 1.6 million miles per day.

The tiny difference here is that we made Voyager.

Another difference is that we sent Voyager traveling orthogonally to Earth's orbit. Well, not exactly, but you get the point...

> Voyager 1 is now leaving the solar system, rising above the ecliptic plane at an angle of about 35 degrees at a rate of about 520 million kilometers (about 320 million miles) a year. Voyager 2 is also headed out of the solar system, diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 470 million kilometers (about 290 million miles) a year.

https://voyager.jpl.nasa.gov/frequently-asked-questions/fact...

Re: Voyager 1 stops communicating with Earth

#415

Post by simonjgreen »

taylorius wrote: post #385
alain94040 wrote: post #192

Earlier quoted context omitted.

Why isn't it linear?

According to Wikipedia, the abrupt change occurs at the point when the solar wind's speed decreases into the subsonic range (speed of sound in the interstellar medium is approximately 100km/s and the sun emits the particles that makeup the solar wind at approximately 400km/s). This transition to a subsonic regime causes compression waves to form, and causes the rapid drop off.

That’s fascinating, and going to send me down a learning hole! I had never before considered speed of sound in space.

Re: Voyager 1 stops communicating with Earth

#416

Post by puzzledobserver »

taylorius wrote: post #385
alain94040 wrote: post #192

Earlier quoted context omitted.

Why isn't it linear?

According to Wikipedia, the abrupt change occurs at the point when the solar wind's speed decreases into the subsonic range (speed of sound in the interstellar medium is approximately 100km/s and the sun emits the particles that makeup the solar wind at approximately 400km/s). This transition to a subsonic regime causes compression waves to form, and causes the rapid drop off.

I didn't know that the speed of sound in the interstellar medium is 100 km/s. That seems surprisingly high, given that there's more atmospheric material here on the surface of Earth, and the speed of sound is only about 330 m/s.

How can sound travel so fast in the interstellar medium?

Re: Voyager 1 stops communicating with Earth

#417

Post by fl7305 »

omeid2 wrote: post #241
vimr wrote: post #201

If someone is wondering about this, it has taken 46 years for voyager 1 to travel 22 light hours. fascinating.

I wonder in how many years from now, we can do the 46 years in 22 months? 22 days? 22 hours?

You can theoretically do the 22 light-hour trip in 1 hour of subjective time if you travel at 99.9% of light speed.

At least if my math is correct (?)

Now, if the time is measured from standing still, it will take a lot longer. At least at accelerations that a human can survive.

Re: Voyager 1 stops communicating with Earth

#418

Post by matwood »

jacquesm wrote: post #280
manicennui wrote: post #246

Earlier quoted context omitted.

There are many, many unmanned missions happening now making amazing discoveries. Cassini was nothing short of mind blowing. I'm somewhat sympathetic to your claims, and I wish more people were intellectually curious, but there are very likely more people in absolute numbers performing scientific research now than ever.

I'll believe it when I see it. For now the Voyagers are the only thing out there that are expanding our envelope of influence, everything else is just data and will eventually evaporate. Think about it from a non-solar system perspective. Nothing we've done since Voyager has had any effect outside of our solar system and if we don't change our attitude it is quite likely that nothing ever will. Everything else we've…

IMO, throwing out more Voyager like probes is not really the next step in humanities evolution towards space. It was a good step in the 70s, but now we're working to the lay the foundation and hope that one day space travel can be nearly routine as air travel is today. Higher volume of launches, bringing down the costs, etc... will allow hundreds and thousands of Voyagers to be sent out aimed at specific, distant locations.

You may dislike Musk, but SpaceX is pushing getting to space forward.

Re: Voyager 1 stops communicating with Earth

#419

Post by kqr »

zeven7 wrote: post #257
alain94040 wrote: post #192

Earlier quoted context omitted.

Why isn't it linear?

I didn’t understand it either but the pictures and graphs on this Wikipedia entry actually helped make a lot more sense of it to me, especially the analogy of the water faucet https://en.m.wikipedia.org/wiki/Heliosphere

That was a good page. At first I thought "But what is out there, outside the solar system?" under the assumption that there was nothing there. And there is nothing there, but nothing in galactic terms: the entire galaxy is there! And apparently it behaves like a gas, despite its low density.

So although solar wind sounds hardcore, at that distance its pressure about matches that of the nothingness that makes up most of the galaxy. Interesting!

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