Voyager 1 hears the hush of interstellar plasma | Hacker News Reader

Voyager 1 hears the hush of interstellar plasma

astronomycommunity.nature.com

277 pointssohkamyung105 comments

It's pretty wild that this probe, launched 44 years ago (1977) and now well beyond the solar system, can still take novel measurements and transmit information back. At that range, our sun looks roughly like any other star. The nuclear radioisotopic thermal generator really is an incredible power source for this kind of application. Some info on the current design here [1].

[1] https://mars.nasa.gov/internal_resources/788/

Curious as to how long does it take for the transmission to reach earth. Where can I learn that?

21h https://voyager.jpl.nasa.gov/mission/status/

I can't say I'm surprised, but it's still pretty crazy to think about that it took us 44 years to get an object to a place it takes light less than 24 hours to get to. It feels both pretty far and also not far at all at the same time.

I think new horizons is much faster, and will catch up. Still the same order of magnitude though

Wikipedia disagrees:

> Provided Voyager 1 does not collide with anything and is not retrieved, the New Horizons space probe will never pass it, despite being launched from Earth at a higher speed than either Voyager spacecraft. The Voyager spacecraft benefited from multiple planetary flybys to increase their heliocentric velocities, whereas New Horizons received only a single such boost, from its Jupiter flyby. As of 2018, New Horizons is traveling at about 14 km/s, 3 km/s slower than Voyager 1, and is still slowing down.

Oh, cool

Not according to this stack exchange answer[0]. It quotes a page from John Hopkins University, although that source page doesn't seem to exist anymore.

> Though New Horizons will also reach 100 AU, it will never pass Voyager 1, because Voyager was boosted by multiple gravity assists that make its speed faster than New Horizons will travel. Voyager 1 is escaping the solar system at 17 kilometers per second. When New Horizons reaches that same distance 32 years from now, propelled by a single planetary swingby, it will be moving about 13 kilometers per second

[0] https://space.stackexchange.com/questions/3520/when-will-new...

Yeah, I had this reaction of like "yeah, only 21 hours? that's not too long"… Then it occurred to me, it's 21 hours at the _speed of light_, something we generally consider effectively "instant" here on Earth. Pretty fascinating stuff. I'm really happy to hear we're still getting transmissions back from Voyager 1 - from nearly 23 billion kilometers away, for that matter!

Also really interesting is the Voyager FAQ, even from the first question (about whether the cameras could be turned back on). "Mission managers removed the software from both spacecraft that controls the camera. The computers on the ground that understand the software and analyze the images do not exist anymore."

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

> something we generally consider effectively "instant"

We are in one of the very few professions where the speed of light is considered annoyingly slow. Just three days ago there was a thread of people lamenting that the closest Hetzner datacenter is about 50 light-milliseconds away

I don't know enough to say, but it wouldn't surprise me if our speed of thinking (and perhaps also time in general) is indirectly tied to the speed of light; meaning, if the speed of light were faster, we'd be thinking faster, and thus the round trip speed to Hetzner would appear just as annoying. I'll be happy to be corrected.

Given the distances involved, here's lightspeed travel from the sun: https://digg.com/video/light-speed-solar-system-travel

Thanks for the that link. I just spent an hour in the Eyes on the Solar System web app and listening to Carl Sagan wax poetic about our Voyagers: https://www.youtube.com/watch?v=H92iCnecYGQ

"…and far from home, untouched by these remote events, the Voyagers, bearing the memories of a world that is no more, will fly on."—C. Sagan

The one-way light times are at the bottom of https://voyager.jpl.nasa.gov roughly 17.5 hours for Voyager2 and 21 hours for Voyager 1

Just About 1200 times longer and it approached the same distance as our nearest star at 4 ly

If we started pursuing nuclear pulse propulsion we could have our first probe arrive in the next star system in a hundred years or so, and eventually get the travel time closer to 40 years.

If?

Theoretical is still theoretical. We have no functioning propulsion that can exceed what the probes are currently travelling at.

At least for something like Project Orion, all the individual components are either verified in prototypes or proven technology. We have existing stockpiles of nuclear bombs. Propelling a craft by exploding something behind it is demonstrated in smaller prototypes with TNT. We know how to do radiation shielding, we know how to do shock absorbers.

Or course combining technologies in a new way comes with lots of engineering challenges, but it's a smaller leap in technology than e.g. the first moon landing.

The energy density of nuclear batteries is astounding. Per the linked spec sheet, at 2.8W/kg and 17y mission duration, that's about 417,000Wh/kg. By comparison a lithium ion battery has 250Wh/kg.

Nuclear fission reactors are even crazier. With breeding you get 22,500,000,000 Wh/kg. Good old E=MC^2.

Technically all batteries are E=mc^2, it's just that nuclear fission converts more of the mass, but still, not all of it.

Lithium batteries do get ever so slightly heavier when charged, but it's basically undetectable.

How do lithium ion batteries convert mass to energy?

The principle of E=mc^2 is of mass-energy equivalence. Any form of stored energy has mass, including the binding energy between atoms in a molecule, and lithium ions convert those chemical bonds to electric currents when a load is applied.

The mass associated with those chemical bonds is miniscule compared to the protons, electrons, and neutrons, but it is not zero.

All (confined?) energy is equivalent to mass, even when that mass isn’t in the form of elections and quarks.

There's a really good joke about Ferengi political situations here, but I'm no economist.

I think quark jokes are a bit cheesy myself. ;)

I find them strange and charming

Hey it is not Reddit, but at least these are not off-color jokes.

Fission is not anywhere near E=MC^2. That would be matter/antimatter annihilation.

It is E=MC^2 though. 0.1% of the mass is converted into energy.

No, it's E=(0.001M)C^2

That is absurd. It is E=MC^2 where M is 0.1% of the total mass of the reactants.

100% of the mass difference is converted into energy.

The GP was talking in relation to W/Kg, and the output per Kg is definitely not e=mc^2. It helps reading things in the context.

You are correct, though it would help to clarify that you're correcting the GP on the "per kilo" part, and not the "energy" part.

I agree, if you're deploying 1 kg of fissile material, only 0.1% of that will be converted to energy. We should talk about energy per mass of fissile material, not energy per mass of "mass difference".

Windup toy cars are also E=mc^2.

E = mc^2 implies that mass (m) is being converted to energy (E), and a windup toy car is definitely not converting mass to energy. Windup cars get their energy from torsional springs, which are E = (1/2) k theta^2.

>and a windup toy car is definitely not converting mass to energy

Ah, but it is. E=mc^2 is always true in the reference frame where the object is stationary. (We assume that we are co-moving with the windup car.) A spring under torsion is heavier than an unwound spring.

> A spring under torsion is heavier than an unwound spring

Does it have more (invariant) mass?

Yes.

So with a nuclear fission reactor NASA could make an immortal space probe! It's very sad that this isn't a project.

Nuclear fission reactors have a lot of moving parts, and creating something that lasts 50 years without one of those moving parts failing, unmanned, and subject to the harshness of space, isn't trivial.

Nuclear batteries are extremely reliable though, as they are fully solid state. A Pu-238 battery can emit useful amounts of power for upwards of a century, and there is virtually nothing to break.

The Russians have a few of those: https://en.wikipedia.org/wiki/BES-5

It appears to be holding up well at 27 years past the age spec too. It is astonishing how something sent out when I was a toddler is still working till this date; kudos to the engineers.

It’s now 22 Billion km away from Earth. Amazing.

One of the few times you can use the unit ‘terametres’.

22Tm.

Or, 22 terametres from Terra.

> It's pretty wild that this probe, launched 44 years ago (1977) and now well beyond the solar system, can still take novel measurements and transmit information back.

Through (according to Wikipedia) the party might end in just a few years: https://en.wikipedia.org/wiki/Voyager_1:

> Voyager 1's extended mission is expected to continue until about 2025, when its radioisotope thermoelectric generators (RTGs) will no longer supply enough electric power to operate its scientific instruments.

What about voyager 2 lifetime ? Humanity hasn't sent any probe having an extra-solar system target since 1977?? If so, this is extremely sad and distant space exploration will die and 50 years will be lost. I attribute this mediocrity to the anti nuclear/RTG lobby at NASA

We haven’t sent another probe, not because of anti nuclear lobby, but because of there was an unique event of planets being nearly on a line around 1970, which allowed NASA to plot a series of gravity assists, instead of one or two, that allowed gaining immense amount of free velocity.

Sun’s gravity well is so immense that escaping it requires a very, very large amount of energy. I am not sure if it could be done with conventional rockets with current technology, without multiple gravity assists.

Edit: As the child comment says, it seems to be possible with current technology. It is very exciting!

> I am not sure if it could be done with conventional rockets with current technology, without multiple gravity assists.

Yes, it can. New Horizons is escaping the solar system only a little bit slower than the Voyager probes, and it was already on an escape trajectory before its single Jupiter gravity assist.

I wonder what hope we have for making probes that will last longer (i.e., “do science even deeper in space”) than Voyager 1, Voyager 2, and New Horizons. Specifically, whether we can make RTGs or other power sources that last longer and/or scientific instruments that operate with lower power (without compromising on quality or quantity of observations). Maybe there just isn’t much science to do beyond the Kuiper Belt (or rather, getting 50 years beyond the Kuiper Belt doesn’t improve science much more than making the same observations from the KB itself due to the vastness of space)?

New Horizons is quite a bit slower and will never overtake the Voyager probes distance wise.

I'm puzzled by the requirement for an alignment. It seems one could gravity assist in arbitrary directions though it might take longer. But should still end up with a similar energy gain.

The gravity assist works by transferring some of the planet's momentum to the craft, and that momentum has a direction, not just an amount.

Slow down with the over-dramatisation buddy. Nothing has been lost, interstellar exploration hasn't died, and I am not exactly sure why an anti-nuclear lobby at NASA has anything to do with either of these things.

The trajectory for the Voyager probes was made possible by the alignment of Earth, Jupiter, Saturn, Uranus and Neptune. A similar alignment will not occur again until the middle of the 22nd century.

Handy coincidence that the last alignment happened just as our technology reached the point where we could take advantage of it.

> Humanity hasn't sent any probe having an extra-solar system target since 1977??

The Voyagers didn't have an extrasolar target either, they were meant to visit the outer planets. If we're looking at probes that leave the solar system after their original mission, we launched New Horizons in 2006 to Pluto, and it's currently in the Kuiper Belt on its way to leave the solar system.

Just to add to that: NH is on it's way out of the system now, after 15 years, and it should have another 15-20 years left in it's RTG.

Meanwhile, there are actual interstellar probes being planned, in addition to several missions to the outer solar system (and which could end up in interstellar space afterwards).

And there's a ton of missions planned for the inner regions of the Solar system -- space exploration is still a thing and there's a lot of exciting things happening.

Its so cool that the entire solar system has a sort of ozone layer (the heliopause), I also really like the diagram that shows how each craft is travelling in different directions.

I think we should have a new mission, send out huge amounts of tiny crafts in all directions at the same time, to get a sort of Google street view of our solar system and interstellar space. I bet we could create crafts with modern tech that where tiny and much less expensive that the original pioneer and voyager crafts.

Street view in space? I think you might be underestimating just how empty the solar system is.

So it should be quite easy to build.

"Oh, it's all black here too" ;)

lol

Maybe it's like Star Trek and space is full of anomalies even 24th century sensors miss.

Of course it’s not exactly like street view!

But it is a sort of map, ok probably Google maps rather than street view :)

The Gaia probe is doing something a little like this to create a full 3D star map. It rotates as it goes and uses parallax to measure the distance and motion between stars exactly.

https://en.wikipedia.org/wiki/Gaia_(spacecraft)

> I bet we could create crafts with modern tech that where tiny and much less expensive that the original pioneer and voyager crafts.

It's harder than you'd expect. At that distance solar panels are essentially useless, so you do need nuclear power, and you're continuously exposed to cosmic rays, so you need radiation-hardened electronics. Both of these drive up the cost. The Voyagers also had the the outer planets in alignment to give it a gravity assist, so if you want to get there on the same time scales you'll need a more powerful rocket as well.

I read somewhere that sending very small spacecraft to far away places was something that was being considered. Unfortunately I don’t remember the details. We just need an artificial gravity machine.

Breakthrough starshot? https://en.wikipedia.org/wiki/Breakthrough_Starshot

That might be our best bet to get to other systems. But it’s still pretty much a fantasy. The engineering challenges behind that project just seem insurmountable unless we work on it as a planet, not just NASA, ESA, Roscosmos, etc.

It doesn’t sound that hard, it’s just laser kites. I bet Elon could do it.

Apart from the insane amount of power required to use lasers as propulsion in this way, they also require a camera, computer, interstellar communications system and nuclear power source within a mass budget of a few grams. It's complete science fiction.

Literally everything in this area starts out as science fiction. I think the general idea of sending lots of small craft is a good idea. It would be great to hear from the people building these things which parts are not possible currently.

Tiny spacecrafts and sails with lasers. Yeah pretty sure that was it. Such a cool idea, and it would only take 30 years, which means a lot of us will still be alive to see it. Imagine seeing actual closeup pictures of “earth 2”.

Anyway if they used the same technology, but sent spacecraft out into space from locations all around the Earth at the same time, then we could gather data as this fleet headed into deep space.

Like one of those big planet explosions in science fiction movies, but instead of an explosion, just tiny space crafts.

There's no way to get a gravity assist in directions orthogonal to the solar plane, which makes travel in those directions either far more expensive or far slower.

I hadn’t thought of that, but your totally right. In the article’s picture, one of the space craft appears to be heading off in a direction outside of the solar plane, but it’s not by a huge amount.

That’s why we need a way to create gravity artificially if we are going to do any space exploration. It would be a bit crap if we could only move in 2 dimensions.

Given the crazy high amount of laser power this requires, maybe placing a satellite close to the sun, and having it focus solar radiation, would be better than an earth based laser grid?

> you do need nuclear power, and you're continuously exposed to cosmic rays

silly question: can CRs be harnessed for power?

Google street view of our solar system

Has anyone ever updated Commodore's Visible Solar System? Very inspiring.

https://www.lemon64.com/?mainurl=https%3A//www.lemon64.com/g...

I had that on my Vic20.

https://www.vic-20.it/visible-solar-sistem-1930/

Thanks. Your comment sent me to Wikipedia, where I found this related snippet:

> In the year 2000, 23 years after production, the radioactive material inside the RTG had decreased in power by 16.6%, i.e. providing 83.4% of its initial output; starting with a capacity of 470 W, after this length of time it would have a capacity of only 392 W. A related loss of power in the Voyager RTGs is the degrading properties of the bi-metallic thermocouples used to convert thermal energy into electrical energy; the RTGs were working at about 67% of their total original capacity instead of the expected 83.4%. By the beginning of 2001, the power generated by the Voyager RTGs had dropped to 315 W for Voyager 1.

There's also a nice picture of one deployed on the moon. The dust on the moon's surface looks spectacular in that picture.

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

How much Watt do they have now 20 years later in 2021?

I can give you half an answer and speculation on the other half.

Given that radioisotopes decay with a halflife pattern, I would expect that you'd see a 16.6% drop in capacity every 23 years. So something like:

    1977: 100% (470 W)
    2000: 83.4% (392 W)
    2023: 69.6% (327 W)

To get a full answer, you'd need to know how the thermocouples degrade. Under the (completely unsubstantiated) assumption that they degrade linearly, that's about a 20% efficiency degradation per 23 years:

    1977: 100% isotope * 100% coupling efficiency -> 470 W (100% of capacity)
    2000: 83.4% isotope * 80% coupling efficiency -> 314 W (67% of capacity)
    2023: 69.6% isotope * 60% coupling efficiency -> 196 W (41% of capacity)

I suspect the thermocouple efficiency degradation is very much non-linear -- or rather, I have no reason to actually expect it to be linear -- so the second half of the above is a total SWAG, but maybe gives you a rough idea :)

> There's also a nice picture of one deployed on the moon.

That was also one of the many issues that cropped up during Apollo 13. They too had an RTG on board that was supposed to stay on the moon[1].

According to the book "Lost Moon" by Lovell and Kluger, a potential explosion of the Saturn V during launch was accounted/planned for, but the RTG "coming home" together with the LEM wasn't.

IMO the book was a bit hazy on how that situation was addressed exactly, but according to Wikipedia that RTG is currently resting somewhere deep in the Pacific[2].

Also an interesting read on that topic is the SNAP program itself that developed the technology in the first place, even shot entire mini-nuclear-reactors into earth orbit[3] and resulted in some stereotypical 1960s nuclear safety shenanigans/mishaps during testing[4][5].

[1] https://en.wikipedia.org/wiki/Apollo_13#Experiments_and_scie...

[2] https://en.wikipedia.org/wiki/Apollo_13#Reentry_and_splashdo...

[3] https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_...

[4] https://en.wikipedia.org/wiki/SNAP-10A#Safety

[5] https://en.wikipedia.org/wiki/Systems_for_Nuclear_Auxiliary_...

I am so impresses that this device is still actually able to do so much after so long... I really hope that the current space probes and rovers do just as well if not better.

I wonder why don’t we send more probes like that in every direction by dozens?

I was thinking it would be interesting to send a stream of them out in one direction (or many streams) with the idea that they could serve as a relay/mesh network, allowing us to communicate with the probes (and vice versa) for longer. Not sure how valuable that would be scientifically.

There's not much, in every direction, for a long ways.

It makes more sense, generally, to send probes to where things (planets, moons, dwarf planets, asteroids, comets) are, that we can reach in reasonable time (years, possibly a decade or more for outer targets).

"Every direction" just takes you to deep space. And that's not going to be particularly illuminating, though a few such probes (say, a high- or low-solar plane one) might be interesting.

Oort cloud is still not confirmed, right? I get that it might be incredibly sparse, but isn't there anything to study there?

Oort is (mostly) in the solar plane AFAIU, and there's every reason to use gravity assist to get there. I don't know that any specific objects are known, and getting into an Oort-observing orbit might be challenging. Otherwise, yesm it's sparse and arbitrary flybys would likely miss anything interesting.

Spraying random probes in all directions makes lttle sense.

Voyager 1 won't reach the Oort Cloud, if it in fact exists, for another three centuries.

I think you're mixing up the Kuiper Belt with the Oort Cloud. Kuiper Belt is in the plane, and within the Oort cloud. Oort cloud is a sphere.

At least, according to ESA [1].

[1] https://esahubble.org/images/opo0204i/

Hence my hedge, mostly.

Though this is well outside my area of expertise.

It’s also wild to compare:

– how far Voyager 1 has already traveled ~150 AU or ~0.002 ly [1]

– how much farther it could go in 40,000 years ~1,000,000 AU or ~17 ly [2] [3]

– the visible diameter of our Milky Way ~6,000,000,000 AU or ~100,000 ly [4]

[1]: https://voyager.jpl.nasa.gov/mission/status/

[2]: https://voyager.jpl.nasa.gov/mission/interstellar-mission/

[3]: https://en.wikipedia.org/wiki/Gliese_445

[4]: https://en.wikipedia.org/wiki/Milky_Way

Could we realistically accelerate a space probe to faster speeds than what Voyagers and New Horizons are currently doing?

With gravity assists you can: https://en.wikipedia.org/wiki/Parker_Solar_Probe

One of the most important parts of the Voyager is apparently a little motor that rotates every 192 seconds to take 360 degree readings of the sky. Each rotation is called a "step" in their lingo .. they built it to run a few thousand steps (or about 4-5 years). And that little motor has now run over 5 _million_ steps over 48 years... and is still running.

More at https://www.nature.com/news/2008/080702/full/454024a.html

> One of our chief goals was to apply the power of signal processing to search for weaker signals in the PWS data, which maybe, just maybe, were hiding between and behind the bright plasma oscillation events that had already been discovered.

So this doesn't mean that Voyager 1 has entered a new region with different characteristics, just that they've used signal processing to tease a little bit more out of the existing data.

I came to this thread a bit too late, but if you're interested in the actual signal that Stella found, take a look at the spectrum vs time on the NASA release [1] - third plot on the page, with a convenient slider that lets you flip back and forth to see the previously known plasma oscillation events and the newly discovered continuous signal. Notice the huge change in scale!

[1] https://www.nasa.gov/feature/goddard/2021/as-nasa-s-voyager-...

As a ham radio enthusiast I find this sort of article fascinating, from the actual frequencies detected to the fact that even Voyager suffers from RFI. :)

I find this tremendously thrilling, and not just for the exciting discoveries about the environment of the outer solar system.

Somehow human spaceflight seems dull to me while I just can't get enough of the cool and crucial work these robots are doing on our behalf.

Never send a human to do a robot's job, I suppose.

>Who knows what discoveries still lie ahead of it?

Its very likely this is the last one. The craft is simply running out of power and the instruments will be forced to shutdown in a few years. The current deep space network will lose its already extremely faint signal in about a decade.

Are there any such probs sent in recent years with latest technology on it?

Well there is New Horizons[0], which launched in 2006 and is now beyond Pluto. But in terms of coolness, I really like The Parker Solar Probe[1] which is going closer and closer to the sun with a massive heat shield and at eye watering speeds. By 2025 it will be going 690,000 km/h (430,000 mph), or 0.064% of the speed of light.

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

[1] https://en.wikipedia.org/wiki/Parker_Solar_Probe

> While I was busy learning the undergraduate physics curriculum, Voyager 1 was treading through the interstellar medium and revealing in stark detail how interstellar plasma and the solar wind collide and interact across a boundary layer called the heliopause, where they engage in a massive pressure-balancing act that shields our heliosphere from the great beyond.

I thought Voyager 1 was out in interstellar space for awhile now, beyond the heliopause, heliosphere, etc. ?

I'll also note,

> Almost 11 years ago, Voyager 1 crossed an unprecedented boundary: it became the first human-made object to enter interstellar space. I was just a high-school student at the time, oblivious to the milestone ...

That's no excuse! :)

What are MAG rolls cited in video?

Related: https://xkcd.com/1189/

Reply on news.ycombinator.com