I really don't want to spoil it, but Reynolds does have something of a solution to the problem of the speed of light being so limiting, and it's based on time dilation. As usual with all things sci-fi, it's not practical, but it's fairly unique and fun to read.
1/r² is for an isotropic radiator, but Voyager 1 mounts (thankfully) a high gain directional antenna. The gains seem to be 36dBi or 48dBi, depending on the frequency [1]. This means that when pointed towards Earth, the signal power is actually between 4000 to 63000 times stronger than what that formula would give you. It's still tiny, but not as bad as that would suggest.
No, it is for any radiator. The gain of the antennas has absolutely nothing to do with the free path loss, it just changes the effective radiated power or the concentration effect of the antenna because of antenna related gains. Every kind of antenna has its own specific gain and corresponding losses diagram based on which way the source is relative to the antenna, with the baseline being an omnidirectional radiator (which no antenna really is, but we assume it is).
GP was very specific when they mentioned free path loss: the implication is that if you know what free path loss is then you also know that those losses are accurately modeled with that formula, no matter how large your ERP or receiver antenna gain is. At those distances it would make zero sense to use an omnidirectional antenna you will need every bit of gain you can get.
And with 50 year old tech! I do wonder if humanity will get to a point where we can retrieve the spacecraft at some point in the future (cue Star Trek fantasies)
I believe they meant that the receivers/transmitters on Earth are likely newer than 50 years old. And you're also probably right that the hardware installed on the voyager could be several years older than the launch date of the craft
I would prefer they just maintain it as long as possible and maybe deploy a proxy for earth that trails behind it indefinitely once it’s finally out of range. Let’s set an unbreakable record.
> the spacecraft, in flight since 1977, is cruising at nearly 38,000 mph (61,000 kph) through the vacuum of space,
The page takes great pains to explain things, but omits a frame of reference for this speed. I’m guessing it’s sun-relative, but it could be relative to its take-off on Earth. Does anyone know?
You're right that Earth is catching up to the Voyagers during part of its orbit for several months in the early part of the year (and you'll see that reflected on the Mission Status page). Consequently I used to wonder if Voyager 1 would reach 1 light day from Earth 3 times - the first time, then a second time when the Earth distance decreased, and then a third time when distance increased again!
If you scroll down on this TheSkyLive page, you can see a graph of Voyager 1's distance from Earth over time and it's an up-sloping ripple instead of a straight line. You can play with the markers to zoom in and see that the catch-up phase happens in the early part of the year:
Checked my bot's post from earlier today (taken from NASA's data[0]) and it says "Velocity relative to the Earth is about 34 km/sec (~77,173 mph); to the Sun about 16 km/sec (~37,763 mph.)"
And the closest known galaxy to the Milky Way, Canis Major Dwarf Galaxy, is just 25,000 light-years away - it's almost incomprehensible how vast the universe is!
I know it's a joke but it's because there's no clearly defined end of the solar system.
Just re-reading Pale Blue Dot by Carl Sagan and he talks about this. If we define the end of the solar system as the point where the suns gravity no longer holds, then it's going to be a very long time for it to escape the solar system.
I'm going to go find that passage in the book. Hopefully I can find it before the edit window closes for this comment.
Edit:
OK, I found it. This excerpt is from the book "Pale Blue Dot" by Carl Sagan, in the Chapter - AN AMERICAN SHIP AT THE FRONTIERS OF THE SOLAR SYSTEM
.
THE VOYAGER SPACECRAFT are bound for the stars. They are on escape trajectories from the Solar System, barreling along at almost a million miles a day. The gravitational fields of Jupiter, Saturn, Uranus, and Neptune have flung them at such high speeds that they have broken the bonds that once tied them to the Sun.
Have they left the Solar System yet? The answer depends very much on how you define the boundary of the Sun's realm. If it's the orbit of the outermost good-sized planet, then the Voyager spacecraft are already long gone; there are probably no undiscovered Neptunes. If you mean the outermost planet, it may be that there are other—perhaps Triton-like—planets far beyond Neptune and Pluto; if so, Voyager 1 and Voyager 2 are still within the Solar System. If you define the outer limits of the Solar System as the heliopause—where the interplanetary particles and magnetic fields are replaced by their interstellar counterparts—then neither Voyager has yet left the Solar System, although they may do so in the next few decades.* But if your definition of the edge of the Solar System is the distance at which our star can no longer hold worlds in orbit about it, then the Voyagers will not leave the Solar System for hundreds of centuries.
Weakly grasped by the Sun's gravity, in every direction in the sky, is that immense horde of a trillion comets or more, the Oort Cloud. The two spacecraft will finish passage through the Oort Cloud in another 20,000 years or so. Then, at last, completely gone long good-bye to the Solar System, broken free of the gravitational shackles that once bound them to the Sun, the Voyagers will make for the open sea of interstellar space. Only then will Phase Two of their mission begin.
Their radio transmitters long dead, the spacecraft will wander for ages in the calm, cold interstellar blackness—where there is almost nothing to erode them. Once out of the Solar System, they will remain intact for a billion years or more, as they circumnavigate the center of the Milky Way galaxy.
We do not know whether there are other spacefaring civilizations in the Milky Way. If they do exist, we do not know how abundant they are, much less where they are. But there is at least a chance that sometime in the remote future one of the Voyagers will be intercepted and examined by an alien craft.
*Radio signals that both Voyagers detected in 1992 are thought to arise from the collision of powerful gusts of solar wind with the thin gas that lies between the stars. From the immense power of the signal (over 10 trillion watts), the distance to the heliopause can be estimated: about 100 times the Earth's distance from the Sun. At the speed it's leaving the Solar System, Voyager 1 might pierce the heliopause and enter interstellar space around the year 2010. If its radioactive power source is still working, news of the crossing will be radioed back to the stay-at-homes on Earth. The energy released by the collision of this shock wave with the heliopause makes it the most powerful source of radio emission in the Solar System. It makes you wonder whether even stronger shocks in other planetary systems might be detectable by our radio telescopes.
End of quotation.
If you're interested, I highly recommend the book and everything by Carl Sagan. He was incapable of writing a dull sentence.
Well, consider that the speed of light itself is pretty slow, relative to what people's perception of the speed of light is. Even if you had a spaceship traveling at 99.99%, it'd take a surprisingly long time even to reach the Oort cloud.
A month or so for you. Enough time to catch up on a few favorite shows and finish a few books. Now if anyone is waiting for you on earth, they will wait considerably longer
Actually - to reach the start of the Oort Cloud from Earth it'd take around 4 hours. That's 2000 AU. The observer on Earth will see it as about 12 days. This is assuming 99.99% of the speed of light which is completely unrealistic of course.
I'm just going to repost stuff from my blog about the Voyager space probes. I've posted this here before -
The two Voyager spacecraft are the greatest love letters humanity has ever sent into the void.
Voyager 2 actually launched first, on August 20, 1977, followed by Voyager 1 on September 5, 1977. Because Voyager 1 was on a faster, shorter trajectory (it used a rare alignment to slingshot past both Jupiter and Saturn quicker), it overtook its twin and became the farther, faster probe. As of 2025, Voyager 1 is the most distant human-made object ever, more than 24 billion kilometers away, still whispering data home at 160 bits per second.
Each spacecraft carries an identical 12-inch gold-plated copper phonograph record.
The contents:
- Greetings in 55 human languages.
- A message from UN Secretary-General at the time and one from U.S. President Jimmy Carter.
- 115 analog images encoded in the record’s grooves: how to build the stylus and play the record, the solar system’s location using 14 pulsars as galactic GPS, diagrams of human DNA, photos of a supermarket, a sunset, a fetus, people eating, licking ice cream, and dancing
The record is encased in an aluminum jacket with instructions etched on the cover: a map of the pulsars, the hydrogen atom diagram so aliens can decode the time units, and a tiny sample of uranium-238 so they can carbon-date how old the record is when they find it.
Sagan wanted the record to be a message in a bottle for a billion years. The spacecraft themselves are expected to outlive Earth. In a billion years, when the Sun swells into a red giant and maybe swallows Earth, the Voyagers will still be cruising the Milky Way, silent gold disks carrying blind, naked humans waving hello to a universe that may never wave back.
And it was Sagan who, in 1989, when Voyager 1 was already beyond Neptune and its cameras were scheduled to be turned off forever to save power, begged NASA for one last maneuver. On Valentine’s Day 1990, the spacecraft turned around, took 60 final images, and captured Earth as a single pale blue pixel floating in a scattered beam of sunlight — the photograph that gives the book its name and its soul.
It was the photograph that inspired this famous quote -
"Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam.
The Earth is a very small stage in a vast cosmic arena. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot.
Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.
The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.
It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known. "
That picture almost didn’t happen. NASA said it was pointless, the cameras were old, the images would be useless. Sagan argued it would be the first time any human ever saw our world from outside the solar system. He won. The cameras were powered up one last time, the portrait was taken, and then they were shut down forever.
I wish we actually did things quickly instead of taking forever and having a million ethical issues about everything. We know how to get close to light speed. You can just explode nuclear bombs behind you. Why don’t we do it? Worried about a high atmosphere nuclear explosion then just put the bomb and escape shuttle like you do with humans or something. Every goddamn thing takes forever. Oh, we’re gonna go to Mars in 2038 fuck that get some volunteers that are OK with dying and go tomorrow. Oh, we can’t go into human trials until we spent five years doing lab testing fuck that get some people that are terminal and let them try weird drugs that will potentially kill them tomorrow. There are a ridiculous number of people that will sign onto incredibly risky things because they feel passionate about it and are OK with giving up their life for it and we should do it.
Maybe the answer to the Fermi paradox is that the universe is so big that you simply never get anywhere.
No message you send out ever gets far enough for anyone to see it. No ship you send out ever reaches another system. It’s just a big empty void.
You stay in your own lame system, browsing lame terrestrial memes and never escape.
The author Alastair Reynolds talks about this in his sci-fi opera books.
Pushing Ice is a great sci-fi novel.
I really don't want to spoil it, but Reynolds does have something of a solution to the problem of the speed of light being so limiting, and it's based on time dilation. As usual with all things sci-fi, it's not practical, but it's fairly unique and fun to read.
> Maybe the answer to the Fermi paradox is that the universe is so big that you simply never get anywhere.
Yes, that is one of the hypothesis
Another is that technology ends up advancing so fast that the odds of a species blowing themselves up before they get beyond the stars approaches one.
HEY! I mean, the memes aren't terrible..
[dead]
Free space pathloss for rf signals is proportional to 1/r^2, absolutely bonkers we can get anything from voyager.
1/r² is for an isotropic radiator, but Voyager 1 mounts (thankfully) a high gain directional antenna. The gains seem to be 36dBi or 48dBi, depending on the frequency [1]. This means that when pointed towards Earth, the signal power is actually between 4000 to 63000 times stronger than what that formula would give you. It's still tiny, but not as bad as that would suggest.
[1]: https://space.stackexchange.com/questions/65801/what-are-the...
No, it is for any radiator. The gain of the antennas has absolutely nothing to do with the free path loss, it just changes the effective radiated power or the concentration effect of the antenna because of antenna related gains. Every kind of antenna has its own specific gain and corresponding losses diagram based on which way the source is relative to the antenna, with the baseline being an omnidirectional radiator (which no antenna really is, but we assume it is).
GP was very specific when they mentioned free path loss: the implication is that if you know what free path loss is then you also know that those losses are accurately modeled with that formula, no matter how large your ERP or receiver antenna gain is. At those distances it would make zero sense to use an omnidirectional antenna you will need every bit of gain you can get.
For clarity, it’s still proportional to 1/r², but with a much larger multiplier than one.
This is a practical big-O notation question just waiting to happen.
They're totally correct though. Besides that, the performance of this system is incredible and gggp seems to pooh-pooh that.
And with 50 year old tech! I do wonder if humanity will get to a point where we can retrieve the spacecraft at some point in the future (cue Star Trek fantasies)
Technically, the receivers need not use 50 years old tech. I am saying that not to be annoying but because I wonder how much that matters.
Indeed, it could have been obsolete tech as of launch. That's typically how it goes.
I believe they meant that the receivers/transmitters on Earth are likely newer than 50 years old. And you're also probably right that the hardware installed on the voyager could be several years older than the launch date of the craft
https://en.wikipedia.org/wiki/NASA_Deep_Space_Network
I would prefer they just maintain it as long as possible and maybe deploy a proxy for earth that trails behind it indefinitely once it’s finally out of range. Let’s set an unbreakable record.
> the spacecraft, in flight since 1977, is cruising at nearly 38,000 mph (61,000 kph) through the vacuum of space,
The page takes great pains to explain things, but omits a frame of reference for this speed. I’m guessing it’s sun-relative, but it could be relative to its take-off on Earth. Does anyone know?
The Voyager Mission Status page has real-time updating distances, speeds (relative to the Sun), and light times for both Voyagers:
https://science.nasa.gov/mission/voyager/where-are-voyager-1...
You're right that Earth is catching up to the Voyagers during part of its orbit for several months in the early part of the year (and you'll see that reflected on the Mission Status page). Consequently I used to wonder if Voyager 1 would reach 1 light day from Earth 3 times - the first time, then a second time when the Earth distance decreased, and then a third time when distance increased again!
If you scroll down on this TheSkyLive page, you can see a graph of Voyager 1's distance from Earth over time and it's an up-sloping ripple instead of a straight line. You can play with the markers to zoom in and see that the catch-up phase happens in the early part of the year:
https://theskylive.com/voyager1-info
https://theskylive.com/voyager2-info
Checked my bot's post from earlier today (taken from NASA's data[0]) and it says "Velocity relative to the Earth is about 34 km/sec (~77,173 mph); to the Sun about 16 km/sec (~37,763 mph.)"
[0] https://eyes.nasa.gov/assets/dynamic/dynamo/sc_voyager_1/now...
Thanks! And probably the earth relative velocity depends on the time of year :)
Yes, and distance from Earth actually decreased during part of the year (I believe)
And the closest known galaxy to the Milky Way, Canis Major Dwarf Galaxy, is just 25,000 light-years away - it's almost incomprehensible how vast the universe is!
And how slow the speed of light is.
Let's try & figure out interstellar travel first, ok?
Yeah the only space tech worth pursuing is Wormholes
I have bad news about that...
Yep, space-worms in there will eat your starship.
Let's hear them
You can't have wormholes.
Voyager I is leaving the solar system again! [1]
[1] https://xkcd.com/1189/
Lol.
I know it's a joke but it's because there's no clearly defined end of the solar system.
Just re-reading Pale Blue Dot by Carl Sagan and he talks about this. If we define the end of the solar system as the point where the suns gravity no longer holds, then it's going to be a very long time for it to escape the solar system.
I'm going to go find that passage in the book. Hopefully I can find it before the edit window closes for this comment.
Edit:
OK, I found it. This excerpt is from the book "Pale Blue Dot" by Carl Sagan, in the Chapter - AN AMERICAN SHIP AT THE FRONTIERS OF THE SOLAR SYSTEM .
THE VOYAGER SPACECRAFT are bound for the stars. They are on escape trajectories from the Solar System, barreling along at almost a million miles a day. The gravitational fields of Jupiter, Saturn, Uranus, and Neptune have flung them at such high speeds that they have broken the bonds that once tied them to the Sun.
Have they left the Solar System yet? The answer depends very much on how you define the boundary of the Sun's realm. If it's the orbit of the outermost good-sized planet, then the Voyager spacecraft are already long gone; there are probably no undiscovered Neptunes. If you mean the outermost planet, it may be that there are other—perhaps Triton-like—planets far beyond Neptune and Pluto; if so, Voyager 1 and Voyager 2 are still within the Solar System. If you define the outer limits of the Solar System as the heliopause—where the interplanetary particles and magnetic fields are replaced by their interstellar counterparts—then neither Voyager has yet left the Solar System, although they may do so in the next few decades.* But if your definition of the edge of the Solar System is the distance at which our star can no longer hold worlds in orbit about it, then the Voyagers will not leave the Solar System for hundreds of centuries.
Weakly grasped by the Sun's gravity, in every direction in the sky, is that immense horde of a trillion comets or more, the Oort Cloud. The two spacecraft will finish passage through the Oort Cloud in another 20,000 years or so. Then, at last, completely gone long good-bye to the Solar System, broken free of the gravitational shackles that once bound them to the Sun, the Voyagers will make for the open sea of interstellar space. Only then will Phase Two of their mission begin.
Their radio transmitters long dead, the spacecraft will wander for ages in the calm, cold interstellar blackness—where there is almost nothing to erode them. Once out of the Solar System, they will remain intact for a billion years or more, as they circumnavigate the center of the Milky Way galaxy.
We do not know whether there are other spacefaring civilizations in the Milky Way. If they do exist, we do not know how abundant they are, much less where they are. But there is at least a chance that sometime in the remote future one of the Voyagers will be intercepted and examined by an alien craft.
*Radio signals that both Voyagers detected in 1992 are thought to arise from the collision of powerful gusts of solar wind with the thin gas that lies between the stars. From the immense power of the signal (over 10 trillion watts), the distance to the heliopause can be estimated: about 100 times the Earth's distance from the Sun. At the speed it's leaving the Solar System, Voyager 1 might pierce the heliopause and enter interstellar space around the year 2010. If its radioactive power source is still working, news of the crossing will be radioed back to the stay-at-homes on Earth. The energy released by the collision of this shock wave with the heliopause makes it the most powerful source of radio emission in the Solar System. It makes you wonder whether even stronger shocks in other planetary systems might be detectable by our radio telescopes.
End of quotation.
If you're interested, I highly recommend the book and everything by Carl Sagan. He was incapable of writing a dull sentence.
Wrote down some of my thoughts on the Voyager probes in my blog here - https://www.rxjourney.net/30-things-i-know
So it is traveling 1/18250 the speed of light. That is pretty fast.
Well, consider that the speed of light itself is pretty slow, relative to what people's perception of the speed of light is. Even if you had a spaceship traveling at 99.99%, it'd take a surprisingly long time even to reach the Oort cloud.
A month or so for you. Enough time to catch up on a few favorite shows and finish a few books. Now if anyone is waiting for you on earth, they will wait considerably longer
Actually - to reach the start of the Oort Cloud from Earth it'd take around 4 hours. That's 2000 AU. The observer on Earth will see it as about 12 days. This is assuming 99.99% of the speed of light which is completely unrealistic of course.
is there a way for Voyager 1 to be still accelerating? like, maybe it is unwanted, but could it, theoretically?
I'm just going to repost stuff from my blog about the Voyager space probes. I've posted this here before - The two Voyager spacecraft are the greatest love letters humanity has ever sent into the void.
Voyager 2 actually launched first, on August 20, 1977, followed by Voyager 1 on September 5, 1977. Because Voyager 1 was on a faster, shorter trajectory (it used a rare alignment to slingshot past both Jupiter and Saturn quicker), it overtook its twin and became the farther, faster probe. As of 2025, Voyager 1 is the most distant human-made object ever, more than 24 billion kilometers away, still whispering data home at 160 bits per second.
Each spacecraft carries an identical 12-inch gold-plated copper phonograph record.
The contents:
- Greetings in 55 human languages.
- A message from UN Secretary-General at the time and one from U.S. President Jimmy Carter.
- 115 analog images encoded in the record’s grooves: how to build the stylus and play the record, the solar system’s location using 14 pulsars as galactic GPS, diagrams of human DNA, photos of a supermarket, a sunset, a fetus, people eating, licking ice cream, and dancing
The record is encased in an aluminum jacket with instructions etched on the cover: a map of the pulsars, the hydrogen atom diagram so aliens can decode the time units, and a tiny sample of uranium-238 so they can carbon-date how old the record is when they find it.
Sagan wanted the record to be a message in a bottle for a billion years. The spacecraft themselves are expected to outlive Earth. In a billion years, when the Sun swells into a red giant and maybe swallows Earth, the Voyagers will still be cruising the Milky Way, silent gold disks carrying blind, naked humans waving hello to a universe that may never wave back.
And it was Sagan who, in 1989, when Voyager 1 was already beyond Neptune and its cameras were scheduled to be turned off forever to save power, begged NASA for one last maneuver. On Valentine’s Day 1990, the spacecraft turned around, took 60 final images, and captured Earth as a single pale blue pixel floating in a scattered beam of sunlight — the photograph that gives the book its name and its soul.
It was the photograph that inspired this famous quote -
"Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam.
The Earth is a very small stage in a vast cosmic arena. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot.
Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.
The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.
It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known. "
That picture almost didn’t happen. NASA said it was pointless, the cameras were old, the images would be useless. Sagan argued it would be the first time any human ever saw our world from outside the solar system. He won. The cameras were powered up one last time, the portrait was taken, and then they were shut down forever.
- https://www.rxjourney.net/30-things-i-know
I wish we actually did things quickly instead of taking forever and having a million ethical issues about everything. We know how to get close to light speed. You can just explode nuclear bombs behind you. Why don’t we do it? Worried about a high atmosphere nuclear explosion then just put the bomb and escape shuttle like you do with humans or something. Every goddamn thing takes forever. Oh, we’re gonna go to Mars in 2038 fuck that get some volunteers that are OK with dying and go tomorrow. Oh, we can’t go into human trials until we spent five years doing lab testing fuck that get some people that are terminal and let them try weird drugs that will potentially kill them tomorrow. There are a ridiculous number of people that will sign onto incredibly risky things because they feel passionate about it and are OK with giving up their life for it and we should do it.
[flagged]
[dead]
So glad voyager has real stuff on it for aliens to see rather than the crap that’s put out today by those with an agenda