The Long Goodbye
September 12, 2013 4:21 PM Subscribe
i feel so small
posted by blue t-shirt at 4:27 PM on September 12, 2013
posted by blue t-shirt at 4:27 PM on September 12, 2013
The craziest part to me is that they're even still capable of communicating with the probe.
From the NASA update:
"Voyager mission controllers still talk to or receive data from Voyager 1 and Voyager 2 every day, though the emitted signals are currently very dim, at about 23 watts -- the power of a refrigerator light bulb. By the time the signals get to Earth, they are a fraction of a billion-billionth of a watt. Data from Voyager 1's instruments are transmitted to Earth typically at 160 bits per second, and captured by 34- and 70-meter NASA Deep Space Network stations."
Monitoring a 23W light bulb from 12 billion miles? That's almost as bad as trying to get a bar's worth of AT&T's 3G signal in the Valley area near Los Angeles. And trust me, that's bad.
posted by Hairy Lobster at 4:29 PM on September 12, 2013 [12 favorites]
From the NASA update:
"Voyager mission controllers still talk to or receive data from Voyager 1 and Voyager 2 every day, though the emitted signals are currently very dim, at about 23 watts -- the power of a refrigerator light bulb. By the time the signals get to Earth, they are a fraction of a billion-billionth of a watt. Data from Voyager 1's instruments are transmitted to Earth typically at 160 bits per second, and captured by 34- and 70-meter NASA Deep Space Network stations."
Monitoring a 23W light bulb from 12 billion miles? That's almost as bad as trying to get a bar's worth of AT&T's 3G signal in the Valley area near Los Angeles. And trust me, that's bad.
posted by Hairy Lobster at 4:29 PM on September 12, 2013 [12 favorites]
Voyager has reached a state of constantly leaving but never quite arriving.
posted by 2bucksplus at 4:30 PM on September 12, 2013 [5 favorites]
posted by 2bucksplus at 4:30 PM on September 12, 2013 [5 favorites]
"Voyager, in case it's ever encountered by extraterrestrials, is carrying photos of life on Earth, greetings in 55 languages, and a collection of music from Gregorian chants to Chuck Berry... including 'Dark Was The Night, Cold Was The Ground' by '20s bluesman Blind Willie Johnson, whose stepmother blinded him when he was seven by throwing lye in his eyes after his father had beat her for being with another man. He died, penniless, of pneumonia after sleeping bundled in wet newspapers in the ruins of his house that burned down. But his music just left the solar system." --famous reference to Johnson from The West Wing.
Dark Was the Night, Cold Was the Ground
posted by DirtyOldTown at 4:31 PM on September 12, 2013 [16 favorites]
Dark Was the Night, Cold Was the Ground
posted by DirtyOldTown at 4:31 PM on September 12, 2013 [16 favorites]
Sweet, more solar radiation for the rest of us.
posted by Brandon Blatcher at 4:34 PM on September 12, 2013 [1 favorite]
posted by Brandon Blatcher at 4:34 PM on September 12, 2013 [1 favorite]
Different probe, but this was what Star Trek I was about, right? I mean, should we really be applauding this development?
posted by Admiral Haddock at 4:36 PM on September 12, 2013 [3 favorites]
posted by Admiral Haddock at 4:36 PM on September 12, 2013 [3 favorites]
I don't get why everyone is celebrating this. Am I the only person who has seen the original Star Trek movie? THIS IS HOW IT STARTS!
posted by NotMyselfRightNow at 4:38 PM on September 12, 2013 [1 favorite]
posted by NotMyselfRightNow at 4:38 PM on September 12, 2013 [1 favorite]
...and Admiral Haddock and I are clearly on the same page on this one.
posted by NotMyselfRightNow at 4:38 PM on September 12, 2013 [1 favorite]
posted by NotMyselfRightNow at 4:38 PM on September 12, 2013 [1 favorite]
Sometimes when I want a big long cathartic cry I read the " music" section of the voyager 1 golden record Wikipedia entry.
posted by The Whelk at 4:40 PM on September 12, 2013 [2 favorites]
posted by The Whelk at 4:40 PM on September 12, 2013 [2 favorites]
Voyager Captures Sounds of Interstellar Space
posted by Blazecock Pileon at 4:40 PM on September 12, 2013 [2 favorites]
posted by Blazecock Pileon at 4:40 PM on September 12, 2013 [2 favorites]
Again? Didn't it do this last year? Am I stuck in some kind of temporal loop where Voyager exits the solar system once a year? IS THIS TEMPORAL LOOP CAUSED BY VOYAGER EXITING THE SOLAR SYSTEM?
I'm scared
posted by axiom at 4:41 PM on September 12, 2013 [19 favorites]
I'm scared
posted by axiom at 4:41 PM on September 12, 2013 [19 favorites]
Just outside the solar system, a giant paddle slowly starts to drift downward towards the galactic core.
Voyager will be back.
posted by robocop is bleeding at 4:42 PM on September 12, 2013 [7 favorites]
Voyager will be back.
posted by robocop is bleeding at 4:42 PM on September 12, 2013 [7 favorites]
Monitoring a 23W light bulb from 12 billion miles?
There is a big difference between the little strip of copper that your phone has for an antenna and a steerable 70 meter diameter dish. About 100db worth of difference.
That means that, if the antenna is pointed correctly, it will have the same signal from a source that's one ten billionth the power.
Of course, your cellphone fits into a pocket and doesn't have to be pointed in a particular direction.
posted by eriko at 4:42 PM on September 12, 2013 [2 favorites]
There is a big difference between the little strip of copper that your phone has for an antenna and a steerable 70 meter diameter dish. About 100db worth of difference.
That means that, if the antenna is pointed correctly, it will have the same signal from a source that's one ten billionth the power.
Of course, your cellphone fits into a pocket and doesn't have to be pointed in a particular direction.
posted by eriko at 4:42 PM on September 12, 2013 [2 favorites]
Or, to put it another way: the gain of th 70m dishes on the DSN turns that 23W transmitter at 1.2 billion miles into the same signal level as a 230W transmitter at just over a mile.
posted by eriko at 4:46 PM on September 12, 2013 [5 favorites]
posted by eriko at 4:46 PM on September 12, 2013 [5 favorites]
When you think about the ratio between gain and diameter of a dish, the more amazing part is that you can pick up a reliable TV signal and decode it from a geostationary satellite 36,000 km away on a tiny satellite TV dish measuring only 70 cm in diameter. In some areas of earth such as Israel and Arabia the Ku-band spot beam gain (added by a satellite's transponder) is as much as 52dB.
posted by thewalrus at 4:51 PM on September 12, 2013
posted by thewalrus at 4:51 PM on September 12, 2013
eriko: your cold hard science can not destroy my childlike sense of wonder.
posted by Hairy Lobster at 4:53 PM on September 12, 2013 [6 favorites]
posted by Hairy Lobster at 4:53 PM on September 12, 2013 [6 favorites]
Voyager, in case it's ever encountered by extraterrestrials, is carrying photos of life on Earth, greetings in 55 languages, and a collection of music from Gregorian chants to Chuck Berry
Fun fact: The golden record was a minor plot point in John Carpenter's Starman, in which the alien arrives on Earth speaking English -- and imitating Dag Hammarskjöld and Mick Jagger.
posted by Gelatin at 4:55 PM on September 12, 2013 [4 favorites]
Fun fact: The golden record was a minor plot point in John Carpenter's Starman, in which the alien arrives on Earth speaking English -- and imitating Dag Hammarskjöld and Mick Jagger.
posted by Gelatin at 4:55 PM on September 12, 2013 [4 favorites]
I love the idea of the gold records.
I'm not as hopeful that anyone out there will be able to decode the playing instructions.
Bon voyage, Voyager!
posted by Thorzdad at 4:56 PM on September 12, 2013 [3 favorites]
I'm not as hopeful that anyone out there will be able to decode the playing instructions.
Bon voyage, Voyager!
posted by Thorzdad at 4:56 PM on September 12, 2013 [3 favorites]
"Seriously, I mean it. This time I'm really leaving."
posted by relish at 5:02 PM on September 12, 2013 [3 favorites]
posted by relish at 5:02 PM on September 12, 2013 [3 favorites]
When the last man has breathed his last, when the Earth lies cold and exhausted, when the sun itself burns through its fuel, balloons up into a red giant, then collapses into a white dwarf, then cools off for billions of years, through it all, Voyager I will probably sail on.
I had an idea for a comic story along these lines once, I never got around to illustrating it, but I remain hopeful it can be produced, someday.
posted by JHarris at 5:07 PM on September 12, 2013
I had an idea for a comic story along these lines once, I never got around to illustrating it, but I remain hopeful it can be produced, someday.
posted by JHarris at 5:07 PM on September 12, 2013
axiom: "Again? Didn't it do this last year? Am I stuck in some kind of temporal loop where Voyager exits the solar system once a year? IS THIS TEMPORAL LOOP CAUSED BY VOYAGER EXITING THE SOLAR SYSTEM?"
You and me both. Hell, I remember thinking "Didn't it do that already?" last time this was in the news. We're not making stuff up, are we? Are there just different definitions of "outside" that V'Ger keeps passing?
posted by brundlefly at 5:10 PM on September 12, 2013
You and me both. Hell, I remember thinking "Didn't it do that already?" last time this was in the news. We're not making stuff up, are we? Are there just different definitions of "outside" that V'Ger keeps passing?
posted by brundlefly at 5:10 PM on September 12, 2013
It takes about 17 hours for its signal to reach Earth.
17 light hours away. The solar system is a big place compared to itty bitty us.
posted by double block and bleed at 5:13 PM on September 12, 2013
17 light hours away. The solar system is a big place compared to itty bitty us.
posted by double block and bleed at 5:13 PM on September 12, 2013
Voyager will be back.
posted by figurant at 5:14 PM on September 12, 2013 [4 favorites]
...Mission Control flips us onto our backs, keeps us fixed on target past any realistic hope of acquisition. They send last-ditch instructions, squeeze our fading signals for every last bit among the static. I can sense their frustration, their reluctance to let us go; once or twice, we're even asked if some judicious mix of thrust and gravity might let us linger here a bit longer.Peter Watts, Blindsight
But deceleration is for pansies. We're headed for the stars.
Bye, Burnsie. Bye, Mission Control. Bye, Sol.
See you at heat death.
posted by figurant at 5:14 PM on September 12, 2013 [4 favorites]
Are there just different definitions of "outside" that V'Ger keeps passing?
That is exactly what's happening.
posted by escape from the potato planet at 5:14 PM on September 12, 2013 [1 favorite]
That is exactly what's happening.
posted by escape from the potato planet at 5:14 PM on September 12, 2013 [1 favorite]
Awesome.
posted by homunculus at 5:17 PM on September 12, 2013
posted by homunculus at 5:17 PM on September 12, 2013
*cough* *cough*
Obligatory xkcd.
Knew I had something stuck in there.
posted by sysinfo at 5:23 PM on September 12, 2013 [4 favorites]
Obligatory xkcd.
Knew I had something stuck in there.
posted by sysinfo at 5:23 PM on September 12, 2013 [4 favorites]
There was no question that the Voyager spacecraft would someday become the first objects made by human beings to get thereI, for one, was holding out hope that Zefram Cochrane would overtake it.
posted by Flunkie at 5:27 PM on September 12, 2013 [2 favorites]
You and me both. Hell, I remember thinking "Didn't it do that already?" last time this was in the news. We're not making stuff up, are we? Are there just different definitions of "outside" that V'Ger keeps passing?
From the article I read on The Guardian this morning:
"The Voyager team waited for a change in magnetic field direction which they thought would signify departure from the solar system. But a solar eruption caused the space around Voyager 1 to echo like a bell last spring. This additional information convinced scientists the boundary was crossed in August last year."
So, yeah. They thought it might have left last year but weren't certain. Then the "bell" struck providing the extra data needed to firm up the assumption.
posted by michswiss at 5:50 PM on September 12, 2013
From the article I read on The Guardian this morning:
"The Voyager team waited for a change in magnetic field direction which they thought would signify departure from the solar system. But a solar eruption caused the space around Voyager 1 to echo like a bell last spring. This additional information convinced scientists the boundary was crossed in August last year."
So, yeah. They thought it might have left last year but weren't certain. Then the "bell" struck providing the extra data needed to firm up the assumption.
posted by michswiss at 5:50 PM on September 12, 2013
I am not even kidding when I tell you this shit is what gives me hope for humanity. With everything, it's still a great time to be alive.
posted by Space Kitty at 6:00 PM on September 12, 2013 [8 favorites]
posted by Space Kitty at 6:00 PM on September 12, 2013 [8 favorites]
It has been said before (not by me) that Voyager I leaving the solar system is much like stepping out of the ocean. As you walk up the beach onto the sand, waves continue to crash and flow up around your feet. Being out-of-the-ocean is difficult to define with certitude until well after it's truly done.
posted by rlk at 6:07 PM on September 12, 2013 [3 favorites]
posted by rlk at 6:07 PM on September 12, 2013 [3 favorites]
Damn it, I want to see self-replicating robot explorer swarms bootstrapping themselves in stages outwards into the great empty with an imperative to just GO MAN GO and SEND DATA HOME before I die.
What could go wrong?
posted by stavrosthewonderchicken at 6:29 PM on September 12, 2013 [1 favorite]
What could go wrong?
posted by stavrosthewonderchicken at 6:29 PM on September 12, 2013 [1 favorite]
in fact i just read on BB that the oort cloud is 50,000 AU from the sun. voyager 1 is currently 125 AU from the sun. the oort cloud is under the sun's gravitational influence... i mean anything at any distance is since the gravity field never quite reaches zero... but there are comets and stuff in the oort cloud, so not exactly insignificant stuff.
if you really want to feel small and have iOS, get the exoplanet app. you can see how far the two voyagers are away from earth... and keep zooming out, and zooming out and zooming out until you finally reach the nearest stars to the sun. voyager is exactly nowhere - it's practically still on our doorstep. the closest star is 265,000+ AU from the sun.
posted by joeblough at 6:56 PM on September 12, 2013 [1 favorite]
if you really want to feel small and have iOS, get the exoplanet app. you can see how far the two voyagers are away from earth... and keep zooming out, and zooming out and zooming out until you finally reach the nearest stars to the sun. voyager is exactly nowhere - it's practically still on our doorstep. the closest star is 265,000+ AU from the sun.
posted by joeblough at 6:56 PM on September 12, 2013 [1 favorite]
If I told you how much I needed this, I wouldn't have time to eat it.
posted by Sphinx at 7:03 PM on September 12, 2013 [1 favorite]
posted by Sphinx at 7:03 PM on September 12, 2013 [1 favorite]
When the last man has breathed his last, when the Earth lies cold and exhausted, when the sun itself burns through its fuel, balloons up into a red giant, then collapses into a white dwarf, then cools off for billions of years, through it all, Voyager I will probably sail on.
My best friend from childhood's father was an electrician in the Air Force and worked at Cape Canaveral in the 1970s. He told us he did some work for the Voyager project. As he put it, "I soldered one little box in one little corner of Voyager."
He died when we were 11 years old of a heart attack. It was an awful tragedy for the family and for me, too, because I didn't have a father and I idolized him. And yet, that one little box in the one little corner of Voyager that he worked on will outlast the entire solar system. One of the many, many reasons I have loved to follow the Voyager projects over the years is because it makes me think of him, and the thousands of others who made little contributions to this project, humanity's ambassadors to the stars.
I forwarded this story on to my friend and his family this morning.
posted by vibrotronica at 7:12 PM on September 12, 2013 [26 favorites]
My best friend from childhood's father was an electrician in the Air Force and worked at Cape Canaveral in the 1970s. He told us he did some work for the Voyager project. As he put it, "I soldered one little box in one little corner of Voyager."
He died when we were 11 years old of a heart attack. It was an awful tragedy for the family and for me, too, because I didn't have a father and I idolized him. And yet, that one little box in the one little corner of Voyager that he worked on will outlast the entire solar system. One of the many, many reasons I have loved to follow the Voyager projects over the years is because it makes me think of him, and the thousands of others who made little contributions to this project, humanity's ambassadors to the stars.
I forwarded this story on to my friend and his family this morning.
posted by vibrotronica at 7:12 PM on September 12, 2013 [26 favorites]
Or, to put it another way: the gain of th 70m dishes on the DSN turns that 23W transmitter at 1.2 billion miles into the same signal level as a 230W transmitter at just over a mile.
You have a few errors in that calculation that make a big difference.
First off the gain of the 70m receiver is only about 74 dB, a reduction in gain of 400 from your 100 db number.
Second, free-space path loss is not linear but instead proportional to the square of the distance. So each doubling of distance requires four times the power or 6 dB.
So 74 dB /6 dB = 12.33 doublings of distance
2^12.33 = 5148 times the distance
Third, the current distance is 11 billion not 1.2 billion miles.
11 billion/5148 = over 2 million miles or about 8 times the distance to the moon.
So it would be like a zero gain antenna picking up a 23 W transmitter at 8 times the distance of the moon. Quite impressive. And why the bit rate is only 160 bps.
posted by JackFlash at 7:33 PM on September 12, 2013 [1 favorite]
You have a few errors in that calculation that make a big difference.
First off the gain of the 70m receiver is only about 74 dB, a reduction in gain of 400 from your 100 db number.
Second, free-space path loss is not linear but instead proportional to the square of the distance. So each doubling of distance requires four times the power or 6 dB.
So 74 dB /6 dB = 12.33 doublings of distance
2^12.33 = 5148 times the distance
Third, the current distance is 11 billion not 1.2 billion miles.
11 billion/5148 = over 2 million miles or about 8 times the distance to the moon.
So it would be like a zero gain antenna picking up a 23 W transmitter at 8 times the distance of the moon. Quite impressive. And why the bit rate is only 160 bps.
posted by JackFlash at 7:33 PM on September 12, 2013 [1 favorite]
Voyager has reached a state of constantly leaving but never quite arriving.
Always leaving but never quite departing. Haven't we all had a lingering houseguest like this?
posted by ricochet biscuit at 7:45 PM on September 12, 2013
Always leaving but never quite departing. Haven't we all had a lingering houseguest like this?
posted by ricochet biscuit at 7:45 PM on September 12, 2013
And one more "previously on Metafilter" AKA the only FPP I've ever made:
Dear Earth: Send More Chuck Berry
posted by Hadroed at 8:12 PM on September 12, 2013 [3 favorites]
Dear Earth: Send More Chuck Berry
posted by Hadroed at 8:12 PM on September 12, 2013 [3 favorites]
2013
Voyager 1
Ok, we finally did it! We've reached Instellar Space! Look at that! It's beau - HEY YOU GUYS! STOP FIGHTING!
Earth
[grabbing sisters arm and flailing it about] Stop hitting yourself! How come you keep hitting yourself? Hey, stop hitting yourself!
posted by CynicalKnight at 9:11 PM on September 12, 2013
Voyager 1
Ok, we finally did it! We've reached Instellar Space! Look at that! It's beau - HEY YOU GUYS! STOP FIGHTING!
Earth
[grabbing sisters arm and flailing it about] Stop hitting yourself! How come you keep hitting yourself? Hey, stop hitting yourself!
posted by CynicalKnight at 9:11 PM on September 12, 2013
Voyager boldly goes beyond our stars --The Australian
Well, beyond the black stump, anyway.
posted by weapons-grade pandemonium at 9:50 PM on September 12, 2013
Well, beyond the black stump, anyway.
posted by weapons-grade pandemonium at 9:50 PM on September 12, 2013
beep, beepbeep, beepbeepbeep.
Oh, for fuck's sake, it's back.
Oh, it's you again! You forgot your K-Tel record? Did you also forget this little nudie plaque we found behind the couch? No, that belongs to the Pioneer twins? But you'll give it to them when you see them? Sure... let me just put that all in a bag for you. Bye again! Bye!
Quick, turn out the lights!
posted by pracowity at 12:38 AM on September 13, 2013
Oh, for fuck's sake, it's back.
Oh, it's you again! You forgot your K-Tel record? Did you also forget this little nudie plaque we found behind the couch? No, that belongs to the Pioneer twins? But you'll give it to them when you see them? Sure... let me just put that all in a bag for you. Bye again! Bye!
Quick, turn out the lights!
posted by pracowity at 12:38 AM on September 13, 2013
I, for one, was holding out hope that Zefram Cochrane would overtake it.
Grr, argh.
Up until the big galactic retcon, the history I studied was that Cochrane was FROM Alpha Centauri ( see Star Trek Spaceflight Chronology Stan Goldstein and Fred Goldstein, illustrated by Rick Sternbach Wallaby (Pocket) )
Therefore, he's going to pass it on the way IN.
posted by mikelieman at 8:24 AM on September 13, 2013
Grr, argh.
Up until the big galactic retcon, the history I studied was that Cochrane was FROM Alpha Centauri ( see Star Trek Spaceflight Chronology Stan Goldstein and Fred Goldstein, illustrated by Rick Sternbach Wallaby (Pocket) )
Therefore, he's going to pass it on the way IN.
posted by mikelieman at 8:24 AM on September 13, 2013
I mean, should we really be applauding this development?
No, no...it's cool. V'Ger was Voyager 6, so we don't have to start worrying for another four probes.
Three Wolf Moon Shirt Man...AWAAAAAYYYY!
posted by Mr. Bad Example at 8:26 AM on September 13, 2013
No, no...it's cool. V'Ger was Voyager 6, so we don't have to start worrying for another four probes.
Three Wolf Moon Shirt Man...AWAAAAAYYYY!
posted by Mr. Bad Example at 8:26 AM on September 13, 2013
First off the gain of the 70m receiver is only about 74 dB, a reduction in gain of 400 from your 100 db number.
Well, I shanked it, but I didn't, because in being very tired and somewhat drunk, I sort of forgot to mention the rest of the equation.
You are correct that the receiver gain from the antenna is 74dBi. There are preamps and such, but they're really there just to reduce some of the losses moving through the system from the antenna reflector to the final receiver.
Voyager has a 23W transmitter. But Voyager doesn't have an omni antenna. It has a 3.7m parabolic antenna, which has 49.8dB gain itself, and results in an EIRP of 2.16MW(!) However, there's a bunch of loss elsewhere (just wave-guide/wire loss is pretty staggering in X-Band, and there's enough free space that there's enough matter to affect the signal) so I handwaved away about 25db of gain from that. And 76-49-25 is about 100db.
I did *completely* shank the distance. So we're down to a 23W system at a mile.
Remember kids, sometimes, you're just wrong. Acknowledge that and correct.
Compare this to the Pioneer 11 system, which has a 2.7M antenna in the S band, so only 33dB transmitter gain, and only 8W transmit power, so an EIRP of only 48KW, which is why we can still hear Voyager, but we can't hear Pioneer 11, despite Pioneer 11 being closer.
This is also why Galileo had so much trouble with data transmission. When the high gain antenna didn't unfold, they lost all that antenna gain. The low gain antenna resulting in an EIRP of 20W, by the time it hit the receiver, they were down to 10-20watts. And yet, we could dig out that -170dbm signal. You can see what a *huge* different the transmitter antenna makes here -- five orders of magnitude more power. (Comparison -- Voyager at Jupiter, with the high gain antenna, could broadcast at 0.002W and put about as much signal into the receiver as Galileo did -- and your cellphone with that sort of antenna (.5W into 49dB gain) would have been about 2000 times louder.
Minus path and other losses, of course. :)
posted by eriko at 9:26 AM on September 13, 2013
Well, I shanked it, but I didn't, because in being very tired and somewhat drunk, I sort of forgot to mention the rest of the equation.
You are correct that the receiver gain from the antenna is 74dBi. There are preamps and such, but they're really there just to reduce some of the losses moving through the system from the antenna reflector to the final receiver.
Voyager has a 23W transmitter. But Voyager doesn't have an omni antenna. It has a 3.7m parabolic antenna, which has 49.8dB gain itself, and results in an EIRP of 2.16MW(!) However, there's a bunch of loss elsewhere (just wave-guide/wire loss is pretty staggering in X-Band, and there's enough free space that there's enough matter to affect the signal) so I handwaved away about 25db of gain from that. And 76-49-25 is about 100db.
I did *completely* shank the distance. So we're down to a 23W system at a mile.
Remember kids, sometimes, you're just wrong. Acknowledge that and correct.
Compare this to the Pioneer 11 system, which has a 2.7M antenna in the S band, so only 33dB transmitter gain, and only 8W transmit power, so an EIRP of only 48KW, which is why we can still hear Voyager, but we can't hear Pioneer 11, despite Pioneer 11 being closer.
This is also why Galileo had so much trouble with data transmission. When the high gain antenna didn't unfold, they lost all that antenna gain. The low gain antenna resulting in an EIRP of 20W, by the time it hit the receiver, they were down to 10-20watts. And yet, we could dig out that -170dbm signal. You can see what a *huge* different the transmitter antenna makes here -- five orders of magnitude more power. (Comparison -- Voyager at Jupiter, with the high gain antenna, could broadcast at 0.002W and put about as much signal into the receiver as Galileo did -- and your cellphone with that sort of antenna (.5W into 49dB gain) would have been about 2000 times louder.
Minus path and other losses, of course. :)
posted by eriko at 9:26 AM on September 13, 2013
There's enough free space that there's enough matter to affect the signal) so I handwaved away about 25db of gain from that. So we're down to a 23W system at a mile.
No, the attenuation due to free-space path loss has nothing to do with dust or other matter in the path. It has to do with simple geometric inverse square law. The signal is attenuated by the square of the distance.
If you work out the numbers for the Voyager distance, the attenuation due to free-space path loss is 315 dB, not 25 dB. With 50 dB of Tx antenna gain and 75 dB of Rx antenna gain, your full path attenuation is 75+50-315=190 dB which is one ten-billionth of a billionth of the original 23W signal.
And if you eliminate the gain of the antennas on both ends, then it is the equivalent of a 23W transmitter at about the distance to the moon, again including free-space path loss. (In my earlier back of envelop calculation I neglected the effect of aperture loss for the 8 GHz frequency and did not include Tx gain).
As the article states, they really are picking up a signal of less than a billionth of a billionth of a watt, even after the gain of the TX and RX antennas. This is quite impressive.
23W at 1 mile is doesn't even pass the common sense test. That is more power than the typical cell tower. We wouldn't be talking at 160 bps. We would be streaming live video from Voyager.
posted by JackFlash at 12:13 PM on September 13, 2013 [1 favorite]
No, the attenuation due to free-space path loss has nothing to do with dust or other matter in the path. It has to do with simple geometric inverse square law. The signal is attenuated by the square of the distance.
If you work out the numbers for the Voyager distance, the attenuation due to free-space path loss is 315 dB, not 25 dB. With 50 dB of Tx antenna gain and 75 dB of Rx antenna gain, your full path attenuation is 75+50-315=190 dB which is one ten-billionth of a billionth of the original 23W signal.
And if you eliminate the gain of the antennas on both ends, then it is the equivalent of a 23W transmitter at about the distance to the moon, again including free-space path loss. (In my earlier back of envelop calculation I neglected the effect of aperture loss for the 8 GHz frequency and did not include Tx gain).
As the article states, they really are picking up a signal of less than a billionth of a billionth of a watt, even after the gain of the TX and RX antennas. This is quite impressive.
23W at 1 mile is doesn't even pass the common sense test. That is more power than the typical cell tower. We wouldn't be talking at 160 bps. We would be streaming live video from Voyager.
posted by JackFlash at 12:13 PM on September 13, 2013 [1 favorite]
Phil Plait: Voyager 1 Reaches Interstellar Space. But Has It Left the Solar System? Wellllll…
posted by homunculus at 1:54 PM on September 13, 2013
posted by homunculus at 1:54 PM on September 13, 2013
Metafilter: "cold hard science can not destroy my childlike sense of wonder."
posted by Mitheral at 8:13 PM on September 13, 2013
posted by Mitheral at 8:13 PM on September 13, 2013
For anyone interested in the nuts and bolts of deep space telecom, the Descanso series is invaluable. The Voyager report includes a full and detailed link budget.
posted by Rhomboid at 11:46 PM on September 13, 2013
posted by Rhomboid at 11:46 PM on September 13, 2013
Thanks, Rhomboid. Table 5-3, page 26 shows what we have been discussing. They have numbers very close to my back of envelop calculation for gain:
48.2 dB for Tx antenna gain, -308.19 dB for space loss, and 74.01 for Rx antenna gain for a total path loss of -186 dB. The difference from my estimate is accounted for by the shorter distance they used for their sample calculation, 7.2 billion kilometers then vs 17.5 billion kilometers today.
The received signal coming out of their dish is less than a billionth of a billionth of the transmitted signal. To detect such a tiny signal they have an extraordinarily sensitive radio receiver. If you had a receiver that sensitive in your cell phone, you would be able to talk directly from a cell tower in New York to a phone in Los Angeles. "Can you hear me now?"
This was all done with 1970s technology. Those people really knew their stuff.
posted by JackFlash at 11:37 AM on September 14, 2013
48.2 dB for Tx antenna gain, -308.19 dB for space loss, and 74.01 for Rx antenna gain for a total path loss of -186 dB. The difference from my estimate is accounted for by the shorter distance they used for their sample calculation, 7.2 billion kilometers then vs 17.5 billion kilometers today.
The received signal coming out of their dish is less than a billionth of a billionth of the transmitted signal. To detect such a tiny signal they have an extraordinarily sensitive radio receiver. If you had a receiver that sensitive in your cell phone, you would be able to talk directly from a cell tower in New York to a phone in Los Angeles. "Can you hear me now?"
This was all done with 1970s technology. Those people really knew their stuff.
posted by JackFlash at 11:37 AM on September 14, 2013
Although, to be fair, your cell phone doesn't have an LNA that's cryogenically cooled to 13K by liquid helium to reduce Johnson noise, and it's not receiving on an X-band channel that's internationally reserved as an interference-free quiet zone for the exclusive use of sensitive deep space instrumentation.
posted by Rhomboid at 1:35 PM on September 14, 2013
posted by Rhomboid at 1:35 PM on September 14, 2013
>This was all done with 1970s technology. Those people really knew their stuff.
We went to the moon using 1960's technology. With 1970's technology, we were supposed to get solar power satellites, lunar and mars colonies and eventually colonize the asteroid belt and beyond.
Fucking Nixon.
posted by mikelieman at 2:03 PM on September 14, 2013
We went to the moon using 1960's technology. With 1970's technology, we were supposed to get solar power satellites, lunar and mars colonies and eventually colonize the asteroid belt and beyond.
Fucking Nixon.
posted by mikelieman at 2:03 PM on September 14, 2013
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