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I don’t understand why we are not sending these off in every direction constantly. The price can’t possibly be that prohibitive considering what we can accompli

I don’t understand why we are not sending these off in every direction constantly. The price can’t possibly be that prohibitive considering what we can accomplish with 40 year old technology.

causi 3y ago
The Voyagers took advantage of a particularly good planetary alignment for gravity boosts.
AllegedAlec 3y ago
The equivalent of about 4 billion dollars in modern day money for both of them. That, plus waiting for some very opportune launch times so that we can gravity boost off of everything.
- HappyDaoDude 3y ago
  Those gravitational boosts are vital. The closest in speed so far would be 'New Horizons'. But even then NH is going at 14.5KM/sec compared with Voyagers 18KM/sec. There are no probes currently that would catch up to Voyager.
  - samtho 3y ago
    18km/s is almost understated in terms of speed, so I looked it up to more familiar measures of speed: 65,000kph or 40,000mph. The only thing I really learned here was how even in the thousands of miles or km per hour, it’s just inconceivable how fast that is. Km per second was a better measure after all.
    - heavyset_go 3y ago
      > it’s just inconceivable how fast that is And even more inconceivable is how slow it still is in terms of human spaceflight outside of the Solar System.
    - 14 3y ago
      What is crazy to me is that even at those speeds, it is over 18,000 years from reaching one light year distance. The closest star is 4.2 light years away. So to ever reach it we would need multi generational ships or some way to go much much faster.
    - ta1243 3y ago
      Round the world in 40 minutes Travelling from New York to LA quicker than playing the song "From New York To LA"
- grishka 3y ago
  But the more copies you make of something, the cheaper they become. The R&D cost is the same and is only paid once whether you're building 2 space probes or 2000.
  - tg16 3y ago
    The probe itself is a relatively insignificant cost. The launch costs and timing windows are the limiting factor. The tyranny of the rocket equation is the fact that to carry more fuel to orbit, you need more fuel to get it into orbit, which itself needs more fuel. That's why gravity assists are so essential for escaping the solar system on a budget. The planetary alignment that enabled the Voyager launch windows only occurs once every 175 years. We should definitely be sending out more probes, but we can't just do it whenever we want, at least not without a lot more expense.
    - dredmorbius 3y ago
      The specific alignment for the Voyager missions was to permit flybyes of all the gas giants: Jupiter, Saturn, Uranus, and Neptune, with only two spacecraft. Both V1 & V2 visited Jupiter and Saturn, with Voyager 2 continuing on to both Uranus and Neptune. All visits were flybyes, that is, the probes were within the vicinity of the target planets, but did not orbit them for any prolonged length of time. More conservative trajectories giving fewer flybyes but relying on more probes would be possible, and are in fact what we've accomplished with the Gallileo & Juno (Jupiter), Cassini-Huygens (Saturn), and New Horizons (Pluto) spacecraft. There are NASA (U.S.) and Chinese proposals for a return visit to Uranus and Neptune, though those remain in planning stages. <https://www.space.com/nasa-uranus-orbiter-and-probe-mission-objectives https://www.space.com/nasa-uranus-orbiter-and-probe-mission-...> The orbiter missions had a much longer time-on-station. For Gallileo, roughly 7 years 9 months, Cassini-Huygens 13 years, and Juno 7 years to date, with another 5 or more possible. The Ulysses solar probe also flew past Jupiter, using the planet for an orbital assist to both slow it down to approach the Sun more closely and incline its orbit above and below the planetary plane so that the Sun's poles could be observed directly.
  - tivert 3y ago
psunavy03 3y ago
Because there are windows to visit certain planets, especially with modern rockets. You can't just point them in the direction of a planet and yeet them into space; there is physics involved.
- larschdk 3y ago
  We did yeet New Horizons at Pluto. It got an assist from Jupiter, but could have reached Pluto without, six years delayed.
- 7373737373 3y ago
  What about electrical propulsion methods?
INTPenis 3y ago
I used to think this until I learned how our solar system moves around the galactic core. Truth is, space is wild. We're like the equivalent of stone age people standing on the shore of the atlantic looking out wondering if we can make it out there. Except the ground beneath us is also moving through the ocean at fantastic speeds, causing huge waves in our wake. This is a huge oversimplification by a layperson, but just as ancient seafarers had to escape the currents caused near their shore, we have to figure out how to escape our solar system first, into interstellar space. You're not safe there, but at least you've exited the wake of our sun. Just like we had to exit the graviational pull of earth to reach the moon.
samtho 3y ago
The only reason why we got these probes as far and as fast as we did was because we were able to fly by each planet and use their gravitational influence to skip to the next one, increasing velocity after each slingshot.
- JumpCrisscross 3y ago
  > use their gravitational influence to skip to the next one You are correct in that the Voyagers' launch window was unique. Nit pick: gravity assist doesn't fundamentally rely on gravity. It extracts energy from planets' motion about the sun [1]. If we could somehow "bounce" a spacecraft off a planet's surface, it would impart momentum similar to that of a gravity assist. (In my opinion, it's a badly-named term.) [1] https://science.nasa.gov/learn/basics-of-space-flight/primer/ https://science.nasa.gov/learn/basics-of-space-flight/primer...
  - Tabular-Iceberg 3y ago
    Good point, it’s a bit like calling hitting a baseball with a bat an “electric assist”. It’s not wrong, it’s just not very helpful. It’s also a good illustration of why we call some forces strong and others weak.
  - baseballdork 3y ago
    > gravity assist doesn't fundamentally rely on gravity I'm not sure how you can make that claim. If you were to bounce off the surface, that would likely not be considered a "gravity assist", no?
  - dctoedt 3y ago
    > If we could somehow "bounce" a spacecraft off a planet's surface, it would impart momentum similar to that of a gravity assist. When my kids were little, I showed them by holding a basketball in one hand and a tennis ball in the other, with the tennis ball on top of and touching the basketball. When I dropped them simultaneously, they fell together and bounced off the driveway — and the tennis ball took off like a rocket (no pun intended).
Sharlin 3y ago
You can take a look at the New Horizons to get an idea of what a moderately capable trans-Neptunian probe costs today (~$700M). If you made several, economies of scale would of course lower marginal costs somewhat. But the money isn’t even the main bottleneck (although it absolutely is a huge one) – power is. Specifically, the RTG radioisotope generators that are our only reasonable way of powering things at distances beyond Jupiter. Synthesis of radionuclides (eg. Pu-238) suitable for RTG use was originally a nice side effect of nuclear weapons production, but these days availability is very low even though the DOE recently restarted production after a long pause. In the 21st century NASA has launched exactly three RTG-powered missions: New Horizons (2006), Mars Science Laboratory/Curiosity (2012), and Mars 2020/Perseverance. The next will be the (very awesome) Dragonfly mission to Titan, planned to launch in 2027. So given a cadence of roughly seven years, and one out of four missions targeting trans-Neptunian space, you could expect to launch an interstellar probe every 30 years or so, barring significant advances in power technology. The next one will most likely be a sorely-needed Uranus or Neptune flyby mission that would possibly launch in the mid to late 2030s. There are maybe a dozen reasonable mission proposals submitted for every mission that actually ends up at the launch pad. The competition is fierce, and any proposal has to argue its return on investment incredibly convincingly to get selected for implementation. We now know many interesting Kuiper Belt objects that would definitely deserve a closer look – but we also know many other things that are much more accessible and would also deserve a closer look! No amount of extra money would realistically allow NASA (or any space agency) to fly missions simply "because we might discover something" because there are always many, many other mission proposals in the pipeline with vastly better justification than merely "because we might discover something".
Tabular-Iceberg 3y ago
Because the inverse square law applies to probes too. We can send them out by the millions, but by the time they get far enough out to see something interesting the probe density will be practically zero.
xnorswap 3y ago
"Every direction" isn't what you think it is. Even if we had a voyager travelling the "opposite" direction, once outside the solar system they'd appear to be travelling at almost the same speed with respect to the orbit of the solar system around the milky way. The solar system is estimated to orbit ~200km/sec around the centre of the milky way. Even with a perfect ejection, at the estimated speed of Voyager you'd end up with one probe going ~180km and the other ~220km, which isn't a huge difference. And that's without the fact that getting Voyager to that speed required some unique planetary alignment.
- daynthelife 3y ago
  On a related note, starting from a circular orbit, it takes 1/(2sqrt(2) - 3) ~ 5.83 times more energy to throw an object to the center of a gravity well than it does to throw it out of orbit. It doesn’t matter how close your initial orbit it, or whether you’re orbiting around the Sun or Sagittarius A*. The ratio is always the same, though gravitational assistance from other bodies often affects the calculations in practice. I expect we’d send a satellite outside the Milky Way long before we get one anywhere near the center of the galaxy. Not that either mission seems particularly feasible with current technology.
- paulddraper 3y ago
  Doing a % comparison makes little sense. Everything in this arm of the Milky Way is moving along with us. The key metric is that their locations would spread by ~40km/sec. Whether that is an interesting amount of distance in an interesting amount of time is debatable, but that's the number.
Yizahi 3y ago
The probes are handcrafted from the unobtanium by the very expensive engineers, and designed individually due to this. We need a heavy lift platform flying for a few years before we could start making much more crude larger probes, with cheaper or even massmarket components. Then it may work.
tg16 3y ago
The cost is the fuel. It takes an insane amount of energy to leave Sol. The voyager probes were able to save 30km/s worth of Delta-V by performing a ton of gravity assists during the "Grand Tour" launch window planetary alignment that occurs once every 175 years. For context, getting something to low earth orbit is about 9.4km/s of Delta-V. From LEO to mars is another 4.3 km/s of Delta-V. Getting from LEO to any solar escape trajectory adds is about 18km/s. As you can see, 30km/s of fuel savings is extremely significant, and that required the 175 year Grand Tour alignment.

I don’t understand why we are not sending these off in every direction constantly. The price can’t possibly be that prohibitive considering what we can accomplish with 40 year old technology.

causi 3y ago

The Voyagers took advantage of a particularly good planetary alignment for gravity boosts.

AllegedAlec 3y ago

The equivalent of about 4 billion dollars in modern day money for both of them. That, plus waiting for some very opportune launch times so that we can gravity boost off of everything.

HappyDaoDude 3y ago
Those gravitational boosts are vital. The closest in speed so far would be 'New Horizons'. But even then NH is going at 14.5KM/sec compared with Voyagers 18KM/sec. There are no probes currently that would catch up to Voyager.
- samtho 3y ago
  18km/s is almost understated in terms of speed, so I looked it up to more familiar measures of speed: 65,000kph or 40,000mph. The only thing I really learned here was how even in the thousands of miles or km per hour, it’s just inconceivable how fast that is. Km per second was a better measure after all.
  - heavyset_go 3y ago
    > it’s just inconceivable how fast that is And even more inconceivable is how slow it still is in terms of human spaceflight outside of the Solar System.
  - 14 3y ago
    What is crazy to me is that even at those speeds, it is over 18,000 years from reaching one light year distance. The closest star is 4.2 light years away. So to ever reach it we would need multi generational ships or some way to go much much faster.
  - ta1243 3y ago
    Round the world in 40 minutes Travelling from New York to LA quicker than playing the song "From New York To LA"
grishka 3y ago
But the more copies you make of something, the cheaper they become. The R&D cost is the same and is only paid once whether you're building 2 space probes or 2000.
- tg16 3y ago
  The probe itself is a relatively insignificant cost. The launch costs and timing windows are the limiting factor. The tyranny of the rocket equation is the fact that to carry more fuel to orbit, you need more fuel to get it into orbit, which itself needs more fuel. That's why gravity assists are so essential for escaping the solar system on a budget. The planetary alignment that enabled the Voyager launch windows only occurs once every 175 years. We should definitely be sending out more probes, but we can't just do it whenever we want, at least not without a lot more expense.
  - dredmorbius 3y ago
    The specific alignment for the Voyager missions was to permit flybyes of all the gas giants: Jupiter, Saturn, Uranus, and Neptune, with only two spacecraft. Both V1 & V2 visited Jupiter and Saturn, with Voyager 2 continuing on to both Uranus and Neptune. All visits were flybyes, that is, the probes were within the vicinity of the target planets, but did not orbit them for any prolonged length of time. More conservative trajectories giving fewer flybyes but relying on more probes would be possible, and are in fact what we've accomplished with the Gallileo & Juno (Jupiter), Cassini-Huygens (Saturn), and New Horizons (Pluto) spacecraft. There are NASA (U.S.) and Chinese proposals for a return visit to Uranus and Neptune, though those remain in planning stages. <https://www.space.com/nasa-uranus-orbiter-and-probe-mission-objectives https://www.space.com/nasa-uranus-orbiter-and-probe-mission-...> The orbiter missions had a much longer time-on-station. For Gallileo, roughly 7 years 9 months, Cassini-Huygens 13 years, and Juno 7 years to date, with another 5 or more possible. The Ulysses solar probe also flew past Jupiter, using the planet for an orbital assist to both slow it down to approach the Sun more closely and incline its orbit above and below the planetary plane so that the Sun's poles could be observed directly.
- tivert 3y ago

psunavy03 3y ago

Because there are windows to visit certain planets, especially with modern rockets. You can't just point them in the direction of a planet and yeet them into space; there is physics involved.

larschdk 3y ago
We did yeet New Horizons at Pluto. It got an assist from Jupiter, but could have reached Pluto without, six years delayed.
7373737373 3y ago
What about electrical propulsion methods?

INTPenis 3y ago

I used to think this until I learned how our solar system moves around the galactic core. Truth is, space is wild. We're like the equivalent of stone age people standing on the shore of the atlantic looking out wondering if we can make it out there. Except the ground beneath us is also moving through the ocean at fantastic speeds, causing huge waves in our wake. This is a huge oversimplification by a layperson, but just as ancient seafarers had to escape the currents caused near their shore, we have to figure out how to escape our solar system first, into interstellar space. You're not safe there, but at least you've exited the wake of our sun. Just like we had to exit the graviational pull of earth to reach the moon.

samtho 3y ago

The only reason why we got these probes as far and as fast as we did was because we were able to fly by each planet and use their gravitational influence to skip to the next one, increasing velocity after each slingshot.

JumpCrisscross 3y ago
> use their gravitational influence to skip to the next one You are correct in that the Voyagers' launch window was unique. Nit pick: gravity assist doesn't fundamentally rely on gravity. It extracts energy from planets' motion about the sun [1]. If we could somehow "bounce" a spacecraft off a planet's surface, it would impart momentum similar to that of a gravity assist. (In my opinion, it's a badly-named term.) [1] https://science.nasa.gov/learn/basics-of-space-flight/primer/ https://science.nasa.gov/learn/basics-of-space-flight/primer...
- Tabular-Iceberg 3y ago
  Good point, it’s a bit like calling hitting a baseball with a bat an “electric assist”. It’s not wrong, it’s just not very helpful. It’s also a good illustration of why we call some forces strong and others weak.
- baseballdork 3y ago
  > gravity assist doesn't fundamentally rely on gravity I'm not sure how you can make that claim. If you were to bounce off the surface, that would likely not be considered a "gravity assist", no?
- dctoedt 3y ago
  > If we could somehow "bounce" a spacecraft off a planet's surface, it would impart momentum similar to that of a gravity assist. When my kids were little, I showed them by holding a basketball in one hand and a tennis ball in the other, with the tennis ball on top of and touching the basketball. When I dropped them simultaneously, they fell together and bounced off the driveway — and the tennis ball took off like a rocket (no pun intended).

Sharlin 3y ago

You can take a look at the New Horizons to get an idea of what a moderately capable trans-Neptunian probe costs today (~$700M). If you made several, economies of scale would of course lower marginal costs somewhat. But the money isn’t even the main bottleneck (although it absolutely is a huge one) – power is. Specifically, the RTG radioisotope generators that are our only reasonable way of powering things at distances beyond Jupiter. Synthesis of radionuclides (eg. Pu-238) suitable for RTG use was originally a nice side effect of nuclear weapons production, but these days availability is very low even though the DOE recently restarted production after a long pause. In the 21st century NASA has launched exactly three RTG-powered missions: New Horizons (2006), Mars Science Laboratory/Curiosity (2012), and Mars 2020/Perseverance. The next will be the (very awesome) Dragonfly mission to Titan, planned to launch in 2027. So given a cadence of roughly seven years, and one out of four missions targeting trans-Neptunian space, you could expect to launch an interstellar probe every 30 years or so, barring significant advances in power technology. The next one will most likely be a sorely-needed Uranus or Neptune flyby mission that would possibly launch in the mid to late 2030s. There are maybe a dozen reasonable mission proposals submitted for every mission that actually ends up at the launch pad. The competition is fierce, and any proposal has to argue its return on investment incredibly convincingly to get selected for implementation. We now know many interesting Kuiper Belt objects that would definitely deserve a closer look – but we also know many other things that are much more accessible and would also deserve a closer look! No amount of extra money would realistically allow NASA (or any space agency) to fly missions simply "because we might discover something" because there are always many, many other mission proposals in the pipeline with vastly better justification than merely "because we might discover something".

Tabular-Iceberg 3y ago

Because the inverse square law applies to probes too. We can send them out by the millions, but by the time they get far enough out to see something interesting the probe density will be practically zero.

xnorswap 3y ago

"Every direction" isn't what you think it is. Even if we had a voyager travelling the "opposite" direction, once outside the solar system they'd appear to be travelling at almost the same speed with respect to the orbit of the solar system around the milky way. The solar system is estimated to orbit ~200km/sec around the centre of the milky way. Even with a perfect ejection, at the estimated speed of Voyager you'd end up with one probe going ~180km and the other ~220km, which isn't a huge difference. And that's without the fact that getting Voyager to that speed required some unique planetary alignment.

daynthelife 3y ago
On a related note, starting from a circular orbit, it takes 1/(2sqrt(2) - 3) ~ 5.83 times more energy to throw an object to the center of a gravity well than it does to throw it out of orbit. It doesn’t matter how close your initial orbit it, or whether you’re orbiting around the Sun or Sagittarius A*. The ratio is always the same, though gravitational assistance from other bodies often affects the calculations in practice. I expect we’d send a satellite outside the Milky Way long before we get one anywhere near the center of the galaxy. Not that either mission seems particularly feasible with current technology.
paulddraper 3y ago
Doing a % comparison makes little sense. Everything in this arm of the Milky Way is moving along with us. The key metric is that their locations would spread by ~40km/sec. Whether that is an interesting amount of distance in an interesting amount of time is debatable, but that's the number.

Yizahi 3y ago

The probes are handcrafted from the unobtanium by the very expensive engineers, and designed individually due to this. We need a heavy lift platform flying for a few years before we could start making much more crude larger probes, with cheaper or even massmarket components. Then it may work.

tg16 3y ago

The cost is the fuel. It takes an insane amount of energy to leave Sol. The voyager probes were able to save 30km/s worth of Delta-V by performing a ton of gravity assists during the "Grand Tour" launch window planetary alignment that occurs once every 175 years. For context, getting something to low earth orbit is about 9.4km/s of Delta-V. From LEO to mars is another 4.3 km/s of Delta-V. Getting from LEO to any solar escape trajectory adds is about 18km/s. As you can see, 30km/s of fuel savings is extremely significant, and that required the 175 year Grand Tour alignment.