5 ms·

Do you mean interstellar probes? The Voyager missions were primarily planetary exploration missions, which NASA and other space agencies continue to run with n

Do you mean interstellar probes? The Voyager missions were primarily planetary exploration missions, which NASA and other space agencies continue to run with new probes every few years. The interstellar exploration piece was kind of a secondary feature of the missions taking advantage of high speeds from all the gravity assists along the way. I don't think we'll see a dedicated interstellar probe for a long time. It just takes too much energy to get out that far in a reasonable amount of time without radical designs or a big leap in propulsion technology.

pierrebai 7y ago
Wouldn't it be possible if we launched from the moon instead? Most of the trust of rocket is loss to get out of the earth gravity well. (Not that we're anywhere near having a rocket factory on the moon... but maybe one could be assembled and fueled in orbit?)
- ars 7y ago
  The only reason to land on the moon would be if you could find fuel there. Which you can't. So that's a no for the moon, but something from orbit could make sense. Have a staging area and just accumulate tons of fuel from multiple launches.
  - outworlder 7y ago
    > Which you can't Of course you can. > By atomic composition, the most abundant element found on the Moon is oxygen. It composes 60% of the Moon's crust by weight, followed by 16-17% silicon, 6-10% aluminum, 4-6% calcium, 3-6% magnesium, 2-5% iron, and 1-2% titanium. You have oxygen. You have aluminum. You can now make a solid rocket. There's some magnesium there too if you want to use that instead.
    - rbanffy 7y ago
      And aluminium, magnesium and titanium are great for building spacecraft, if we can get the mining and manufacturing capability there.
    - saalweachter 7y ago
      It's kind of hilarious that the hardest thing to find in the inner solar system, off Earth (and, of course, the Sun), isn't precisely water but hydrogen.
    - seppel 7y ago
      > You have oxygen. You have aluminum. Not exactly. You have aluminium oxide, which you could split into aluminium and oxygen using huge amounts of energy, like we do on earth. Helium-3 could be interesting, though.
      - behringer 7y ago
        Energy isn't a problem when you can build nuclear power plants without worry.
        AnimalMuppet 7y ago
        You then have the problem of building the nuclear power plant, though...
- btilly 7y ago
  Most of the thrust of rocket is loss to get out of the earth gravity well. I believe that this is wrong. The Earth weighs 5.96e+24 kg and has radius 3.37e6 meters. The Sun weighs 1.98e30 kg and our orbit has radius 1.496e11 meters. That means that the potential well for getting away from Earth is about 11,800,000 joules/kg while for getting out of the Sun's gravity well is about 882,800,000 joules/kg. Assuming that I did the math right, that's about 7.5 times as hard. It therefore takes a lot more energy to climb out of the Solar System than it does to climb out of Earth's gravity well. Voyager got a LOT of energy from those gravitational slingshots.
  - GlenTheMachine 7y ago
    You're trying to compare apples to apples here, when the situation we have is actually apples to oranges ;). A probe has to launch from the surface of the earth. But counterintuitively the probes start out already in solar orbit, even before they're launched -- because the earth is in solar orbit. More than half the energy required to achieve escape velocity is needed just to get into a roughly circular relatively low orbit around the gravitating body you're trying to escape from, and by virtue of being launched from the earth the probes get that velocity for free. Furthermore, the earth's orbit isn't really "low" with respect to the sun. We're fairly far out there, so the fraction of the energy needed to go from earth orbit to a solar escape trajectory is even less. Put another way: a probe launched from the earth gets no help leaving earth's gravity well. But once it does it gets a huge automatic gravity assist from the earth itself as it enters solar orbit.
    - Jeff_Brown 7y ago
      That was very helpful to read, thanks.
  - outworlder 7y ago
    There's a saying among KSP players: "Orbit is halfway to anywhere". It takes a lot of energy to escape Earth's gravity well. It takes a comparatively tiny amount to escape the Sun's, as a sibling poster pointed out. It would be actually harder to visit, say, Mercury, as you now have to shed all the energy Earth has given you for free, in order to "fall" into the Sun's well. Voyager wanted to visit multiple planetary bodies – changing orbital parameters is not cheap. But if all it wanted was to get out of the system, burning straight out would probably be cheaper (in Delta-V terms). The closer to Earth the better, for the Oberth effect.
- rbanffy 7y ago
  > Wouldn't it be possible if we launched from the moon instead? It would be cheaper in fuel terms, and require less thrust, but it'd also require us to manufacture propellant on the lunar surface and fly everything we can't build there from Earth (and landing on the Moon is purely propulsive).
HarryHirsch 7y ago
The propulsion technology for an interstellar mission is available today, there are proposals for probes powered by RTGs or even nuclear reactors and driven by ion engines. Jupiter-Saturn conjunctions that can be exploited for gravity assists happen every 20 years or so: https://en.wikipedia.org/wiki/Interstellar_probe#Proposed_interstellar_probes https://en.wikipedia.org/wiki/Interstellar_probe#Proposed_in... It's entirely a political problem. There is no will to fund such a mission, and what's worse is that in the US funding is approved year by year.
- Jeff_Brown 7y ago
  In nuclear engines the fuel and propellant is separate. I keep wondering how much gas a rocket needs to take with it in order to have something to push against. Nuclear fuel is incredibly energy-dense, but the density of the gas used for propulsion in a nuclear rocket can't be much different from what's used in conventional rockets.
  - HarryHirsch 7y ago
    The JIMO mission was supposed to have 12 tons of xenon on board, a substantial amount of the yearly production (~ 70 tons). You do wonder how Elon Musk's Starlink madness will affect the xenon price.
    - tlb 7y ago
      The StarLink satellites use krypton thrusters instead of xenon [0]. They need more electic power to run, but produce higher specific impulse [1]. And krypton is cheap. [0] https://www.spacex.com/sites/spacex/files/starlink_press_kit.pdf https://www.spacex.com/sites/spacex/files/starlink_press_kit... [1] http://ngpdlab.engin.umich.edu/electric-propulsion/krypton-HET http://ngpdlab.engin.umich.edu/electric-propulsion/krypton-H...
jandrese 7y ago
With launch costs plummeting it may be possible to launch a bigass booster and give an interstellar probe a real kick even without a magical planetary alignment. The question then becomes: what instruments would you put on this that would tell us something the Voyager probes have not? What is your mission beyond "making something go even further away from us"?
- tempestn 7y ago
  As per the article, exploring the trailing edge of the heliopause would be interesting and is something that hasn't yet been done. But yes, presumably instrumentation has also improved over the last 50 years, so hopefully we could get better data as well.
blacksmith_tb 7y ago
There's a (partly funded!) project to send a 'chain' of probes to α Centauri[1], as long as they don't need to slow down when they get there, they can shoot right through and relay results back, as I understand it. 1: https://www.skyandtelescope.com/astronomy-news/100-million-for-probes-to-alpha-centauri-yes-really/ https://www.skyandtelescope.com/astronomy-news/100-million-f...
- marcoseliziario 7y ago
  Russian Billionaires just got a lot more respect in my book. This looks like just something right from a Jules Verne book.

pierrebai 7y ago

Wouldn't it be possible if we launched from the moon instead? Most of the trust of rocket is loss to get out of the earth gravity well. (Not that we're anywhere near having a rocket factory on the moon... but maybe one could be assembled and fueled in orbit?)

ars 7y ago
The only reason to land on the moon would be if you could find fuel there. Which you can't. So that's a no for the moon, but something from orbit could make sense. Have a staging area and just accumulate tons of fuel from multiple launches.
- outworlder 7y ago
  > Which you can't Of course you can. > By atomic composition, the most abundant element found on the Moon is oxygen. It composes 60% of the Moon's crust by weight, followed by 16-17% silicon, 6-10% aluminum, 4-6% calcium, 3-6% magnesium, 2-5% iron, and 1-2% titanium. You have oxygen. You have aluminum. You can now make a solid rocket. There's some magnesium there too if you want to use that instead.
  - rbanffy 7y ago
    And aluminium, magnesium and titanium are great for building spacecraft, if we can get the mining and manufacturing capability there.
  - saalweachter 7y ago
    It's kind of hilarious that the hardest thing to find in the inner solar system, off Earth (and, of course, the Sun), isn't precisely water but hydrogen.
  - seppel 7y ago
    > You have oxygen. You have aluminum. Not exactly. You have aluminium oxide, which you could split into aluminium and oxygen using huge amounts of energy, like we do on earth. Helium-3 could be interesting, though.
    - behringer 7y ago
      Energy isn't a problem when you can build nuclear power plants without worry.
      - AnimalMuppet 7y ago
        You then have the problem of building the nuclear power plant, though...
btilly 7y ago
Most of the thrust of rocket is loss to get out of the earth gravity well. I believe that this is wrong. The Earth weighs 5.96e+24 kg and has radius 3.37e6 meters. The Sun weighs 1.98e30 kg and our orbit has radius 1.496e11 meters. That means that the potential well for getting away from Earth is about 11,800,000 joules/kg while for getting out of the Sun's gravity well is about 882,800,000 joules/kg. Assuming that I did the math right, that's about 7.5 times as hard. It therefore takes a lot more energy to climb out of the Solar System than it does to climb out of Earth's gravity well. Voyager got a LOT of energy from those gravitational slingshots.
- GlenTheMachine 7y ago
  You're trying to compare apples to apples here, when the situation we have is actually apples to oranges ;). A probe has to launch from the surface of the earth. But counterintuitively the probes start out already in solar orbit, even before they're launched -- because the earth is in solar orbit. More than half the energy required to achieve escape velocity is needed just to get into a roughly circular relatively low orbit around the gravitating body you're trying to escape from, and by virtue of being launched from the earth the probes get that velocity for free. Furthermore, the earth's orbit isn't really "low" with respect to the sun. We're fairly far out there, so the fraction of the energy needed to go from earth orbit to a solar escape trajectory is even less. Put another way: a probe launched from the earth gets no help leaving earth's gravity well. But once it does it gets a huge automatic gravity assist from the earth itself as it enters solar orbit.
  - Jeff_Brown 7y ago
    That was very helpful to read, thanks.
- outworlder 7y ago
  There's a saying among KSP players: "Orbit is halfway to anywhere". It takes a lot of energy to escape Earth's gravity well. It takes a comparatively tiny amount to escape the Sun's, as a sibling poster pointed out. It would be actually harder to visit, say, Mercury, as you now have to shed all the energy Earth has given you for free, in order to "fall" into the Sun's well. Voyager wanted to visit multiple planetary bodies – changing orbital parameters is not cheap. But if all it wanted was to get out of the system, burning straight out would probably be cheaper (in Delta-V terms). The closer to Earth the better, for the Oberth effect.
rbanffy 7y ago
> Wouldn't it be possible if we launched from the moon instead? It would be cheaper in fuel terms, and require less thrust, but it'd also require us to manufacture propellant on the lunar surface and fly everything we can't build there from Earth (and landing on the Moon is purely propulsive).

HarryHirsch 7y ago

The propulsion technology for an interstellar mission is available today, there are proposals for probes powered by RTGs or even nuclear reactors and driven by ion engines. Jupiter-Saturn conjunctions that can be exploited for gravity assists happen every 20 years or so: https://en.wikipedia.org/wiki/Interstellar_probe#Proposed_interstellar_probes https://en.wikipedia.org/wiki/Interstellar_probe#Proposed_in... It's entirely a political problem. There is no will to fund such a mission, and what's worse is that in the US funding is approved year by year.

Jeff_Brown 7y ago
In nuclear engines the fuel and propellant is separate. I keep wondering how much gas a rocket needs to take with it in order to have something to push against. Nuclear fuel is incredibly energy-dense, but the density of the gas used for propulsion in a nuclear rocket can't be much different from what's used in conventional rockets.
- HarryHirsch 7y ago
  The JIMO mission was supposed to have 12 tons of xenon on board, a substantial amount of the yearly production (~ 70 tons). You do wonder how Elon Musk's Starlink madness will affect the xenon price.
  - tlb 7y ago
    The StarLink satellites use krypton thrusters instead of xenon [0]. They need more electic power to run, but produce higher specific impulse [1]. And krypton is cheap. [0] https://www.spacex.com/sites/spacex/files/starlink_press_kit.pdf https://www.spacex.com/sites/spacex/files/starlink_press_kit... [1] http://ngpdlab.engin.umich.edu/electric-propulsion/krypton-HET http://ngpdlab.engin.umich.edu/electric-propulsion/krypton-H...

jandrese 7y ago

With launch costs plummeting it may be possible to launch a bigass booster and give an interstellar probe a real kick even without a magical planetary alignment. The question then becomes: what instruments would you put on this that would tell us something the Voyager probes have not? What is your mission beyond "making something go even further away from us"?

tempestn 7y ago
As per the article, exploring the trailing edge of the heliopause would be interesting and is something that hasn't yet been done. But yes, presumably instrumentation has also improved over the last 50 years, so hopefully we could get better data as well.

blacksmith_tb 7y ago

There's a (partly funded!) project to send a 'chain' of probes to α Centauri[1], as long as they don't need to slow down when they get there, they can shoot right through and relay results back, as I understand it. 1: https://www.skyandtelescope.com/astronomy-news/100-million-for-probes-to-alpha-centauri-yes-really/ https://www.skyandtelescope.com/astronomy-news/100-million-f...

marcoseliziario 7y ago
Russian Billionaires just got a lot more respect in my book. This looks like just something right from a Jules Verne book.