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Thread: Cleaning out the vacuum

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    Cleaning out the vacuum

    Would there be any remotely plausible way to recover spent volatiles from the vacuum of space? Rocket exhaust and leaks for instance.

    I know some molecules can go into orbit around a gravity source and some are blown away by sunlight. Solar wind is also a factor, as are magnetic fields. So is gone always permanently forgotten?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    You'd probably better just harvesting free hydrogen.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

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    And the non-hydrogen elements?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Gaseous Emissions

    Why would you want to collect anythng emitted into space as a gas? For all practical purposes, it is probably oxidized and so tenuous as to be uncollectable.

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    When I first saw the thread, it reminded me of a joke about a student who was asked, "can you hear sound in a vacuum?" and answered "It depends on whether the vacuum is turned on or off."
    As above, so below

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    Quote Originally Posted by John Mendenhall View Post
    Why would you want to collect anythng emitted into space as a gas? For all practical purposes, it is probably oxidized and so tenuous as to be uncollectable.
    That is a big assumption. In space , structures can be very big and travel very fast. So a large collector net can sweep a lot of particles. What to do then is the big question. You might have both hydrogen and oxygen, or you could regard all as mass to be propelled by your nuclear power plant.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by profloater View Post
    That is a big assumption. In space , structures can be very big and travel very fast. So a large collector net can sweep a lot of particles. What to do then is the big question. You might have both hydrogen and oxygen, or you could regard all as mass to be propelled by your nuclear power plant.
    What kind of collector net would be needed?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    What kind of collector net would be needed?
    Well, a simple metalised mylar would catch atoms, or like I toyed with before, you could ionise particles with electrons and then attract them using charge. That would mean a web like net. The plastic net would fold really small and could then be a parabolic funnel shape when unfurled. High velocity particles might then punch holes unfortunately. So some clever self healing? A small robot crawler could wander over the surface, mending holes. Metalised Mylar polyester is used for helium balloons and very light mirrors.
    You might accelerate in furled state, then at desired speed unfurl to funnel. Small tubes could be inflated to form the shape. I wonder how big it could be before scale effects kick in? In space I guess self gravity might be a limit. The finished craft would accelerate very gently, or the thrust could be used to steer. I gave up on using charge so it needs some kind of energy, light from stars or onboard nuclear .
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    But if you put this "net" behind your rocket exhaust (as suggested in the OP), the atoms that were caught would impart a thrust to your net (and thus the spacecraft it was attached to) in the opposite direction that you want to go. The more efficient you were in catching them, the more you would slow down your rocket. It seems worse than pointless.

    I still don't understand the purpose of this exercise.
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    Quote Originally Posted by Swift View Post
    But if you put this "net" behind your rocket exhaust (as suggested in the OP), the atoms that were caught would impart a thrust to your net (and thus the spacecraft it was attached to) in the opposite direction that you want to go. The more efficient you were in catching them, the more you would slow down your rocket. It seems worse than pointless.

    I still don't understand the purpose of this exercise.
    BEHIND the rocket?!? Wow, that's one I never thought of. I meant something to move through orbital space as a catcher. Like a scoop.

    My main thought was, the resources of the Solar System are not unlimited. Once we use them up, they're gone into the void. I wanted to know if it's possible to recover some of that lost material.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Well it is a thought exercise for an interstellar system that can take as long as it likes but can steer, so only for a robot long term probe in the spirit of what might an alien interstellar craft look like. It uses the one resource ; a few atoms
    or particles per cc. It might have to spend tens of thousands of years to reach another star. I don’t expect we will see one.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by Noclevername View Post
    BEHIND the rocket?!? Wow, that's one I never thought of. I meant something to move through orbital space as a catcher. Like a scoop.

    My main thought was, the resources of the Solar System are not unlimited. Once we use them up, they're gone into the void. I wanted to know if it's possible to recover some of that lost material.
    I'm still not understanding why you think we need to. We don't recover it here on earth, and taking as an example rocket fuel, the combustion products are no longer usable for fuel. Gathering free hydrogen, of which I believe there is a lot (though very widely distributed), might make more sense.
    Of course, if you are burning hydrogen and oxygen, the resulting water could be of some use.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

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    Quote Originally Posted by Noclevername View Post
    BEHIND the rocket?!? Wow, that's one I never thought of. I meant something to move through orbital space as a catcher. Like a scoop.
    Iím not sure what the all-caps and wow are forÖ

    I think the issue that was being raised is, suppose you have a catcher going through orbital space. The particles you catch are going to have an impact on the velocity of the craft, and you might need to use fuel to counteract that. I think the crux of the issue is whether the particles you collect would impart a net acceleration or not. To be honest Iím not sure whether they would or would not.

    So it may or may not be important, but I think itís a valid issue to consider.


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    Quote Originally Posted by Noclevername View Post
    My main thought was, the resources of the Solar System are not unlimited. Once we use them up, they're gone into the void. I wanted to know if it's possible to recover some of that lost material.
    Itís an interesting question. What happens to the used fuel from rockets? Does it forever remain in the void or does it eventually return somewhere? And what is the balance between particles coming into the solar system versus those being expelled by the sun? And how much fuel would we need to burn to alter that equation? Again, I donít know the answers but would want to consider that.


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    As far as the thread is concerned, I think there is an issue of exactly what propulsion systems come into use. With chemical rockets, I suspect that a lot of the burns will be near objects (usually there are course corrections but the major burn is near some object), and is often in the opposite direction of the orbit or intended orbit, so I think the spent fuel will often be captured by the object. With ion thrusters, I think it's quite dispersed and so I wonder how much there would be compared to the background level of particles. And with solar sails, there won't be any spent fuel.
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    Quote Originally Posted by Noclevername View Post
    My main thought was, the resources of the Solar System are not unlimited. Once we use them up, they're gone into the void. I wanted to know if it's possible to recover some of that lost material.
    I have to believe that the mass of atoms scattered in the vacuum is insignificant compared to the mass of the planets, comets, asteroids, Saturn's rings, etc.

    The value of a mined resource is directly proportional to the concentration of the target material. I find it hard to imagine a time when picking up individual hydrogen atoms in the vacuum is going to be better than some other means, such as collecting ice from numerous other sources and splitting out the hydrogen, or collecting hydrogen from the gas giants.
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    Quote Originally Posted by Swift View Post
    I have to believe that the mass of atoms scattered in the vacuum is insignificant compared to the mass of the planets, comets, asteroids, Saturn's rings, etc.

    The value of a mined resource is directly proportional to the concentration of the target material. I find it hard to imagine a time when picking up individual hydrogen atoms in the vacuum is going to be better than some other means, such as collecting ice from numerous other sources and splitting out the hydrogen, or collecting hydrogen from the gas giants.
    I have not done the calculation. There is a lot of space with from one to fifty(?) atoms per cc to compare to planets, but the spirit in which I took the thought experiment, and in a few moments appropriate to a forum post, not a lecture, the context was interstellar travel, far from light sources and not for practical human travel but just a technical approach. At speeds linked loosely to Earth escape velocity, I estimated an order of ten thousand years per light year of star separation. So the only method that sprung to mind was to use the very low density medium. Working within our, or any solar system is a different kettle of fish.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    Quote Originally Posted by Jens View Post
    I’m not sure what the all-caps and wow are for…
    Shock and amazement.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by profloater View Post
    Working within our, or any solar system is a different kettle of fish.

    The context I intended was within the Solar System, around bodies with enough gravity to capture gas molecules in orbit.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    Shock and amazement.
    Shock and amazement for what?
    As above, so below

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    Quote Originally Posted by Jens View Post
    Shock and amazement for what?
    The idea of putting the "net" right behind a rocket, to block its thrusters. That makes no sense to me, and I was startled at Swift's interpretation.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    The idea of putting the "net" right behind a rocket, to block its thrusters. That makes no sense to me, and I was startled at Swift's interpretation.
    Swift was merely saying that he didnít understand what you were saying and needed further clarification. Couldnít you just explain what you wanted to ask?
    As above, so below

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    Quote Originally Posted by Noclevername View Post
    The idea of putting the "net" right behind a rocket, to block its thrusters. That makes no sense to me, and I was startled at Swift's interpretation.
    He wrote:

    Quote Originally Posted by Swift View Post

    I still don't understand the purpose of this exercise.
    So clearly he didnít understand what you were trying t9 argue. I think you just need to be more clear about what youíre describing.
    As above, so below

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    OK, this is becoming a derail. I already clarified.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    The context I intended was within the Solar System, around bodies with enough gravity to capture gas molecules in orbit.
    Sorry If I went at a tangent, i would expect less material within a planet system than in interstellar space because of the gravity sweeps. No doubt I was still thinking of what to look for in alien activity from other stars. Not very fruitful as it turned out.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    There is a way for the exhaust to get collected...
    in a supernova blast wave. We live in a solar system in the Local Bubble
    see:https://www.discovermagazine.com/the...bubble-is-born
    Discovered about 30 years ago, the relatively clean vacuum of a giant bubble, enables UV astronomy of the nearby systems whilst the UV is extinguished further out.
    The Centaurus-Scorpio association of hot, large, short lived stars is thought to have have contributed multiple supernovae blast waves over the last few million years, some of which were proposed by Brian Fields et al, as contributing to the radioactive iron-60 found in deep ocean sediments.
    Sometimes the blast waves clear out the bubbles, sometimes they sweep the debris back towards us. So , if your house is particularly dusty, you set off a supernova in the fireplace, and it will clear out the dust in a hurry, and if your neighbor sets one off, a nanosecond later, it will return your exhaust quickly.....course you need a pretty big fireplace in the first place..
    pete

    Also see:content://com.android.chrome.FileProvider/images/screenshot/1625237373107784076783.jpg
    Last edited by trinitree88; 2021-Jul-02 at 03:12 PM. Reason: links

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    Rocket exhaust is what makes the rocket accelerate.

    If you capture it and bring it with you, well . . .

    If some other craft captures it, then it will absorb the linear momentum in the exhaust, which is the same in magnitude but opposite in direction from the linear momentum of the craft that generated the exhaust.

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    Quote Originally Posted by TheManWithNoName View Post

    If some other craft captures it, then it will absorb the linear momentum in the exhaust, which is the same in magnitude but opposite in direction from the linear momentum of the craft that generated the exhaust.
    If all the rocket exhaust stayed together and was intercepted at the same time, yes it would have that effect. In a vacuum it will be widely dispersed, and you'd pick up momentum a microscopic bit at a time, just as there's a small drag from the upper atmosphere on objects in LEO.

    Any collection method with a large surface area like an artificial magnetosphere or solar sail is both a potential source of drag, and propulsion.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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