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Thread: Harvesting Iron Asteroids and bringing them down from orbit?

  1. #1 Harvesting Iron Asteroids and bringing them down from orbit? 
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    Hi,

    I'm writing a science fiction story and in the future we are having to bring iron asteroids down to Earth. These asteroids are 1 to 3 miles in diameter and shaped charges brake up the asteroid and push it down into the atmosphere in such a way that the house size chunks land in an unpopulated area.

    But... will they burn up in the atmosphere? I know natural ones do but these are traveling at great velocities. How could I bring iron asteroid material down to Earth in such a way that there's enough left to make it worth the effort?

    Is there a better forum or place to ask this?

    Thanks,
    Rusty


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    Well, if you are writing an SF story, you should be ready to give up on real science a little bit. However, I will try to help you, and you are basically in a good place.

    First of all, I hope you have really fast transport in the future, as house-size chunks landing would obliterate anything in a radius of 300 to 500 km, meaning you would have to transport it at least that distance before being able to exploit it. (Or would exploit it on spot, but would than have to find another place for landing of future asteroids.)

    However, if you wanna go into real economical aspect of the procedure, nothing you could do would make it work the effort. Quite simply, even if you bring down asteroid several km in diameter (which would destroy half the continent), you still wouldn't be able to pay off the launch costs. My proposal for your book, if you want to stick to science, is to find a way to stop and process the asteroids in orbit.


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    Some nice big mirrors could provide plenty of sunlight to smelt the metal in space. Without all the extra rock, getting it down would be easier. If you have a space elevator, bringing it down safely would be doable, even if it required a lot of trips.

    Space elevators would be considered fairly hard sci-fi, since there seem to be only engineering and social considerations in the way of us actually builing one. I think the same would be true for space-based smelters. There's plenty of reasons we haven't done it, but AFAIK scientific impossibility isn't one of them.
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    The main one being, the iron is still way too cheap...
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    You'd have to come up with an economic scenario where iron became expensive. They're not hard to devise. Scrap iron prices spiked really high for a while a couple years ago. For a little while, if you had an old car, you could get more selling it for the scrap than you could selling it to someone to drive.


    To bring down all that iron, I think you'd want to build aerodynamic barges out of it, and then guide them down like the space shuttle. You might have to coat them in some heat resistant materials as well. Maybe you should choose something more valuable than iron,though. Why not decide that they find an asteroid made out of platinum, gold, or uranium instead? Something that is definitely worth the trouble.
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    Quote Originally Posted by kojax
    Why not decide that they find an asteroid made out of platinum, gold, or uranium instead? Something that is definitely worth the trouble.
    The quantities of rarer metals within iron asteroids is sufficiently large that these would be economic to mine.
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  8. #7 Re: Harvesting Iron Asteroids and bringing them down from or 
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    Quote Originally Posted by rrw4rusty
    Hi,

    I'm writing a science fiction story and in the future we are having to bring iron asteroids down to Earth. These asteroids are 1 to 3 miles in diameter and shaped charges brake up the asteroid and push it down into the atmosphere in such a way that the house size chunks land in an unpopulated area.

    But... will they burn up in the atmosphere? I know natural ones do but these are traveling at great velocities. How could I bring iron asteroid material down to Earth in such a way that there's enough left to make it worth the effort?

    Is there a better forum or place to ask this?

    Thanks,
    Rusty
    1) The impact of an asteroid of that size, and you are talking about a swarm of them, would be catastrophic. You need not worry about loosing the mass due to atmospheric heating. You do need to worry about surviving the event. Remember what killed the dinosaurs ? These will also be traveling at great velocity, and there is nothing that you can do about that. In oder to change the velocity appreciably you need to expend momentu equal to that which you wish to "cancel" -- and that is one hell of a lot of momentum and WAY beyond our capability.

    2) It is essentially impossible to make any such venture commercially viable. Gold maybe, but not iron. Of course, even with gold there is the problem of living to spend the profits.
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    I think everyone here is being way too negative. He's talking about bringing down house-sized chunks. You won't want to be standing within a few miles of wherever that lands, but you can always just drop it at a designated landing site in the middle of the desert somewhere.

    As for economics, a ball of iron 1 mile in diameter would be worth around $5 trillion. That would cover an awful lot of launch costs. A house-sized cube of iron 30 meters on each edge would be worth something like $60 million today. Depending on what economics are like in the future, it might be worth considerably more than that.

    Quote Originally Posted by Sindrato
    First of all, I hope you have really fast transport in the future, as house-size chunks landing would obliterate anything in a radius of 300 to 500 km, meaning you would have to transport it at least that distance before being able to exploit it.
    300-500 km is a ridiculous figure that I'm pretty sure you just pulled out of your ass. If a cubic chuck 30 meters/edge hits at around 6-7 km/sec, you're looking at an energy of around 1 megaton. The blast would only be dangerous to unprotected people out to maybe 10 miles away, and you could build reinforced structures a lot closer than that. You could have a hardened railway line near the landing area to cart off the chunks for further processing after you carved it up.
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    Quote Originally Posted by Scifor Refugee
    I think everyone here is being way too negative. He's talking about bringing down house-sized chunks. You won't want to be standing within a few miles of wherever that lands, but you can always just drop it at a designated landing site in the middle of the desert somewhere.

    As for economics, a ball of iron 1 mile in diameter would be worth around $5 trillion. That would cover an awful lot of launch costs. A house-sized cube of iron 30 meters on each edge would be worth something like $60 million today. Depending on what economics are like in the future, it might be worth considerably more than that.

    Quote Originally Posted by Sindrato
    First of all, I hope you have really fast transport in the future, as house-size chunks landing would obliterate anything in a radius of 300 to 500 km, meaning you would have to transport it at least that distance before being able to exploit it.
    300-500 km is a ridiculous figure that I'm pretty sure you just pulled out of your ass. If a cubic chuck 30 meters/edge hits at around 6-7 km/sec, you're looking at an energy of around 1 megaton. The blast would only be dangerous to unprotected people out to maybe 10 miles away, and you could build reinforced structures a lot closer than that. You could have a hardened railway line near the landing area to cart off the chunks for further processing after you carved it up.
    I like this post the best LOL! It also sounds the most informed. Its also definitely in the minority. But I guess if no one challenges Scifor Refugee that says a lot. I also have other sources which, I need to check. Oh, this is not Earth and it is definitely worth the cost and effort. Ten miles huh. I'll have to look but I think I used 15.

    Thanks,
    Rusty
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    Could you slice them up with a solar-powered laser beam (a big nasty one), carving them into giant maple keys that auto-rotate down, thus alleviating the "impact", both to the iron and the Earth?
    Grief is the price we pay for love. (CM Parkes) Our postillion has been struck by lightning. (Unknown) War is always the choice of the chosen who will not have to fight. (Bono) The years tell much what the days never knew. (RW Emerson) Reality is not always probable, or likely. (JL Borges)
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    Quote Originally Posted by jrmonroe
    Could you slice them up with a solar-powered laser beam (a big nasty one), carving them into giant maple keys that auto-rotate down, thus alleviating the "impact", both to the iron and the Earth?
    No, too much change.

    Okay, I guess the bottom line is the story revolves around a process I've already written. It was not very bright of me to write the book (its completed) and then worry about how possible the asteroid harvesting project was but in truth I was all over this forum and others worried about the more fantastic elements of my story. Remember this is not Earth but very simular.

    The asteroids are nudged from the Trojan points of two of their gas giants and they have about 100,000 iron asteroids from 2 to seven miles spiraling in towards their planet. Is 100,000 way too many? Is spiraling in towards planet way to dangerous? How about the asteroid sizes? All these details can easily be changed but not the basic way they are brought down.

    As the asteriods approach Homeworld (the planet) the composition and shape and size of the asteroid is analyzed and six to twelve 'shaped charge units' are placed on it. These 'units' can drill down 100 feet, laser out shaped pocket and plant the explosive in it. These break the asteroid up into the proper size chunks and also nudge these downward so they fall out of orbit. A desert about the size of the Sahara has three landing areas and the asteroid chunks land in one of these (how? I thought directing them would be enough).

    Planting the ‘shaped charge units’ on the asteroid and using these is needed for the plot.

    Of the things I can do given the technological level of the planet Homeworld (100 to 200 years ahead of us) and constraints imposed by the story plot is:
    • A ‘cloud’ of some material could be in orbit below the asteroid and this could coat the house size chunks with something to help with burn up.
    • We can dictate the direction and speed of the asteroid before the charges go off.
    • The ‘Shaped Charge Array Units’ could liquefy the asteroid though to what end I’m not yet sure.
    • I know of no way that we could shape liquefied pieces of asteroid
    • We could partially melt the chunks to make them smooth.
    • The ‘Shaped Charges’ could give the asteroid chunks some very basic shapes by breaking up the asteroid in certain ways… basic shapes like flat and wide, or rod like (long and skinny).

    Thanks for all your help!!
    Rusty
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    If you want to realistically predict your craters and such, this site might help.

    http://geology.com/meteor-impact-craters.shtml

    Quote Originally Posted by Scifor Refugee
    As for economics, a ball of iron 1 mile in diameter would be worth around $5 trillion. That would cover an awful lot of launch costs. A house-sized cube of iron 30 meters on each edge would be worth something like $60 million today. Depending on what economics are like in the future, it might be worth considerably more than that.
    You also have to consider local inflation effects if a mineral starts to become more abundant world wide than it was before the project. The price would depend on how the world's economy planned to use the metal. If large chunks of the third world were trying to industrialize themselves rapidly, or the first world was building massive iron sky rails or something, then the price of iron would stay pretty high.

    If it's just a cheaper alternative for existing economies to be able to say... build cheaper automobiles at the present quantities, then you'd be dealing with a much lower price.
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    Quote Originally Posted by Scifor Refugee
    300-500 km is a ridiculous figure that I'm pretty sure you just pulled out of your ass. If a cubic chuck 30 meters/edge hits at around 6-7 km/sec, you're looking at an energy of around 1 megaton. The blast would only be dangerous to unprotected people out to maybe 10 miles away, and you could build reinforced structures a lot closer than that. You could have a hardened railway line near the landing area to cart off the chunks for further processing after you carved it up.

    To tell you the truth, I haven't calculated, but I used Tunguska's event as an staging point, and it has created 10-15 megaton explosion. As the Tunguska's asteroid wasn't too big, I supposed that the explosion can't be much weaker...
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    Quote Originally Posted by Sindrato
    Quote Originally Posted by Scifor Refugee
    300-500 km is a ridiculous figure that I'm pretty sure you just pulled out of your ass. If a cubic chuck 30 meters/edge hits at around 6-7 km/sec, you're looking at an energy of around 1 megaton. The blast would only be dangerous to unprotected people out to maybe 10 miles away, and you could build reinforced structures a lot closer than that. You could have a hardened railway line near the landing area to cart off the chunks for further processing after you carved it up.

    To tell you the truth, I haven't calculated, but I used Tunguska's event as an staging point, and it has created 10-15 megaton explosion. As the Tunguska's asteroid wasn't too big, I supposed that the explosion can't be much weaker...
    True, but the Tunguska meteor probably already had a considerable relative velocity to Earth prior to entering the atmosphere, not just from Earth's gravity alone. These iron blocks would be entering from the most favorable angle and velocity that their handlers could manage.
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    Quote Originally Posted by Sindrato
    To tell you the truth, I haven't calculated, but I used Tunguska's event as an staging point, and it has created 10-15 megaton explosion. As the Tunguska's asteroid wasn't too big, I supposed that the explosion can't be much weaker...
    First off, even a 10-15 megaton explosion (like Tunguska) wouldn't come close to the 300-500 km figure that you claimed, so I'm still not sure where you got those numbers. At Tunguska trees were knocked over out to around 50 km. Second, the Tunguska asteroid (or whatever it was) exploded in the air, which gave it a much bigger damage radius than it would have had if it had struck the ground. Presumably these iron chunks will reach the ground intact, instead of breaking up in the air, which would give it a much smaller blast radius. And third, these chunks would be going a lot slower than whatever hit in Tunguska. An asteroid coming in for an uncontrolled collision might be going 20-30 km/sec, while these chunks that he's talking about might be going only 7 km/sec or so when they hit.
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    I think this site may prove very useful to you: http://impact.ese.ic.ac.uk/ImpactEffects/

    It lets you calculate the effects (both global and local) of an impact and how it depends on parameters such as size nad density of asteroid, angle of impact, velocity, target density and your distance to the impact.

    Should give a pretty good estimate of what can be expected. Pretty cool tool.

    For example my results for a 30 meters diameter pure iron asteroid were a 160-200 meters deep crater. 100 km you would sure notice the impact, but it wouldn't pose any significant danger at that distance. (see full report here)
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    Riiiight - a lot of what you say makes sense.

    BUT - Earth is getting damned crowded -
    In the future there will probably be NO safe place to be
    bringing big Iron Meteorites down on the surface.
    Anyway - do you really want to be making a mess of the
    surface of Planet Earth.

    In my Alt. Feature - in 2130's - we are doing the Mining ON the Asteroids.
    Much safer. We are doing loads of other stuff as well.
    As you are a Writer of Sci Fi - good stuff.

    I am Writing Sci Fi in a a different way, almost "living" it - in my Krissyverse
    which is a Play-By-Post Sci Fi Game on another Site.
    I am the G.M. of that Game.
    There are some 14 Players in that Game.
    We are mostly working within known Physics and Chemistry -
    although FAST FTL Drives are obvously Sci Fi,
    and our Science Director is now working on Wormholes.

    However - Earth has a Population of 12 Billion in 2130 -
    much too crowded for your idea to be safe really.
    We have LOADS of Power available - Second Generation
    Fusion Reactor Powerplants, safe and clean -
    well shielded and using Hydrogen as fuel.
    Apart from on Earth - there is Millions of Tons of Hydrogen as
    "Atmospheres" of the Moons of Outer Planets.
    And of course, we have Bases on lots of those Moons.

    Having Fast FTL Drives - of course we are expanding and Colonising,
    and fairly early on we made contact with some Aliens who are
    building an Empire of Slavery, stretching across 60% of this Galaxy.
    So, we do not want to be enslaved - we are at WAR with them.
    However - we have Alliances with six Species of Friendly Aliens.

    Good on yer - for writing Sci Fi though.
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    You could attach a meneuvering rocket on the asteroid, and then maneuver the asteroid for an aerobreaking procedure: such that you could slow down the asteroid in Earth's upper atmosphere until it became slow enough for a safe touch down on earth. Naturally, without a maneuvering rocket (or even an aerodynamic surface): the asteroid will be deflected off the earth's atmosphere (if the approach angle is too low) or will explode in the lower dense atmosphere (if it came straight on/ direct impact). Attaching a rocket to the rock is most practical IMO, but is most risky because you didn't know if the rocket is strong enough or it could be (accidentally) detached during re-entry...

    This way you could sent an unmanned vehicle to blast the asteroid, knock it off its orbit, and then guide it for re-entry to earth.

    EDIT:
    But the rocket must be very strong and reliable; because the rock is coming at earth at very fast velocity and was very heavy, imagine how long it would take to bleed off that much energy in the atmosphere and how long that rocket must work during that harsh condition...

    And imagine what happen if the rock melt into an irregular shape during re-entry?? this will alter the aerodynamic property of the rock, and worse: that aerodynamic force could be much higher than the maneuvering thrusters' and it could overwhelm them (rendering them useless)...

    But you could attach a heat shield on it; and this'll solve the aerodynamic problem... however this mean bringing too much gear up to space, meaning that this endeavour could became almost economically-unpractical (fuel requirement for a launch vehicle will increase by the power of 2 for each extra Kg of payload if I'm not mistaken == massive rocket).
    Last edited by msafwan; August 30th, 2011 at 07:31 PM.
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  20. #19  
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    Quote Originally Posted by rrw4rusty View Post
    Quote Originally Posted by jrmonroe
    Could you slice them up with a solar-powered laser beam (a big nasty one), carving them into giant maple keys that auto-rotate down, thus alleviating the "impact", both to the iron and the Earth?
    No, too much change.

    Okay, I guess the bottom line is the story revolves around a process I've already written. It was not very bright of me to write the book (its completed) and then worry about how possible the asteroid harvesting project was but in truth I was all over this forum and others worried about the more fantastic elements of my story. Remember this is not Earth but very simular.

    The asteroids are nudged from the Trojan points of two of their gas giants and they have about 100,000 iron asteroids from 2 to seven miles spiraling in towards their planet. Is 100,000 way too many? Is spiraling in towards planet way to dangerous?
    The asteroids won't "spiral in". In order to get your asteroids from their present orbits to a trajectory that will intersect with your planet, you have to change their orbits into ones that have a periastron that matches the orbital distance of your planet.

    Let's take the example of an asteroid in one of Jupiter's Trojan points and bringing it to Earth. At present, it orbits at about 778 million km. You need to change its orbit to one that has a perihelion of ~150 million km (it will maintain a aphelion of 778 million km). Such an orbit has an orbital velocity of ~7.4 km/sec. The asteroid's velocity in it's original orbit is ~ 13 km/sec. This means that you will have to change its velocity by ~5.6 km/sec (a little bit more than a "nudge".)



    As the asteriods approach Homeworld (the planet) the composition and shape and size of the asteroid is analyzed and six to twelve 'shaped charge units' are placed on it. These 'units' can drill down 100 feet, laser out shaped pocket and plant the explosive in it. These break the asteroid up into the proper size chunks and also nudge these downward so they fall out of orbit.
    Planting the ‘shaped charge units’ on the asteroid and using these is needed for the plot.

    Using the same example, upon reaching Earth orbit distance, our asteroids will have a velocity of ~38.6 km/sec. They will be paralleling the Earth trajectory which will be traveling at 30 km/sec. This gives a velocity difference of 8.6 km/sec.

    This is fast enough that unless you slow them down considerably, there is no way that the Earth could ever capture them in orbit and if they didn't hit the Earth, they would just fly by. If you were to allow the asteroids to just impact with the Earth, Earth's gravity will increase the relative speed by about 11 km/sec, so at impact they will be moving at something like 19.6 km/sec. which means, that in order to get the impact speed down to something like the 7-8 km/sec range mentioned, you are going to have to slow your asteroid by about almost 12 km/sec. This is the equivalent of lifting it from the Earth's surface to escape velocity. (With present day rockets, this would take over 13 times the mass of the asteroid in fuel)
    msafwan likes this.
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    Janus, just a small pedantic nitpick. The approach velocity and the effect of earth's gravity are not additive; rather the final velocity is the square root of the sum of the approach velocity squared, and the gravitational acceleration squared. SQRT(8.6^2+11.2^2)

    So for your 8.6 km/s approach velocity, after gravity it would be 14.1 km/sec.

    We meteor guys do this stuff all the time

    It doesn't change your point that the energy required for capture would be astronomical.

    Would make a nice fireball though if it just grazed the top of the atmosphere!

    MW
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    Quote Originally Posted by MeteorWayne View Post
    Janus, just a small pedantic nitpick. The approach velocity and the effect of earth's gravity are not additive; rather the final velocity is the square root of the sum of the approach velocity squared, and the gravitational acceleration squared. SQRT(8.6^2+11.2^2)

    So for your 8.6 km/s approach velocity, after gravity it would be 14.1 km/sec.

    We meteor guys do this stuff all the time

    It doesn't change your point that the energy required for capture would be astronomical.

    Would make a nice fireball though if it just grazed the top of the atmosphere!

    MW
    Yep, your correct. Serves me right for doing a fast, off the top of my head estimate and not backing it up with an energy conservation check.
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    In your story does planet have moon?

    Earth Moon rich in rutile, making good heat shield/aerobraking material.

    So planet is deficient in metals? You may enjoy Big Planet by Jack Vance.

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    all the governments on earth would tell your iron miner to GFY.
    but that's why its Scifi.
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    Sorry to be so late on all this, but why would anyone want to bring an iron asteroid into the earth's gravity well in the first place? My guess is that when the very first asteroid becomes an official Impactor, there will be laws passed prohibiting them from coming anywhere near the planet.

    And why would anyone want to process one primarily for the iron? Keep in mind that in the near future, we will scientifically be able to mass produce carbon nanotubes, or other advanced carbon products, which will be many orders stronger, lighter, and cheap. When this comes to fruition, iron will no longer be the metal of choice for structural strength.


    But putting that aside, the inherit danger of having an asteroid get loose and kill a billion humans, more or less, is the most important issue here. Keeping that in mind, there is one certain way space industries are going to be worked, with relation to earth, and the surrounding orbital area.

    Initially asteroids moved into the inner system for exploitation will almost certainly be moved to the two earth orbit Trojan points, located sixty degrees before, and behind, the planet. It will be easy to get them there, and the chance of causing catastrophic damage to the planet is minimal. All raw material can be harvested, and broken down there. Both Trojan points are ideal spots for massing industry.

    Now once the raw material, i.e.commodities, are processed and refined, it will be an easy thing to tie them up within carbon nanotube nets, which will safely hold them together for travel back to earth. For the Trojan point in front of earth, all that would be required would be for shuttles to move those nanotube nets into an outer orbit, where they would be slower, allowing earth to eventually catch up with them. For the Trojan point trailing earth, the nanotube nets can be towed inward, creating a faster orbit, where they will eventually catch up with earth.

    Eventually there would be large streams of nanotube nets moving closer to earth, where they could be individually corralled and taken to the lunar Trojan Points, where the finish manufactering would be conducted. Any nanotube net that got loose and feel to earth would be small enough not to do serious damage. Once the system came on line, there would be a continuous feeding of materials for industry to use. And harvesting the Oort Cloud could accomplish the same goal. Just nudge the comets inward, and work them to the earth Trojan Points for break down into the needed commodities.

    And as a last part, the use of space elevators would be able to cheaply move finished products to the planet, or even act as sling shots for moving payloads to anywhere in the system.
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    It seems to me that the main problem is the cumulative energy involved, I think Rusty said he was planning to crash land a hundred thousand iron chunks on his planet. Even if you can aim them at uninhabited areas that's a monumental amount of heat released into the atmosphere. You could end up melting the crust of your planet. This is bad if you are planing on living there in the next couple thousand years.
    You need to postulate some sort of "hand wavium" gravity control device so as to put them down gently. That would also help with the notion of stealing those chunks of iron out of orbit around a gas giant. They are there in the first place cause the GG has a serious gravity well.
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    Maybe grab them from Tojan points of gas giant. Plus, changing delta vee deep in gravity well results in gains in speed, does it not? Versus same change farther out.

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    Grab them? If they came in from a gas giant's orbit, they would be moving 40 km/sec as they passed by (or smashed in to) earth.
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