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Writing: Input Wanted Designing a space ship and need help with the dust shield

  1. Feb 16, 2016 #1

    DHF

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    Hello everyone, I am designing a ship for my sci fi story and I need input regarding the shield. I am trying to make my story as hard sci fi as I can get away with. The story takes place a few centuries from now and details the first expedition to Alpha Centuri. The ship will have a cruising velocity of 12-15%c and I am currently trying to figure the best way to protect it from collisions with dust and other schpleh it encounters along its merry way. Would the shape of the shield have any baring? Lately I have wondered if it was possible to construct the shield in such a shape that it deflected impacts rather then absorbing them. would this work or would it not make any difference when you are moving at those speeds?

    Any other ideas for the shield? I am open to ideas.
     
  2. jcsd
  3. Feb 17, 2016 #2
    What other technologies do humans have at the time? Can they create exotic matter? A shield made out of neutronium should be able to handle pretty much anything.
     
  4. Feb 17, 2016 #3
    I thought about a strong magnetic field deflect charged particles.
    And use X-lasers, or electron and proton beams to charge uncharged ones.
     
  5. Feb 17, 2016 #4

    DHF

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    Yes Nutronium would be a super shield but it is off the table for my characters for a few reasons, This is their first exploration outside of the Sol system so they wouldn't have access to Neutron stars. I also feel that fabricating such a material would be well beyond their technical capabilities. fabricating Neutron material and you are talking about a society that is likely tens of thousands of years ahead of us. I was trying to keep my tale within a few hundred years because I want the world the characters come from to be recognizable to the reader.

    I also wanted to keep mass and fuel within reasonable limits. I am capping the ship's speed at no more then .15c because I want to keep the fuel consumption within believable limits. Most of the ship's mass is already going to be the fuel, I was hoping there was a way to get off with having a less massive shield. I was thinking that if the shield were cone shaped or had channels built into it, it might be able to deflect most of the kinetic energy of impacting dust and micro meteors at a significant portion of the speed of light. I just don't know if this is feasible or just wishful thinking on my part.
     
  6. Feb 17, 2016 #5

    DHF

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    I had considered that as well but I was wasn't sure about energy based shields because the trip will take around 30 years and I wasn't convinced they could afford to keep a powered shield running for decades at a time.
     
  7. Feb 17, 2016 #6

    Nidum

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    Use clear path technology . Look ahead and collision avoidance systems backed up with seek and destroy defensive systems .
     
  8. Feb 17, 2016 #7
    Compared to propulsion requirements, i think its affordable, besides, ionization dont need to be constant, i'm not sure whether superconductors can upheld the magnetic field without constant energy supply?
     
  9. Feb 17, 2016 #8

    mfb

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    Fuel can act as shield.

    Your particles hit the spacecraft at 10 MeV/nucleon. You will get nuclear reactions and some interactions with electrons, all directed towards the ship (as seen in the frame of the ship) in a shallow angle. While you cannot deflect the incoming particles themself, a very long nose cone might be able to have some reaction products escape without damaging the shielding further.

    Every 1 milligram speck of dust will have the same energy of ~240 kilograms of TNT, and I don't see how you can detect or destroy them in any realistic way. You will get some explosions at the front.
     
  10. Feb 17, 2016 #9

    DHF

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    Are you referring to using some of the hydrogen as a shield by spraying it in front of the ship and letting incoming dust impact the mist of fuel particles to absorb the impact?
     
  11. Feb 18, 2016 #10
    Wont that result in fuel tank leak?

    In another topic, we speculated about liquid/ferrite dust/nano armor, that held by a magnetic field, so it immediately restores damages.
     
  12. Feb 18, 2016 #11
    Wouldn't you need one anyway? Interstellar space is full of cosmic rays that would have to be deflected as well.

    You say neutronium is too far off for you, what about superheavy elements? Are your people advanced enough to synthesize these? We have no idea if the physics are correct or not, but theoretically there should be stable elements around number 146: https://en.wikipedia.org/wiki/Island_of_stability#Hypothetical_second_island. It's still not very dense compared to neutronium, but should provide some shielding.
     
  13. Feb 18, 2016 #12

    DHF

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    A very dense and massive shield is certainly within the limits of the society I am While the ship is being privately funded it will still need to take into account that every kilogram of mass I add to the ship is going to cost more fuel to move it. I am not putting a figure down for how much it all costs but I wanted to be respectful of realism. So yes the shield will need to be made strong enough to withstand countless contact explosions of nuclear strength. Constructing the shield out of a very dense metal was one idea. Carving a cylinder of ice several hundred meters thick and pushing it ahead of the ship is another idea. Ice is pretty cheap and easy to come by in space and a very thick layer would absorb a lot of radiation. In this particular post I was exploring ways to reduce the mass of the shield while still making it tough enough to withstand the punishment it will undergo.
     
  14. Feb 18, 2016 #13

    mfb

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    I'm not sure if that would help, and gas would disperse.

    A thin shield in some distance to the remaining ship might help. Individual molecules would induce some radiation damage to the lattice, but that can be repared. Specks of dust would produce holes, and the debris is then scattered sufficiently to reduce the impact on the main ship.
    Solid fuel?
    Macroscopic forces can be too strong for magnets, and for things like lattice defects those structures are too large.
    There is no realistic way to deflect cosmic rays. Use shielding.
    Even if they are stable, which is highly questionable: are you limited by space? Twice the number of lead atoms do the same job for the same mass.
    "Neutronium" in the way neutrons stars have it is stable in neutron stars only.
     
  15. Feb 19, 2016 #14

    Ryan_m_b

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    I was going to say this too. Deploy a thin shield far ahead of the ship (perhaps push/keep it there with lasers). It's not going to stop debris but if something problematically big (>10 micrograms) hits it then the resulting explosion would hopefully be enough to deflect/spread debris over a much wider point. Then you either repair the Sail Shield or leave it and deploy another.
     
  16. Feb 19, 2016 #15

    DHF

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    I am liking this idea.
     
  17. Feb 19, 2016 #16

    Ryan_m_b

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    I have no idea how to work out how feasible the sail shield idea is, given the speeds involved any debris (I'm guessing) would shoot straight through without interacting. But if the tiny portion of the sail material that is hit explodes into a plasma it would hopefully be enough to knock the whole thing off course, maybe in pieces.

    If anyone knows a quick and dirty way to putting numbers to that it would be cool.
     
  18. Feb 19, 2016 #17

    mfb

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    Individual atoms would get stopped within a millimeter for anything at least as dense as water. I don't think it will be different for dense massive objects - the collisions happen at timescales where the motion of the atoms in transverse direction is negligible. They won't get fully stopped, but they interact sufficiently to get a relatively uniform motion of the collision products.

    For order of magnitude estimates, let everything have the density of water. Taking the milligram object from above again, let it collide with a shield 1 cm thick. I would expect most atoms in the millgram object to interact with the shield material. We get a small ball of plasma with a mass of roughly 11 mg mass, probably with some charge separation (electrons get accelerated easily, the nuclei not so much), so the whole thing makes a coulomb explosion. The available energy for transverse motion should be way in excess of 10 eV per nucleon, which is 1/100,000 of the total energy. That would give a speed of at least 1/1000 of the spacecraft velocity. But the mass of the plasma comes mainly from our shield, so it just moves at 1/10 the spacecraft velocity relative to the spacecraft. So we have a velocity ratio of 1 to 100. A shield at a distance of a few hundred times the diameter of the spacecraft should work. Probably less.
     
  19. Feb 19, 2016 #18

    DHF

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    So by the time that ball of plasma hits the cone shaped main shield of the ship, it is hitting it at a much slower velocity then the original object. So instead of 1mg striking the ship at .15, you instead have a 11mg mass hitting the main shield at .015c?
     
  20. Feb 20, 2016 #19
    One trend I see is the use of ram scoops. Right now it is one of the best alternatives for interstellar travel we know and the ram scoop takes care of the problem pretty well.

    Other solutions I have heard about is a good layer of ice.

    Lastly, the best solution is simply don't reveal the technology. It just works (whatever it is) and the less you write about it, the better.
     
  21. Feb 20, 2016 #20

    mfb

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    Ideally you have most of it missing the spacecraft. But even that change reduces the energy by 90% and spreads it over the front.
     
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