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Thread: Making it work for you: Bussard Ramjet and magnetic field

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    Making it work for you: Bussard Ramjet and magnetic field

    Instead of using a wide magnetic field that creates drag, could a starship use a stream of ionized gas to conduct a magnetic field forward in a line? Gather matter from the IM only in front. Would this make any significant difference in drag force? Could the pull of the magnetic field be leveraged towards the direction of travel this way?
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    How big could you scale up something like an electrolaser? A particle beam? Put the high beams on and zap your way to the stars.
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    Assuming a fusion drive and dusty-plasma radiators what would such a ship look like from the outside when it turned on its main drive? Too bright to look at naked eye, I'm sure, but it would probably be a pretty spectacular sight by optical telescope.
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    Just from a very general perspective, as opposed to addressing your specific idea, it seems to me that if the means of manipulating particles in the interstellar medium to be used by the ships propulsion system is in any way coupled to the ship that there is no way to avoid drag. It seems to me that the only way to avoid drag would be to use other means completely uncoupled from the ship to direct particles into the path of the ship at a velocity close to the ships velocity. Similar to the idea of launching fuel pellets from a home base (think Motie light-sail craft launching lasers scale effort) at various calculated speeds, to match a planned flight profile from acceleration through deceleration, along your ships flight path so you don't have to carry your fuel with you. At that point it wouldn't really be a Bussard Ramjet.

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    So if you can't avoid drag (kinda thought so) how could it be minimized?
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    What about related design concepts, like Scramjet and RAIR (Ram Augmented Interstellar Rocket)
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    What would spinning the magnet at high speeds do to the field lines?
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    Quote Originally Posted by Noclevername View Post
    Instead of using a wide magnetic field that creates drag, could a starship use a stream of ionized gas to conduct a magnetic field forward in a line? Gather matter from the IM only in front. Would this make any significant difference in drag force? Could the pull of the magnetic field be leveraged towards the direction of travel this way?
    It's already going to pass through that region of the IM, so what's there to gain?

    You need a scoop with a cross section sufficient to scoop up enough interstellar hydrogen to use as propellant. Regardless of how much you collect, you then need to fuse that hydrogen and accelerate the reaction products out the back at a velocity higher than the velocity of the craft relative to the medium. If you can't do that, then drag is going to exceed thrust no matter what.

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    Quote Originally Posted by cjameshuff View Post
    It's already going to pass through that region of the IM, so what's there to gain?

    You need a scoop with a cross section sufficient to scoop up enough interstellar hydrogen to use as propellant. Regardless of how much you collect, you then need to fuse that hydrogen and accelerate the reaction products out the back at a velocity higher than the velocity of the craft relative to the medium. If you can't do that, then drag is going to exceed thrust no matter what.
    Yes, that's the point.
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    Quote Originally Posted by cjameshuff View Post
    It's already going to pass through that region of the IM, so what's there to gain?
    Ah, I see what you mean. I was looking at it from the Newton's Laws angle, but I suppose magnetic attraction between the IM and the mass of the starship would not transfer much momentum to the latter.
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    And you want drag to use as a brake. Refuel and slow down all at the same time perhaps.

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    Quote Originally Posted by publiusr View Post
    And you want drag to use as a brake. Refuel and slow down all at the same time perhaps.
    Sure, but you don't want it on all the time!
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    So let's see if I can make this work:

    Assume a RAIR starship, carrying its own power supply, something energetic but not too massive. Collected antimatter from the gas giants magnetospheres, maybe catalyzing a fusion reaction.

    Start with launch, straight out of the dock. Assume some kind of large drop tank to provide the initial propellant; the "lollipop on a stick" school of design.

    After that's used up and the tank is dropped, use a mass beam to transfer momentum from a large space body to the starship. (This might be accomplished by a linear accelerator or a stream of laser-driven mini lightsails, the starship uses its magnetic field to "catch" the projectiles)

    Then the matter beam switches to seeding fuel or propellant along the starship's flight path. Something it can scoop with minimal effort and ramscoop cross section.

    Once the ship has built up enough acceleration it's on its own. Goes into a cruising mode, shielding itself from the IM with a dense magnetosphere.

    Magnetic scoop/shield also can expand to act as a magsail to brake, and also gives a cheap way to maneuver at the destination point. Power and propellant have run dry, switches to use local materials and energy sources.

    Here endeth the journey.*

    ADDED: *A return trip would entail building extensive, all new infrastructure at the destination. Not a job for the first-in arrivals.
    Last edited by Noclevername; 2019-May-28 at 11:31 AM.
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    Quote Originally Posted by Noclevername View Post
    Then the matter beam switches to seeding fuel or propellant along the starship's flight path. Something it can scoop with minimal effort and ramscoop cross section.
    This has to be done prior to launch and initial acceleration. Otherwise you'll have to sling the propellant past the starship at a velocity far greater than that of the starship itself, and the starship will never be able to catch up with it. It makes more sense to sling it directly at the starship at that point...the direct matter beam phase only requires you to launch the propellant fast enough to reach the starship before the starship reaches its destination.

    Braking propellant can be sent after the starship, because it'll catch up after the braking process begins. This will be less effective than overtaking pre-launched braking propellant, though, due to the higher velocity of the propellant.

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    Quote Originally Posted by cjameshuff View Post
    This has to be done prior to launch and initial acceleration. Otherwise you'll have to sling the propellant past the starship at a velocity far greater than that of the starship itself, and the starship will never be able to catch up with it. It makes more sense to sling it directly at the starship at that point...the direct matter beam phase only requires you to launch the propellant fast enough to reach the starship before the starship reaches its destination.

    Braking propellant can be sent after the starship, because it'll catch up after the braking process begins. This will be less effective than overtaking pre-launched braking propellant, though, due to the higher velocity of the propellant.
    OK. That also allows the matter beam system to be tested and perfected years before the starship launches.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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