1. mugen shiyo
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    mugen shiyo Contributing Member

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    Gravity/Solar Energy As Propulsion?

    Discussion in 'Plot Development' started by mugen shiyo, Sep 23, 2011.

    What do you think about gravity as a source of propulsion in space?

    But you know how a sail uses the wind to navigate. There is no wind and space and currently no known fuel that you could store in sufficient quantity that would enable you to make a very long journey. I was wondering about a psuedotech that would have found an ore capable of strong reactions to gravities energy the same way a magnet reacts to magnetic energy. But shifting the polarity of said ore, a ship using these special sails could control the rate of attraction and repulsion to a gravitational body.

    The differing levels of gravity from different and moving sources create shifting gravitational currents that require professionals to interpret and navigate. Because of this, a ship may be able to latch on to large planetary bodies and such in leap-frogging fashion. This would be the equivalent of land-hugging for a spaceship where it could only employ useful navigation where the gravitational density was considerable.

    An alternative to this would be using the Solar Wind as propulsion through the solar system. Of course, this would limit the range and effectiveness of said ships the further from the sun it gets.
     
  2. Cogito
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    Cogito Former Mod, Retired Supporter Contributor

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    Sure, if your characters live forever and are innately patient. Space is so vast and the magnitude of gravitational force so weak on average throught space that you would be talking about millenia to cross to the nearest star.

    Light sails are slightly better. You're probably only talking about tens of years between neighboring stars, but "practical" light sails need to cover hundreds of square miles and wegh only a few tens of pounds for a craft that could hold only a couple travellers.
     
  3. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    Yes, I agree with Cogito. Gravitational force drops off dramatically over distance, so that's a tough one for interstellar travel.
     
  4. psychotick
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    psychotick Contributing Member Contributor

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    Hi,

    You're speaking about antigravity, and if you have a means of achieving it, yes its a viable method for travelling interstellar distances. But the system as you've described it limits you. If AG is only a thrust system, then the maximum acceleration you can maintain is about one gravity, because at more then that your crew will start to be squashed and suffer health effects. If you can somehow extend the antigravitational field around the entire ship so that in effect it is all zero gravity within, then you can accelerate at hundreds of gravities, because in effect the ship and everyone in it would be weightless and simply falling away from the gravitational body. One gravity means reaching light speed in just over a year, hundreds in proportionally less time.

    However the next problem you face is that as the distance from your object, planet perhaps, increases, the gravitational force it exerts upon your ship decreases. In short even if your drive gives you hundreds of gravities, it will only give you that acceleration relatively close to the gravitational source its falling away from. To maximise this, you should probably use a star, which means getting your toes all nice and crispy, and accelerate as fast as possible knowing that soon your acceleration will peak. Its like pulling a slingshot as far back as you can before releasing the stone, and hoping nothing breaks.

    After that relativity says you can't go faster then the speed of light, so you have a theoretical maximum speed there, which may well be lower then the theoretical maximum you AG drive could give you.

    Solar sails run off the solar wind, and are slow. In essence they run off the radiation pressure of the star, and the accelerative force they can provide is tiny, and worse yet its becomes smaller the further you get away from the star pushing them.

    There are also hydrogen collectors, (scoops and rams), which people often confuse with sails, and the hydrogen they gather can be used as fuel. The good thing about them is that there is plenty of interstellar hydrogen out there, so the ship hopefully doesn't need to carry vast amounts of fuel with it, which makes it lighter. The bad is that while they are considerably theoretically better propulsion systems then sails, and the distance from the sun doesn't affect their thrust, they are still slow.

    You can google all of these for much more detail. And also NASA just reported a major success earlier this year with a solar sail satellite,which you may find interesting.

    Cheers.

    ---------- Post added at 11:17 AM ---------- Previous post was at 11:16 AM ----------
     
  5. Monodokimes
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    Monodokimes New Member

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    Gravitational energy as propulsion is a no go, but solar sails are much more promising.

    They work through the physical energy of ions colliding with the sail. However tiny this energy is, it still works, as perpetual momentum is possible in space.

    The acceleration is also tiny, it would take about 30 years for a ship to accelerate to practical speeds from the Sun's light.

    A way of keeping the acceleration up further away from the Sun would be using a powerful laser, aimed directly at the receding ship.

    That's all I've got, hope it helps.
     
  6. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    Maybe the Bussard Ramjet or Ramscoop is a better way to go.
     
  7. Cogito
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    Cogito Former Mod, Retired Supporter Contributor

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    Bussard ramscoops have been disappointing in quantitative analysis. The collectors must extend over a huge area, and the drag increases roughly as the square of the relative velocity. The peak velocity would therfore be fairly limited. Also, the density of interstellar gas varies considerably, sor teh ramscoop size and geometry will probably require continual adjustment for optimal performance. Also, the density of gases other than hydrogen will increase the drag without contributing to the propulsion energy.
     
  8. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    What is the most plausible science fiction mechanism for interstellar travel? Outside of just normal propulsion and something like a generation ship or cryo while people get to where they are going.
     
  9. dave_c
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    dave_c Active Member

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    im not entirely sure as to what some of you are talking about,
    1. gravity has no maximum speed in a frictionless environment like space
    2. antigravity would not work as propulsions, anti gravity is simply a method of artificially removing the force of gravity

    this is what came to mind when you said using gravity/anti gravity as a propulsion system

    1. the ship gets pulled toward a star by gravity
    2. the ship usues some kind of anti gravity device to stop JUST that star exerting gravitational forces
    3. it uses the momentum to catapult itself towards another star, lather, rinse, repeat. kind of like web slinging on a universal scale :)

    there is no friction in space so there would be no loss in speed so every time it reached a star it would get faster and faster, this would of course require an initial burst of energy to get things moving at a good speed.

    just steal a bit from star trek. sling shot is the way to go, you wont travel through time, but for increasing speed its viable. purhaps you could even sling shot round every star (assuming your tech is high enough to shield you)
     
  10. Croga
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    Croga Member

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    Maybe this is stupid I don't know.
    Find a way using the LHC (large hadron collider) or something similar to expose and harvest vast quantities of dark matter.
    If you do this then find a way to shield it within a massive combustion tank until it hits the 'piston' then release the shields adding matter and set off an explosion your piston will how to harness.
    If I'm right this would offer immense power and so much energy that it would suit the needs.
    Of course there is a lot of issues with this like the output of the LHC being very limited and that output being viewed as certain even if science develops a new and better LHC the extremely explosive Dark matter takes years to produce only insignificant amounts of the stuff and normally requires more energy to produce than it can equal.
     
  11. psychotick
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    psychotick Contributing Member Contributor

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    Hi Dave,

    I'm assuming you're talking to my post. First (and I'm no physicist so you should probably check some of this out for yourself), there is a 'speed of gravity'. This is the speed at which a gravitational wave / field spreads out, and in classical relativity its the same as the speed of light. So to explain this a little better (I hope) if a partical / world / sun suddenly popped into existence somewhere into the universe, and you were one light year away from it, it would be one year before you as an object with mass could feel / measure the gravitational attraction from it on yourself.

    Second, relativity says the speed of light is it as far as objects with mass go. So you can sling shot your way around stars and use it to constantly increase your speed, but only to that theoretical maximum speed. (In the wake of the neutrino speed studies,which may turn out to be some sort of measuring error or may mean that relativity has to be somewhat amended as a theory, this has to be taken with a grain of salt.)

    Third antigravity, if it exists, does not have to be just a system of removing the effects of gravity from a mass. It could be that, but I would see no reason to limit it to that. Consider, if you can create an artificial field that is opposed to normal gravity, i.e. its repelled by gravity, it can instantly become a drive. Say you created it on Earth, stood in it and switched it on, you would, assuming you've got it right, have the strange experience of falling away from the Earth.

    As for slingshotting around stars. People use this idea a lot, but it comes with its own problems. Consider comets. They do this very thing. At roughly a third of a lightyear out they start feeling the effect of the sun's gravitational field upon them and start falling towards it. As they fall towards itthey gain speed, so that by the time they're near the sun they're moving along at a good little clip. Unfortunately after they go around the sun and start their journey back to the comet body, they slow down, giving up all the kinetic energy they gained from falling towards it as the sun's gravitational field holds them back. To use the slingshot system, you have to have a way of stopping this. An antigravitational system would do this.

    Cheers.
     
  12. dave_c
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    dave_c Active Member

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    it wasnt aimed to be offensives so i apologise if it came across as such (i get the feeling i offended you, sorry) i just organize my brain in numbers so generally write in that way.

    basically you cant go faster than light because there (apparently) isnt enough energy in the...everything to do so (this i don't personally believe this but its what the tech heads will tell you) this is all based upon Einsteins e=mc2. i should point out that there are currently studies which are showing this "Law of physics" to be false. basically this means that potentially faster than light travel is possible (though im about to get flamed by anyone and everyone who studied physics lol.

    there is an awful lot we dont know about standard gravity so i cannot wrightly say, there is no such thing as anti gravity......but.....chances are minimal in my opinion.

    your example of it taking a year for the gravitational field to reach somewhere i cannot comment on i have never done any research on the expansion of gravitational fields. The rate of the expansion of the gravitational field does not dictate the rate or force of pull which it exudes, it may be able to only expand at the speed of light, however that does not mean that the rate of pull is the same. gravity is like magnetism; if you continuously move the force generating matter away from the force recipient, they will get faster and faster and faster and theoretically if you COULD KEEP moving the force emitter away you could theoretically (and i emphasis the word theoretically) pass the speed of light. however this would require you to use (lol) anti-magnetism which to my knowledge is at a similar level of Sci-Fi as anti gravity.

    on the fictional side of things however where sling shots are concerned you could simply sling shot round a star then use the anti gravity to void the effects of leaving the orbit. (ain't it great to be able to bend the laws of physics :D)

    i may be miss informed or just out right wrong but i can only reply based on what i have been told, have read and learned over the years of being friends with total nerds, haha. again sorry if i caused offence :)
     
  13. Steerpike
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    Steerpike Felis amatus Supporter Contributor

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    There is faster than light interaction, however. Entanglement. Einstein called it 'spooky action at a distance,' and he and others were opposed to this ramification of quantum mechanics. It looks like Einstein was wrong on that one, however.
     
  14. psychotick
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    psychotick Contributing Member Contributor

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    Hi Dave,

    No worries, I wasn't offended by anything you said. And I'm not enough of a physicist to worry about whether the speed of light is an absolute speed limit or not.

    I like your idea of moving the source of the gravitational attraction away to keep accelerating a ship, but it does rather mean moving planets around which sort of defeats the point of having a space ship anyway.

    Cheers.
     

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