h a l f b a k e r yAlas, poor spelling!
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Solutions that have been suggested include harvesting interstellar hydrogen. Collecting starlight and converting it to hydrogen would be terribly inefficient. |
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The Bussard Ramscoop as a design is [widely-known-to-exist]. |
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Inverse-square law means that in interstellar space, the amount of energy that can be harvested with photovoltaics is derisory. |
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Aquiring more reaction mass can be achieved by bouncing a gas giant and scooping up some of the upper atmosphere on the way through, or grabbing comets and crunching them up. |
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(not our fishbone, by the way). |
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I'd have to check, but I think you'll find that if you're in a situation where you've got an energy source, but no reactive mass, you're much better off using a photon drive rather than making some reaction mass and putting it through an ion drive. |
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Of course, if you're going to use solar panels to gather the energy (inneficiently), then use that energy to run a photon drive, then why not use a solar sail? |
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I've read some discussions about craft using a solar sail with some of the surface covered in photovoltaics, which charge batteries for use in a photon drive for directional control/maneuvers. Or something like that. |
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Photon drive? Whazzat? A big flashlight? |
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Yep. You're better off using the momentum of those photons, as they will give you the maximum thrust for the energy. |
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[+] "starlight drive": cool... wouldn't work but still cool. |
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wonder if Dr Bussard designed his ramjet to be regenerative. |
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I agree with Custardguts and ldischler. |
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So you have two options: set m to zero and get a photon with E/c momentum (for a photon drive); or set p to zero and get a mass of E/c^2 (for an ion drive) (which you'd then have to accelarate to some velocity* to get an equivalent amount of momentum). |
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*the equation implies you'd need to accelarate it to c (the speed of light), but that's not taking into account relativistic effects. So it's probably less than c but pretty close. |
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Since all you really want for propulsion is momentum, photon drive is clearly the better option. |
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