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I have recently had a renewed interest in comets and how comet tails are formed. From studying this process, a thought occurred to me that perhaps plasma ions can be created within a long hollow cylinder (say 50 ft long with a 3 ft diameter), open at one end and closed at the other, and when these plasma ions interact with the Sun’s solar wind, this cylinder/rocket will be propelled away from the Sun at a high velocity. Ideally, this rocket would be launched as close to the Sun as possible to gain the maximum effect of the solar wind.

The working principle of this rocket is that the open end of the rocket will be pointed directly at the Sun so that the solar wind will continually flood the interior of the rocket. At the closed end of the rocket, several gallons of water, or water ice, will be injected into the interior of the rocket, and this water will be quickly transformed into hydrogen and oxygen ions by the solar wind. The solar wind will then pickup these ions and push them against the closed end of the rocket. I think that these trapped ions pushing against each other will create a strong internal dynamic pressure and this pressure will continually push out against the solar wind flowing into the rocket. This interaction may create a ‘bow shock’ somewhere within the interior of the rocket. This bow shock should keep the ions trapped within the rocket. As this rocket is being accelerated, retrorockets will keep this rocket pointed in line with the outward flow of the solar wind.

Moreover, if this rocket were to be sent to another star, the solar wind from that star can be used to decelerate the rocket. Its retrorockets will simply rotate the rocket 180 degrees before it enters that solar system.

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The density of the solar wind is far too low for this to be effective. Around Earth, density is 3-7 atoms/cm3. Water has on the order of 1020 atoms/cm3, so it would take on the order of 1020 seconds to split all the water.

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  • $\begingroup$ I am thinking that this type of rocket would best be launched from about the same distance that Mercury is from the Sun since the density of the solar wind will be higher there. Also, instead of using water/water ice, I think as an alternative fuel source, oxygen ions could be injected directly into the interior of the rocket from some type of pressurized cylinder. Oxygen ions should immediately be picked up by the solar wind flowing into the rocket and be thrown against the closed end of the rocket, providing the dynamic pressure to propel the rocket away from the Sun. $\endgroup$
    – user26242
    Jun 18, 2018 at 18:20
  • $\begingroup$ Distance of Mercury to the Sun is ~0.5 AU, so the solar flux there is only 4 times higher than at Earth's orbit. 20 atoms instead of 5. Still far too little to get noticeable thrust $\endgroup$
    – Hobbes
    Jun 18, 2018 at 19:10
  • $\begingroup$ When a solar ion picks up an oxygen ion, its speed drops immediately: kinetic energy stays the same but is now distributed over a much larger object. The amount of thrust you can get from this setup is not higher than you'd get from just letting the solar ions collide with your spacecraft. $\endgroup$
    – Hobbes
    Jun 18, 2018 at 19:11
  • $\begingroup$ Since oxygen ions are negatively charged particles and that they repel each other, when the solar wind charged particles enter the rocket and slam into them, these oxygen ions should then bounce off each other like billiard balls on a pool table. These oxygen ions should transfer the kinetic energy they received from the solar wind particles to the closed end of the rocket and this should propel the rocket away from the Sun, yes? $\endgroup$
    – user26242
    Jun 19, 2018 at 12:12
  • $\begingroup$ Whatever they do, doesn't matter. There are far too few of them (by 20 orders of magnitude) for them to have any effect. $\endgroup$
    – Hobbes
    Jun 19, 2018 at 12:18

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