This question asks: How large a body could a probe with ion engines land on and launch from? and made me think could an ion engine that is the payload be mounted in a way to assist in the launch?
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1$\begingroup$ @Uwe Good point. Muze are you talking about launching from earth or from an airless body? $\endgroup$– IngolifsApr 8, 2019 at 22:33
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5$\begingroup$ Ion engines can only operate in vacuum. That means you can't use them to take off from earth's surface. Even in vacuum, the thrust of ion engines is abysmal, and as the question you linked states, you could probably only use it to lift off from a rock 100 m wide. The 'help' that an ion engine will impart during a takeoff would be essentially nil. A similar thrust can be achieved by having a kid hanging off the rocket throwing crumpled pieces of paper downward. $\endgroup$– IngolifsApr 9, 2019 at 0:11
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3$\begingroup$ @Ingolifs “Ion engines can only operate in vacuum.“ Technically speaking, that's wrong youtube.com/watch?v=boB6qu5dcCw but I agree with you ;-) $\endgroup$– Everyday AstronautApr 9, 2019 at 10:34
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2$\begingroup$ @EverydayAstronaut 1, 2, 3, 4 $\endgroup$– uhohApr 9, 2019 at 13:07
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2$\begingroup$ @Ingolifs: The question isn't all that misguided. The idea of using vacuum-optimized engine within the atmosphere to aid the boosters is not new, and a reasonable one. There's no use for the child sitting on the rocket, meanwhile the same ion engine could be used to accelerate the craft in orbit, and still be of some use during lift-off instead of being a dead weight. The problem of course is that the scarce millinewtons really don't contribute anything worth the headache, even if you get it to work in the atmosphere at all. $\endgroup$– SF.Apr 9, 2019 at 13:09
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1 Answer
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For earth
If you:
- Designed an ion engine that could operate in non vacuum
- Found a way to power it
- Found a way to route the exhaust
All that while not adding any mass or drag (else it's pointless)
It could do something. However
- An ion engine has a thrust in the order of magnitude of 0.1N
- A rocket have a thrust in an order of magnitude of 10000000N
...
It would be pointless.
Sure, for a small body it might provide a greater fraction than a chemical rocket, but it will still be a rounding error.
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$\begingroup$ You are right for Earth. Maybe there is more to the question (with a little stretch). What if you want to land on but don't want to mess up the delicate, eons old dust surface of a tiny asteroid or comet? That would be prohibitive of chemical engines. Maybe there is a scenario in which you could land on and take off from a small space rock with just ion thrusters, where chemical rockets would not just alter its surface but might also change its orbit. Not saying ion drives would be the only option, but perhaps they could be one. $\endgroup$ Apr 9, 2019 at 10:45
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1$\begingroup$ @EverydayAstronaut ion thrusters will also have an exhaust, with the same energy as the chemical thrusters. Here, the question is about combining them, which precludes it anyway. I suggest you to google ion exhaust plums, it's beautiful :) $\endgroup$– AntziApr 9, 2019 at 11:24
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$\begingroup$ the exhaust of ion thrusters is much less dense but much more energetic per particle than the exhaust if chemical rockets. Just thinking about if there could be a use case ... $\endgroup$ Apr 9, 2019 at 11:43