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A comment on LightSail 2 Spacecraft Successfully Demonstrates Flight by Light. Parent comment

Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by jimktrains2 on Wednesday July 31, 2019 @06:21PM (#20579170)
Perhaps I'm being a dunce right now, but doesn't the fan exert a force on the car opposite the direction of flow, and wouldn't that force necessarily be greater than the force of capturing the same flow in a sail?

Also, why not just use the fan or laser or led as the means of propulsion directly?

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Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by umvi on Wednesday July 31, 2019 @06:42PM (#20579354)
No, because of conservation of momentum. Same reason a jet engine can move a piece of metal to reverse its thrust
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Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by jimktrains2 on Wednesday July 31, 2019 @09:06PM (#20580319)
Sure, the air hitting the sail would impart a force on the craft, but there is also a force from the fan?

I guess I think of reversers as redirecting the jet blast in a controlled manner, I guess I don't think of the sail as redirecting the wind in a controlled manner.

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