LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by Skunkleton on Wednesday July 31, 2019 @07:15PM (#20579602)

This is just a complicated way of saying the same thing. Of course a jet engine is not just a really fast propeller. And if you hooked a "bag of air" to a propeller, that would also work in space.

Either way, an LED is not generating any meaningful thrust, and pointing that thrust at a sail adds no benefit.

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Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by wiredfool on Thursday August 01, 2019 @05:31AM (#20582354)

No, it's not.

A propeller makes thrust like a paddle, by pushing off of something. A jet/rocket engine makes thrust by recoil, using conservation of momentum.

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Re:LightSail 2 Spacecraft Successfully Demonstrates Flight b... by 8456523 on Thursday August 01, 2019 @05:44AM (#20582415)

Almost all modern jet engines have (ducted) fans. In planes that never go supersonic, e.g., all current commercial airliners, the fan provides most, but not all, the propulsion. And the only difference between a fan an a propeller is how many blades it has. (The presence of a duct around the fan does not change anything basic.)

But even if they did not have fans, there is no fundamental difference between using a propeller or fan to speed up the flow of air and heating the air inside a chamber to speed up the flow of air. (The fan is used because at subsonic speeds it can be made more efficient.)

In other words, all 3 means of propulsion work by conservation of momentum.

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