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A comment on Factories in Space. Parent comment

Re:Factories in Space by f154hfds on Tuesday May 30, 2023 @12:07PM (#36126541)
The 'feeling' of weightlessness is pretty much an indication of 0 (micro) gravity. Gravity always exerts a force, the problem is on Earth we have ground exerting an equal and opposite force contrary to gravity. When you feel weightless whether in orbit or just falling off a cliff you're in free fall experiencing none of that upward opposition to gravitational force.

For example, it was very hard to replicate the moon's gravity when training pilots to land on the moon. How do you 'fake' a different gravity on Earth? It's pretty hard to do: https://www.youtube.com/watch?v=aw8kRZEvh_s

EDIT: to your question about centripetal force, either you experience acceleration or you don't. Since gravity is in equilibrium with centripetal force relative to movement around Earth you shouldn't get acceleration from this. However, you will get micro g's from rotation of the station itself, etc.

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Re:Factories in Space by RC_ITR on Tuesday May 30, 2023 @12:45PM (#36127102)
>centripetal force relative to movement around Earth you shouldn't get acceleration from this.

If there is no acceleration, then how are objects changing direction?

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Re:Factories in Space by f154hfds on Tuesday May 30, 2023 @03:00PM (#36129059)
The ISS will do a 360 degree rotation every 90 minutes to maintain its orientation relative to the surface of the Earth. This will result in bodies inside the ISS slowly rotating in the opposite direction of that rotation. However, this is unrelated to acceleration - these are constant angular velocities. The micro gravity I believe is the result of atmospheric drag, and the occasional boosting required to account for it.

Also I should add, it is confusing thinking about 0g, because obviously bodies in a gravity well are experiencing a gravitational force. Really we're talking about 0 acceleration, where g is the acceleration due to gravity. In orbit this g acceleration is cancelled out by centripetal acceleration to produce 0 acceleration, or free fall.

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Re:Factories in Space by heavenlyblue on Tuesday May 30, 2023 @06:48PM (#36132163)
Aren't bodies inside ISS rotating with it? Or are you implying that the rotation of ISS is not inertial but is constantly propelled by engines? If engines are driving it constantly, why is not constantly accelerating it's rotation?
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Re:Factories in Space by f154hfds on Wednesday May 31, 2023 @10:04AM (#36138562)
True - thanks for the clarification. As long as the ISS is rotating at a constant rate anything oriented to it inside of it will not perceive it to be rotating. It's rotating relative to a stationary perspective on the surface of the Earth but by the time anything docks to it, everything in the system will be rotating at the same rate. Thanks for pointing this out!
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Re:Factories in Space by RC_ITR on Wednesday May 31, 2023 @01:24AM (#36134753)
>However, this is unrelated to acceleration - these are constant angular velocities.

If it were not for the force of gravity, an object in motion would move in the direction of its instantaneous velocity. It does not do that, it instead accelerates toward the center of the gravitational body.

>In orbit this g acceleration is cancelled out by centripetal acceleration to produce 0 acceleration, or free fall.

But again, they do not "cancel out," otherwise how is the instantaneous velocity constantly changing direction?

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Re:Factories in Space by f154hfds on Wednesday May 31, 2023 @09:55AM (#36138454)
You're bringing up the bizarre thing about gravity here. The only way we could be in 'free fall' undergoing 0 acceleration while still going in circles is if space itself were warped around an object.
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