Asteroid Mining and Space Elevators (split from Are billionaires rich enough yet?)

[skepticalbip]

If you have a rotating sphere out in space away from gravity and attach a tether to the surfaceI expect the system will rotae about the center of gravity. On an asteroid you may end up with wild uncontrolled behavior.

Planets are 'tethered' to the Sun.

That was Newton's understanding. Uncle Al suggested that planets move in straight lines through spacetime that was bent by the mass of the Sun. Uncle Al liked Newton's third law of motion ( A body in motion remains in constant motion along a straight line unless acted upon by an external force.). Since "action at a distance" isn't allowed, he saw that the Sun couldn't exert a force on the planets but the Sun's mass could bend the fabric of spacetime.

 

[steve_bank]

The simple point was the solar system does not revolve around the Sun. The Sun and planets revolve around a point that is not the center of mass off the sun, the rotation point is the center of mass of the total system.

Attach a teher to an asteroid tht has rotation and I think results coould be erratic.

 

[atrib]

Planets are 'tethered' to the Sun.

No, they are not. Planets, and all celestial bodies follow equipotential lines along the curved surface of spacetime. They are not tethered to the sun by a force - they are simply conserving the kinetic energy they have acquired over their past history of formation and interaction with other objects.

EDIT: Here's another way to think about it. If you throw a ball up in the air vertically, the ball will lose energy due to drag resistance (having to push air out of its path) and friction. And, due to its initial trajectory, the ball is also moving across equipotential surfaces (of gravitational potential) around the earth's surface. Or in other words, the ball is moving through a region of spacetime that is heavily distorted due to the presence of the earth. Eventually the ball will slow down enough that the earth, which is also in motion, catches up to the ball and the two collide. The ball never experiences a force (other than air resistance), even though it is possible to model its motion to a great deal of accuracy using the concept of Newtonian force.

 

[steve_bank]

Planets are 'tethered' to the Sun.

No, they are not. Planets, and all celestial bodies follow equipotential lines along the curved surface of spacetime. They are not tethered to the sun by a force - they are simply conserving the kinetic energy they have acquired over their past history of formation and interaction with other objects.

Sigh,.. metaphor dude.

 

[atrib]

Planets are 'tethered' to the Sun.

No, they are not. Planets, and all celestial bodies follow equipotential lines along the curved surface of spacetime. They are not tethered to the sun by a force - they are simply conserving the kinetic energy they have acquired over their past history of formation and interaction with other objects.

Sigh,.. metaphor dude.

Lets look at your full post:

If you have a rotating sphere out in space away from gravity and attach a tether to the surfaceI expect the system will rotae about the center of gravity. On an asteroid you may end up with wild uncontrolled behavior.

Planets are 'tethered' to the Sun.

In the first paragraph you are talking about attaching a tether to the surface of an an object in space that is "away from gravity" (we'll come back to that). In the next paragraph you say planets are tethered to the sun. A reasonable assumption would be that you are referring to the force of gravity as a tether - the planets are tied to the sun by gravity. I am pointing out that that is not true.

What you are saying is that the object is spinning and tumbling as it moves through space, and that suddenly attaching a physical tether to the object would dramatically change the trajectory of the object since the energy associated with the object's spin would have to be directed somewhere. But I'm not sure how this relates to the sentence which states the planets are tethered to the sun. What is your point?

There is no "away from gravity". The presence of the sphere causes the spacetime around the sphere to distort. But I understand what you are trying to say and we can overlook this simplification.

 

[steve_bank]

Planets are 'tethered' to the Sun.

No, they are not. Planets, and all celestial bodies follow equipotential lines along the curved surface of spacetime. They are not tethered to the sun by a force - they are simply conserving the kinetic energy they have acquired over their past history of formation and interaction with other objects.

Sigh,.. metaphor dude.

Lets look at your full post:

If you have a rotating sphere out in space away from gravity and attach a tether to the surfaceI expect the system will rotae about the center of gravity. On an asteroid you may end up with wild uncontrolled behavior.

Planets are 'tethered' to the Sun.

In the first paragraph you are talking about attaching a tether to the surface of an an object in space that is "away from gravity" (we'll come back to that). In the next paragraph you say planets are tethered to the sun. A reasonable assumption would be that you are referring to the force of gravity as a tether - the planets are tied to the sun by gravity. I am pointing out that that is not true.

What you are saying is that the object is spinning and tumbling as it moves through space, and that suddenly attaching a physical tether to the object would dramatically change the trajectory of the object since the energy associated with the object's spin would have to be directed somewhere. But I'm not sure how this relates to the sentence which states the planets are tethered to the sun. What is your point?

There is no "away from gravity". The presence of the sphere causes the spacetime around the sphere to distort. But I understand what you are trying to say and we can overlook this simplification.

Put a tether on an asteroid and there is the potential for erratic behavior.

As analogy the solor system rotates around the system center of mass not the center of the Sun.

Add a tether to an asteroid and the asteroid - tether become a dynamic system. Dynamics 101.

There is also the problem of resonance. Google galloping gerdie video.

Make as much hay out of tha as you want.

For shits and giggles givne an asteroid tumbling through space with an irregular shape and variable density, where would attach a tether?

 

[Bomb#20]

Planets are 'tethered' to the Sun.

No, they are not. Planets, and all celestial bodies follow equipotential lines along the curved surface of spacetime. They are not tethered to the sun by a force - they are simply conserving the kinetic energy they have acquired over their past history of formation and interaction with other objects.

Well, if it comes to that, objects are not tethered to one another even by tethers. It's not as though there's any minitether holding two adjacent atoms in a tether together -- they are simply being found in probable locations after the myriad improbable histories in which they separated from each other have destructively interfered.

 

[steve_bank]

Teething on a tether.