"Halo" Orbit

[cubinator]

On 7/24/2018 at 12:11 PM, p1t1o said:

 

Question - if you had a hypothetically perfect sphere of uniform mass distribution, rotating on a vertical axis, orbiting a body.

This body could *not* become tidally locked?

It would become tidally locked, because the gravity field affects it in the same way - higher pull on the side facing the parent body.

[sevenperforce]

2 hours ago, cubinator said:

It would become tidally locked, because the gravity field affects it in the same way - higher pull on the side facing the parent body.

Not if it was rigid.

A spherically symmetric body cannot become tidally locked unless it is subject to deformation.

[sevenperforce]

2 hours ago, cubinator said:

It would become tidally locked, because the gravity field affects it in the same way - higher pull on the side facing the parent body.

Not if it was rigid.

A spherically symmetric body cannot become tidally locked unless it is subject to deformation.

[Cheif Operations Director]

Let me clarify what I mean 

A satilitte circling earth only around one pole. Pretty much follow the arctic circle directly. 

[sevenperforce]

5 minutes ago, Cheif Operations Director said:

Let me clarify what I mean 

A satilitte circling earth only around one pole. Pretty much follow the arctic circle directly. 

Then no. Cannae happen.

I mean, if you have a ship with TWR > 1 and infinite Isp, then I suppose anything is possible. But there is no closed orbit like that. 

[Xd the great]

10 hours ago, Cheif Operations Director said:

Let me clarify what I mean 

A satilitte circling earth only around one pole. Pretty much follow the arctic circle directly. 

Theorectically if you are far enough from earth, the twr should be very low.

Still you need somsthing to drive it.

[FireKerb]

The thing is, gravity doesn't pull towards the axis of the planet.

It pulls towards the center of mass.

[sevenperforce]

On 7/26/2018 at 5:23 AM, FireKerb said:

The thing is, gravity doesn't pull towards the axis of the planet.

It pulls towards the center of mass.

....yes.

But due to the gravitational gradient of the parent body, the satellite is stretched longitudinally along the axis connecting it to the center of mass. If it's rotating faster than one revolution per orbit, then it rotates out of alignment, and the gradient produces net torque to reduce the rotation rate.

[FireKerb]

I was talking about the question the OP had.

[Xd the great]

19 hours ago, sevenperforce said:

....yes.

But due to the gravitational gradient of the parent body, the satellite is stretched longitudinally along the axis connecting it to the center of mass. If it's rotating faster than one revolution per orbit, then it rotates out of alignment, and the gradient produces net torque to reduce the rotation rate.

So, everything will be tidally locked, given enough time.

[magnemoe]

3 hours ago, Xd the great said:

So, everything will be tidally locked, given enough time.

Yes, this depend a lot of the gravity gradient. Also Mercury managed to end up in an resonance instead while all major moons are tidal locked, wonder if gravity gradient for Mercury is less?  
Orbits will also circulate, this takes far longer Moon is not in an circular orbit even if it tidal locked fast it still wobbles because the non circular orbit.

[sevenperforce]

6 hours ago, Xd the great said:

So, everything will be tidally locked, given enough time.

An isolated two-body system comprising nonrigid bodies will always either mutually tidally lock or enter an orbital resonance, given time→∞. But in an n-body system, tidal locking or orbital resonances are not necessarily assured. The amount of torque inducing locking or resonance is often on the order of gravitational perturbations from other bodies.

[Gargamel]

On 7/25/2018 at 6:39 PM, Cheif Operations Director said:

A satilitte circling earth only around one pole. Pretty much follow the arctic circle directly.

With an infinite amount of dV at your disposal, yes this would be possible, but it would just be one long continuous burn to keep the craft in the correct 'orbit'. 

The center/foci of an orbit is around the barycenter (center of mass) of the body/system.  In this case, the barycenter would have to be directly over the pole, and then we get into the issue of what the planet would be doing in response.  

Sooo.. if you had two binary planets, orbiting each other along their poles, with the barycenter directly between them, you could have a satellite in a stationary polar orbit.   But, this scenario is so full of holes (feel free to poke them!), it wouldn't be stable for very long.    

[Xd the great]

Well, that force can be from solar sails.