Does every orbiting object have spin

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Discussion Overview

The discussion revolves around the concept of spin in orbiting objects, specifically comparing the behavior of the Moon and artificial satellites in orbit around Earth. Participants explore whether an object, like a basketball or an arrow, would maintain a specific orientation or spin while in a circular orbit, and how this relates to tidal locking and angular momentum.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that an object thrown into orbit without initial spin would not rotate, maintaining a consistent orientation relative to Earth, while others argue that tidal deformation could eventually lead to changes in this orientation.
  • There is a discussion about whether an arrow thrown into orbit would experience changes in orientation, with some suggesting it would be parallel or perpendicular to the Earth's surface at different points in its orbit.
  • Participants mention that artificial satellites like the ISS are likely oriented using small steering jets to maintain a specific alignment with Earth.
  • Some contributions highlight that all objects in orbit are subject to tidal deformation, which could lead to tidal locking over time.
  • There is a suggestion that some satellites may be designed to be tidally locked from the start, while others may require adjustments to maintain their orientation.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the behavior of orbiting objects and the effects of tidal forces. The discussion remains unresolved, with no consensus on the specifics of spin and orientation in various scenarios.

Contextual Notes

Limitations include assumptions about initial conditions, the dependence on specific definitions of spin and orientation, and the potential influence of external forces like solar wind on satellite behavior.

Moazin Khatri
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Our moon rotates around Earth in such a way that we always see the same face. But Earth orbits Sun in a different way. It keeps spinning. My question is, If I were to go to space and put a basketball in a circular orbit around Earth in such a way that at the time I throw it a particular face is facing Earth would it orbit Earth like the moon does(always the same face) or would it have a much faster spin?
 
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Moazin Khatri said:
Our moon rotates around Earth in such a way that we always see the same face.
No coincidence, but the ultimate result of tidal deformation.

Your baseball would spin at whatever spin rate you give it when throwing. If you throw exactly hard enough for a circular orbit and don't give it any spin, it wouldn't rotate, just orbit. (i.e. on your location on Earth you always see the same side, but your antipodes see the opposite side). In the long run this tidal deformation might change that -- see link.

Think of the central character of the gravitational force and conservation of angular momentum.
 
BvU said:
No coincidence, but the ultimate result of tidal deformation.

Your baseball would spin at whatever spin rate you give it when throwing. If you throw exactly hard enough for a circular orbit and don't give it any spin, it wouldn't rotate, just orbit. (i.e. on your location on Earth you always see the same side, but your antipodes see the opposite side). In the long run this tidal deformation might change that -- see link.

Think of the central character of the gravitational force and conservation of angular momentum.
Thanks for your answer. Just clear one more thing .. Just to confirm If I have properly understood what you're saying...
If instead of a baseball I use a physical arrow .. throwing it hard but no spin at all .. is it true that in its circular orbit there will come a time when the arrow will be parallel to the surface of the Earth and there will also come a time when it will be perpendicular?
And if this is true then why is it that whenever we see pictures of artificial satellites like ISS orbiting Earth .. their main body seems parallel to the surface of earth? Do they add spin when they launch it?

P.S: The arrow thing will only be true if velocity vector is parallel to the body of the arrow .. If it is perpendicular then it will always remain parallel to earth. And the same might be true with ISS. Looking forward to your reply!
 
The consequence of what I wrote would indeed be as you describe: orientation in space invariant, so wrt Earth center it will rotate once per orbit.
ISS and other earth-facing satellites will probably be oriented properly with small steering jets.

@haruspex: are you aware of any mechanisms that would be helpful (or unhelpful) in this ?
 
BvU said:
The consequence of what I wrote would indeed be as you describe: orientation in space invariant, so wrt Earth center it will rotate once per orbit.
ISS and other earth-facing satellites will probably be oriented properly with small steering jets.

@haruspex: are you aware of any mechanisms that would be helpful (or unhelpful) in this ?
Hmm... Thank You
 
BvU said:
The consequence of what I wrote would indeed be as you describe: orientation in space invariant, so wrt Earth center it will rotate once per orbit.
ISS and other earth-facing satellites will probably be oriented properly with small steering jets.

@haruspex: are you aware of any mechanisms that would be helpful (or unhelpful) in this ?
I agree with what you posted. All objects would be subject to some tidal deformation, and over time that would lead to tidal locking.
Some satellites would be set into a one spin per orbit mode deliberately, so tidally locked from the start. Others might need to be in constant sidereal orientation, so might need a very small jet to maintain that. But without doing the calculation, I would guess the effect is small compared with, e.g., the solar wind on the solar panels.
 
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