# Orbital mechanics

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If the earth spins around its own axis ccw (Counter Clock Wise), do the earth sats (natural and artificial) spin around earth in a CCW motion too? What about a space-craft landing/taking off from earth do they have a tendence to slip in a CCW motion during landing, takeoff? [Edited by - Calin on June 1, 2009 7:35:25 AM]

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If you disregard influences like gravity gradient torque and nonsphericity of a planet's gravity field then you can say that things up there have no rotational effect on one another. Sats can orbit in whatever orbit they are inserted into.

If you want to have your sat stationary over a certain region, you go "ccw" and geostationary. If you wanna cover the entire globe, you go for a polar orbit. And if you need a high-latitude geostationary coverage, then you go for a molniya orbit.

As for a spacecraft's orbit when launched/wanting to enter and land on a planet - generally, yes. At the equator the Earth's spinning at about a 1000 mph, so when you're taking off in the direction of rotation you get a free 1000 mph bonus to your velocity relative to the center of Earth. The same thing applies for landing - 1000 mph less velocity to shake off.

It's not a tendency though, it's a choice. You can choose to launch in the other direction (you may need to), but it's gonna cost you extra.

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That's pretty cool, thanks for making the post

I asked because I found the wikipedia entry very generic. Nothing/scattered on human made satelites

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Quote:
 Original post by toriIf you disregard influences like gravity gradient torque and nonsphericity of a planet's gravity field then you can say that things up there have no rotational effect on one another.

Unless you consider general relativity, then that might change, but only by an immeasurable amount generaly :P

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Quote:
Original post by luca-deltodesco
Quote:
 Original post by toriIf you disregard influences like gravity gradient torque and nonsphericity of a planet's gravity field then you can say that things up there have no rotational effect on one another.

Unless you consider general relativity, then that might change, but only by an immeasurable amount generaly :P

Technically, the latest experiments show that frame dragging is indeed observable (and measurable) in the case of the slowly rotating Earth. :)

http://einstein.stanford.edu/

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Quote:
 Original post by luca-deltodescoUnless you consider general relativity, then that might change, but only by an immeasurable amount generaly :P

Oh yeah, I forgot to add "in a fairytale newtonian universe". In long duration space flight relativistic issues are of great importance, both SR and GR.

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I was just scratching the surface, i'm not good at maths at all.

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Quote:
Original post by tori
Quote:
 Original post by luca-deltodescoUnless you consider general relativity, then that might change, but only by an immeasurable amount generaly :P

Oh yeah, I forgot to add "in a fairytale newtonian universe". In long duration space flight relativistic issues are of great importance, both SR and GR.

Or if you are concerned with precision like with GPS ;)
"The precision of GPS measurements is so great that it requires the application of Albert Einstein’s special and general theories of relativity for the reduction of its measurements.
"
GPS and relativity

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Quote:
 Original post by daviangelGPS and relativity

Seems like not a lot has changed since that was written in 1999.. and i thought i was all cool gettin a "navigator" at the rental car place..

I definitely think it's sweet that relativity is very real, and used everyday by anything in space.

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