Orbital frame of reference: a frame of reference with its origin on the orbit and x-axis pointing towards the velocity vector and z-axis towards the center of mass of the earth. the y-axis completes the right-handed system.

While I know what frames of reference are and about the different types of frames of reference, I've hit a block. I can't seem to figure out the purpose of an orbital frame.

  • $\begingroup$ because, in some ways, that frame of reference is how the satellite experiences things. as far as it's concerned it's hanging weightless z above Earth, and its ground track weaves about y as it wanders along x $\endgroup$ – JCRM Sep 24 '19 at 15:07

You are describing the Local Vertical Local Horizontal (LVLH) frame of reference.

It is used to describe the orientation of the spacecraft in relation to the Earth's surface.

For example, if you wished to point an instrument at the point on the Earth directly below the spacecraft, the craft would fly in a constant LVLH attitude. But its inertial attitude would be rotating once per orbit.

The ISS flies in a more-or-less constant LVLH attitude so that its 'nadir' axis points at the center of the Earth.

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Coordinate Systems for the Space Shuttle Program

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  • $\begingroup$ Is speed also relative to Earth surface (ie, for geosync, equal to zero)? I can't quite tell from just this, and it seems like there might be pros and cons either way. $\endgroup$ – Roger Sep 24 '19 at 14:48
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    $\begingroup$ The value of 'speed' depends on what coordinate frame you are expressing it in. I don't know what you mean by pros and cons. $\endgroup$ – Organic Marble Sep 24 '19 at 14:48

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