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I'm trying to understand how SPICE software works, but I'm afraid that I need to understand a lot of astronomy concepts.

One of the kernels I have use has this description:

These kernels contain orientation data for planets, natural satellites, the Sun, and selected asteroids.

What is orientation data? Or better, what is orientation?

I think orientation is an astronomy concept that those files don't explain.

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    $\begingroup$ The orientation files are usually text and human readable with a wealth of information about the contents. E.g. naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/pck00010.tpc $\endgroup$ Mar 18 at 19:02
  • $\begingroup$ @GregMiller What is orientation in astronomy? I think orientation is an astronomy concept that those files don't explain. I'm asking about orientation, not about the PCK kernel file concept. Thanks. $\endgroup$
    – VansFannel
    Mar 18 at 19:06
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    $\begingroup$ Orientation is a common English word that means the direction in which something is facing $\endgroup$ Mar 18 at 21:34
  • $\begingroup$ The specific properties given in the files are the direction of the pole, and the rotation around that pole. $\endgroup$ Mar 18 at 22:24
  • $\begingroup$ @ScienceSnake Yes, but I need to know what is that something. Now I know it. $\endgroup$
    – VansFannel
    Mar 19 at 8:07

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At a very bare minimum, orientation tells where an object's instantaneous axis of rotation is pointing relative to some inertial frame of reference, possibly as a function of time. The axis of rotation can change due to external torques, internal transfers of angular momentum, and a misalignment between an object's angular momentum and angular velocity vectors.

Knowing where the axis of rotation points does not tell everything about how an object in space is "oriented". This more detailed orientation data information is available for some objects. For example, if one wants to have a vehicle land near a specific location on Mars, knowing the detailed orientation of Mars is rather important. (This detailed information is available for Mars, and also the Moon and the Earth.)

Orientation is very important for spacecraft as spacecraft need to know where to point their scientific instruments, their communications equipment, and if equipped, their solar panels and thrusters. A lot of spacecraft do not know where they are in space, but they absolutely need to know how they are oriented. Attitude determination and control are absolute essentials for almost all spacecraft. "Attitude" essentially is a synonym of orientation.

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