Nadir for a craft orbiting the Earth would be radially in, is nadir always pointed towards the Earth or is it pointed towards the celestial body that the craft is orbiting?
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1$\begingroup$ slightly related but not a duplicate; In “spacecraft talk” is nadir just a fancy word for “down”? I assume it's the 2nd option "towards the celestial body the craft is revolving about" but I can't thing of a good way to support that. $\endgroup$– uhohCommented Jun 29, 2018 at 4:31
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$\begingroup$ Actually not all spacecraft have fixed attitude to Earth during flight. For example. Soyuz is spin-stabilised during 2-day transfer to ISS blogs.esa.int/iriss/2015/09/03/spinning-the-soyuz $\endgroup$– HeoppsCommented Jun 29, 2018 at 9:07
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Nadir is always pointed down to the object below. In more rigorous terms the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location. (see for example Wikipedia , Merriam Webster)
For a satellite orbiting the moon, the nadir vector would point at the moon surface. For a satellite orbiting Mars it would point at the Mars surface.
