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When a spacecraft orbits around earth (assume a "long" spacecraft, so that it can have an axis along its length), does its axis PITCH so as to maintain itself (axis) tangential to the earth's surface, or it remains by and large, pointing to the same direction it had when it went into orbit? To clarify the question further, assume that the craft reaches the orbit while being exactly overhead our north pole, and at that point, its axis is parallel to the tangent over the north pole. When the craft reaches overhead the equator, does its axis pitches by 90 degrees, so that the axis is again parallel to the tangent at the equator or its axis remains in the same direction - now being perpendicular to the tangent?

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Short answer- the long/pitch axis will be whatever the controller of the vehicle wants it to be.

The pointing can be controlled, and can be fixed with respect to the earth, fixed with respect to the sun or any required combination. Skylab was mostly sun fixed, the ISS normally keeps the cupola module 'down', so rotates once each orbit. Space shuttle generally orbited upside down and backwards. Space telescopes like Hubble need to point at stars, so will be rotating with respect to both Earth and the sun.

Long objects will tend to end up long axis towards earth due to gravity gradients unless the vehicle control system provides other forces.

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  • $\begingroup$ Excellent answer. Thank you so much, it clarified so many other things. Thanks again. $\endgroup$
    – Niranjan
    May 31, 2022 at 3:57

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