In 2010: Odyssey Two, the Russian spacecraft Cosmonaut Alexei Leonov finds the derelict spacecraft Discovery rotating around its pitch axis (end-over-end). In the book, I believe this is explained as angular momentum which has transferred over the years from the centrifuge room to the rest of the spaceship. I don't think they bother to explain it in the film.

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I'm not sure if there's a canonical layout of the interior of the Discovery, but all of the fan art on the Internet places the centrifuge at the back of the globe structure, with the centrifuge's central axis in line with the ship's long axis. And in fact, there's kind of a "cap" on the back of the globe that might help accomodate the centrifuge:

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But if the centrifuge's axis is along the Discovery's roll axis, then transferring that momentum to the rest of the ship would cause it to spin along its roll axis, not its pitch axis. So why is it found to be spinning the way it is?


Rotation around the roll axis of a long thin object isn't stable; a mathematical explanation of why can be found in this Physics StackExchange question. Even if Discovery was initially tumbling on its roll axis the instability would cause conversion to end-over-end rotation over time.

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    Reading through the physics SE page leads to this book which cites a real-world example of the phenomenon. The torpedo-shaped 1958 satellite Explorer 1 was supposed to spin on its long axis, but precessed to end-over-end while in orbit. – Kenster Sep 1 '15 at 21:34

In the original book, the Discovery's centrifuge (carrousel) spins on the yaw (vertical) axis of the sphere.

from chapter 17 of 2001:

The equatorial region of the pressure sphere - the slice, as it were, from Capricorn to Cancer - enclosed a slowly rotating drum, thirty-five feet in diameter. As it made one revolution every ten seconds, this carrousel or centrifuge produced an artificial gravity equal to that of the Moon. This was enough to prevent the physical atrophy which would result from the complete absence of weight, and it also allowed the routine functions of living to be carried out under normal - or nearly normal - conditions.

So it should be tumbling on that axis - sideways rather than bow-up/stern-down. It looks like this got lost or confused somewhere between the first book, first movie, second book, and second movie. The pod bay scenes in particular seem to indicate the centrifuge is on the yaw axis (the same as in the book), but other scenes seem to show it on the roll axis.

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    The original production blueprints of the Discovery interior reprinted on p. 49 of 2001: The Lost Science show the centrifuge hub at the back of the sphere, just as in the cutaway diagram Kenster posted (which according to this page comes from this book.) And Clarke's 2010 book was more a sequel to the movie than the first book. – Hypnosifl May 11 '15 at 15:26

If the ship had a torque applied to it perpendicular to the axis of rotation, conservation of angular momentum would cause the centrifuge to start to precess, inducing an end-over-end flipping.

Such a torque could happen from the air slowly leaking out through the airlock doors (HAL was not online to make corrections).

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