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Comment by RobotToaster | Hacker News Reader

Wouldn't it be possible to "simply" match it's tumble?

No, when it tumbles, it does it around its centre of mass. You'd have to get a craft that has empty area inside.

If you know Elite, it has space stations where you dock by going inside, while matching station's rotation. That's only in one axis (and note the hangar goes through the axis of rotation, i.e. centre of mass). To add rotation around another axis would make the task impossible.

like that station that is in orbit around a pulsar star and destroys anything trying to take off from it ?

It might be possible if you have very powerful thrusters, functionally unlimited RCS fuel, and G forces don't matter...

Only if it is only spinning along one axis. Very likely to be spinning on multiple axis. That said, with enough money and effort I'm sure we could figure something out, like shooting it strategically with small projectiles to slow the spin, etc.

Unless acted on by an external force, all rigid objects only rotate about a single axis, do they not? That axis just might not be aligned with any useful parts you'd want to grab on to.

You might enjoy this, if you haven’t seen it: https://www.youtube.com/watch?v=1n-HMSCDYtM

Anything "spinning among multiple axes" is just spinning around a single compound axis? There's no reason for a spacecraft to limit itself to any earthbound reference frame when it comes to matching frame with an incoming body from outer space.

In three dimensions, the rotation around one axis can affect the distribution of mass around other axes of rotation. That change in the moment of intertia causes acceleration, which can result in chaotic motion even without the addition of any outside forces.

What do you mean by "other axes of rotation"? As long as the object is rigid and not acted upon by external forces, its axis should never change, since both the direction and magnitude of angular momentum are conserved.

Wikipedia talks of "chaotic rotation" of astronomical objects, but only over long timescales due to gravitational interactions and thermal effects. On short timescales, its axis shouldn't change much at all, unless you bump into it and apply an off-axis torque.

Look at the Dzhanibekov effect

https://www.youtube.com/watch?v=8DOY21HnJII

Alright, that makes more sense, the trick is that the (conserved) angular momentum vector need not be parallel with the angular velocity vector, the simplest example being torque-free precession [0]. It doesn't help that most examples of non-constant angular velocity have external forces in the mix to confuse the reader.

[0] https://en.wikipedia.org/wiki/Precession#Torque-free_or_torq...

Reminds me of the tumbling T-handle. A small tool is spun up in one axis, and due to some interesting physics, ends up flipping over on another axis every few seconds.

https://rotations.berkeley.edu/a-tumbling-t-handle-in-space/

I wonder if it's reproducible in vacuum or the air is necessary to destabilize it?

It's about angular momentum and happens whenever the axis of rotation differs - even slightly - from the semi-major axis. Interaction with a fluid is not necessary.

You can demonstrate it at home with your smartphone (or, more canonically, a tennis racket), and see for yourself that the tumbling happens much too quickly to be explained by whatever force the air is imparting.

Does it really work this way? If the craft is rotating along any other axis than its direction of travel, wouldn't the matching craft have to be revolving around it, not just rotating?

That sounds absolutely terrifying for the astronaut. Imagine the whole universe spinning past you every second. Not to mention the forces.

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