4
$\begingroup$

If we look at Von Braun's Space Station, we can see that the axis is not completely symetrical. It is longer from one side:

Von Braun Space Station 1956 - YouTube

that looks a lot like this T-shaped object which we know for a fact that exhibits the effect:

T-shaped object

So would such a station also suffer from it?

Or in case the station's axis was symetrical, but what if a ship arrives and docks in one of the axis extremes, making it a T-shaped object?

edit to add images of Von Braun concept enter image description here

$\endgroup$
4
  • $\begingroup$ The video link does not work. $\endgroup$ Sep 20 at 12:43
  • $\begingroup$ youtube.com/watch?v=1x5UiwEEvpQ shows effect very well. $\endgroup$
    – BradV
    Sep 20 at 13:38
  • 3
    $\begingroup$ the shape of the spinning wheel is not the least bit similar to the T shape that exhibits the flipping effect. The distribution of mass at the wheel perimeter makes the wheel hub axis the most dynamically stable and basically immune to flipping. $\endgroup$
    – BradV
    Sep 20 at 13:58
  • 2
    $\begingroup$ I'm also baffled how a circular wheel "looks a lot like" a T. $\endgroup$ Sep 20 at 14:09

2 Answers 2

10
$\begingroup$

No... a Von Braun wheel would not ever 'flip' from Dzhanibekov effect. The effect comes from spinning something about its intermediate (and inherently unstable) axis. A Von Braun station is spinning about its primary, most stable axis. The T shape you think you see seems to come from stripping away (not considering the inertial contribution of) the perimeter wheel mass which is what creates the primary rotational inertia, thereby making the wheel axis 'stable' and flip proof. Just try to get a spinning bicycle wheel to flip. It cannot be done.

$\endgroup$
2
$\begingroup$

Starting with a circular wheel spinning on its axis of symmetry (maximum inertia), can one then add masses in such a fashion that the conserved angular momentum ends up on an intermediate axis?

The answer to this is 'yes'. Add a massive long cylinder through the axis of rotation and a massive even longer cylinder across a diameter and then the resulting object would be rotating around an intermediate axis. The added masses should be much larger than the wheel.

intermediate axis picture

$\endgroup$
9
  • 3
    $\begingroup$ But...that's not anything like the configuration the question was asking about. $\endgroup$ Sep 20 at 17:18
  • 1
    $\begingroup$ @OrganicMarble I'm docking four spacecraft to a Von Braun space-station. I assume you can do it with two. But I don't see a way of doing it with just one - unless it's a very odd shaped spacecraft $\endgroup$
    – Roger Wood
    Sep 20 at 17:51
  • 1
    $\begingroup$ If you incrementally move around mass... eventually you can turn a bowling ball shape into a tennis racket shape. What Roger Wood proposes is a common thought experiment that can be turned into an actual physical demonstration. $\endgroup$
    – BradV
    Sep 20 at 18:02
  • 1
    $\begingroup$ It would be criminally stupid to design a Von Braun station with a docking system that created the potential for catastrophic failure like this. The massing differences between spinning rim and docked craft would mean very oversized docked craft. $\endgroup$
    – BradV
    Sep 20 at 18:11
  • $\begingroup$ @BradV it's an interesting question for the ISS. It looks like it orbits 'sideways' so that it rotates around the minimum inertia axis. Presumably it won't maintain a stable orientation if you try to you orbit with the main y-axis pointing along the orbit. $\endgroup$
    – Roger Wood
    Sep 20 at 18:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.