How is spin stability used in spacecraft?

I understand the basic concept inasmuch that the gyroscopic effect is used and that the rigid body is given an initial spin around an axis of maximum mass moment of inertia (MMOI).

However, can someone clarify this concept, perhaps with some examples?

• What do you want to know? How spin-stabilized spacecraft work or anything else? As stated, the question needs more details to be answered. Jul 31, 2013 at 10:55
• Hey Deer Hunter. Thanks for the reply. Yes, how it is used in spacecraft. Just details on the physics of it. Jul 31, 2013 at 10:58
• Would advise to check out Wertz J.R. Spacecraft Attitude Determination and Control in your library. Jul 31, 2013 at 11:18
• Yeah I've heard that this book is pretty clear. Thanks. I will check it out. :) Jul 31, 2013 at 11:23
• @TopGun Clear is the wrong term. It is the bible in this field ;-) Jul 31, 2013 at 22:09

You are asking for examples ...

Stabilizing a space craft or rocket with a spin is a rather easy way of keeping its trajectory straight while it is under powered flight. You do not need to gimbal rocket engines and you can work without thrusters or active control surfaces.

A typical example in terms of rockets are sounding rockets. Within the first few seconds of the launch, they are spun up to a few rotations per second (by fixed control surfaces) and therefore keep their pre-arrange trajectory while under powered flight. At motor burnout, you can de-spin them with yo-yos, if you like. There is no better way to show this than with a video: http://www.youtube.com/watch?v=5nlVcRtBTLQ (yo-yos are used at 1:50).

Some space probes are stabilized in a similar fashion. The following video is a computer animation of the MERs' flights to Mars: http://www.youtube.com/watch?v=XRCIzZHpFtY The several stages of the Delta II itself are stabilized with gimbaling rocket engines and gyros. However, at 1:18, you can see how the final 'stage' for insertion on a trajectory towards Mars is spun up before it is ignited. Once the engine has stopped at 1:37, you can see the yo-yos.

The nice aspect about spin stabilization is, that it allows rather simple designs. You can save a lot of moving parts, weight and complexity. If you do not need to change your orientation while engines are running, it is a perfect concept.

• This was a really interesting read and to see the concept in action was especially exciting. About the yo-yo despin mechanism; so, as I understand it, the weights at the end (the 'yo-yo's') take up some angular momentum of the rigid spinning body, which stops it from spinning. However, are these weights then jettisoned? Aug 1, 2013 at 7:37
• @TopGun Yes, this is the usual procedure. Note, that the 'bodies' never stop spinning entirely if you are using yo-yos. So jettisoning them is another measure of mechanical simplification of the problem if you want to work with gyros or thrusters afterwards. Aug 1, 2013 at 7:45
• Note that the sounding rocket example is spinning around its axis of minimum rather than maximum inertia. Steering clear of the maths and definitions of what stability actually is, this means it will only be stable under some conditions. If it were to have flexible modes, or liquid propellant, this could well be enough to make it divergent, i.e. not stable. Mar 28, 2017 at 18:48