Running at 150,000 RPM, a tiny motor could help satellites

For those curious how a spinning motor can be used to orient a satellite, I&#x27;d suggest Scott Manley&#x27;s video on reaction wheels in Kerbal Space Program (don&#x27;t worry if you don&#x27;t play KSP, the bulk of the video is about the real world applications).<p><a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=7Js5x4NhUxU" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=7Js5x4NhUxU</a>

There&#x27;s also Passive Magnetic Attitude Control System (PMACS) that uses magnets, and does away with motors and reaction wheels. I guess PMACS is good enough for most of the nano&#x2F;pico&#x2F;femto satellites. It was recently used in an Indian student satellite &quot;Swayam&quot;[0].<p>[0] <a href="http:&#x2F;&#x2F;www.coep.org.in&#x2F;csat&#x2F;subsystems&#x2F;acs&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.coep.org.in&#x2F;csat&#x2F;subsystems&#x2F;acs&#x2F;</a>

I worked in a company that makes pumps with magnetic bearings for high purity applications, i.e. semiconductor manufacturing. The impeller is a magnet completely coated in a really inert material, e.g. PTFE, so no metallic (bearings, shafts) parts touch the liquids. Efficiency is pretty low with these types of bearings, we got like 60-80%. Not sure if this is ideal for a satellite.

I always assumed satellites and probes used small jets of hydrazine to orient themselves. I know fule capacity is limited but I just figured they used it sparingly.<p>It interesting to see how they actually do it. There is a video of a walking cube on the Web I suppose it&#x27;s the same principal, it seems like magic.<p>I wonder if the magnets will interfere with sensors?

I can&#x27;t quite tell, I think this is describing a miniaturised momentum wheel [1], but I had the impression that control moment gyroscopes [2] where generally preferred.<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Reaction_wheel" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Reaction_wheel</a><p>[2] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Control_moment_gyroscope" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Control_moment_gyroscope</a>

A little misleasing, as technically, this &quot;motor&quot; will not do anything to the satellite course - but just change its orientation. It&#x27;s &quot;only&quot; a new spin (SCNR) on gyroscopes. Interesting nonetheless, even though magnetic bearings aren&#x27;t that new either as a concept. Wish they&#x27;d write what&#x27;s actually new about them.

Even if the rotor is held by magnetic fields, the centrifugal forces exerted on the rotor must be huge. I guess it is small enough, but I&#x27;m curious if it was a problem or not (CDs will crack if they spin too fast).

Correct me if im wrong, but I would assume that the motor must still be &#x27;attached&#x27; somewhere, else the momentum would not translate into moving the satellite. (Wouldnt it be akin to having a gyroscope just floating inside of a satellite- Suddenly stopping it would have no effect on the satellite since it would not be actually attached- ala, the fly in a car scenario) - So, with that, if it is indeed attached somehow, wouldn&#x27;t the friction component still be at play?

This technology has been proposed for some time for use on wind turbines as frictionless bearings. I am not sure why they are not in common use yet.<p><a href="http:&#x2F;&#x2F;www.treehugger.com&#x2F;renewable-energy&#x2F;the-worlds-first-magnetic-levitation-wind-turbines-unveiled-in-china.html" rel="nofollow">http:&#x2F;&#x2F;www.treehugger.com&#x2F;renewable-energy&#x2F;the-worlds-first-...</a>

Am I the only one thinking about the 150k RPM wear-and-tear on the reduction box ?

Can anyone do the math on the access speed of a 150,000 RPM disk drive?