A Unique Satellite Reaction Wheel

Can we make a reaction wheel using liquid metal and the Magnetohydrodynamic effect?

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=== References ===
- Grau, Sebastian. Contributions to the Advance of the Integration Density of CubeSats. Technische Universitaet Berlin (Germany), 2019.
- Noack, Daniel, and Klaus Brieß. "Laboratory investigation of a fluid-dynamic actuator designed for CubeSats." Acta Astronautica 96 (2014): 78-82.
- Barschke, Merlin, et al. "Initial results from the TechnoSat in-orbit demonstration mission." 32nd Annual AIAA/USU-Conference on Small Satellites. 2018.
- Grau, S., D. Noack, and K. Brieß. "Rapid prototyping of a combined channel/pump structure for liquid metal actuators used as angular momentum storage device for picosatellites." Proceedings of the 66th International Astronautical Congress (IAC). 2015.
- Grau, S., L. Kobow, and F. Fürstenau. "Investigation of Redundancy Strategies in Fluid-Dynamic Attitude Control." Proceedings of the 68th International Astronautical Congress (IAC), Adelaide, Australia. 2018.
- Martens, Bas. "A fluid loop actuator for active spacecraft attitude control-A Parametric Sizing Model and the Design, Verification, Validation and Test with a Prototype on an Air Bearing." (2019).
- Gu, Youlin, et al. "Design and analysis of MHD-based momentum ring for satellite attitude adjustment." 4th International Symposium on Power Electronics and Control Engineering (ISPECE 2021). Vol. 12080. SPIE, 2021.

[BreakingTaps]

- Power calcs
I'm bad at everything and misread the current limit of the buck converter. It's limited to 12A, so power efficiency was notably better than I mentioned (albeit still pretty bad). Oops 🙃

- Temperature!
Sorry, I should have mentioned this: galinstan has a freezing point around -18 to -20C, which is near the lowest temperature experienced in LEO orbit. So it _might_ need a small heater to keep liquid, but maybe not depending on how much heat is retained from the sunwards pass of the orbit. The liquid metal will have a fairly large amount of thermal mass, and contained in an insulating polymer of some type. Also will experience some self-heating from joule losses during operation. Missions farther from the sun would need a heater to stay liquid however.

[IsZomg]

Satellite reaction wheel bearings used to fail all the time, but the problem was solved in recent years. They've stopped using metal ball bearings and now use ceramic ones instead. The ceramic ones require no lubricants and are not susceptible to static electricity surface pitting slowly destroying them.

[NineToFiveGamer]

You can find unprotected 18650 cells for sale at almost every local vape shop as well. 99% of "vape" batteries dont have protection because the mod or vape has those built into it by law, so it allows those cells to offer much higher constant current draw and many times that in peak current

[Convolutedtubules]

9:05 The protection circuit is located at one end of the battery, under the insulation. It can safely be removed. I recommend getting high output cells, such as the ones used in power tool batteries.

[MordecaiV]

Glad to see you closing the magnetic circuit with the iron. Even if there isn't enough, you're making a static field so hysteresis isn't really a big deal. Too many people just don't bother understanding a flux circuit and just rely on the unreasonable strength of rare earth magnets to leave all kinds of magnetic performance untapped, or just double the magnetic material required.

[-pz]

In addition to reaction wheels, satellites also use control moment gyroscopes, which are a similar device that uses conservation of angular momentum to control satellite orientation. The key differences in performance between the two are that reaction wheels are more power efficient for smaller satellites, and larger manoeuvres, and CMGs are more power efficient for larger satellites and smaller manoeuvres. CMGs also provide more torque for less power.

There's also a difference in how they operate. Reaction wheels change angular momentum by spinning up and down. CMGs change momentum by changing the wheel's axis of rotation without needing to change the angular velocity.

Reaction wheels have their place, because many satellites are very small. But for larger craft, like the International Space Station, they use CMGs. The ISS has four.

[ravenmaxted-b]

For the galinstan corrosion risk there’s always the option of option in a, potentially vacuum rated, epoxy. Especially if it’s not necessary to service it as it’ll be unlikely to react to any galinstan that escapes it’s primary containment

[enilenis]

We called'em mercury vortex engines. I've made them as far back as 30 years ago. I never thought about space application. I imagine friction makes conventional reaction wheels more energy efficient, than a fluid that is going to be continuously venting energy through heat.

[tlum]

I remember when I was a kid (a very very long time a go) there was a short article in Pop Sci or some such (paper) magazine about some scientists making a mercury "gyroscope" using magneto hydrodynamics to push the mercury around a metal tube loop. They hinted it could be used in place of spinning wheel gyros with then poor reliable ball bearings. This was before even the 1st satellites. Your video dredged up that long forgotten memory. What goes around comes around.

[MiggyManMike]

Wait, did you essentially make a liquid metal railgun moshpit ?

[samsonsoturian]

Here's an idea: You can reverse these devises to be a rotation detector. Any rotation with induce a current in the motor (this is how people detect rotation)

[staryduren]

Metal electrodes are doomed in this application sooner or later. Maybe try some graphite? Something not dissolving in metal (mercury?)

[trg]

11:08 Beesat-9 was a nice reminder of the recent Beesat-1 resurrection video (38c3).

[RiffZifnab]

The reason you had such poor efficiencies with the magnetohydrodyanamic reaction wheel was that your base plate was of an inferior pre-famulated amulite composition. You should also test out a lotus-o-delta configuration to minimize waneshaft side fumbling.

[alexradac]

A flywheel would keep a constant attitude with no extra power but such a liquid reaction wheel would start counter rotating as soon as the power is cut due to fluid friction loses slowing the inner liquid. interesting concept nonetheless

[LilMissMurder]

IT VIRKS! <insert demented mad scientist laughter here>

I used to work with a guy who was convinced in his idea for a reaction motor for linear motion in space. Basically an arm with a counterweight spinning around an axis fixed to the spacecraft body. The arm could move in and out of the axle - the idea being that as the counterweight spins, it is retracted and extended along the desired axis of motion using a rack and pinion setup, "push/pulling" the spacecraft forward in space. Needless to say, he didn't understand the physics of conservation of momentum.

[theCodyReeder]

I love this! However, it definitely requires mercury. I understand reluctance to use it, but Galinstan is neither particularly dense nor conductive, and its melting point is significantly higher than that of a mercury alloy.

[AnonymousAnarchist]

Thank you for the use of a back iron to redirect magmetic forces. I think a lot of people get discouraged from thier projects when they see the costs assoicated with the magnets per pound of strength and just give up then and there when really a lot of projects could be done will far lower costs by just using a back iron

[kstricl]

If my memory serves me, Canon used air bearings on the laser assembly of their earlier color copiers. The model 100 I know had it, I believe the 1000 did as well. If you somehow come across one of these dead, might want to grab that assembly - it likely wouldn't work for this type of project, but be real fun for scattering a laser beam around.

[Convolutedtubules]

6:55 If the sides of the horseshoe shaped parts tapered out slightly, the parts could be stacked and very little sheet metal would go to waste.