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The Centrifugal Battery (flywheel as an energy storage device) has been around since at least 1857. This comment and geoffc's answer (batteries and Bearings) got me wondering what would the advantages and disadvantages of what in theory (with ceramic/magnetic bearings) could be a battery without end to its rechargeable life would be.

Or said another way; Assuming a Centrifugal Battery built with ceramic/magnetic bearings which would essentially be capable of endless (or 10,000 year) recharging capability. Would the low (Mars, Moon, etc) or zero gravity, make the Centrifugal Battery a better or worse option then it is on Earth. As Kinetic energy recovery systems these have been in use on Earth since the 1950's.

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The Centrifugal battery you link to is a gun: basically a variation on a trebuchet. How do you see this being used to store energy? –  Hobbes Jun 11 at 17:29
    
@Hobbes Not sure what there is to not get. Rotationally kinetic energy is just as viable regardless of it used to power a trebuchet, vehicle or uses an electrical motor to provide electricity for electrical devices.. –  James Jenkins Jun 11 at 17:34
    
@JamesJenkins But no sooner than one begins to draw power, the rotation will slow down –  Everyone Jun 11 at 17:49
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@James: ah, you meant a flywheel. The 1857 link was talking about a battery in the sense of a gun battery, so the terminology threw me off, so to speak. –  Hobbes Jun 11 at 17:55
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@self. : Rovers on Mars and Earth's Moon are neither always in sunlight, nor always in constant shadow. Satellites in geosynchronous orbit occasionally spend over an hour each day near the equinox passing through Earth's shadow. Low-altitude satellites enter Earth's shadow several times every day. –  David Cary Jun 12 at 2:16

2 Answers 2

up vote 5 down vote accepted

There are two issues I see with this idea:

  1. The overall mass of the system necessary to be able to store meaningful amounts of energy.
  2. The effect of such a device on the attitude control capabilities of a spacecraft.

If those can be solved, or at least mitigated, this might be a viable idea.

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On your item 2, would two counter rotating flywheels (with balanced input/output) be off little or no impact to the attitude control? RE Dynamics of counter-rotating flywheels –  James Jenkins Jun 11 at 18:29
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If it works properly, potentially. Keeping them balanced is another issue entirely though. –  Tristan Jun 11 at 19:04
    
Use four of them same as a quadcopter. You could even use six of them and then you'd have complete ship attitude control without spending reaction mass. I wouldn't synch them mechanically, losses would be horrendous, but you might do it magnetically. Presumably there's something wrong with this idea or NASA would be using it. –  Peter Wone Jun 12 at 9:37
    
Two counterrotating flywheels exert a different amount of torque because they're not at the same distance from the center of gravity. You could compensate for that by adding/extracting energy at a different rate so the forces will balance out. @Peter, NASA already uses flywheels (called reaction wheels for this purpose) for attitude control. It works well, until you reach the maximum speed of the flywheel, then you have to unload the flywheels using the thrusters. Overall it uses less fuel than thrusters alone. Reaction wheels are among the most failure-prone items in a spacecraft though. –  Hobbes Jun 12 at 10:40

You are correct that flywheels can be used for energy storage like batteries. As with all engineering trades, this comes down to many factors: mass, cost, efficiency, lifetime, reliability ...

Being in 0g means you don't have to support the weight of the flywheel on the bearings. That is an advantage, but not a huge one, compared to 1g. Having electromagnetic bearings will eliminate bearing wear as a failure mode, but there will be a complex electronic unit to handle suspension and power transfer. It will have some failure rate.

The fact that we see so many batteries in use indicates which way the trade seems to come out.

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Seeing batteries in use does not negate the potential application of better devices. Flight qualification counts towards a lot in the decision process. –  FraserOfSmeg Jun 11 at 22:08
    
Tidal energy systems use the moon as a huge flywheel on a gravity-balance bearing. Eventually it will fall to Earth as a result of tides removing its angular momentum. –  Peter Wone Jun 12 at 2:03
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@PeterWone: the tidal forces are actually raising the moon's orbit as it steals angular momentum from the earth and slows the earth's rotation. See space.com/3373-earth-moon-destined-disintegrate.html –  Ross Millikan Jun 12 at 3:58
    
Um, ok certainly the literature (that piece and others I found) agrees with you, but now I'm rather puzzled as to why momentum is transferring to the moon. I'd expect dragging all that water around to brake both the planetary spin and the lunar orbit (obviously I thought so or I'd never have made my earlier comment). On the face of it, a lot of water is dragged back and forth dissipating energy as heat due to friction. In fact I think I'll pose this as a question in its own right. –  Peter Wone Jun 12 at 7:46
    
Since the earth is rotating faster than the moon's orbit, the tides lead the moon ever so slightly, causing a net prograde force on the moon. Due to the quirks of orbital mechanics, this does indeed slow the moon down in the long term, as it moves into a higher orbit. –  Tristan Jun 12 at 15:21

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