Perpetual motion machines and rocketry

Question

In my current worldbuilding project, humans find themselves struggling to survive on a cold, dead world with minimal sunlight and the aid of magical machines called "spinners". Spinners are two identical cubes adjoined by a face, always counter-rotating w.r.t one another at a constant rate. No amount of ungodly toque can slow their rate of counter-rotation, betraying unlimited, tappable work.

People use these machines for generating heat and powering machines and vehicles. My question is, what is the best way spinners may be incorporated into the design of a rocket engine? (Couple notes: the fastest spinners rotate at around ~1 Hz which, due to their unwillingness to be slowed by counter-torque, can be geared-up to hundreds, thousands, or hundreds of thousands of Hz by a gearbox; the engine need not necessarily have a thrust-to-weight ratio of 1:1 or greater--the focus is maximum delta-v.)

This sort of perpetual motion won't necessarily get you off the ground and into orbit for free. Rockets will still need exhaust to push on to generate thrust in a vacuum. So, spinners neither eliminate the need for fuel nor the tyranny of the rocket equation.
My knowledge of rocketry is weak, but I imagined a spinner-powered thermal device could be used to heat some propellant, say, liquid hydrogen, up to a few thousand Kelvin like in a typical nuclear thermal rocket, except the nuclear energy doing the heating is replaced by this spinner-powered thermal device. The thermal device could work by forcing a great deal of electricity through many tightly-wound metal coils (the spinners would be used to generate the strong rotating electromagnetic field). The friction in the coils would heat the propellant and so on. However, I don't think there is a metal or metal alloy that doesn't start vaporizing above ~2000 K (probably less than that, actually). At that point, one may as well forget about spinners and use nuclear elements instead.

Is what I suggest feasible? If not, is there another way to feasibly incorporate spinners into rocket technology? (I don't want to continue with the development of my world into the off-world without knowing the applications of spinners in space.)

Answer 1

Electrolysis & Fuel Generation Until You're In Orbit

Not only are you correct about the temperatures at which your heating coils would start to fail, the gearbox needed to generate that kind of power would be prohibitive in terms of of the space required on board the vessel. So...

If you've got life, you've got water (or other materials from which hydrogen and oxygen can be extracted). That gets you into orbit - nice traditional cryogenic launches.

Once you're (most of the way) out of the gravity well, however, that's when your spinners can really shine. You've got unlimited energy, so you want to minimize reaction mass; perfect situation for an ion engine. You could have unlimited burns. It would take a while to get anywhere, but you would have effectively unlimited range.

Answer 2

The machines provide the ability to have a reasonably compact source of enormous electrical power. Let's assume this power is "infinite" for practical purposes. In reality it will be limited, but the limitation is with the material science they can screw onto the ends of that cube. With cube size not specified this is hard to estimate.

So.. Ample electrical power. At the very least, some hundreds of megawatt to gigawatt of power.

To get to orbit:
Electrical propulsion. Ingest atmospheric air, superheat it to plasma. Eject the plasma through an acceleration grid. Simple, strong and horrendously inefficient. Fortunately, with "infinite" on one side of the scale, efficiency is a mere footnote.

In space:
If you are in a hurry: Your fuel is whatever matter you can lay your hands on. Lighter atoms are more useful, hydrogen is ideal. But plain old water will work fine.
Same story as in the air, just superheat the stuff to plasma, then violently shove the plasma to the rear using strong magnetic fields. Something like the VASIMR engine. But again, because we have near infinite power available, we can leverage the reaction for thrust and fuel efficiency, rather than being worried about power as mere mortals have to.

If you are not in a hurry, near a planet with magnetic field, and refuse to spend fuel:
Just hang a long tether overboard, run Thor's own electrical current through it, and use the interaction of that magnetic field with the planetary magnetic field to move around in your orbit. Slow, burn silly amounts of power for very little acceleration, but power is free and it uses absolutely zero fuel.

If you are not in a hurry, and nowhere near a magnetic field, and still refuse to spend fuel:
Use your electrical power to run a photon torch drive. This is the point where you realize that your "infinite" electrical power is anything but infinite, and true infinity would have been useful. Still, a couple of gigawatt of power is enough to power a workable photon drive that will take a light starship to relativistic speeds in years, rather than centuries or millennia.

Answer 3

Forget launch rocketry, use an elevator, then use an ion thruster in space

If nothing in the universe can stop a spinner from spinning, then use them to power a space elevator. It might take a day or two to complete the transit, but you're guaranteed to do so regardless the weight of the load (ignoring the mechanical specifications and/or limitations of the car & elevator tower).

Once you're in space, you can use ion thrusters to move around.

Answer 4

Space based jackass merry go round to anywhere

Taking one of these things to low Earth orbit should be relatively cheap. From there you can reach to the stars.

Now have a launcher that is a long cylinder, with such a spinner attached to, and powering a reaction wheel.

You can make the reaction wheel spin arbitrarily fast, and with it the external surface of your launcher. Now all you need is a decoupler on that surface.

Mount your interstellar vessel on that decoupler. Accelerate the launcher to the necessary angular velocity. Activate the decoupler, and the vessel leaves the launcher on a tangential with the same velocity as the launcher's surface's linear velocity.

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If you are having trouble visualizing how this contraption would work: the launcher is this merry go round, the reaction wheel is the back wheel of the motorcycle connected to the merry go round's axis, the spinner is the motorcycle's engine and the vessel to be launched is the guy who gets a lesson in cruel physics.

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Wanna escape the Earth? I remember its escape velocity at LEO is below 11 km/s (the escape velocity at sea level), so using that value will do. Wanna escape the sun? You just need to be going at 42.1 km/s when you exit Earth's sphere of influence. If you wish to reach any specific star or even galaxy, you just need to figure out a trajectory and the proper speed - and the spinner + reaction wheel combo will make sure you can reach the latter in finite time. No delta-v budget is too expensive anymore.

If you wish for an orbital injection at the destination, you can make it so that the main vessel also has a spinner and a reaction wheel, and then you can do this mad maneuver in reverse. You will have all the time of the trip to build up angular speed for this secondary launcher.

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Edit: As per Harabeck's comment:

SpinLaunch is a real company trying to do something close to this conceptually.

It was founded in 2014, so the concept for the space based jackass merry go round has been a thing for quite a while now.

Also in space you don't need a perpetual motion machine - sunlight is practically unlimited, and you can keep converting solar energy into reaction wheel love as long as the materials involved can take the stress.

Answer 5

For getting into orbit, you could use the spinners fairly easily to power a Lofstrom loop. The classic issue here is largely "you really want several nuclear reactors to power the thing" (which has political issues among other things), which you sidestep fairly easily. (Why nuclear? Because it requires a fair bit of power, and rather reliable power at that. Both of which you have here.)

(There are ways to deal with a power failure on a Lofstrom loop, mainly involving stealing momentum from the cable itself to keep the containment going, but it's, uh, hair-raising at best.)

(For reference: a Lofstrom Loop (or Launch Loop) is effectively just a really large loop of cable, spinning quickly enough that its own inertia holds it up against gravity. To launch, just steal momentum from the cable.)

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Once you're in orbit, a couple of possibilities spring to mind.

One obvious approach is an EDT (electrodynamic tether). An electrodynamic tether is essentially just using the magnetic field of whatever you're near as the magnet for a generator/motor. Normally these are largely used "in reverse", to provide power at the expense of decaying your orbit, but you can use this as a motor too (taking power to raise your orbit, essentially).

They do have a bunch of downsides (power-hungry, relatively low acceleration, can interfere with nearby craft, etc.), but their main drawback is simply the power use - and you've got power in spades. And they don't use reaction mass.

One more classical approach here is an ion drive. Normally an ion drive has a relatively low effective Isp, mainly due to the mass of the engine's power supply - but you have power to burn. So you can run at very high power consumptions (which boosts efficiency). Still a very low power-to-weight ratio however.

A photonic drive sounds great initially. Honestly however, this likely isn't worth it. Even assuming "infinite" power, we don't have any good way to produce anywhere near the photon density required to make it worthwhile.

(As an aside, I'd expect the early space program to focus far more heavily on magnetohydrodynamic drives for airplanes than we did. They have largely been discounted for us due to a lack of a decent power supply... but given these you could probably build a fairly decent spaceplane.)

(As another aside: I actually think that it'd be rather difficult to use these. The required torque (and hence, mass) to get a decent amount of power from a 60RPM rotation is not exactly small. 1 horsepower would require ~550 pound-feet of torque (for comparison, a bicycle is, what, 50-100 pound-feet of torque?). Someone who is more patient than I could probably work out the maximum effective amount of power you can get out of one of these based on material limits at the attachment point... but I expect it to be surprisingly small.)

Answer 6

This sort of perpetual motion won't necessarily get you off the ground and into orbit for free.

Actually, it can (maybe), if your engineering is good enough. Leaving aside PcMan's answer...

We know how to produce thrust by pushing air around. Getting to orbit isn't a matter of getting high enough (well, unless you want to get really, really high; so high that, without a reaction-less drive, this approach simply isn't practical thanks to the tyranny of the rocket equation) but of going fast enough. So... do this in the atmosphere so that you can use the planet's air as reaction mass rather than having to haul your own. If necessary, produce downward thrust to keep yourself in the atmosphere until you've got to your desired speed. You might still need to bring along some delta-V for orbital corrections (though, see other answers), but not nearly what you would need to just get to orbital velocity.

The trouble comes when you need to balance the required speed against certain unfortunate effects of atmospheric heating, which means you probably need to do this at a sufficient altitude that the air is thin enough for this to be manageable. Thus, you probably are looking at something like a ramjet engine. Also, really, really good heat shielding.