Kinetic batteries - The potential for nearly unlimited power storage
Kinetic batteries offer a number of attractive concepts, one of the most useful which would be the very high power they could potentially store. The only limit to a kinetic battery's energy storage is how fast or how hot the storage medium can go, which in theory is limited only by the speed of light. In theory, such a battery could store energy approaching that of nuclear fuels, or even in hypothetical theory that close to anti-matter, which is millions of times that of fuel types such as gasoline or jet fuel, and hundreds of millions of times that of batteries. The energy density of hydrogen is roughly 140 megajoules per kilogram and is the most energy any chemical substance currently known can store. Jet fuel is around 40-46 megajoules along with gasoline and most other common hydrocarbons like kerosene or diesel, while ethanol has around 30. Lithium ion batteries by comparison can perhaps have .5 to 1 megajoule per kilogram, if they are relatively high end. This disparity in energy storage is why chemical energy storage, such as gasoline, is generally more efficient than chemical batteries at the moment. Lithium ion simply isn't able to store the amount of energy that gasoline can; rp-1, or rocket fuel, has a comparable amount of energy. Getting in to space is barely possible, as 90-91% of the rockets weight is fuel, and 8-9% is the rocket weight, with perhaps .3-1% being cargo. Rockets are only able to get in to space because their weight reduces as they burn fuel.
But a kinetic energy storage device, theoretically, could store that power, bridging the gap between nuclear and chemical energy, and it could be released as electrical battery. An object traveling At 3-4 kms when the energy efficiency of combustion engines is considered would have the same energy as a car with gasoline; at 8 kms it’s theoretically efficient enough to go in to space, and past 20 kms it could do it multiple times. The problem is storing something moving that fast; generally they spin in a circle, like a fly wheels. Fly wheels under such strain however would break and shatter due to the torque. Fly wheels experience a huge amount of strain when spinning; eventually they get traveling so fast that they break, which limits their energy.
However, flywheels are spun from the inside, rather than the outside. Like a helicopter, enormous strain is placed on the blades; although in theory helicopters are exponentially more powerful the longer the blades get, the strain placed on them makes long blades too weak to handle the stresses. These blades bend substantially, and then break. However, tip jet helicopters have significantly less stress as they’re spun from the outside. They often don’t need tail rotors due to the lack of strain. They do however have issues with stability as getting exactly equal power on both sides of the blades is difficult. Tandem rotors often spin in opposite directions to cancel this out. For the purpose of storing energy, by “spinning” an object, it might not be ideal to have it spin at all. Instead one can imagine an object levitating on a magnetic track, like a maglev train, going around in a circle at high speeds in a vacuum. The object would be accelerated like a railgun accelerates with magnets, while energy would be extracted like an alternator when the magnet passed by the copper coils, which would be lowered to extract energy, as the closer they get the more power they’d produce. You can also have two spin in opposite directions so as to reduce vibrations on the mechanism itself. Although I’m not sure of the sheer limits of such a device, it should reduce torque enough to greatly exceed a flywheel in terms of strength.
The most complicated thing would be making the projectile. It would need to be magnetically levitated, making it magnetic to a degree, but also capable of changing charge so it can be accelerated, and so it will release energy from the alternator. The exact design and construction of the device will depend heavily on the materials and its size, but it should be simple in theory to construct. Magnetic levitation and being in a vacuum should reduce drag, so as little energy is lost as possible from the projectile moving along the track. A small amount will be lost due to the coils being within close proximity. Power output will be adjusted by lowering or moving the coils closer to the projectile
