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A space fountain is a megastructure that uses a stream of projectiles to hold a structure aloft, with the means of suspension being the same as a Frisbee being dammed by water. It would need to be enclosed in a vacuum and use magnetic levitation. It holds more promise than a space elevator as its height would not be limited by the tensile strength of the material. The tower would be built incrementally from scratch, and power and projectile streams should be redundant to prevent disaster.
A space fountain is a hypothetical active structure that would use the momentum of a stream of projectiles to hold a structure aloft. Because a Space Fountain would need to be hundreds or thousands of miles tall, it’s referred to as a megastructure, and the cost of building it would be prohibitively expensive for at least the next couple of decades.
Unlike a space elevator, which uses pulling force to stay aloft, a space fountain’s means of suspension would be the same means a hypothetical Frisbee would use that is being dammed up by a stream of water from a pipe. For a space fountain, the projectile stream would have to be enclosed in a vacuum to prevent a massive loss of power. The vacuum would be contained by a tube that uses magnetic levitation to remain unencumbered by the stream of projectiles. For this reason, one of the few serious studies of a space fountain uses a continuous, segmented iron ribbon only 2 cm in diameter as a projectile stream.
Despite the initial energy investment required to operate the projectile stream, the Space Fountain ultimately holds more promise than the Space Elevator because its height would not be limited by the tensile strength of the material. Exotic materials like carbon nanotubes would not be needed to keep the tower aloft: conventional materials would suffice.
A space fountain was imagined alternatively as a huge bight or as a single tower with two paths for pellets to enter and exit. In one tower, the pellets would be slowed down as they reached the top by electromagnetic drag devices that would harvest energy from the accelerating objects. They would then return to the Earth’s surface via gravity, where some of their momentum would be gathered again. The energy gained through this process would then be used to power a mass driver that launches the pellets back into space, where they transfer momentum to a floating platform and start the process all over again.
The construction method would also vary from the space elevator. Instead of being built from the ground up, the tower would be built incrementally from scratch. For one cycle, an extremely long hollow tube would start at rest on the earth’s surface. Then, the stream of bullets would start slowly, with the pellets being fed into the tube at a slight upward angle, causing the tube to slowly but surely rise from the earth’s surface. Eventually, the climax of the cycle would come in space. A closed circuit would also be used for a tower, but the outgoing and incoming flows would be next to each other.
Power and projectile streams for any space fountains should be redundant. If the circuit were to break and the bullets were to be released, a huge disaster could ensue. A ring of a space fountain falling towards the ground at re-entry speeds would be akin to lashing the Earth with a huge flail.
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