Space Fountains and Orbital Rings

Applications of mass stream technology and momentum transfer

Space Fountain
Image from Anders Sandberg

The transfer of momentum by the use of massive particles is a technique which has become widely used in the Terragen Sphere, particularly in the Beam-Rider method of space propulsion, but also in the construction of large, dynamically supported megastructures. Space fountains can be used to support structures on planets larger than any which can be built with materials in compression or tension; while truly large structures such as orbital rings and supramundane worlds can be built above the surface of any object with gravity.

The Space Fountain system is used to support structures on the surface of a planet, structures which often reach to the edge of space, hence the name. A Space Fountain incorporates continuous mass driver which propels captive particles with significant mass inside a closed loop. These particles must consist of, or be coated with, a material which is strongly affected by magnetic fields. The particles are projected upward from the bottom of the tower, and on the way up are controlled and partially braked by electromagnetic devices, which generate both electricity and a certain amount of lift. The particles are redirected back down by a large bending magnet once they reach the top, and the force of redirection holds the top of the tower up. The particle beams must be contained within evacuated tubes to avoid friction, especially in the lower parts of a planetary atmosphere. Often the space fountain is used for access to space, however the top of the tower is not travelling at orbital speed so some other method of acceleration, such as tether technology, reaction drives or mass drivers must be used to place payloads in orbit.

Dynamic compression member
Image from Steve Bowers

Space fountain technology can be used inside buildings as so-called dynamic compression members to add extra strength, allowing construction to reach heights impossible with non-dynamic methods. Giant buildings reaching far into space are sometimes built on planetary surfaces using fountains as internal support. Dynamic Compression Members can be used in space to support large structures against their own gravity, and to strengthen light sails and magnetic sail systems. Large beamrider ships often have sails strengthened by a number of mass streams.

Dynamic orbital ring
Image from Steve Bowers

Orbital Rings are a more advanced application of mass-beam momentum transfer technology, first proposed in the information age by Paul Birch. A continuous stream of magnetic particles are placed in orbit around a planet, and encased in a tube lined with electromagnetic devices which accelerate the mass of the stream until it is moving faster than orbital speed. The stream will exert a net force outwards as it attempts to move into a higher orbit, but it is constrained by the tube and the electromagnetic control systems, which redirect the mass-stream back towards the planet, creating a net outwards force in the ring which can be used to support a payload.

In practice a typical, circular orbital ring around a terrestrial world consists of a continuous ring of dense material, often a silicate (glass-fibre) hoop or cable, which is coated on the outside with a ferromagnetic or paramagnetic material. On the other hand, larger rings, elliptical or otherwise irregular rings use mass-streams made up of individual mass particles, an arrangement which is more flexible.

Venus after terraforming
Image from Steve Bowers
Venus is surrounded by a Dynamic Orbital Ring

The Orbital ring need not be located around the equator; sideways acceleration can control precession so that the ring can have any inclination. If several rings are superimposed, gradually a sphere can be constructed in the so called 'ball of string' configuration; more rings in a gridlike-x-y-z configuration can be added on top eventually forming a supramundane structure (or a suprastellar structure above a star. (see Supermundane Worlds and Artificial Planets)
Mass stream technology has other uses too; transport (vehicles can be coupled to a mass stream and accelerated in the same way as the streams are, but on the outside of the stream); and cooling (objects can transfer heat to mass streams which then radiate the energy to space in a remote location). Both applications are extensively used in the Xi Scorpii system among the Kiyoshi dyson shells.

Partially orbital bridge
Image from Steve Bowers

Partial Orbital Ring Systems can be constructed, consisting of only a part of an orbital ring with deflector magnets at each end. Bridges have been constructed on a number of worlds reaching far across an ocean from one continent to another; PORS systems are also convenient for ground to orbit access if they are used to support a payload acceleration system above the atmosphere. A related concept is the Lofstrom Loop.

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Development Notes
Text by Steve Bowers
Initially published on 08 June 2007.


The Paul Birch Archive at Orion's Arm