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Vacuum Balloons
Technology > Application > Transportation > Atmospheric Transport
Technology > Technology Type or Material > Drytech/Hylotech
Technology > Technology Levels > High Tech / Hitech
Technology > Technology Type or Material > Drytech/Hylotech
Technology > Technology Levels > High Tech / Hitech
Floating structures that utilize vacuum to achieve buoyancy | |
 Image from Steve Bowers | |
| A dynamically-inflated balloon is filled with vacuum, but uses internal momentum beams to resist collapse against atmospheric pressure | |
The structure containing the vacuum must resist the compression of the surrounding atmosphere. This can be done with simple compressive strength, magnetic pressure, or momentum pressure.
With compressive strength, the vacuum chamber is a rigid shell, sometimes with a lightweight truss of diamondoid bracing inside. The shell and bracing must be strong enough to resist buckling under any variations in stress, increasing the mass. Larger chambers require internal bracing, the mass of which increases in proportion to the enclosed volume. Finally, the rigidity of the components makes them relatively inflexible. Therefore, this method tends to provide the least lift per unit volume, and is rarely used except for vacuum chambers with unusual shapes. Aerovac foam, which utilises evacuated bubbles with a minimum diameter of 50cm, is perhaps the most commonplace and flexible form of vacuum balloon technology.
With magnetic pressure, the interior skin of the balloon is a charged superconducting solenoid, inflated by the magnetic pressure inside it. Because the envelope is flexible, magnetic balloons can be easily be deflated and packed into a small volume for transport. The maximum pressure a magnetic balloon can provide before the superconductor quenches is the same as its energy density — approximately 200GPa (2 million bars). The most efficient shape for a magnetic vacuum balloon is a torus, but additional tension cables can be used to deform the balloon into other shapes, at the cost of additional mass. Otherwise, they can be extremely light, because the envelope is in tension and only needs to be strong enough to resist variations in stress, allowing it to be very thin. Larger balloons will be subject to more stresses due to winds, requiring extra reinforcement, and if the atmosphere is hot enough to quench the superconductor, the outer envelope needs to be protected with vacuum-insulated membranes, which, although light, increase the mass considerably. A rare variant of magnetic balloons use embedded monopoles rather than superconductors. These have a much greater temperature resistance, and can survive ambient temperatures of up to 1500K, but can only be inflated by actively adding monopoles.
With momentum pressure, two or more loops rotate at high velocity inside the envelope, serving as momentum-stiffened compression members. The envelope is a membrane under tension, held open by the loops. As with magnetic vacuum balloons, the entire structure is flexible, and can be deflated and packed into a small volume. Momentum vacuum balloons have a roughly spherical geometry: The loops stand are visible as circular ribs, while the envelope between them sags inward under the atmospheric pressure. The loops must have enough mass to serve as effective compression members, which provides the main limiting factor of momentum balloons. They have a minor aesthetic advantage over magnetic balloons in that, apart from the loops, the envelope can be made transparent.
 Image from Steve Bowers | |
| Magnetically-inflated balloons use electromagnetic repulsion to maintain their structure, and often take the form of toroids containing superconducting loops | |
Uses
In anything other than hydrogen and helium atmospheres, vacuum balloons only provide marginally greater lift than a hydrogen/helium lifting gas would. (In an Earthlike atmosphere, for every Newton of lift provided by vacuum, an equal volume of hydrogen or helium would provide 0.93 or 0.86 Newtons respectively.) The primary advantage of magnetic and momentum balloons here is their convenience: They can be inflated using a local energy supply, without needing a supply of lifting gas.In hydrogen/helium atmospheres, vacuum balloons are the standard solution. (Hot air balloons can also provide some lift, but require either heavier fully insulated envelope or constant supply of heat.)
They are frequently used in vacuum dirigibles for slow cruises in an atmosphere, for example in the airships of NeoAtlantia, some Lifts on Kiyoshi, and by some wandering hermits in Cableville.
They are also ubiquitous in bubblehabs. The toroidal geometry of a magnetic balloon naturally provides a sheltered region in the central hole, where a habitable space can be located or suspended.
A more subtle use of vacuum balloons is in ordinary construction. Magnetically inflated structural members will usually have vacuum interiors. While they may not be large enough to provide lift, their effective weight in an atmosphere can be very small, which proves particularly useful in bubblehabs or very tall skyscrapers.
Finally, vacuum balloons can be useful in moving gaseous planets. Many large vacuum balloons are pushed deep into the atmosphere by mass beams. Through buoyancy, the planet exerts an upwards force on the balloons, and therefore the balloons exert a reciprocal downward force on the planet. This allows the mass beams to exert a force on the planet, slowly accelerating it. (This method is far less disruptive to the atmosphere than fusion candles. However, if moons are present, they often serve as better anchors for the mass beams.)
 Image from Todd Drashner | |
| Cloud Cities on Cumulus are supported by aerovac foam technology | |
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Development Notes
Text by Liam Jones
Rewritten 2025 from an original article by Todd Drashner
Initially published on 16 February 2004.
Updated 30/9/25 by Liam Jones
Rewritten 2025 from an original article by Todd Drashner
Initially published on 16 February 2004.
Updated 30/9/25 by Liam Jones
