Closed atmosphere habitats

(tented/bubble habitats)

Many research facilities are built on planets and moons with absent or unbreathable atmospheres, but rather than confining a substantial research team to live subsurface in pressurized warrens, more often than not a tented surface habitat is created which contains a pleasant open environment for the research facility and provides relief from an otherwise barren landscape.

These tented habitats are technically described as closed atmosphere habitats, and these tend to be divided into two types, there are habitats that are erected in environments with little or excessive atmosphere, and there are the kind that are constructed in an environment with an unsuitable atmosphere. The construction of the later is somewhat simpler, as the stresses on the structure are less, and minor failure does lead to rapidly fatal environments.

The major factor behind the creation of these kind of settlements is temperature, if external temperatures are habitable then no special requirements are needed to regulate internal temperature, in cooler environments the internal airspace may need to be heated but this problem is easily solved as many of the habitat’s machinery generate waste heat which can be used for this purpose. The greatest challenges are in excessively warm environments where the interior needs to be cooled, this kind of environment requires dedicated cooling systems that unlike heating systems cannot be turned off for any great period of time. The general limits for these tented habitats range from 180’K to 350’K, and although technology can extend this range much further, it is considered to risky with such extreme environments, and that failure would be catastrophic.

The second important consideration is that of external pressure, vacuums cause a net pressure outward, trying to pull apart the tent, where as high atmospheric pressure attempt to crush it. Vacuum, or near vacuum environments have been extensively worked with in man’s exploration of Mars, and the engineering behind these structures has become very familiar, but high pressure environments are somewhat rarer and harder to deal with. Generally deficient pressures are easier to deal with than excessive pressures. The general pressure range for tented habitats range between vacuum and 1.5 bar, pressures beyond 2 bar can be achieved though this requires increased pressurization of the habitat, and also depressurization procedures for any personnel who want to return to a normal atmosphere. (Problems also arise with high-pressure atmospheric composition, as simply increasing the pressure of normal air raises the partial pressure of oxygen, which has undesirable health effects, consequently gas mixtures are changed at high pressures, often by increasing the amount of noble gases and nitrogen).

The defining construction material of these tented habitats is the envelope, according to the local environment this thin transparent layer may have to buffer against temperature, shield from harmful radiation, resist external storms, and retain the internal atmosphere over long periods of time without significant loss. A standard envelope has a ‘backbone’ fabric of laminate diamond and transparent polymer, this tough material provides the transparent air tight membrane, which other layers may be added to. Layers of highly transparent aerogel can be added to act as thermal insulation, in addition this material can have filters introduced to cut out certain wavelengths, or change the apparent colour of the sky. Other filters may be added to cut out other frequencies of radiation, which is particularly important in vacuum environments as the surface is bombarded with solar and cosmic radiation. (A general thickness for an envelope is hard to define, but they can range to being a film maybe only a few millimeters thick, for just separating a poisonous atmosphere from a breathable one, to a many metre thick construction [though very light] which can cope with vacuum, radiation and micrometeorite hazards.)

The envelope generally rests over a frame, which maintains its shape and takes most of the structural stresses. In a vacuum environment the difference in pressure helps to inflate the envelope, and a frame serves to support the envelope in the event of collapse. In atmospheric environments, frames help to support the envelope and also protect against the buffeting of the wind. In high pressure, or same pressure environments frames are essential, as pressure differences do not aid in supporting the structure, and frames maintain the structure of the envelope against pressure that wants to crush it.

Frames are usually modular in construction, made from prefabricated light metal struts that are quickly assembled into a sturdy metal framework dome, the layer of envelope can lay over this, or be installed as ‘cells’ in the gaps between the metal work. There are advantages to both types of envelope deployment, where frames have been established, and are of the same size, single membrane envelopes are quicker to install, and less likely to fail in the installment stages, but cellular modules are easier to store and repair in the event of failure, cellular components also offer the ability of complete repair without depressurizing the habitat, for this reason this type of system is predominantly used.

An alternative to the framework concept is to have an inflatable dome, where an airgap in the envelope is inflated with a gas, and this gives a structural rigidity to the structure, this system also has the added bonus of quickly detecting puncturing by a loss in internal pressure, though this might lead to partial collapse if not repaired quickly. Inflatable domes tend to be used as temporary measures before more permanent structures can be built.

The construction process depends on the amount of machinery that can be assigned to the project, theoretically a domed habitat can be constructed in less than a day if good foundations for frame attachment, and also the ground proof against air leakage, but these two requirements are the most time consuming aspects and may require weeks of excavation and extensive ground restructuring, (such as vitrification of rock and regolith material to create air tight seals).

In the modern federation few people live under such habitats, though if one includes the envelope system of asteroid colonies, then the actual population may run almost into the billion range, generally domed surface habitats are the preserve of research teams in hostile environments or terraforming teams on planets being changed for colonization.