Inflatable domes are an exceptionally common habitat used on asteroids, moons, and planetary bodies. They are ideal for being lightweight and portable as well as quick and easy to assemble (many assemble themselves). They range from small encampment models to ones large enough to contain a massive city. Most are simply composed of plastic ﬁlms supported entirely by the internal air pressure, sometimes contained with a high-tensile strength restraint net. Strong enough to withstand hurricane winds, micrometeorite strikes, and heavy snow or dirt loads, they are buttressed with hardened shutters in dangerous environments. Some are transparent, some opaque with reﬂective surfaces. Larger city domes are constructed from sturdier materials like aerogel, transparent alumina, and diamond.
Domes for temporary settlements are simply inflated on any available flat surface. For more permanent installations, they are used to cap off craters, canyons, or shallow holes dug in easily removable regolith. Though the atmosphere on large domes helps protect against radiation, smaller ones are buried for protection. Domes are often protected with multiple insulating layers and damage-sensing autorepair networks.
Under the dome, the settlement consists of whatever structures the residents desire. In smaller domes in airless environments, tin can habs and underground warrens are used to protect against solar radiation and cosmic rays. The larger domes of Martian cities cover massive skyscrapers and urban cityscapes. Multiple domes are often joined together to cover larger areas. Airlocks provide access to the outside, while ventilators pipe out unwanted gases from the air plant and life support machinery.
Planetary domed habitats vary a great deal in terms of security arrangements. The big Martian cities like Valles-New Shanghai and Elysium have fairly relaxed customs arrangements, with anyone able to enter with only a cursory ID scan.
Large Lunar and Titanian cities are also very easy to enter, at least for citizens of their respective polities. Smaller settlements vary a lot. Farm towns like Pilsener City on Mars have almost non-existent security, while high security corporate domes like New Dazhai on Mars will subject visitors to full-on customs procedures.
Breaching dome walls varies in difficulty based on the age of the dome and the level of security present. Newer domes usually have smart hull repair and are heavily monitored for atmospheric breaches, while older settlements tend to lack both the fancy hardware and the tight security. Domes also don’t offer as many service hatches and drone bays for clandestine access, as domes do not generally have the busy ﬂeets of harvester and repair drones that accompany space habs. Some domes are accessible via underground tunnel networks with remote access points. Domes have a vulnerability in that a significant amount of damage to their structure can create an irreparable breach or breaches, possibly strong enough to vent the atmosphere in seconds.