Opening of the first free area on the Moon.
The free area is connected to the moon base Vegas. It is covered by an immaterial dome, but otherwise the area is open to space like earth's surface. Earth-like atmospheric conditions are created by technical means without employing a solid dome, massive shields or side walls.
The free area comprises a circle of five kilometers. The atmosphere is three kilometers high. But only the lower 100 meters are habitable. Beyond that the layered containment system begins. The system provides a pressure of 0.7 bar at ground level and an oxygen partial pressure which allows unlimited abidance without additional life support.
A combination of transparent shields and active measures keeps the atmosphere inside and protects against radiation. Actually, the area is not completely open to space. It is covered by multiple layers of transparent grating struts to which electromagnetic near field projectors are attached restricting the movement of atmospheric molecules to the inside. Major components in the sky are rendered invisible using metamaterials for optical wavelengths. For security reasons, there is also a passive protective shell made of transparent ceramics.
Thus, the free area is not really different from other transparent domes. Yet, its effect is highly impressive. Leaving Vegas through the new free area exit, you walk down the grand staircase into a green park under a dark blue sky as on Earth. This is a spectacular difference to most of the lunar surface which is dominated by hard vacuum, deadly radiation, and toxic particulates.
The free area is continuously expanded over time. A 100 years later with the extension to 10 kilometers the protective dome is omitted, since the other measures have proven to be very reliable.
The free area becomes a popular destination for locals and for tourists. The possibility to dwell under an open sky makes Vegas very attractive. For a long time Vegas is the headquarters of the Solar Coalition. For many people Vegas is the capital of the solar system, although the system is never really united. Free areas contribute significantly to making people feel at home in interplanetary space during earth's isolation.
During the System War in the 26th century Coalition troops land in the free area of Vegas. The containment system is partially destroyed. But emergency measures prevent a catastrophic decompression. The advantage of landing in the free area is that Coalition forces can operate under normal atmospheric conditions just like former paratroopers. This tactic allows dropping a unusually large number of ground troops for space combat. They overrun the defending troops. Earth's forces have to pull back from the moon after Vegas has been taken.
At the beginning of the 28th century over a billion people lives in interplanetary space. There are many free spaces with a total area of over 200 square kilometers on Moon, Mars and other airless celestial bodies. The interplanetary population shrinks during the Kisor war and many free areas are abandoned in order to save the maintenance cost. In the final phase of the war the Vegas / Luna metropolitan area is a military target due to its industrial capacity. The free area of Vegas suffers severe damage during early attacks on lunar infrastructure. It is finally destroyed.