The Timetable of Space Colonization

Space travel is immensely technology intense. Colonization within the Earth-moon system alone was practically impossible for the longest period of time because of the immense costs of any space travel. Space colonization has roughly been divided into three stages, limited by what the technologies of the time made possible or practical. It took an immanent threat of an ice age to plant the seeds of space colonization, and even there it was a rough beginning.

The First Steps
The first generation of space technology (1949 to 2018) was limited by chemical rocketry. Chemical rockets are notoriously inefficient and low-energy content, so this generation was largely defined by putting satelites into Low Earth Orbit and sending out a few tentative probes beyond that. Manned missions into space were maintained at great expense, and in retrospect were more possible than practical.

The First Generation of Colonization
In 2018 the Induced Fusion Drive was invented, and for the first time an engine existed powerful enough to make manned missions in space practical. This, however, did not have any affect on space travel for some years because there was no infrastructure in space.

NOAA released a study in 2021 indicating that the Earth would abruptly enter another ice age, and that within fifty years the Earth's food production would be less than fifty percent of what it had been. This spurred politicians to try to find some remedy, from welcoming any source of greenhouse gasses to designating NASA with putting mirrors in space, to reflect sunlight onto the Earth's surface.

NASA, partnering with the European Space Agency, took their task's definition loosely. Rather than launching many mirrors from the Earth at great total costs, they put a small, remote-operated base on the moon's Southern polar cap. This base and the rovers on it would construct a colony on the moon, which could in turn create a factory to create the mirrors.

On paper the idea was dynamite; the moon's gravity was much weaker than the Earth's, and the moon has no atmoshpere to hamper with launches. In practice, however, the process was slow and NASA's budget was cut when the first mirrors proved to be less than effective. The colony lay abandoned for some time, with NASA continuing to use the remote operations to build a colony. Finally, as the ice age began to approach, NASA began using Luna Prime's capacities to build the components of a free-floating space colony which could be put in a barycenter between Earth and the moon.

First Geration Space Colonies
First generation colonies were notoriously cramped and difficult to live in, comparable to life on a World War 2 submarine. They were little more than construction yards built in space rather than on the ground, with a centerfuge to generate artificial gravity for the living quarters. By 2035 all five Barycenters held at least one space colony of this type, manned almost exclusively by dedicated engineers from NASA and the ESA. They operated almost exclusively with materials and provisions provided by Luna Prime--launches and landings to and from Earth were prohibitively expensive. But, with this poorly manned fleet of colonies the space agencies built ships with IF drives to send manned expeditions to all the major planets. Gas Giant expeditions in particular required Astronauts to stay away for years, mapping and studying rings, the compositions of moons, and the cloud patterns of the planets.

Interplanetary colonization
The technology required to colonize the planets came together very abruptly when fusion became a practical source of power. A few probes had been sent to the stars using an experimental Particle Drive, but this was an energy hog, well beyond fission's ability to power. Combining Particle Drives with nuclear fusion suddenly allowed for interplanetary travel to become relatively easy, taking weeks rather than months or years. Much of the human population of Earth--spurred by both an oncoming ice age and persistent radio bandwidth rationing--spread out across the solar system, constructing over twenty five thousand space colonies between 2090 and 2150, both intended to house human settlers as well as preserve Earth's biomes.