To spread Terran legacy and avoid overpopulation on Earth throughout the Solar System Earth Govs put in place the Earth Migration Program, with its currency, the Earth Stay Time / EST /. On birth, all get the same amount of ‘Space Creds’ and a lifelong EST. When someone deliberately wants to leave Earth it gets an amount of ‘Space Creds’ to start a new life out of Earth based on their age / how younger how more /. Those amounts can get quite high depending on country/corporation. Some settlements were fully funded with those Creds.
To help people to stay together, EST can be transferred between them only if they do so to leave at the same time.
Some elements / actions can shorten the EST of a person as birth control, criminal activity, and activity against one’s community, what most of the dissidents call: “anti-govs” actions, as riots, sabotage and more. EST creds can vary depending on the issuing governments. Most of Sub-Saharan Africa countries tend to issue the most mainly because they were the first to massively migrate to space due to their alarming population levels at the start of the human expansion. They had large incentives from the start, giving them a step ahead on the rest of Earth. Those incentives were very fast paid back through African expansionist sending creds to their families and beloved ones. A lot of expansionist entrepreneurs were by then also making bridges between the Asteroid Belt and their origin countries.
Heavily controlled traffic towards Earth makes it difficult to return and to leave forcing people to exchange their EST into Space Creds.