Space settlement precursors are activities that really ought to be perfected before space settlement is attempted.
For instance, short suborbital space tourist jaunts will create demand for longer orbital space tourist trips. Longer orbital trips will create demand for destinations in space: orbital hotels. And a space hotel is not that much different from what a space settlement will look like. A space hotel will require all the same characteristics a space settlement will need: high reliability, comfort and security for the dozens or hundreds of people aboard. So, before we have space settlements, we need to build space hotels. And before we build space hotels, we need reliable human transportation to orbit. The beginnings of which are being built now in the form of suborbital space tourism providers (e.g. Virgin Galactic and Blue Origin).
Space tourism, satellite servicing and 3D printing are three examples of space settlement precursor activities.
Satellite servicing is another precursor activity, one that is likely to start in the early 2020s (link, link). Moving fluids and gases around in microgravity and perfecting long-range telerobotics will be essential to constructing and managing a space hotel and, eventually, a space settlement. And, luckily for settlement and space manufacturing, it appears a golden age of satellite construction is about to begin with numerous companies planning multi-hundred (or thousand) satellite constellations in the next five years. All many of those satellites will be designed to receive servicing, repair and replacement. Perhaps the facilities to provide some of those services can be located in orbit? The lessons learned at a satellite repair facility will be useful in constructing and maintaining space settlements.
Additive manufacturing is another space settlement precursor. Ideally a large portion of a space hotel or space settlement will be 3D printed on orbit using feedstock delivered very cheaply to orbit by gun-launcher systems or, maybe, super-huge (and super cheap) rockets like SpaceX’s ITS. This construction strategy will allow for more flexible settlement geometries: the modules won’t be constrained by the dimensions of a rocket fairing. An added bonus: 3D printing can theoretically be adjusted to accept feedstock derived from asteroidal or lunar resources in the future. So it’s an investment that can be amortized over the very long-term and used throughout cislunar space, and beyond. Luckily, at least one company, Made In Space, is already working on putting 3d printers in the vacuum of space at the ISS.
There are likely more precursors. Can you think of a few? Please make suggestions in the comments.