> The problem with orbital mining is that it depends on the presence of orbital manufacturing.
I'm sorry, but that's a very confused statement. It is quite possible to build a space tug that mines rock from an asteroid, and delivers it to another orbit where it is needed. If the need is for radiation shielding, then no manufacturing steps are required. The more general flow of industry goes:
Extraction -> Raw Materials Processing -> Ready to Use Materials -> Parts Fabrication -> Assembly
Using steel as an example, iron ore, coal, and limestone are extracted at their respective mines. They are combined in a blast furnace to process them into iron. The iron is further processed into a particular alloy of steel, in a useful shape (sheet, bar, rod, etc). This is the ready to use material. The steel is fed to machine tools to make finished parts, which are then assembled into some kind of machine, like a car engine.
Parts fabrication and assembly are together called manufacturing, but they are not necessary if your space product is usable as a material. For example, some asteroids contain hydrated minerals. If you heat them to 200-400C, the hydrates will decompose to water + a different mineral. The water can then be used as water by human crew, or further processed to oxygen and hydrogen by electrolysis for rocket fuel. The dehydration furnace and electrolysis units can come from Earth, ready to use. In fact, the Space Shuttle used the reverse process in a fuel cell, combining H2 and O2 to make water and electricity.
Shielding, water, and fuel are commonly needed items in space, so it makes sense to bring up equipment to produce them, if you can produce more than their weight in products. The actual return ratios are in the range of 100:1, meaning for each 1 ton of asteroid tugs and furnaces, you eventually get 100 tons of products. When launch costs are high, it makes a lot of sense to do that. More complicated manufacturing, like turning metallic asteroids into parts and machines, will come later, if it makes economic sense.