The tether near the counterweight (in orbit) experiences the greatest stress. This means it needs to be thicker, which means more weight...which means more stre

The tether near the counterweight (in orbit) experiences the greatest stress. This means it needs to be thicker, which means more weight...which means more stress. The ratio at which stress/weight climbs is determined by density and tensile strength. Basically only one material we know of meets these requirements, and manufacturing at scale is far away. Once you figure out how to make them en masse, now you have to figure out how to secure the strands into a bundle. Less of a challenge than warp drive, but still...quite hard. https://en.m.wikipedia.org/wiki/Colossal_carbon_tube https://en.m.wikipedia.org/wiki/Colossal_carbon_tube