Tau.Neutrino said:

Robot successfully builds space structure in first autonomous construction demo

A robotic truss builder that was conceived, designed and built by Caltech researchers has successfully built a structure in space—without the help of astronauts—for the first time. The truss builder, part of DARPA’s Novel Orbital and Moon Manufacturing, Materials, and Mass-efficient Design (NOM4D) program, consists of an autonomous manipulator that picks up struts and joints held in nearby dispensers to repeatedly assemble identical sections, or bays, of a perimeter truss.

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For maintenance, a continuous rail would be handy to have.