In 1987 work was initiated on the Automated Structural Assembly Laboratory (ASAL) at NASA/LaRC to demonstrate the feasibility of robotic construction in orbit. To move itself as the structure grows, the robot is mounted on a carriage that traverses a beam which moves longitudinally, similar to a gantry crane. Gantry motions will be operated by the self-sufficient robot with its wrist roll motion. Interfaces for the robot at each gantry motor shaft are provided for that purpose. Wrist roll is limited by the large and growing number of wires that must communicate thru the wrist joint to connect the end-effector to power, sensory devices, and computation services. Rotation-Rectifiers applied to robot mobility simplify the end-effector to motor shaft interface, reduce the number of interface operations that must be performed, and convert oscillating robot wrist roll motions to continuous rotation in either direction.