Welded Joints for Robotic, On‐Orbit Assembly of Space Structures

A preliminary design concept for a weldable joint for on‐orbit assembly of large space structures is described. The joint was designed for ease of assembly, for structural efficiency, and to allow passage of fluid (for active cooling or other purposes) along the member through the joint. The members were assumed to consist of graphite/epoxy tubes to which were bonded 2219‐T87 aluminum alloy end fittings for welding on‐orbit to nodes of the same alloy. A modified form of gas tungsten arc welding was assumed to be the welding process. The joint was designed for the thermal and structural loading associated with a 37 m diameter tetrahedral truss intended as an aerobrake for a mission to Mars. It was concluded that the assembly process could lock large loads into the truss members and that the assembly robot could be required to exert large forces while aligning pairs of nodes during assembly. It was also concluded that the connections between the composite struts and the aluminum fittings will be subjected to very high service stresses due to the effects of differential thermal expansion.