Development and characterization of a standardized docking system for small spacecraft

Since the first mating manoeuvre in space, performed in 1966, many different docking mechanisms were developed, mainly for large manned spacecraft. The few systems recently conceived for small satellites have never been verified in space nor scaled to CubeSat size. In the near future, small spacecraft docking procedures could acquire great importance due to the need to share resources between clusters of low-weight and low-cost vehicles: in fact, small spacecraft market is rapidly growing, focusing on commercial low risk application, low budget scientific and educational missions. In this context, this document presents a novel docking mechanism to provide small spacecraft with the ability to join and separate in space, to realize multi-body platforms able to rearrange, be repaired or updated, thus overcoming the actual on board limitations of single small-scale satellites. As for now, the few proposed docking ports present (1) simple probe-drogue interfaces, unable to dock with same-gender ports, or (2) androgynous geometries, that can overcome that problem, but usually employing complex and non-axis-symmetric latches to perform the docking manoeuvre, that would demand robust and stringent navigation and control systems. The proposed solution overcomes the aforementioned drawbacks, using a semi-androgynous shape-shifting mechanism that actuating one interface changes the port into a “drogue" configuration, letting the other port penetrate it and closing around to create a solid joint. The mechanism design through the requirement definition and a trade-off between different concepts is presented, followed by the analysis of the dynamic behaviour of the selected solution, with particular attention to two aspects, i.e. the loads transmitted between the mating ports and the alignment tolerances requested to perform successful docking manoeuvres. Such analysis led to the definition of an instrumented prototype to verify the solution through simple validation tests, which demonstrated the mechanism operations and defined the alignment ranges, that lie in the range of +- 15 mm and up to 6 degrees. Last, a comparison with SPHERES UDP is presented, as part of the activities performed during a visit period at MIT Space Systems Laboratory