Docked with Cosmos 188; First automated docking. Recovered October 31, 1967 08:20 GMT. Achieved automatic rendezvous on second attempt. Capture achieved but hard docking and electric connections unsuccessful due to misallignment of spacecraft. Star tracker failed and had to make a high-G ballistic re-entry.
Cosmos 186 (the active spacecraft - 7K-OK(A)#6 was launched 27 October 67 from LC31. It was followed on 30 October by Cosmos 188, (the passive spacecraft). The passive spacecraft was placed in the planned orbit, only 24 km from Cosmos 186, and an automatic first orbit rendezvous and docking was commanded. To the astonishment of the ground crews, the spacecraft proceeded to accomplish the first-ever automated rendezvous and docking. Unfortunately docking occurred only out of range of ground tracking stations, so only post-facto analysis of telemetry indicated that problems had occurred.
The first docking attempt failed when the active spacecraft flew past Cosmos 188 at a distance of 900 m after the system lost contact. The spacecraft set itself up for a second attempt and achieved soft-dock. However when hard-dock was attempted an excessive lateral movement led to the directional steering of the active spacecraft torquing, and the detailed interface latches and connectors of the docking rings did not join. The spacecraft had hard docking but without full latching and electrical connections. There was also a significant over-expenditure of propellant in the docking process.
The landings began on 31 October with Cosmos 186. Due to failure of a star tracker a guided lifting re-entry of 3-4 G was not accomplished. A ballistic re-entry of 7-8 G however resulted in a successful soft landing in the target zone. References: 1 , 2 , 6 .