Cosmos 871 to 878

Cosmos 871 to 878 are satellites of the Strela-1M constellation. These satellites operate as mailboxes: they remember the received messages and then resend them after scheduled time, or by command from the Earth. Some sources state the satellites are capable of only three months of active operation, but in accordance to others they can serve for about five years. The satellites are used for transmission of encrypted messages and images.