Mars 4 and 5
Date: 23 Jul 1973
Mars 4 and 5 were to orbit Mars. They were to take pictures and conduct remote-sensing experiments on the atmosphere and surface, and to serve as a communications relay for the Mars 6 and 7 landers.
Mars 4 didn't achieve Mars orbit and flew by instead. Mars 5 was damaged by a possible micrometeoroid and its science mission was cut short.