Complex sentence: After two failures, Zond 3 was sent on a test mission, photographing the far side of the Moon (only the second spacecraft to do so) and continuing out to the orbit of Mars in order to test telemetry and spacecraft systems.
Split into simpler sentences: After two failures, Zond 3 was sent on a test mission, becoming the second spacecraft to photograph the far side of the Moon. It then continued out to the orbit of Mars in order to test telemetry and spacecraft systems.