Complex sentence: Viking 1 was launched on 20 August 1975 and Viking 2 was launched 9 September 1975 this orbiter/lander mission was to photograph Mars in detail and to find water and life on the surface.
Split into simpler sentences: Viking 1 was launched on 20 August 1975 and Viking 2 was launched 9 September 1975. This orbiter/lander mission was to photograph Mars in detail and to find water and life on the surface.