Phobos encounter trajectory and maneuver design

In February 1977, the Viking 1 Orbiter made repeated flybys of the Martian satellite Phobos at distances near 100 kilometers. These close encounters allowed a detailed scientific investigation of the nature and origin of Phobos. A sequence of three maneuvers was required to achieve the encounters. This paper presents the trajectory analysis performed to accommodate the scientific objectives and the spacecraft propulsive maneuver strategy used to achieve the desired trajectory while satisfying operational constraints. The actual maneuvers executed and the resultant Phobos encounter conditions are presented.