During a spacecraft's fly-by operation, the moment when a celestial target can be better resolved by the spacecraft's on-board instruments than by those on Earth. This phase usually occurs a few months before the fly-by. Encounter command-sequences on board begin to activate observations of the target, and ground stations become operational in support. The observatory phase follows the interplanetary cruise phase, and occurs before the far encounter phase (FE).
Subjects: Astronomy and Astrophysics.