A period during a spacecraft's flight in which it undergoes routine on-board operations, such as receiving new command sequences, establishing attitude control, tracking the Earth with its high-gain antenna, and deploying booms and other appendages. The spacecraft also begins collecting data for its mission during this phase.

The cruise phase comes between the launch phase and the encounter phase. It may last only for a few months or for years. At NASA, it is normally managed from the Space Flight Operations Facility at the Jet Propulsion Laboratory.