Each Voyager spacecraft has 16 hydrazine thrusters. These small chemical thrusters provide attitude control, helping the probe maintain its orientation and keep its high-gain antenna pointed toward Earth.
The thrusters are arranged for both maneuvering and redundancy. Four are used for trajectory-correction maneuvers, while the remaining thrusters are organized into two redundant six-thruster branches. Only one attitude-control branch is needed at a time, allowing the spacecraft to continue operating if a component or an entire branch fails.
Hydrazine was chosen because it can decompose rapidly over a catalyst, producing hot gas without requiring a separate oxidizer. The fuel is stored in a spherical titanium tank. Unlike a large launch rocket engine, these thrusters deliver small, precise impulses suited to pointing and fine course adjustments.
The number 16 refers to the thrusters installed on each spacecraft, not the number firing simultaneously. Voyager’s long life has required careful management of fuel, valve wear, and clogged propellant lines as the probes continue their journey through interstellar space.