What is the propellant used for Voyager’s attitude-control thrusters? The propellant is hydrazine. Voyager’s small monopropellant thrusters use hydrazine to produce the controlled pulses needed to point the spacecraft and keep its antenna aimed toward Earth.
The Voyager spacecraft carry sixteen hydrazine MR-103 thrusters. Their attitude-control system can rotate the spacecraft around its three axes, allowing the high-gain antenna and scientific instruments to maintain the required orientation. Separate thrusters support trajectory-correction maneuvers.
Hydrazine is useful for deep-space missions because it can decompose over a catalyst without a separate oxidizer. That makes the plumbing and engine system relatively simple, though hydrazine is highly toxic and must be handled carefully. It is stored as a liquid in a spherical titanium tank.
A common mix-up is to associate Voyager propulsion with the solid rocket motor used during launch or early ascent. That motor helped provide launch energy, but the long-lived attitude-control system aboard the spacecraft relies on hydrazine monopropellant.