Vernier thrusters are rocket engines used on spacecraft for fine adjustments to the attitude or velocity of a spacecraft. They are used when a heavy spacecraft requires a wide range of different thrust levels for attitude or velocity control, as for maneuvering during docking with other spacecraft. On space vehicles with two sizes of attitude control thrusters, the main ACS (Attitude Control System) thrusters are used for larger movements, while the verniers are reserved for smaller adjustments.
Rockets primarily use a gimbaled thrust system, which swivels the engine nozzle on two axes to change direction and rotate during launch and ascent. In space, it uses a Reaction Control System, utilizing reaction wheels, gyroscopes, and smaller thrusters for directional and orientational maneuvers.
Rocket motors used in spacecraft are designed to propel and maneuver them in space. They are typically smaller and less powerful than the motors used for launch vehicles. Still, they must be highly reliable, efficient, and versatile to enable the spacecraft to travel long distances and perform complex missions. Some rockets have used additional vernier rocket motors to give control, but they are not used as much because of the extra weight and different fuel needed.
Therefore, vernier thrusters and Reaction Control System (RCS) are the types of rocket engines used to maneuver spacecraft during flight and adjust their trajectory.
