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How Is a Rocket Steered?

One of the most important parts of rocketry is stability and control of the rocket. A rocket requires a steering system not only to point it in the right direction but also to deal with instability caused by aerodynamic forces. Consequently, rocket scientists and hobbyists have developed ever more versatile systems to maneuver rockets, from small model rockets to enormous space rockets.

Atmospheric Steering
- Tailfins are used on nearly all rocket boosters.
  
  For rockets that operate exclusively in the Earth's atmosphere, such as hobby rockets, steering can be accomplished in the same way as an airplane. A rocket can steer by using pivoting tailfins similar to the adjustable control surfaces (e.g. the elevators or rudder) on an airliner. By adjusting airflow over the tailfins, a force can be created to push the rocket in a new direction. Even if a rocket uses some other means as its main method of steering, tailfins still help to provide passive aerodynamic stability.
Exhaust Vanes
- By placing structures similar to tailfins behind the exhaust of the rocket rather than in the aerodynamic slipstream, the exhaust gas itself can be directed by rotating the fins, which will in turn direct the entire rocket. Such surfaces are known as exhaust vanes. The infamous German V-2 rocket -- the first ballistic missile -- made use of exhaust vanes along with tailfins to steer. However, the obstructive graphite vanes caused some loss of thrust.
Gimbaled Rockets
- The most effective method of directing rocket exhaust is to rotate the entire engine. By mounting the engine in a "gimbal" -- a mount that includes a gyroscope for orientation and a guidance system to adjust electrical actuators -- the engine nozzle can be rotated by a few degrees. This changes the direction of the exhaust relative to the center of gravity of the rocket, creating a torque that changes the direction. Most modern rockets use gimbaled engines with digital computers to adjust the direction of thrust.
RCS Thrusters
- The Space Shuttle used small RCS thrusters to steer in space.
  
  Reaction control system (RCS) thrusters, or "verniers," are small auxiliary rocket engines mounted on the side of a rocket, fired in short bursts to provide thrust off to the side of the vehicle. RCS thrusters allow a rocket or spaceship to steer without using its main engines or to adjust steering errors caused by the main engine. However, as RCS thrusters have only a fixed thrust, the rotation rate can be changed only by a fixed amount.

Astronomy