A vernier thruster is a thruster

Rocket engine

A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...

 used on a spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 for attitude control. It is a smaller thrust motor than main attitude control motors and is used for fine adjustments to the attitude or velocity of a spacecraft. A vernier rocket is a smaller rocket engine

Rocket engine

A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...

 used for attitude control in conjunction with a larger spacecraft propulsion

Spacecraft propulsion

Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...

 engine.

Vernier thrusters are used when spacecraft control requirements, such as maneuvering during docking with other spacecraft, dictate a wide range of different thrust levels for attitude or velocity control. Main attitude control thrusters are used for larger movements, verniers for minor adjustments.

As an alternative, larger thrusters which can fire for very short durations or pulses may be fitted instead.

The Space Shuttle

Space Shuttle

The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

's reaction control system

Reaction control system

A reaction control system is a subsystem of a spacecraft whose purpose is attitude control and steering by the use of thrusters. An RCS system is capable of providing small amounts of thrust in any desired direction or combination of directions. An RCS is also capable of providing torque to allow...

 had six vernier engines or thrusters. During STS-130

STS-130

STS-130 was a NASA Space Shuttle mission to the International Space Station . 's primary payloads were the Tranquility module and the Cupola, a robotic control station with six windows around its sides and another in the center, providing a 360-degree view around the station...

 commander Zamka and pilot Terry Virts used the space shuttle Endeavours vernier thrusters to reboost the International Space Station to its correct altitude.

See also

• Reaction control system
  Reaction control system
  A reaction control system is a subsystem of a spacecraft whose purpose is attitude control and steering by the use of thrusters. An RCS system is capable of providing small amounts of thrust in any desired direction or combination of directions. An RCS is also capable of providing torque to allow...
  
  
• Space propulsion
• Attitude control
• Cold gas thruster
  Cold gas thruster
  A cold gas thruster is a rocket engine/thruster that uses a gas as the reaction mass.A cold gas thruster usually simply consists of a pressurized tank containing gas, a valve to control its release and a nozzle, and plumbing connecting them...