Inertial reference unit
Appearance
An inertial reference unit (IRU) is a type of inertial sensor which uses only gyroscopes to determine a moving aircraft’s or spacecraft’s change in angular direction (referred to as "delta-theta" or Δθ) over a period of time. Unlike the inertial measurement unit, IRUs are generally not equipped with accelerometers, which measure acceleration forces.[citation needed]
IRUs are used for attitude control and navigation of vehicles with relatively constant acceleration rates, such as geosynchronous satellites and deep space probes.