What does IRU stand for in navigation systems?

• A. Internal Radar Unit
• B. Inertial Radar Unit
• C. Inertial Reference Unit
• D. Independent Reference Unit

Answer: (C)

In navigation systems, the key idea is to have a stable, internal reference of motion and orientation that the rest of the system can trust. An Inertial Reference Unit is the component that houses the inertial sensors—accelerometers and gyroscopes—that measure how the vehicle is moving (linear accelerations) and rotating (angular rates). This data provides the reference frame the navigation computer uses to determine attitude, velocity, and position, especially when external signals like GPS aren’t available. The term “inertial” comes from relying on Newtonian motion rather than external references, and “reference” indicates that this data serves as the baseline for calculations. The other options describe sensing methods or labels that don’t match the standard terminology—radar-based terms imply a different sensing principle, and internal or independent references aren’t the conventional naming for this unit.