On deck, what must be done with the INS before use?

• A. The INS must be given a known starting point and aligned to that point.
• B. It can be initialized automatically without any starting data.
• C. It requires GPS to be connected at all times.
• D. No special initialization is required.

Answer: (A)

Initializing an INS sets its reference frame, so you must provide a known starting point and align the instrument to that reference before use. The INS estimates position and attitude by integrating measured accelerations and angular rates, but sensor biases and noise cause drift over time. Starting from an accurate position with a carefully established initial attitude (alignment) keeps the navigation solution from starting with large errors and reduces early drift as you begin moving. Alignment uses gravity to determine roll and pitch and a known heading reference to set the initial yaw. GPS can aid or update the INS later, but it isn’t required to be connected at all times, and some INS can operate standalone. Without this initialization, the system would have an unknown reference and diverge quickly.