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How does an inertial navigation system track a vehicle without outside signals?

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Cruise ship captain in uniform studies navigational charts with a compass on a table in the ship's bridge. — navigation Officers on a passenger ship using charts for navigation.

An inertial guidance system tracks a vehicle’s position, velocity, and acceleration without external signals by utilizing gyroscopes and accelerometers connected to a computer.1

The system functions through the principles of mathematical physics and calculus. Accelerometers measure the vehicle's acceleration, which the computer then processes through two successive numerical integrations:2
* First integration: Converts acceleration data into current velocity.12
* Second integration: Converts the calculated velocity into the vehicle's current position.12

Gyroscopes provide the necessary frame of reference for these measurements, either by maintaining a stable platform (gimbaling systems) or by sensing the craft's turning rates (strapdown systems). Because these systems rely on dead reckoning, errors can accumulate over time. Consequently, they often require periodic reinitialization using independent sources like the global positioning system to maintain high accuracy.12