Strapped-down INS

A strapdown INS is an inertial navigation system whose accelerometers and gyroscopes are fixed rigidly to the hull instead of mounted on a mechanically stabilized gimbal platform. The sensors measure acceleration and angular rate in body axes, and a computer transforms them into a navigation frame mathematically, resolving the readings against the ship’s changing attitude in software. Strapdown replaced the older gimballed platform because it has no moving stabilization machinery, costs less, weighs less, and is more reliable, made practical by ring-laser and fiber-optic gyros fast enough to track full hull motion. Every modern marine and aircraft INS is strapdown; the gimballed platform survives only in legacy systems.