Inertial Guidance

Inertial guidance is a navigation technology that monitors changes in location by measuring cumulative acceleration. In inertial guidance, the motion of the object in three-dimensional space is measured continuously. This enables a special computer to provide related real-time information about velocity (speed) and location.

An inertial-navigation system (INS) does not use information from an external reference once it has been placed in operation, in contrast to less-sophisticated navigation techniques. Gyrocompasses, older navigation aids that are dependent on the position of the stars or sun for guidance, are internally self sufficient, relying on precision gyroscopes for direction reference. However, gyrocompasses will drift with time as a result of slow, friction-induced gyrations and must be readjusted occasionally. Radiolocation navigation systems use precisely timed radio signals from distant transmitters or satellites. Radar mapping and optical terrain matching navigation require interaction with the earth's surface.

In contrast to these navigation tools, inertial navigation systems need only sense the inertial force that results from changing velocity. These forces are not dependent upon external references, but can be measured by accelerometers in a sealed, shielded container.

Inertial navigation was first applied for military uses—guiding deeply submerged submarines, ballistic missiles, and airplanes. Inertial navigation gave results that were more accurate than could be obtained with conventional navigation. An inertial-navigation system is effectively immune to deliberate interference, an obvious advantage in wartime.

In addition, inertial navigation functions as well near the earth's poles as it does at the equator. This feature is in marked contrast to the limitations imposed by a magnetic compass's unreliable performance in the Arctic or Antarctic regions of the earth. Magnetic compasses are also undependable in the earth's polar regions because of day-to-day variations in the earth's magnetic field strength and direction. Magnetic storms caused by solar disturbances that affect the earth are particularly troublesome near the magnetic poles.