TABLE OF CONTENTS Navigation is simply the science or more accurately the art of computing the location and the velocity of a craft on land, sea or space. Depending on its mission, the craft is equipped with certain sensors to achieve such a task. For example, a Global Positioning System (GPS) receiver may be enough for a land or sea cruisers, but an aircraft will require far more instrumentation, namely air pressure sensors to measure altitude and airspeed. Although magnetic sensors are still used to find azimuth, modern aircraft now widely use inertial navigation system.
Inertial navigation systems are very popular because of their accuracy, long mean time between failure (MTBF), and self-reliance. Short of power supply they do not rely on any additional external sources for their operation. These systems use inertial sensors accelerometers and gyros to detect linear and angular motion of the craft. Incidentally, inertial sensors acquired this name because the motion they sense is with respect to a universal non-moving (inertial) space.
The mechanical structure of the original inertial systems was very elaborate and very sophisticated. In such a structure, the inertial sensors were mounted on a stable platform, which itself was mounted in the center of three (or more) perpendicular gimbals. These gimbals were used to allow the stable platform to maintain a certain attitude in the space. Although these systems were very accurate they also were highly expensive to manufacture and maintain. Soon, as computer technology matured, the much cheaper strapped down systems...
