How inertial navigation system works?

Answer 1

Inertial Navigation uses the principles of dead reckoning, a method of using known location, velocity and time to give distance, therefore new location.

The INS uses sensitive accelrometers and gyroscopes on a stable platform that senses the change in acceleration, that can be intergrated into velocity then again displacement.

As the body, as an example an aircraft, moves the accelerometers sense the change in movement and produce and output signal that is sent off to an internal computer to be used as navigation information, ie velocity.

3 accelerometers are used to sense the North and South component of movement, another to sense East and West and a third to measure the vertical or Z axis of movement, this is all to paint a 3D picture to the computer.

From the computer the output can go to many systems such as course, heading, autopilot, Horizontal situation indicators...etc

An error pointed out from Einstien is that gravity and acceleration are indifferent and are non linear, therefore the accelerometers are effected and feel gravity. This will constantly hold the accelerometers in error and give a constant output proportional to gravity which is fed off to be computed.

To keep the error constant and linear a gyroscopic stabling system is used to keep the platfrom level to the surface of the earth.

The gyroscopic system utilises 3 directional gyros each having 2 axis of rotation, X, Y and Z.

As the earth rotates the gyros will maintain the platfrom stable relevant to space, therefore the earth rotates around the gyro.

An error felt by the accelerometers called Earth Rate Drift and needs to be compensated for.

Errors, such as Earth rate drift, transport drift, mechanical drift (all errors from a gyroscopic system) and other errors that effect the accelerometers, such as Coriolis, Centripetial error and the problem of schular's tuning, need to be compensated.

The system takes in these errors and elminates them via a process of digital intergrating. To give a representation of only the acceleration forces the body/aircraft/ship is doing. NOT the acceleration forces felt from the earth.

Therefore, Inertial Nav systems takes in information, then elminates errors felt from the earth, (Gravity, Drifts, Coriolis...) to isolate the accelerations felt by movement of the body only.

Then integrate to give displacement to dead reckon and navigate across the globe.