Inertial Navigation and IRS Flashcards
1st integration
= acceleration x time = speed
Must know a starting speed
2nd integration
Speed x time = distance
Distance is a modified position
Must know starting speed and distance so can’t happen without 1st integration
Alignment process - INS
Gyro spins up and liquid warms
Platform will be physically levelled
Works out its position in space - using gravity and direction to true north using the earth rotation and associated drift
Typical alignment time - INS
10 mins
Errors of using INS
Can’t change the start position during flight
Bounded/unbounded errors
Bounded errors - INS
Fixed, constant over time
May be compensated for if you know the error
Schuler period - 84.4 mins
As everything is tied to the centre of the earth, the INS will be pendulous over 84.4 mins flights
Unbounded errors - INS
Varying over time so cannot be compensated for
E.g sensing errors
Can be seen as residual GS when parked after a flight
Position uncertainty is worst
INS is “ “ system
Stabilised platform system
Gyros in a INS
Vertically aligned
3x rate gyros with 1 degree of freedom - sense all 3 axis
Accelerometers in a INS
2x accelerometers - N/S aligned and E/W aligned
Can have 3 if doing altitude
Outputs from the INS
POS lat/long GS Track Attitude/HDG - not all sense these W/v
Inputs to the INS
Only requires TAS for w/v
Loss of alignment in flight - INS
Navigation loss
Maybe realigned for attitude
Inertial reference system is a “ “ system
Strapdown system
Physically fixed to the a/c structure
Laser gyro on a IRS
Uses the Doppler principle to measure acceleration
Rotation of the fringe pattern = acceleration
Change in the phase difference/freq of the 2 lasers = acceleration
