DOPPLER INERTIAL NAVIGATION SYSTEM

1,200,029. Inertial navigation systems. SINGER GENERAL PRECISION Inc. May 15, 1968 [July 17, 1967], No.23089/68. Heading G1C. An inertial navigation system for a craft comprises a platform 14 having a mounting with only two degrees of freedom i.e. about the eastwest axis E and the vertical axis Z deviations of the platform 14 from a level orientation about a third axis orthogonal to the other two i.e. the northsouth axis - N being determined by comparison in a circuit 104 of the velocity of the craft along the axis E as determined by integration of the output of an accelerometer 42 on the platform and by a Doppler radar equipment 48, the circuit generating electric signals to compensate the operation of the apparatus for deviations of the platform from level orientation about the axis N. The Doppler radar is provided with an antenna 10 carried by a platform 12 having two degrees of freedom about the craft roll and pitch axes. The platform 12 also supports the platform 14 a pick-off 16 giving heading information in terms of the altitude of the craft in relation to the axis N. The platform 14 is stabilized by a two-degree of freedom gyro 40 sensitive to movement about the Z and E axes, torques 28, 38 maintaining the platform aligned in azimuth and level about the axis E respectively in response to signals from the gyro. The platform 12 is maintained level by torque motors 24, 26 acting in response to signals from a level sensor 18. The Doppler radar gives heading and crossheading velocity information for the craft, and by comparison in a resolver 52 with heading information from the platform 14, these velocity signals may be resolved to give velocity components along the axes N and E respectively. The accelerometer 42 is also sensitive to accelerations along the axis N and by integration of this output in a circuit 77, a signal representative of the north-south velocity may be obtained, which by comparison in a circuit 78 with the Doppler radar derived northsouth velocity may be used to determine any misalignment of the gyro 40 spin axis 56 in azimuth the derived error signal being used to correct the gyro alignment and provide automatic gyrocompassing. The system is also corrected for the effects of earth rate and by means of circuits 100, 122, Coriolis acceleration.