##### From Global Positioning Systems, Inertial Navigation, and Integration

9.4.4 Gimbal Attitude Implementations

The primary function of gimbals is to isolate the ISA from vehicle rotations, but they are also used for other INS functions.

9.4.4.1 Accelerometer Recalibration Navigation accuracy is very sensitive to accelerometer biases, which can shift as a result of thermal transients in turnon/turnoff cycles, and can also drift randomly over time. Fortunately, the gimbals can be used to calibrate accelerometer biases in a stationary 1-g environment. In fact, both bias and scale factor can be determined by using the gimbals to point the accelerometer input axis straight up and straight down, and recording the respective accelerometer outputs aup and adown. Then the bias abias = (aup + adown) /2 and scale factor s = (aup - adown) /2glocal, where glocal is the local gravitational acceleration.

9.4.4.2 Gyrocompass Alignment This is the process of determining the orientation of the ISA with respect to locally level coordinates (e.g., NED or ENU). Gyrocompassing allows the ISA to be oriented with its sensor axes aligned parallel to the north, east, and vertical directions. It is accomplished using three servo loops. The two "leveling"

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Accelerometers
Accelerometers are instruments for measuring, displaying, and analyzing acceleration and vibration.
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Antennas are structures or devices used to collect or radiate electromagnetic waves.
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Satellite communications equipment is used for the transmission, conditioning, and reception of satellite signals in worldwide telecommunications.
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##### Topics of Interest

Strapdown Attitude Implementations 9.4.5.1 Strapdown Attitude Problem Early on, strapdown systems technology had an "attitude problem," which was the problem of representing attitude rate in...

9.1.3 Feedback Control Technology 9.1.3.1 Feedback Control Practical inertial navigation began to evolve in the 1950s, using technologies that had evolved in the early twentieth century, or were...

9.5.3 Sensor Error Propagation Errors made in compensating for inertial sensor errors will cause navigation errors. Here, we derive some approximating formulas for how errors in individual...

Overview Practical inertial navigation systems may take a variety of forms. These forms generally fall into one of two basic categories, stable platform systems; strapdown systems. Although the...

The gyroscope is an instrument where the input is a rate of turn (angular rate). Any gyroscope is a torque-in, torque-out device. Therefore, the output of the gyro is a change in the gimbal angle (the...

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