Which components are typically included in the strapdown INS state vector?

• A. Only position and velocity.
• B. Position (latitude/longitude/altitude or ECEF/LLA), velocity, attitude, gyro biases, accelerometer biases, and gravity if modeled.
• C. Only attitude.
• D. Satellite clock bias and orbit elements.

Answer: (B)

In a strapdown INS, the state vector must capture everything the navigator needs to predict motion and correct for sensor errors over time. That means including position and velocity to know where you are and how fast you’re moving, plus attitude to know which way you’re pointing. Gyro biases and accelerometer biases are included because the sensors drift, and estimating those biases lets the filter compensate as you integrate measurements. Gravity is included if you model it because the gravity vector influences the specific force readings and the overall dynamics; incorporating gravity as part of the state (when a gravity model is used) can improve accuracy. Satellite clock bias and orbit elements belong to external navigation systems like GNSS, not the strapdown INS state.