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Unlike stable-platform IMUs, which are fixed in space and therefore inertial, strapdown IMUs are fixed to the vehicle's body and therefore noninertial.

Would noninertial effects distort the strapdown IMU's integrating accelerometer's readings? I'm wondering if those would need correcting for or if they could be used as is on a rocket launch (well, after some signal filtering and other processing, sure---but otherwise "as is" without the need for noninertial correction terms).

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – called2voyage Feb 9 at 20:35
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The accelerometer's axes in a strapdown IMU are not aligned with inertial. The sensed acceleration must be transformed to inertial to perform the integration. This can lead to issues if the rocket's or spacecraft's orientation with respect to inertial is not well known. The vehicle's orientation with respect to inertial is fairly well known once the vehicle gets above the bulk of the atmosphere and the vehicle's star trackers get a lock.

But during launch, the star trackers don't work. Many vehicles have doors on their star trackers that are closed during launch and entry so as to protect them from the hazards of passing through the atmosphere. This means a launching rocket is either dead reckoning with regard to attitude during launch or is relying on much less accurate magnetometers.

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