How often should the INS position be compared with GPS?

• A. Every minute
• B. Every 10 minutes
• C. Only when divergence is suspected
• D. At least once per hour

Answer: (D)

Regularly checking the INS against GPS is about catching and correcting drift. The INS estimates position by integrating the vehicle’s motion, but tiny errors in sensors accumulate over time, causing the INS position to gradually drift away from the true location. GPS provides an independent, accurate reference, so comparing the two helps you detect when the INS has wandered and reset or constrain its error estimates.

Doing this at least once per hour offers a practical balance: it’s frequent enough to catch gradual drift before it becomes large, yet not so frequent that it becomes unnecessary or burdensome. Checking more often, like every minute, isn’t typically needed for most operations and can be excessive, while waiting until divergence is suspected risks having a significant position error before you notice. Checking only every 10 minutes could miss drift that accumulates between checks, and relying on divergence alone isn’t timely enough. An hourly cross-check keeps the navigation solution reliable and within expected accuracy.