Research on case rotating modulation for nuclear-spin comagnetometer in space-stable INS

To restrain the effect of the bias error of nuclear-spin comagnetometer in space-stable Inertial Navigation System (INS) for long-endurance independent navigation, the case rotating modulation for comagnetometer was researched. The structure of comagnetometer case rotating in space-stable INS was presented and the modulation equation is derived. By comparing the modulation results of three types of rotating schemes, the four-positing rotating scheme was considered optimal. Modulation result showed that comagnetometer constant bias and partial magnetic-field related errors can be averaged out, low-frequency random errors in one rotating modulation period can be averaged out as constant errors; high-frequency random errors are affected by rotating modulation. Semi-physical simulation test results show that the accuracy of the K-Rb-21Ne comagnetometer data is effectively improved by case rotating modulation with the bias mean value decreasing from the magnitude of 0.01°/h to 10−4°/h and the bias stability improving from the magnitude of 0.01°/h to 0.001°/h.