On initial alignment methods for manned Lunar Ascent Module

Since the orbit injection accuracy of the Lunar Lander Ascent Module (LLAM) is largely determined by the accuracy of inertial navigation system (INS), an accurate alignment of INS is crucial and needed to be implemented before LLAM leaves the lunar surface. Lunar alignment differs from ground alignment in low rotational rate and gravity. To provide satisfying results, new alignment methods should be adopted. In this paper, a novel technique named star tracker aided alignment is proposed which combines inertial and stellar observations using a Kalman filter algorithm. Performance of the approach is compared with that of traditional self-alignment method using simulation data. The results show that the star tracker aided alignment can effectively estimate the misalignment angels. Besides, the gyro accuracy deeply affects the heading accuracy of self-alignment method, while having no influence on star tracker aided alignment.