<p>Aiming to address the low efficiency of the traditional calibration method for star sensors, we propose a calibration method using two-dimensional (2-D) Dammann grating, which can generate a dot array with uniform intensity and a certain interval. This method is based on theoretical analysis of the diffraction angles of 2-D Dammann grating relative to the tilt angles of incident light. We calculate the angles using a fitting method and further calculate the geometric parameters, such as principal point and principal distance of the star sensor. Finally, we establish a calibration system using 2-D Dammann grating and a nanostar sensor with a 25-mm focal length and 15-deg full field of view has been calibrated. The results show that the calibration accuracy for single-star measurement is better than 6 arc sec, which satisfies the requirement for high-efficiency star sensor calibration and validates the proposed method.</p>
A large aperture space telescope with a passive structure with high stiffness and thermal stability can maintain a good image quality in a large span of disturbance. However, for the proposed more stringent requirements, it is beneficial to add active optics to the conventional design. In these telescopes, the off-axis design provides more design variables than the coaxis system and also provides greater adjusting ability for the active optics. We introduce an active optics system prototype deployed on an off-axis space telescope working at low Earth orbit. By adjusting the low-order aberrations of the primary mirror shape and adjusting the positions and attitudes of certain mirrors and the focal plane, the optical system’s image quality corrupted by gravity discharge and temperature variation is increased to the undegraded level in the average sense in the full field of view.