No abstract

No abstract

AstroSat is India's first mission dedicated to space-based Astronomy and carries a complement of instruments sensitive over a wide spectral region covering visible, ultraviolet, soft X-ray and hard X-ray bands. The spacecraft platform provides the required stability, pointing, power, thermal control, and interface requirements. Among the critical functions of the Attitude and Orbit Control System (AOCS) were, manoeuvre the spacecraft from one target source to another in an optimal way while avoiding the sun, compensate for the rotational disturbance torque created by the scanning of the SSM payload on the other payloads, primarily the UVIT payload, provide for calibration of all the payloads, which involved manoeuvring through 2-dimensional target patterns. All the above novel control functions, along with the routine house-keeping operations, were designed, developed, and tested extensively on ground, before declaring them as flight-worthy. The payload performance and the resulting science are a testimony to the excellent performance of the on-board Control System.

Solar sailing is a promising means of propulsion for space probes and satellites in the near future. Various methods for the control of the attitude and orbital motion of a solar sail have been proposed and thoroughly studied. One such method of control of a solar sail's attitude is through the means of spar-tip articulated vanes. The energy consumption of a solar sail's collective attitude control system is a major concern, and must be minimized for the better performance of the sail. A mathematical model has been developed and presented in this paper for vanes which are both sides reflective, and thus allow for continuous, uninhibited rotations. A novel optimization procedure (HypoTan) for the minimization of the energy expenditure of a maneuver for a solar sail whose attitude is controlled by four spar-tip vanes is also presented, and is applied to the mathematical model that is developed. Results are compared with the best existing technique of optimization proposed for a solar sail and the method presented in this paper gives consistently better results than the existing technique on the energy expenditure metric while providing equally satisfactory results as the existing technique in all other metrics.

No abstract