Spin-stabilisation

Abstract: Aryabhata, India’s first satellite, was successfully launched into a nearearth orbit on 19 April 1975, from a USSR Cosmodrome. The primary objective ofAryabhata was to establish the indigenous capability in satellite technology.Aryabhata, weighing 358 kg, was quasispherical in shape, and had body-mounted solar cells and Ni-Cd chemical batteries as primary power sources. Other features of the spacecraft include power control systems, passive thermal control system, PCM/FM/PM telemetry system transmitting data at 256 bits/s in real time and 2560 bits/s in the stored mode, PDM/AM/AM telecommand system, cold gas spin stabilisation system with nutation damper and a number of sensors. The satellite also included three scientific experiments—one on x-ray astronomy, the second for observing solar neutrons and gamma rays and the third on aeronomy. The present paper gives an overview of the basic features of the satellite, associated ground stations and a brief account of the fabrication, testing and (in-orbit) performance of the satellite. Results of some of the technological experiments carried out inAryabhata are also briefly described.

Abstract: Motion of spinning satellite during deployment of n asymmetrical appendages, noting Pioneer spacecraft

Abstract: A spin-stabilized cylindrical satellite is suspended either magnetically or electrostatically from a gravity-gradient-stabilized reflector that directs a pencil beam of radiation emanating axially from the satellite toward the earth. Solutions for the motion of a gravity-gradient boom with reference to the local vertical are obtained. The dynamics of the satellite combining spin stabilization with gravity-gradient stabilization result in a stable system with a fixed nutation frequency that can be made high by design. Vibrations in the roll and yaw axes are easily damped by a nutation damper in the spinning cylinder. Damping of the pitch vibration of the reflector can be obtained with a single, cold-gas, pulsed jet that also can be used to prevent angular velocity decay of the spinning cylinder and to control the orbital period for station-keeping. The system described is basically passive as far as the control torques are concerned; however, active means are used to damp pitch vibrations of the nonspinning reflector. Thus, this system can achieve high accuracy of stabilization, in addition to the advantages of high reliability.

Abstract: The attitude stabilisation ofAryabhata was accomplished by spinning it about its axis of maximum moment of inertia. The spin stabilisation ensures satisfactory thermal control, uniform power generation through the body mounted solar panels and the scan capability for the scientific payloads. To bring down the nutation of the spinning spacecraft to a value well within the specified limits, a fluidin-tube damper was also provided.