A Passive Gravitational Attitude Control System for Satellites

Abstract

It is shown how the gravity‐gradient effect may be utilized to design a long‐lived, earth‐pointing satellite attitude control system which requires no fuel supplies, attitude sensors or active control equipment. This two‐body system is provided with a magnetic hysteresis damper which effectively damps out oscillations (librations) about the local vertical. The long rods, which must be extended in space from coiled up metal tapes, provide the required large moments of inertia and possess adequate rigidity and sufficient strength to endure the rigors of the extension process. The system is compatible with the requirements of multiple satellite launchings from a single last‐stage vehicle. Analysis indicates that the gravitational torques are sufficient to keep the disturbing effects of solar radiation pressure, residual magnetic dipole moments, orbit eccentricity, rod curvature, eddy currents, and meteorite impacts within tolerable limits. It is believed that the high‐performance, earth‐pointing system described and analyzed in this paper represents an essential step in the development of high‐capacity communications satellites requiring long life.

A new passive hysteresis damping technique for stabilizing gravity-oriented satellites.

“…(3) and (4) to give the damper torque T = RAN E h (dyne-cm) (5) When the damper configuration uses hysteresis materials in the form of a flat sheet of thickness t that is magnetized between inside radius RI and outside radius R 0 from the rotation axis, the design equation for the magnetic hysteresis torque becomes T = -Ri 2 )tNEh (dyne-cm) (6) Any of the parameters could be varied as a function of the angle of rotation in order to produce a torque variation. Some of the values of hysteresis loss that have been obtained by torque measurements on damper systems that employ a narrow-zone magnetizing system (Fig.…”

“…(2) follows directly from the basic hysteresisloss equation, since 1 erg is equivalent to the application of a force of 1 dyne through a distance of 1 cm ; and a unit volume of material might be represented by a 1-sq-cm strip of hysteresis material being forced a distance of 1 cm past the magnetizing circuit. For a rotary damper arrangement in which the hysteresis material is at a mean radius R from the axis of rotation, the torque developed due to the hysteresis drag force is T = (RAN/I*) £ HdB (dyne-cm) (3) In gathering materials data for comparison, it is convenient to have unit dissipation values E n = (1/4*0 £ HdB (ergs/cm 3 /cycle) (4) obtainable from the hysteresis loops. For some materials, plots are available of Wh (joules/cm 3 /cycle) as a function of the peak magnetization force H (1 joule = 10 7 ergs and is the equivalent of 10 7 cm-dynes).…”

“…The earliest presentation of the application of magnetic hysteresis effects to the damping of gravity-stabilized satellites was made by Paul, West, and Yu. 4 This paper describes the development of a single-axis gimbal with a magnetic hysteresis device coupled across the joint. The hysteresis mechanism consists of a bar magnet suspended on the rotor, and a disk of magnetic material attached to the stator.…”