Explanation of the anomalous spin behavior of satellites with long, flexible antennae.

Abstract

Two satellites, Alouette I and Explorer XX (S-48), have exhibited anomalous spin behavior—• i.e., rapid spin decay—'that could not be explained on the basis of structural, mechanical, aerodynamic, or electrodynami c actions. The common feature of these satellites is the presence of long, extensible, tubular metal antennae (STEM's). The spin behavior is shown herein to be mainly a consequence of the joint action of solar-heating -induced bending of the antennae and solar radiation pressure. A theory of this phenomenon is derived, and the available test data confirm it. The theory pointed the way to a means of preventing the spin changes—i.e., tip plates perpendicular to the antennae—which was applied to Alouette II. The spin data on the latter satellite verify the theory. Both spin-up, and large-amplitude resonant behavior are predicted as possible modes of behavior for this class of vehicles. Nomenclature J diameter of boom deflection f unction [Eq.( 11)] flexural stiffness of boom total moment of inertia about spin axis thermal bending constant length of boom mass of tip plate radiation pressure local heat flux, per unit length of boom area of tip plate