Mechanical design and dynamics of the Alouette spacecraft

A general review is presented of the highlights associated with the mechanical engineering of the Canadian Alouette I and II spacecraft. Of special interest was the development of the extendible ionospheric sounding antenna, first used to form 75-ft by 150-ft tip-to-tip crossed dipoles on Alouette I. The use of such long antennas made Alouette I the first earth satellite to be launched that exhibited flexible body characteristics over a long period of time-- years, in fact. The problems concerned with the design and use of the antennas and how their flexibility affected the dynamics of Alouette satellites in orbit are reviewed. The most significant result obtained from the mechanical engineering aspects of the Alouette program was the discovery of the phenomenon of passive spin of symmetrical flexible bodies by coupling of the sun´s thermal and radiation (photon) pressure fields. The effect of this mechanism on the spin behaviors of Alouette I and II is described.