ELEMENTS OF SPIN MOTION

For use in numerical studies of rotational motion, a set of elements i s introduced for the torque-free rotational motion of a rigid body aro und its barycenter. The elements are defined as the initial values of a modification of the Andoyer canonical variables. A computational pro cedure is obtained for determining these elements from the combination of the spin angular momentum vector and a triad defining the orientat ion of the rigid body. A numerical experiment shows that the errors of transformation between the elements and variables are sufficiently sm all. The errors increase linearly with time for some elements and quad ratically for some others.