The natural frequencies and modes of a flexible elastic ring fixed at one point are determined numerically by solving an eigenvalue problem for the differential operator of the equation of its motion. The ring models a large circular antenna that slowly expands under zero gravity. Bending and torsional vibrations in a plane perpendicular to the antenna plane are studied Introduction. The problem of determining the natural frequencies and modes of either in-plane or out-of-plane vibrations of a ring arose in studying the dynamics of a spacecraft that carries an antenna of variable geometry (a compact roll of an elastic ribbon slowly deployed, in a programmed manner, into a ring). Assuming that the deployment duration is much longer than the period of vibration of the ring in the first mode, we can neglect the perturbations of natural modes of the ring caused by the variation in its radius with time.Structures as a circular antenna can be modeled by thin curved bars. If the elongation is small, the question whether such a model is applicable can be answered only after solving the appropriate problem of elasticity.If it is, then it remains to be seen whether the model involves factors that disturb the vibrations. The linear analysis of the free and forced vibrations of curved bars is based on the assumption that the displacements and angles of rotation are small. In this case, the Bernoulli hypothesis applies well and vibrations are described by a system of differential equations for the vector of displacements and angular rates of rotation [1,4,7].Though the natural modes and frequencies of a ring were already studied hundred years ago, modern computers allow us to approach this problem from a qualitatively different level. There are published numerical data on the several first natural frequencies and modes of in-plane and out-of-plane vibrations of closed rings with certain boundary conditions. The majority of publications address a free ring for which periodicity conditions play the role of boundary conditions. However, the accuracy of these data is low because they were mainly obtained with simplified methods [2,3,9]. An extensive bibliography on the subject can be found in [2,3,11]. We failed to find any discussion of the case of an elastic ring with one fixed point in the literature.The present paper continues the studies of the modes and frequencies of flexural in-plane vibrations of a circular ring fixed at one point [13,14]. In the present paper, we will discuss the natural modes and frequencies of such a ring under zero gravity that were obtained by solving a boundary-value problem for the equations of motion of an elastic ring with direct numerical methods easily implementable on modern computers. A similar problem was addressed in [12].1. Problem Formulation. Let us determine the natural modes and frequencies of free flexural in-plane vibrations of a ring fixed at one point. Without loss of generality, we assume that the ring is fixed at the points j = 0 and j p = 2 , where j is the