Abstract: The CubeSat umbrella antenna is composed of wire mesh, two folding ribs, a central hub and other structures. The clearance errors in the ribs affect both the deployment process and the position accuracy after deployment. To evaluate the effects of rib clearance errors on the deployment process for the 0.5m Ka-band CubeSat umbrella antenna, a mathematical model of the influence of the hinge clearance errors on the rib deployment process is established based on the effective rod theory. With the model, the numerical characteristics of the kinematic performance of the rib deployment process are obtained. It is obtained that the position error of the vertex of the root rib is less than 0.08mm and the position error of the vertex of the antenna tip rib is less than 014mm under the constraints of four common shaft holes and hinges. It can provide a theoretical basis for the selection of the hinge clearance errors of both the root and tip ribs.