Abstract: Based on the Hertz contact theory,an analysis method for the repeatability of the primary mirror deployment mechanism was put forward.By this method,the repeatability of the Boyes couplings and Kelvin couplings arranging in two typical modes were analyzed.The analysis results show that the repeat position error of the Boyes coupling caused by the inconsistency of the locking force is less than that of the Kelvin coupling.The repeat position error(absolute value) caused by the inconsistency of the locking force decreases slowly as the diameters of the location balls increase.In the perpendicular direction to the rotation axis of the petal,the repeat position error is most sensitive to the position error of the locking force.