Space optical systems generally require near-theoretical performance in hostile environments within size, weight, and cost constraints. We have addressed the challenge of achieving an optimum image quality through a cost-effective tolerance analysis scheme. Two different space optical systems are considered: the UV imager for the International Solar Terrestrial Physics (ISTP) Mission and an afocal telescope for the Advanced Polarized IR Imaging Sensor (APIRIS). These systems are described along with their required performances and designs. A tolerance study is conducted, and the effect of tolerances on image quality and cost is presented.