A key consideration when choosing optics for use in space is radiation resistance. Exposure to high-energy radiation progressively reduces the transmittance of standard optical glass. Adding cerium oxide to the composition enhances radiation resistance and stops the glass browning and losing transmission. Radiation resistant cerium doped glasses typically have a much longer life cycle in space, though exhibit lower transmission in the blue compared to standard glasses. For space applications where the lens need only be operational for a relatively short amount of time, you can choose standard optical glass thereby trading the lifespan of the lens, for better performance in the blue end of the spectrum.
Learn more: https://www.resolveoptics.com/why-use-cerium-doped-glasses/