The problem of reinforcing the mirror surfaces of space-based astronomical optics and their protection against external factors is discussed. To solve this problem, the possibility of the deposition of diamond-like coatings onto them is considered. Using mirrors with Al and Cu coatings as an example, it has been experimentally demonstrated that the pulsed laser deposition of a carbon layer with a thickness of 30 nm onto them leads to an increase in the surface hardness by 25 and 100%, respectively. It has been established that the reinforcing coating has no effect on the shape deviations of mirrors and decrease their surface roughness. In this case, the reflection factor appreciably decreases in the visible region (400–780 nm), whereas its decrease in the infrared region (above 780 nm) is no more than 5%.