self-weight deflection – the deflection of a structure due to the effect of gravity acting on its mass. It can be one of the most significant sources of error in optical systems, affecting both the relative alignment of optical elements and the form of individual optical surfaces.
In space-based optical systems that are built and aligned under the effects of gravity but operate in the absence of gravity, special consideration must be given to the change in alignment and optical surfaces when gravity is removed. This is called gravity release.
