each segment of the segmented telescope is a solid body having 6 degrees of freedom exposed to the gravitation force, wind blowing, and other mechanical forces. if the position of each segment is not controlled the resolution of the whole telescope will be the same as if telescope had the diameter equal to the size of one segment. to achieve a resolution commensurable with that of a monolithic telescope of the same diameter the segmented surface must be controlled with a precision better than formula_1 surface rms.