As a follow-on question to What's the largest optical lens put in space? I'd like to ask about mirrors this time.
Question: What's the largest optical telescope mirror ever put in space?
Optical could include infrared, visible and ultraviolet, but not microwaves. It also needs to be a single mirror, not an array of separate sub-mirrors like the JWST design. It could be a telescope's objective mirror or a part of an optical assembly of mixed elements, or it could still be in its shipping crate. It could be curved or flat, as long as it's used in an optical telescope.
Answers to What's the largest aperture telescope sent beyond the Earth-Moon system? are in the 0.5 to 1.4 meter ballpark for deep space, but what about closer to home?