The state of the art in manufacturing large one piece metal mirrors has advanced dramatically in the past 10 years, following important pioneer work by NASA's Jet Propulsion Laboratory in 1965. Since that time, several additional large solar simulator mirrors have been manufactured. Careful mechanical and thermal design analysis and structure material selection are important elements in a successful finished product. Manufacturing techniques for mirror structure fabrication borrow from the heavy metal industry, while optical processing still follows relatively classical methods. Requirements for electroless nickel plating, sea transportation, and improved long term optical surface protection are challenges that have resulted in innovative practical solutions. The recently completed 5.5 meter (18 foot) diameter mirror for the Japanese National Space Development Agency's new space center at Tsukuba, Japan, exemplifies much of the technical advancement achieved over the last 10 years.