Progress and upscaling of adhesive-free fused closed back ZERODUR® light weight structures

Lightweight mirror blanks for space applications must balance volume, weight, and stiffness to enable effective thermomechanical performance within rocket transport space restrictions. Closed back mirrors enable optimal performance at smaller overall Volume and reduced weight. Bonding the back with adhesives might affect the thermomechanical stability of the mirror. SCHOTT has recently presented closed back ZERODUR® mirror blanks produced with adhesive-free fusing on 480 mm diameter scale. The quality of the fused interface enables a high degree of strength and almost monolithic quality in terms of stress birefringence and CTE homogeneity. Meanwhile the technology moved forward on the path of maturing, being upscaled to almost meter sized structures and further characterization of properties. This paper gives an update on the development of adhesive-free fusing of ZERODUR® structures with a focus on light weight closed back mirror blanks.