Manufacturing of thin glass shells for future space telescopes

We present a method for the manufacturing of thin shells of glass, which appears promising for the production of lightweight mirrors for future space telescopes. The method exploits the synergy of different mature technologies, while it takes advantage of the commercial availability of large, high-quality sheets of glass, with thickness up to few millimeters. The first step of the method foresees the pre-shaping of flat substrates of glass by replicating the accurate shape of a mold via hot slumping technology. The replication concept can be strongly beneficial for making large optics composed of many identical or similar segments. After the hot slumping, the shape error residual on the optical surface is addressed by applying a deterministic sub-aperture technology as computer-controlled bonnet polishing and/or ion beam figuring. Here we focus on the bonnet polishing case, during which the thin, deformable substrate of glass is temporary stiffened by a removable holder. In this paper, we report on the latest results achieved on a 130 mm glass shell case study.