  We present a method for the manufacturing of thin shells of glass, which
appears promising for the development of active optics for future space
telescopes. The method exploits the synergy of different mature technologies,
while leveraging 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
is advantageous 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
results so far achieved on a 130 mm glass shell case study.
