The fabrication of lightweight mirror assemblages via a replication technique offers great potential for eliminating the
high cost and schedule associated with the grinding and polishing steps needed for conventional glass or SiC mirrors. A
replication mandrel is polished to an inverse figure shape and to the desired finish quality. It is then, coated with a
release layer, the appropriate reflective layer, and followed by a laminate for coefficient of thermal expansion (CTE)
tailorability and strength. This optical membrane is adhered to a mirror structural substrate with a low shrinkage, CTE
tailored adhesive. Afterwards, the whole assembly is separated from the mandrel. The mandrel is then cleaned and
reused for the next replication run. The ultimate goal of replication is to preserve the surface finish and figure of the
optical membrane upon its release from the mandrel. Successful replication requires a minimization of the residual
stresses within the optical coating stack, the curing stresses from the adhesive and the thermal stress resulting from CTE
mismatch between the structural substrate, the adhesive, and the optical membrane. In this paper, the results on
replicated trials using both metal/metal and ceramic/ceramic laminates adhered to light weighted structural substrates
made from syntactic foams (both inorganic and organic) will be discussed.
The use of monolithic glass to produce large, rigid segmented members for lightweight space-based mirror
systems appears to have reached its limits due to the long production lead times, high processing costs, and launch
load/weight requirements. New material solutions and processes are required to meet the US Air Force's optical needs
for directed energy, reconnaissance/surveillance, and communications. Mirror structural substrates made out of
advanced materials (metal, ceramic, and polymer), composites, foams, and microsphere arrays should allow for CTE and
modulus tailorability, low-density, and high values in strength, stiffness, thermal conductivity and toughness.
Conventional mechanical polishing to visual specifications for figure and surface finish roughness requirements will be
difficult, due to the multi-phase complexities of these new systems. Advances in surface removal technologies as well as
replication processes will be required to produce the required optical finishes with reduced schedule and cost. In this
paper selected material and process solutions being considered will be discussed.