Small space missions such as CubeSats frequently require telescopes with highly sophisticated optical systems that are also low in mass and cost. The very limited spacecraft volume and mass limits also preclude adjustments to maintain critical alignment with change in temperature. Existing systems, especially those that employ folded optical paths with freeform optics, are expensive to fabricate. The optics, and support and metering structures, are also heavy due to the use of high-density material such as glass, aluminum, or nickel.
A new type of telescope has been invented that is low-cost, compact, very lightweight, and insensitive to temperature changes. Nanocomposite telescopes have low mass because the material has low density — typically 1.2 g/cc. The support structures can be formed in molds designed with topology optimization and fabricated by 3D printing. Therefore, both the optics and the structures have high ratios of stiffness to mass. The low cost is a result of replication using nanocomposite materials. Although a single mandrel can cost thousands or tens of thousands of dollars, many dozens of replicas can be made. The cost of each unit is therefore reduced. Furthermore, since replication permits off-the-shelf availability of multiple identical units, missions are easier to design, and the cost of flying constellations is reduced. Finally, temperature changes do not affect the optical system since all the optical and mechanical components are made of the same material, and hence expand or contract at the same rate.
A folded path unobscured Cassegrain telescope consists of two surfaces: an off-axis conic primary mirror and a freeform optics secondary mirror. Both optical surfaces can be produced by applying diamond turning or magnetorheological fluid (MRF) polishing to a solid block of metal or glass to generate convex reflective surfaces. A nanocomposite telescope is assembled as follows:
Vacuum coat the convex surfaces with Ag or Au (to serve as release layer), then SiO followed by Al.
Design topology-optimized supporting structures with high stiffness-to-mass ratio.
Produce mold for support structure by 3D printing.
Apply nanocomposite resin on outside of block.
Release from block. The result is a coated telescope assembly.
The replica may have to be made in two parts to allow mandrel release. If so, some type of alignment or pinning mechanism can be designed into the support structure. This approach has the additional advantage of allowing some small adjustments to be made in the optical alignment. The replicated telescope is athermal. All optics and structures are made of the same material and expand and contract at the same rate. The telescope is therefore insensitive to temperature changes.