In a previous paper, we presented the concept of using shape memory alloy sheets as the substrate for normal incidence multi-layer coated mirrors. A shape set sheet has been shown to deploy a figure good to 1 micron. This shape is good enough for a “light bucket.” However, if imaging is desired, then post-deployment corrections can be applied. We provide an update on the improvements we have made to our study. These improvements include ray tracing, polishing, adhesion, and fine (nm) surface adjustments.
Based on the science case for the SMEX ESCAPE mission, a normal incidence EUV mirror mission would be an interesting follow on. Our provisional SmallSat/CubeSat design has a 1 m diameter primary deployable mirror. The mirror would be coated with multilayers for normal incidence EUV reflectivity. The deployable mirror substrate is a shape memory alloy (SMA). The SMA needs to be over coated with a material that can be polished and then smoothed further. The combination that worked well on an aluminum cylinder is a high phosphorous content electroless nickel (eNiP) super-polished and then coated with carbon nitride (CNx). The multilayers were deposited on the eNiP+CNx stack. We report here our progress toward putting in place the pieces for a proof of concept. We discuss a scale up of previous return to shape on sheets of NiTi and the ray tracing results that demonstrate a sufficient return to shape of 1 micron. Furthermore, corrections post deployment are possible if desired.
KEYWORDS: Shape memory alloys, Magnetism, Smart materials, Space telescopes, Space mirrors, Mirrors, New and emerging technologies, Specular reflections, Surface finishing
The desirability of making deployable mirrors for space telescopes has been known for years. Yet, once the wave lengths are longer than the short wave radio, progress has been slow. Therefore, we are exploring a new technology based on using a magnetic smart material film deposited on a shape-memory alloy (SMA) sheet. Our preliminary result is that when we apply an about 0.1-0.35 T in-plane magnetic field, we can produce greater than micron deflections in the SMA. Furthermore, we have shown the SMA can return to shape to within 1 micron. We will present an update on how long these deflections can be maintained and our progress toward making the SMA surface smooth enough to produce specular reflection. In addition, we assess the brightness and shininess of the NiTi piece before and after heating that is needed to produce a return to shape.
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