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.
Thin-walled X-ray optics are going to be required to meet the demands of large collecting area versus volume and mass for the next generation X-ray astronomy Flagship Mission. We report here our progress on our concept of meeting the challenge of producing these mirrors. The case we address is the one where the initial fabrication process requires post-fabrication figure correction. Our technology can be applied prior to launch and also enable in-flight figure corrections. Our process is to coat a film of magnetic smart material onto the backside of the thin-walled X-ray mirrors. Then, an electromagnet is used to produce an in-plane stress and thus reshape the mirror. We show in this paper that 500 μm thick Si wafers can be coated and after coating remains significantly flat, i.e. they have a radius of curvature of about 30 m. We have carried out deflection measurements as a function of the external magnetic field of about 0.1 to 0.3 T and found a nearly linear relationship. We also revisited the stability of induced deflections for up to nearly 70 hours and also demonstrated that the process can produce deflections for fine-scale figure adjustments of order (10 nm) range deflections.
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