Thin, segmented mirrors have been fabricated from monocrystalline silicon blocks. The material is economically viable, and is virtually free of internal stress because of its nearly perfect crystalline structure. The mirror surfaces will first be accurately figured and finished on thick silicon blocks, then sliced off at the desired thickness by wire electro-discharge machining. A finishing process has been conceived in which existing mirror-finishing processes are adapted to be capable of quickly and accurately figuring and finishing damage-free, segmented, monocrystalline silicon mirrors in a cost-efficient manner.

To ensure a constant contact area, a magnetic pad shape corrector is placed after the contact area to reshape the magnetic pad, which deforms after contacting the silicon substrate. This substrate is positioned at a certain angle to encourage runoff of excess slurry in order to maintain a constant number of available cutting edges. The end effector assembly (wheel-magnetic pad-nozzle-shape corrector) is mechanically connected to the machine tool arm via a low-friction linear bushing (e.g., an air-bearing-based, linear bushing). The linear bushing transmits motion in the x and y directions only, allowing only the end effector’s weight and wheel rotation dynamics, both of which are controllable, to influence the finishing pressure. Errors in the machine tool z position are not physically able to affect the finishing pressure in this process.

This work was done by Raul Riveros and Hitomi Greenslet of University of Florida for Goddard Space Flight Center. GSC-16891-1

NASA Tech Briefs Magazine

This article first appeared in the November, 2014 issue of NASA Tech Briefs Magazine.

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