Nasa Tech Briefs
Custom horizontal machining centers
Mitsui Seiki USA
Franklin Lakes, NJ

Image Axsys Technologies of Rocky Hill, CT is producing the James Webb Space Telescope (JWST) mirror segments for NASA, including a 6.5-m mirror that is comprised of 18 beryllium segments, each measuring 1.5 m across. Axsys chose Mitsui Seiki to machine the mirror segments. Mitsui custom-built horizontal machining centers to produce the mirror segments, creating a massive structure with a column weight of 11 tons, and a bed of 20 tons, with the ability to position within a few microns anywhere in the machining envelope.

The 540-pound beryllium billet is fixtured vertically onto an angle plate on one of the eight machines. The billet is 4" thick, 54" across, and 62" from point to point. The backside of each mirror segment has 600 pockets that are each about 2.5" square. There are 22 mounting pads and 249 light-weighting holes. After pocket milling on the backside, the billet weighs 275 pounds and is heat treated. The mirror side is roughed before another stress relief treatment. Roughing removes another 50 to 60 pounds of material.

Each mirror segment requires 18 weeks of machine time, two weeks for heat treatment, and a week for inspection. The mirror segments are shipped to another company for months of polishing.

The JWST is scheduled for launch in June 2013, effectively replacing the Hubble Space Telescope. The JWST will study the earliest galaxies and some of the first stars formed after the Big Bang.

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