Coatings.

NuSTAR glass atop cylindrical quartz mandrels being placed into an oven at Goddard Space Flight Center.

The NuSTAR team has developed a novel approach to building these optics, focusing on a light-weight design. The mirror substrates are thin sheets of flexible glass, akin to laptop and cellular phone displays, which start out as flat sheets. At NASA's Goddard Space Flight Center in Greenbelt, Maryland, the glass is heated in an oven and slumped over precision polished cylindrical quartz mandrels to achieve the right curvature. The slumped mirror segments are then deposited with a multilayer coating at the DTU-Space at the Danish Technical University in Copenhagen.

The optics are built from the inside out, shell upon shell, spaced apart by graphite spacers and held together by nothing but epoxy. This precision assemblage is done at Columbia University's Nevis Laboratory outside New York City and provides very light and flexible optics.

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That's all from the NuSTAR webpage. The most interesting part to me is the coating. How do you suppose they deposit multilayer coatings on the glass? Funny you should ask, because when I was demoted from pinball repairman to semiconductor line maintenance technician, I was luckily assigned to high vacuum equipment. It proved to be fascinating in many ways.

The first machine I worked on was an RDI evaporator that was probably close to obsolete even then. That machine evaporated aluminum onto wafers. How did that work? Good question! The RDI was a cylinder with a clamshell top. The top contained a rotating planetary to which wafers were attached.

The fun part was getting the metal onto the wafers. I put aluminum pellets into a water-cooled copper crucible. Attached to the crucible was a source that contained a filament, similar to those you see in incandescent lightbulbs, but much larger. After all of the components were prepared, the clamshell was closed.

Needless to say, air would muck up a lot of things. For one, the filament would burn out in a second. So the chamber was pumped to high vacuum, which I might say something about later. When the air was removed, voltage was applied to the filament, creating an electron beam. Using both permanent and variable magnets, the electron beam left the source and was bent 270 degrees and directed upon the aluminum, which, TAH DAH, evaporated!

Line dollies loaded and unloaded the RDI, and I operated and maintained it.

I thought that was way cool!