Think how much more productive you could be if you could study a book, check your computer, watch the television and consult a newspaper all at once. Now imagine you could see twice that. Ten times. A hundred times.
Sadly, human beings can't eye more than one thing at a time. But Webb's Near Infrared Spectrograph (NIRSpec) can, thanks to a piece of technology miniscule enough to be threatened by the motes of dust floating in the air.
NIRSpec is Webb's spectrograph, the instrument that breaks light into its component colors, called a "spectrum," for scientists to analyze. Because Webb studies such faint, far-away objects, it takes a long time - at least a day or as long as a week -- for NIRSpec to collect enough light to see a good spectrum. If NIRSpec could only look at one object at a time, the telescope would be able to observe very few objects throughout its life.
On Earth, the solution to this typical telescope problem is easy. Scientists use metal plates drilled with holes to block out light from surrounding objects and focus on the multiple objects they want to analyze. Each time they do a new set of observations, they drill and insert a new set of plates.
Obviously, that isn't a possibility for a telescope four times farther from Earth than the Moon. So engineers came up with a tiny, creative solution: the microshutter assembly.
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The microshutter assembly is a collection of four postage-stamp sized devices called arrays. Each inch-and-a-half square contains 62,000 microscopic shutters that open and close to allow only the light from targeted objects to enter NIRSpec. With the microshutter assembly, NIRSpec can look at 100 objects at once.
The tiny size is necessary because Webb focuses all the light it collects into an intense single point in order to create the best possible image. When it's done, each galaxy is just about the size to fit into one of the shutters. The shutters are just 100 microns long and 200 microns wide; for comparison, a human hair is about 75 microns wide.
The arrays are created out of silicon nitride wafers, the kind typically used to make transistors. The silicon nitride, a combination of silicon and nitrogen gas, is grown atop a layer of silicon and glass. Engineers add layers of metals and other materials to the blank wafer, making it etching-resistant in the areas they want to leave untouched, like protecting a wall with masking tape while painting.
They then etch the unaltered portions, carving into the wafer. They repeat this process time and again until they have the final result. It's a difficult, jigsaw-like process, since they have to keep adding materials, and eventually every attempt affects some layer.
But when they're done, they have a grid of thousands of closed windows, each attached to a strip of wafer only two microns wide - too small to be seen in detail without an electron microscope.
These strips are the shutter hinges. The thinness of the hinges are why the array works - they're so fine that they twist without breaking and snap back into shape.
The shutters are lined with magnetic strips and placed in a metal box that can be electrically charged. In its resting state, all the doors of the microshutter are closed.
A magnet is designed to sweep over the shutters, repelling the magnetic strips on the doors and pushing them all open. The box is charged with electricity, pinning the doors to the side. Electronics on the telescope cut off most of the charges, allowing those doors to close. Only those aligned with the objects to be observed are kept ajar.
The light from distant galaxies pours through the open doors, each door encompassing a different object. The light is split by a grating into a spectrum of colors, then directed toward the detector for analysis.
Thanks to the microshutters, Webb's NIRSpec has 100 tiny eyes at its disposal, each focused on another cosmic sight.
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