Consider how much more productive you could be if you could read a book, check your email, watch TV, and read the newspaper all at the same time.
Now imagine being able to see twice as much at least ten times. A hundred times. The Near-Infrared Spectrograph (NIRSpec) aboard the James Webb Space Telescope can do that, allowing astronomers to capture more data.
What Is A NIRSpec?
Webb’s primary spectrograph, NIRSpec, is a device that separates light into its constituent colours, creating a vast spectrum for scientists to study.
It can take at least a day and up to a week for NIRSpec to collect enough light to get a good spectra for extremely weak, faraway objects like distant galaxies.
NIRSpec would not be able to observe many objects during its mission if it could only look at one object at a time.
On Earth, the answer to this common telescope problem is very straightforward. Astronomers block out light from nearby objects with metal plates pierced with holes or fiber-optics positioned by robots, allowing them to focus on the various objects they wish to study.
Why Is It Difficult To Insert Fresh Plates?
Inserting fresh plates is not possible because Webb’s viewing point is 1 million kilometres beyond the Moon. As a result, engineers devised a tiny, ingenious solution: the microshutter assembly.
Webb’s Microshutters
Four arrays, each about the size of a postage stamp, makes up the microshutter assembly. Each inch-and-a-half square array contains 62,000 microscopic shutters that open and close to enable only light from specific objects to reach NIRSpec’s detector. The microshutter component allows NIRSpec to focus on 100 objects at once.
The shutters are 100 microns in length and 200 microns in breadth. In comparison, human hair is about 75 microns wide. To get the greatest image, Webb concentrates all of the light it collects into a single strong point, hence the shutters must be narrow. When it’s finished, each star or galaxy will be about the right size to fit into one of the shutters.
Compositions Of The Arrays
The arrays are made of silicon-nitride wafers, which are commonly used in the fabrication of transistors. A layer of silicon and glass is developed on top of silicon nitride, which is a mixture of silicon and nitrogen gas.
Engineers put metals and other elements on top of the blank wafer to make it etching-resistant in the places they want to keep intact, similar to how masking tape protects a wall when painting.
Why Was It So Difficult?
It was a challenging, jigsaw-like process. Webb, on the other hand, was ready, with a grid of thousands of closed shutters, each mounted to a two-micron-wide strip of wafer, too small to see in detail without an electron microscope. The shutter hinges are these strips. The array works because the hinges are so tiny that they can twist without breaking and snap back into shape.
How Does It Work?
Magnetic strips border the shutter doors, which are housed in a metal box that may be electrically charged. Each shutter can be charged independently.
All of the microshutter’s doors are closed in its resting condition. A magnet sweeps across the shutters, repelling the magnetic strips on the doors and forcing them open all at once.
The box is charged electrically, pinning all the doors open. The voltage on the shutters that the controllers want to close is then changed, allowing the magnet to close the doors when it sweeps a second time. Only the shutter doors that must be aligned with celestial objects on the schedule to be examined are left open.
Then from the open shutter doors comes the light of distant galaxies or stars, each looking at a distinct object. The light is split into a spectrum of colours before being directed at the detector.
Webb’s NIRSpec has 100 small eyes at its disposal thanks to the microshutters, each working independently and at the same time to explore diverse regions of the universe.