As you know, we have followed the James Webb Space Telescope’s story very closely since its launch.
NASA recently announced that the telescope is entering the final phases of commissioning with the last being a deep dive into the device’s scientific instruments.
First is the thermal stability test before the telescope arrives at its “final cryogenic temperature.”
This involves the telescope’s instruments such as the “Near-Infrared Camera (NIRCam), Near-Infrared Spectrometer (NIRSpec), Near-Infrared Imager and Slitless Spectrometer (NIRISS), Mid-Infrared Instrument (MIRI), and the Fine Guidance Sensor (FGS)” in addition to operating “their mechanisms and detectors, including filter wheels, grating wheels, and the NIRSpec microshutter assembly.”
Then a final calibration using a “variety of astronomical sources” will be undertaken to measure the “throughput at multiple wavelengths of light by observing standard stars whose light emission is known from data obtained with other observatories combined with theoretical calculations.”
Scott Friedman of the Space Telescope Science Institute (STScI) explains that “astrometric calibration of each instrument maps the pixels on the detectors to the precise locations on the sky, to correct the small but unavoidable optical distortions that are present in every optical system.”
“We do this by observing the Webb astrometric field, a small patch of sky in a nearby galaxy, the Large Magellanic Cloud. This field was observed by the Hubble Space Telescope to establish the coordinates of about 200,000 stars to an accuracy of 1 milli-arcsec (less than 0.3 millionths of a degree). Calibrating this distortion is required to precisely place the science targets on the instruments’ field of view. For example, to get the spectra of a hundred galaxies simultaneously using the NIRSpec microshutter assembly, the telescope must be pointed so that each galaxy is in the proper shutter, and there are a quarter of a million shutters!”
They will then test the sharpness of the telescope, target acquisition capabilities, and a final round of tests and measurements to make sure everything is operating as planned. It’s all pretty heady stuff but Scott Friedman does a great job breaking it down over on NASA’s blog.
There are some other photography news articles on Light Stalking you might like to read at this link right here.