May 25, 2024

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The problem was discovered on the James Webb Space Telescope – MIRI Anomaly

James Webb Space Telescope MIRI Spectroscopy: The beam of light coming from the telescope is then displayed in dark blue as it enters the device through the pickup mirror located at the top of the device and acts like a binoculars.
Next, a series of mirrors redirect the light towards the bottom of the instruments where there is a set of 4 spectral units. Once there, the light beam is split by optical elements called dichroism into 4 beams corresponding to different parts of the mid-infrared region. Each ray enters its own integrated field unit; These components split and reformat light from the entire field of view, ready to be scattered into spectra. This requires bending, bouncing, and splitting the light multiple times, making this probably one of Webb’s most complex light paths.
To finish this amazing journey, the light of each beam is scattered by gratings, creating spectra that are then projected onto two MIRI detectors (two beams per detector). Amazing engineering feat! Credit: ESA/ATG medialab

Mid-infrared device operations update

The[{” attribute=””>James Webb Space Telescope’s Mid-Infrared Instrument (MIRI) has four observing modes. During setup for a science observation on August 24, a mechanism that supports one of these modes, known as medium-resolution spectroscopy (MRS), exhibited what appears to be increased friction. This mechanism is a grating wheel that allows astronomers to select between short, medium, and longer wavelengths when making observations using the MRS mode. Following preliminary health checks and investigations into the issue, an anomaly review board was convened on September 6 to assess the best path forward.

The Webb team paused scheduling notes using this monitoring mode while they continued to analyze its behavior. They are also currently developing strategies to resume MRS observations as soon as possible. The observatory is healthy, and the other three MIRI monitoring modes – imaging, low-resolution spectroscopy, and coronagraph – are operating normally and remain available for scientific observations.

The James Webb Space Telescope’s (MIRI) instrument sees light in the mid-infrared region of the electromagnetic spectrum, with wavelengths longer than our eyes can see.

MIRI allows scientists to use multiple observational techniques: imaging, spectroscopy, and chromography to support the full range of Webb’s scientific goals, from observing our solar system and other planetary systems, to studying the early universe.

To pack all of these modes into a single instrument, the engineers designed a complex optical system in which the light coming from the Webb telescope follows a complex 3D path before finally reaching the MIRI detectors.

This artist’s rendering shows the path to the shooting mode of MIRI, which provides both photocopy and chorograph capabilities. It also contains a simple spectrophotometer. We first look at its mechanical structure with three prominent pairs of carbon fiber trusses that will attach to the Webb instrument compartment at the back of the telescope.

The pickup mirror, which acts like a binoculars, receives the light from the telescope, shown in dark blue, and directs it to the imaging unit at MIRI. Inside the device, a system of mirrors reconfigures and redirects the light beam until it reaches the filter wheel where the desired range of mid-infrared wavelengths is selected from a set of 18 different filters each with its own function (the beam takes on a light blue color in the animation).

Finally, another set of mirrors takes the beam of light emerging from the filter wheel and reconstructs the image of the sky on the MIRI detectors.

Credit: ESA/ATG medialab

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