James Webb Space Telescope Trouble Spotted – MIRI Anomaly

Webb MIRI Spectroscopy Animation
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Webb MIRI Spectroscopy Animation

James Webb Space Telescope MIRI Spectroscopy Animation: The light beam from the telescope is then displayed in dark blue, entering the instrument through a pickup mirror located at the top of the instrument, which acts as a periscope.
An array of mirrors then directs the light down to the bottom of the instruments, which house a set of 4 spectroscopic modules. Once there, the light beam is split into 4 beams corresponding to different parts of the mid-infrared region by optical elements called dichroics. Each ray enters its integral unit area; these components split and reformat light from the entire field of view, ready to scatter into spectra. This requires the light to be folded, bounced, and split multiple times, making it probably one of Webb’s most complex light paths.
To complete this amazing journey, the light from each beam is scattered by gratings and then projected onto 2 MIRI detectors (2 beams per detector) creating spectra. An incredible feat of engineering! Credit: ESA/ATG medialab

Mid-Infrared Instrument 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.

Webb’s team has taken a break from planning observations using this particular observing mode while they continue to analyze its behavior. They are also currently developing strategies to summarize MRS observations as quickly as possible. The observatory is in good health and MIRI’s three other observing modes – imaging, low-resolution spectroscopy and coronagraphy – are operating normally and available for science observations.

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

MIRI enables scientists to use many observational techniques: imaging, spectroscopy, and coronagraphy to support the full range of Webb’s scientific goals, from observing our own Solar System and other planetary systems to studying the early Universe.

To collect all these modes in one instrument, engineers developed a complex optical system in which light from the Webb telescope follows a complex 3D path before finally reaching the MIRI detectors.

It shows this path for MIRI’s imaging mode, which provides imaging and coronagraphy capabilities in this artist’s rendering. It also includes a simple spectrograph. We first look at its mechanical structure, with three protruding pairs of carbon fiber mounts that will attach it to Webb’s instrument compartment at the back of the telescope.

Acting as a periscope, the selective mirror receives light from the telescope, shown in dark blue, and directs it to MIRI’s imaging module. Inside the instrument, a system of mirrors reformats the light beam and directs it until it reaches a filter wheel where the desired range of mid-infrared wavelengths is selected from 18 different filters, each with its own function (light blue in the animation).

Finally, another set of mirrors picks up the light beam from the filter wheel and recreates the image of the sky on the MIRI detectors.

Credit: ESA/ATG medialab

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