Problem Detected on the James Webb Space Telescope – MIRI Anomaly

Mid-Infrared Instrument Operations Update
The 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 has paused in scheduling observations using this particular observing mode while they continue to analyze its behavior. They are also currently developing strategies to resume MRS observations as soon as possible. The observatory is in good health, and MIRI’s other three observing modes – imaging, low-resolution spectroscopy, and coronagraphy – are operating normally and remain available for science observations.

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

MIRI allows scientists to use multiple observing techniques: imaging, spectroscopy, and coronagraphy to support the whole range of Webb’s science goals, from observing our own Solar System and other planetary systems, to studying the early Universe.

To pack all these modes in a single instrument, engineers have designed an intricate optical system in which light coming from Webb’s telescope follows a complex 3D path before finally reaching MIRI’s detectors.

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

The pick-off mirror, acting like a periscope, receives the light from the telescope, shown in deep blue, and directs it into MIRI’s imaging module. Inside the instrument, a system of mirrors reformats the light beam and redirects it till it reaches a filter wheel where the desired range of mid-infrared wavelengths is selected from a set of 18 different filters each with its own specific function (the beam takes a light blue color in the animation).

Lastly, another set of mirrors takes the light beam coming out of the filter wheel and recreates the image of the sky on MIRI’s detectors. (NASA)

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