James Webb’s MIRI instrument is back to full operations

By Georgina Torbet November 13, 2022

Shortly after the James Webb Space Telescope began its science operations in July this year, there was a problem with a mode on one of its instruments, the Mid-Infrared Instrument or MIRI. Now, engineers have found a way to deal with the issue, and the instrument can return to full operation.

NASA announced in September this year that one mode of the MIRI instrument was not working. Each of Webb’s four instruments can operate in multiple modes, and although MIRI was still working in three modes and able to capture some stunning images like a spooky version of the Pillars of Creation, the medium-resolution spectroscopy (MRS) mode had stopped working on August 24.

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The problem was caused by a grating wheel, a piece of moving hardware that changes the filter used by the instrument mode to allow it to switch between different wavelengths for observations. There was increased friction in the wheel so the teams decided to stop using the mode while they figured out what the problem was.

Now, the team has concluded its investigation and found that the problem “is likely caused by increased contact forces between sub-components of the wheel central bearing assembly under certain conditions,” according to a NASA update. The good news is that they have found a way to use the mode safely, as they are now able to predict how much friction will be experienced when the wheel is used.

That means that the MRS mode can be used again and has resumed observations this weekend. The mode will be used to study the poles of Saturn, which are only visible to Webb for a short time.

Future observations using the MRS mode will be limited to make sure the wheel continues to be healthy and in balance, and if it continues to operate well, it will be returned to full operations in the future.

MIRI is unlike the other three Webb instruments, which operate in the near-infrared range, as it operates in the mid-infrared. That means it requires different sensors and has to operate at a lower temperature than the other instruments, and is useful for different types of science. While the near-infrared instruments are excellent for tasks like looking back at the earliest galaxies, the mid-infrared range is useful for studying stars and planets.

“It’s such an exciting wavelength range in terms of the chemistry that you can do, and the way you can understand star formation and what’s happening in the nuclei of galaxies,” said Gillian Wright, the principal investigator for the European Consortium behind the MIRI, in a statement about the instrument.

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