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The James Webb Space Telescope is experiencing a problem with one of its instruments, the Near Infrared Imager and Slitless Spectrograph, or NIRISS. The instrument is currently offline with no indication of when it will come back online, but engineers are working to resolve the issue and the telescope’s equipment remains safe.

As alarming as it sounds, it’s not uncommon for such problems to arise, especially in space telescopes. Because performing physical maintenance on space telescopes is extremely difficult, software troubleshooting is done slowly and carefully to prevent any damage from occurring. That’s why on space telescopes you’ll see instruments like Hubble or the Swift Observatory go into safe mode to protect themselves when something goes wrong.

In the case of James Webb, the problem with the NIRISS instrument was due to communication latency. “On Sunday, January 15, the James Webb Space Telescope’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) experienced a communication delay within the instrument, resulting in a timeout of the flight software,” NASA said in a statement. “The instrument is currently unavailable for science observations while NASA and the Canadian Space Agency (CSA) work together to determine and correct the root cause of the delay.”

NIRISS sits next to a sensor called the Fine Guidance Sensor, or FGS, which allows the telescope to precisely aim its targets. NIRISS can work as both a camera and a spectrograph, and has a special feature called an aperture mask that allows it to block light from particularly bright sources to better see the faint sources around them. The instrument is used for tasks such as detecting and investigating exoplanets, as well as observing distant galaxies.

According to NASA, planned science observations that were scheduled to use NIRISS will now be rescheduled.

This follows another Webb issue that occurred in December 2022. Due to a software problem in the attitude control system, some instruments entered safe mode on December 7, and scientific observations were suspended. It was fixed until December 20, when all scientific work resumed.

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