James Webb Space Telescope successfully cools

NASA said that the main mirror of the James Webb Telescope (James Webb) and scientific instruments continue to cool successfully. This process will continue for quite some time and will not interfere with the alignment of all segments of the main mirror.

Image source: NASA

The cooling system of James Webb’s infrared telescopes is largely passive by radiating excess heat in open spaces. Before 2000, infrared space telescopes and infrared telescopes on rockets and balloons used forced cooling with liquid helium. Subsequently, with the exception of cooling of individual infrared receivers (cameras), the designers switched to passive cooling of the working components of infrared space telescopes. “James Webb” in this became a masterpiece in design thought.

The James Webb Telescope is protected by a huge sun shield the size of a tennis court. The screen reduces the power of direct solar radiation and solar rays reflected from the earth and moon from hundreds of watts to milliwatts, which are successfully spread into space. In addition, a small amount of heat comes from the telescope’s chassis, which is created by the electronics and the scientific instruments that work on board. There is still no balance between absorbed and dissipated heat, says NASA, but over time it will occur.

The Agency expects the primary mirror to cool below 50 kelvins (approximately -223 ° C) and that the near-infrared instruments reach temperatures of around 40 kelvins (-233 ° C). An intermediate infrared camera (MIRI) must be even cooler, so it also has an active heat dissipation system. It is important that if previous helium simply evaporated in space during the cooling of infrared instruments in space telescopes, then Webb has a closed cooling system installed, which in itself can extend the telescope’s operation. The MIRI instrument must operate at temperatures below 7 Kelvin or -266 ° C.

Image source: NASA

Image source: NASA

In this image from NASA, you can see the temperature of the main mirror segments on February 9th. The front secondary mirror (SMA) has already cooled to operating temperature, and the segments of the primary mirror are cooled by a noticeable temperature difference. The main segments will cool with another 10 kelvins each, but the difference of 10-20 kelvins can remain forever, as for example the lower parts of the mirror closest to the sun visor heat up more than those closer to its upper part. The segment setting should compensate for this difference.

Interestingly, at the beginning of the cooling process, some of the instruments on the cold side of the telescope were specially heated to prevent fogging on the work surfaces and the formation of ice. But this step has long been completed, and all devices are steadily dropping the temperature. For example, near-infrared monitors have cooled to 75 kelvins (-198 ° C), although it will take several weeks to cool down to operating temperature. Meanwhile, the telescope continues to focus on the primary mirror segments, and NASA promises to report on the success of the first week of focusing these elements in the near future.

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