NASA's massive James Webb space telescope just keeps getting colder -
That's because the 18 hexagonal segments of the primary mirror, as well as the secondary mirror, are all made of beryllium and coated with gold. "At cryogenic temperatures, beryllium has a long thermal time constant, which means that it takes a long time to cool or to heat up," Gardner explained.

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The $10 billion telescope has been cooling ever since its launch on Dec. 25, 2021, and it's making good progress so far, Gardner said. All of the primary mirror segments are below the mark of 55 Kelvin (minus 360 F or minus 218 C) necessary for MIRI to operate. Further cooling "will only enhance its performance," Gardner said.

Of the 18 primary mirror segments, just four of them are above the 50 Kelvin (minus 370 F or minus 223 C) mark. Since these segments all have some mid-infrared light that reaches MIRI detectors, the agency stated, officials would prefer to see them cool by an additional 0.5 to 2 Kelvins each before starting the next phase of alignment.

These temperatures are all subject to fluctuation, Gardner noted. The telescope and sunshield operate together when the telescope is aimed at something. There is a "tiny amount of residual heat," he says, that can move through the five-layer sunshield to the primary mirror depending on the angle the sunshield presents to the sun, or the attitude.

"Since the mirror segment temperatures change very slowly, their temperatures depend on the attitude averaged over multiple days," he said. In fact, Webb has been spending most of the commissioning period pointing at the poles of the ecliptic, or the plane upon which solar system planets orbit the sun.

Webb still should be finished its commissioning in about June, Gardner said. "Is Webb at its final temperature? The answer is almost," he concluded.

Timestamp -
00:00 Introduction
01:00 James Webb Space Telescope Is Cooling to Deep Space Temperature
02:00 Exploration of James Webb
03:00 Conclusion

About the Video -
Mobilebharat Originals Season 1, Episode 7.

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