NASA’s massive new space telescope is getting colder.
while the James Webb Space TelescopeNASA officials wrote that the slow cooling process is coming to an end UpdateThere is no set timetable for when all components of the observatory will meet operating temperatures. That’s because most of this phase of the telescope’s months-long operating period goes back to physics, as mission managers wait for the mirrors to naturally cool to a temperature to allow the alignment to continue.
All observatory instruments are at their final temperature, including the mid-infrared instrument (MIRI), which is very sensitive to heat and gets some help from cryogenics to stay within 7 degrees Kelvin (minus 447 degrees Fahrenheit or minus 266 degrees Celsius) . Webb needs to keep ultra-cold temperatures to detect infrared light at emitting wavelengths.
Mirrors “are not quite there yet,” Jonathan Gardner, deputy chief scientist for the Web project, said in the update published Thursday (April 21).
That’s because the eighteen hexagons of the primary mirror, as well as the secondary mirror, are all made of beryllium and coated with gold. “At very cold temperatures, beryllium has a long thermodynamic time constant, which means it takes a long time to cool down or heat up,” Gardner explained.
Since then, the $10 billion telescope has started to cool off launch it It’s December 25, 2021, Gardner said, and he’s making good progress so far. All parts of the primary mirror are below the 55 K mark (minus 360 degrees Fahrenheit or minus 218 degrees Celsius) needed to run MIRI. More cooling “will only enhance its performance,” Gardner said.
Of the 18 primary mirror pieces, only four are above the 50 K mark (minus 370 F or minus 223 C). Since all of these parts have some mid-infrared radiation reaching the MIRI detectors, the agency said, officials would prefer to see them cool off an additional 0.5 to 2 Kelvin each before beginning the next stage of the alignment.
Gardner noted that these temperatures are subject to fluctuations. The telescope and the sun shield work together when the telescope is pointed at an object. There is “a tiny amount of residual heat,” he says, that can travel through the five-layer sun visor to the primary mirror depending on what angle the sun visor is to the sun, or position.
“Because the temperatures of the mirror part change very slowly, their temperatures depend on the average position over several days,” he said. In fact, Webb spent most of the commissioning period pointing to the poles of the ecliptic, or the plane at which Planets of the solar system revolve around the sun.
This polar position, Gardner said, “is a relatively hot one.” But he added that this is temporary. “During scientific operations, starting this summer, the telescope will have an even distribution of signals over the sky. The average heat input for the warmer parts of the mirrors is expected to decrease slightly, and the mirrors will cool slightly more.”
Soon after the start-up, Gardner added, the team plans to test Webb’s ability to go from a “hot situation” to a “cold situation.” This heat flow process “will inform us of how long it will take for the mirrors to cool or heat up when the observatory has been in these positions for any given period of time.”
Gardner said Webb’s run still needs to be completed around June. “Is Webb at his final temperature? The answer is roughly,” he concluded.
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