On 7 April, Webb's Mid-Infrared Instrument (MIRI) – a joint development by
MIRI needs to be cold because the instrument sees in mid-infrared light and every object emits infrared radiation, or heat, all the time. Therefore, MIRI must be cooled to make sure its detectors do not pick up any background heat from the instrument itself, obscuring what the astronomers actually want to see.
On the hot side, parts of Webb will reach temperatures as high as 85 degrees Celsius, or 185 degrees Fahrenheit! Meanwhile, on the cold side Webb will be about -233 degrees Celsius, or -388 degrees Fahrenheit.
By necessity, MIRI's detectors are built using a special formulation of Arsenic-doped Silicon (Si:As), which need to be at a temperature of less than 7 kelvins to operate properly.
The low temperature is necessary because all four of Webb's instruments detect infrared light – wavelengths slightly longer than those that human eyes can see.
The lowest temperature ever recorded on Earth is -89.2 °C and was registered at the Vostok station in Antarctica on July 21, 1983. On James Webb, the temperature is much lower — 6.4 Kelvin, which is equivalent to -266.75 °C.
Has the James Webb Space Telescope Cooled Down to Its Final Temperature? The Mid-Infrared Instrument (MIRI) on NASA's James Webb Space Telescope is now cooled by a gaseous helium cryocooler to under 7 kelvins (minus 447 degrees Fahrenheit, or minus 266 degrees Celsius).
As with all infrared instruments NIRSpec will operate at cryogenic temperatures (~ -233 °C; ~40 K).
These instruments have detectors formulated with Mercury-Cadmium-Telluride (HgCdTe), which work ideally for Webb at 37 kelvin. We can get them this cold in space "passively," simply by virtue of Webb's design, which includes a tennis court-sized sunshield.
To best protect your instrument, look for steady and moderate temperatures. Musical instruments of all types do well in temperatures of about 70 degrees Fahrenheit, at humidity levels of between 40-60%.
Webb won't be looking at Earth, but it will observe more distant planets in the Solar System as well as exoplanets orbiting other stars. Some of these exoplanets may be very similar to Earth.
Webb is telling us more about the atmospheres of extrasolar planets, and perhaps will even find the building blocks of life elsewhere in the universe. In addition to other planetary systems, Webb is also studying objects within our own Solar System.
How far back will Webb see? Webb is able to see what the universe looked like around a quarter of a billion years (possibly back to 100 million years) after the Big Bang, when the first stars and galaxies started to form.
The baseline temperature of outer space, as set by the background radiation from the Big Bang, is 2.7 kelvins (−270 °C; −455 °F).
In most cases cryocoolers use a cryogenic fluid as the working substance and employ moving parts to cycle the fluid around a thermodynamic cycle. The fluid is typically compressed at room temperature, precooled in a heat exchanger, then expanded at some low temperature.
Temperature fluctuations could also potentially warp Hubble's mirrors, so the mirrors are kept at a constant temperature of about 70 degrees Fahrenheit (21 degrees Celsius).
Not Cold Enough
Isn't space, especially the area around Webb's halo orbit around Lagrange point L2, already cold enough? In a word, no — the infrared astronomy Webb's instruments are designed for, space is nowhere near cold enough.
Webb uses two different types of detectors: mercury-cadmium-telluride (abbreviated HgCdTe) "H2RG" detectors for the 0.6-5 μm "near-infrared" and arsenic doped silicon (abbreviated Si:As) detectors for the 5-28 μm "mid-infrared".
NIRSpec was built for ESA by a consortium of European companies led by Airbus Defence and Space, with NASA's Goddard Space Flight Center in Greenbelt, Maryland, providing its detector and microshutter subsystems.
The drawbacks of NIRS include its low sensitivity, due to low absorption coefficients, which causes the detection limit to be higher, and the fact that NIRS is an indirect method that requires the development of a multivariate calibration model against a suitable reference method.
The NIRSpec enables scientists to obtain simultaneous spectra of more than 100 objects in a 9-square-arcminute field of view. It provides medium-resolution spectroscopy over a wavelength range of 1 to 5 micrometers and lower-resolution spectroscopy from 0.6 to 5 micrometers.
JWST was designed with 10 years of fuel. And as any good engineer knows, if its supposed to last 10 years, you need to build it for 13, just in case. So in 13 or 14 years as its fuel runs out it will slowly fall out of its orbit of the second Lagrange point and drift into its own orbit of the sun.
If the deployment fails, Webb's battery will last mere hours before the telescope runs out of power entirely. (Credit: NASA/James Webb Space Telescope team.) An unsuccessful deployment will cause power failure after mere hours, ending Webb's life prematurely.
The Earth's gravitational pull force on JWST at 1,200,000 km away seems to be about 0.046N at that position and the speed of JWST is 0.3683 km/s at that point according to NASA. At that speed, Earth's gravity is acting to slow down JWST. By knowing that F=Ma or a=F/M and V=at the time is about 600 days.