Slowly but surely, James Webb is cooling down in the vacuum of space. Using sensors, NASA monitors temperatures on both sides (hot and cold) of its telescope.
His instruments are all on, but James Webb is far from ready to observe the Universe. NASA’s new space observatory must gradually cool down to a temperature of around -223°C. It is essential to allow James Webb to observe in the past, further than Hubble can do.
The JWST arrived at its destination, orbiting the Lagrange point L2, an equilibrium point located 1.5 million kilometers from our planet — behind the Earth, relative to the Sun. From there, the JWST communicates with NASA. But how can the space agency check James Webb’s temperature, such an essential criterion?
Where are James Webb’s thermometers?
The observatory embeds several temperature sensors, located on the various instruments. They are positioned on the main structure of each instrument, as seen in this diagramshared by the European Space Agency (which is contributing to the mission) on February 2, 2022.
You can also follow the temperatures recorded by these sensors online, via the NASA site to find out where James Webb is in space. Data is refreshed once a day (and rounded to the nearest whole number). We learn for example, on February 2, 2022, that MIRI reached a temperature of 126°C, while the FSM pointing mirror is colder, with a temperature of -206°C.
On this site, and on the image above, in addition to the numbers referring to the instruments, we see letters. They allow you to compare the temperatures between the sides of the telescope, separated by the heat shield:
- “a” (sunshade) and “b” (equipment panel) are on the “warm” side of the observatory;
- While “c” (primary mirror) and “d” (mirror module heatsink) are on the cold side.
On February 2, it was 56°C on the sun visor (hot side) and -214°C on the primary mirror (cold side).
Not cold enough = no observations possible
” Temperature control is a critical aspect of Webb’s design, engineering and operation », affirms the ESA. If its instruments are not sufficiently cooled, the JWST will not be able to correctly observe objects shining mainly in the infrared. And so, the distant past of the Universe.
The Universe is expanding: therefore, the further we look into its past, the faster objects move away from us. This produces what is called redshift (light appears redder). To see the formation of the first stars and galaxies in the Universe, you need a telescope optimized for this light. And that implies that the telescope is both spatial and very cold.