It may seem surprising, but ice can form on components of the James Webb Telescope, even in space. How is this possible and what is NASA doing to limit the risks?
Gradually, James Webb Space Telescope (JWST) adjusts its “vision” of our Universe. Launched into space at the end of 2021, the observatory is in the process of aligning its mirrors. It should be ready for its scientific activities in the summer of 2022. This involves cooling the telescope, which is designed to operate in the infrared.
One of its instruments, MIRI (which must observe in the mid-infrared), requires an operating temperature below -266°C. For it, as recalled NASA on March 30, 2022, it is equipped with a refrigerator. ” But it also requires radiators to control its cooling and prevent the formation of ice in space. “, adds the agency. One may be surprised that ice can thus form on the observatory, right in the middle of space.
But where does this water come from?
To understand this, you have to go back a little, to the time of the launch of the JWST. ” Moist air was trapped between components, such as the sun visor membranes and its many insulating layers », highlighted the space agency. To this must be added the materials of the telescope which were able to absorb the value of water, present in the Earth’s atmosphere. ” Most of this air escaped only 200 seconds after liftoff, but some moisture remained “, completes NASA.
In space, water does not behave like on our planet. « In a perfect vacuum, water can only exist as a gas, but even space is not a perfect vacuum. », Explain the space agency. In this other environment, water degasses (loses its gas) above -113°C (160 Kelvin). ” If water molecules float and come into contact with a surface colder than 140 kelvins [ndlr : -133°C], they will stick to it in the form of ice and will never come off. This is extremely important to avoid for the Webb telescope », affirms the Nasa.
In order not to find itself in this situation, NASA has planned the cooling of James Webb, and this as soon as the deployment of the heat shield. The drop in temperatures was carefully managed, the order in which the components had to cool down was not chosen at random. ” This allowed water to escape into space rather than freezing on sensitive components. »
Regarding MIRI, the refrigerator is therefore responsible for transporting heat to the other side of James Webb’s sun visor, where it is hot. It is essential to eliminate the water in order to cool MIRI properly, or to store the water in areas provided for this purpose. Know that you can follow in line the cooling of this instrument. The objective is to cool MIRI below 6 kelvins (-270°C), without “spoiling” it by letting water freeze on this instrument — hence the importance of having an appropriate heating technique.