The light then continues its path through the secondary and tertiary mirrors inside the telescope and enters the NIRCam instrument. When the telescope is pointed at a star, the light from the star first hits the primary mirror, in which the individual segments are now aligned reasonably well. In this process, rather than moving the mirror segments, the small optics inside NIRCam are moved instead. This is where the fine alignment happens. However, there were still minute alignment errors that needed to be corrected to obtain the best possible image. In coarse alignment, the mirror segments were moved vertically (up and down) until they aligned to form one giant mirror. Once they had this information, there were two crucial tasks to complete before the segments could function as a single, monolithic mirror: coarse alignment and fine alignment. NASA scientists used a mathematical analysis called “ phase retrieval” to study how the movement of each individual segment changed the sharpness of the final image. This precision (to within a fraction of a wavelength of light) is important for obtaining high-quality images from the telescope. The motors can move the mirrors very precisely, to within about 1/10,000th of the diameter of a human hair. This motor can adjust the tension of the struts to optimize the curvature of that mirror segment. The seventh motor is at the center and is connected to the mirror’s six corners with struts. Six of these motors are grouped in pairs, equally distanced, and located around each mirror segment. Their purpose is to move and reshape the curvature of each segment so that all 18 can act as a single large mirror. There are seven small motors fixed behind each of the JWST’s 18 slightly curved hexagonal mirrors. The NIRCam is the optical system that captures images on the James Webb Space Telescope. The image was taken using the near infrared camera (NIRCam)one of the telescope’s four key science instruments. The JWST has now completed this alignment process, giving us the first unified image. Once the mirror segments were unfolded, they had to be aligned so all 18 combined to form a single 6.5m-diameter curved mirror. The main challenge with the JWST was being able to unfold it to its fully extended form in space, under extreme conditions of heat and cold, and with no human assistance. This technology has been in use for a few decades now, by some of the largest optical telescopes in the world, including the Keck Observatory in Hawaii (which has two 10m-diameter mirrors, each made of 36 hexagonal segments). The telescope uses segmented mirror technology. As such, it was designed to be neatly folded to fit inside the cargo hold atop an Ariane 5 launch vehicle. It’s so big that none of our rockets can carry it when fully extended. The JWST is the largest telescope humans have ever felt into space.
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