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Using Light Waves to Align the James Webb Space Telescope

Engineers at NASA's Johnson Space Center in Houston used light waves to align the James Webb Space Telescope's mirror segments to each other, so they act like a single, monolithic mirror in the cryogenic cold of the center's iconic Chamber A.

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    Transcript

    00:00:00 The James Webb Space Telescope is moved inside this massive cryogenic vacuum chamber at NASA’s Johnson Space Center called Chamber A. This chamber simulates the vacuum and super cold environment of space in which Webb will operate about 40 K or about minus 388 degrees Fahrenheit or minus 233 degrees Celsius The Webb telescope mission team uses Chamber A to further verify the entire telescope, including its optics and instruments, will work correctly in space. Part of this test includes aligning Webb’s 18 mirror segments into a perfect, monolithic mirror. The process is similar to the way the mirrors will be aligned in space. Actuators behind each mirror enable the aligning, or “phasing,” of the telescope’s 18 hexagonally shaped primary mirror segments to function as a single 6.5-meter mirror.

    00:01:09 The mirror’s actuators can move in steps that are a fraction of a wavelength of light, or about 1/10,000th the diameter of a human hair. In space, a star will be used to as the light source to align the mirrors. Engineers will move each mirror and determine which image is coming from which mirror. Then, through a process called Wave Front Sensing and Control, the mirrors will be aligned and very finely focused. For this test, the Webb team uses a special laser to act as the ‘star’ and a test device called a multi-wavelength interferometer. By analyzing the interference signal between these two light beams, engineers determine the mirror shape and the alignment of the mirrors to within one wavelength of light.

    00:01:58 The James Webb Space Telescope is the scientific complement to NASA's Hubble Space Telescope. It will be the most powerful space telescope ever built. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency. music. beep. beep.