![]() With the mirrors aligned, engineers test Webb’s optics using a piece of support equipment called the ASPA, a nested acronym that means “AOS Source Plate Assembly.” The ASPA is a piece of test hardware that sits atop Webb’s Aft Optics Subsystem (AOS) and sends test laser light into and out of the telescope, thus acting like a source of artificial starlight. This test verifies the actuators have enough range of movement once they are in space, at their operational temperature of about 40 K (or about minus 388 degrees Fahrenheit / minus 233 degrees Celsius), to put the telescope’s primary mirror into its correct shape so it can accurately survey the universe. The ability to change the mirror alignment and shape is critical because the mirror must be unfolded from its unaligned stowed position when the telescope deploys. These actuators can also be used to precisely reshape each mirror segment to ensure they all match up once aligned. “They can move in steps that are a fraction of a wavelength of light, or about 1/10,000th the diameter of a human hair,” explained Feinberg. ![]() The actuators on each mirror segment are capable of extremely minute movements, which allow engineers to align the entire primary mirror by finely adjusting each mirror segment. ![]() For each segment, six of these actuators are placed into groups of two, at three equally spaced points along the outside of the mirror (to adjust the segment’s position), and one is attached to six struts that are connected to each of the hexagonal mirror segment’s corners (to adjust the segment’s shape). When the engineers need to adjust the positions and shapes of the mirror segments to achieve precise alignment, they use the seven actuators (tiny mechanical motors) attached to the back of each one of the mirror segments.
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