NASA’s Webb Telescope Mirror Shatters ‘Most Optimistic Forecast’ After Final Alignment

Over the past four months, by comparison, nearly all of JWST’s work has focused on the much less obvious and much smaller alignments and calibrations. Each of JWST’s 18 main mirror segments slowly but surely hold micrometer by micrometer in position while large areas of the telescope are slowly cooled to ambient temperatures – essential for maximum performance. At the same time, all of Webb’s initial instruments achieved first light and entered the early stages of calibration and commissioning. Only after the instruments painstakingly calibrated, the mirror is perfectly aligned, and the critical instruments are cooled to temperatures as low as -449°F (-267°C), can Webb begin to observe the universe and revolutionize large subsets of space science.

The first and most important step – aligning the mirror – is now complete. The alignment process began in February 2022, six weeks after takeoff. First, images were taken with the misaligned mirror to help determine exactly what state it was in. One by one, each of the 18 Webb mirror segments was moved individually to determine which image each mirror was responsible for, allowing the ground controllers to correctly focus each mirror view of the target star. In a process known as ‘coarse phases’, once these 18 optical points had been well resolved and attached to a particular mirror segment, the segments were gradually oriented on top of each other to produce a single image.

“Coarse” severely reduces the almost unfathomable precision required to complete the move. To reach its full potential, each Webb Telescope mirror segment must be aligned within 50 nm from each other. According to NASA, “If the initial Webb mirror was the size of the United States, then each fragment would be the size of Texas, and the team would need to align the heights of those Texas-sized portions with each other to an accuracy of about 1.5 inches.”

This is followed by a subtle increment, involving a set of more esoteric operations designed to focus the mirror as fully as possible. The resulting image was then modified to properly align it with the field of view of each of the Webb’s four main science instruments. Finally, some steps of the seven-step alignment process have been completely redesigned or refined to optimize the mirror to the satisfaction of Earthbound creators and potential users.

In the end, the Webb Telescope’s alignment was extraordinarily successful, producing an image clearer and purer than even the “most optimistic predictions” made by its engineers. NASA says the image is so detailed that it effectively reached the physical resolution of a mirror the size of the Webb Telescope, meaning it would have to violate known laws of physics to resolve any other details.

With the mirror alignment complete, JWST has only one major hurdle left before scientific operations can begin: device operation. Commissioning is a comprehensive statement covering the broad range of calibration, analysis, testing, and optimization required to verify that the four major JWST tools behave as expected and perform the work they are designed to do as accurately and reliably as possible.

At some point, the use of highly complex scientific instruments becomes akin to an art form, and a certain degree of trust must be built between scientists and their hoped-for commercial instruments before they can confidently nail the chisel to marble and begin delving into the universe with unprecedented width and detail. If operation goes as smoothly as deployment and alignment, the JWST team may be ready to capture and share the first actionable telescope observations of the universe as early as July 2022.

NASA’s Webb Telescope Mirror Shatters ‘Most Optimistic Forecast’ After Final Alignment