Astronomy

Webb optics alignment achieves near perfect focus

A sharply-focused image of a nondescript star 100 times fainter than the human eye can detect served as a suitable target to demonstrate the near-perfect alignment of the James Webb Space Telescope’s optical system. Image: NASA/STSci

Engineers have achieved nanometre precision aligning the 18 hexagonal segments of the James Webb Space Telescope’s 6.5-metre (21.3-foot) primary mirror, unveiling a razor-sharp image of a star using the observatory’s Near Infrared Camera, or NIRCam.

Along with the sharply focused star, the infrared image shows a multitude of faint galaxies strewn across the field of view, highlighting the sensitivity of the $10 billion space observatory. The nondescript star in question, 2MASS J17554042+6551277, is about 100 times fainter than the human eye could see.

“I’m happy to say that the optical performance of the telescope is absolutely phenomenal, it is really working extremely well,” Lee Feinberg, Webb optical telescope element manager at the Goddard Space Flight Center, told reporters during a 16 March teleconference.

“We said last fall that we would know that the telescope is working properly when we have an image of a star that looks like a star. And now we have that, and you’re seeing that image.”

Said Thomas Zurbuchen, director of space science at NASA Headquarters in Washington: “This is one of the most magnificent days in my whole career at NASA. … Today we can announce that the optics will perform to specifications or even better. It’s an amazing achievement.”

The NIRCam instrument capture a “selfie” of sorts showing Webb’s primary mirror with its 18 segments aligned with nanometer precision. Webb’s secondary mirror and the three struts holding it in place are also seen. Image: NASA/STSci

Marshall Perrin, Webb deputy telescope scientist, said the telescope’s mirror segments were initially aligned to within about a millimeter of each other. To adjust them so all 18 act together as if part of a single mirror, “they need to be lined up to within a few nanometers (billionths of a meter) of one another, it’s a few hundred atomic diameters.”

Using high-tech actuators on the back of each mirror segment, the 18 initially separate reflections of an alignment star were brought to a single point as mapped out by NIRCam in incremental steps. Over the next two months or so, the optics will be fine-tuned to bring sharply focused light to Webb’s other three science instruments.

Jane Rigby, the Webb operations project scientist at NASA’s Goddard Space Flight Center, said “the telescope performance so far is everything that we dared hope.”

“The goal here was to build a telescope 100 times more powerful than anything we’ve had before,” she said. “From the early engineering data that we have seen so far, we know that we’re on track to meet those very demanding science requirements.”

Based on results to date, the first science images are expected in the June-July timeframe, or roughly six months after Webb’s Christmas Day launch.

Source: https://astronomynow.com/2022/03/21/webb-optics-alignment-achieves-near-perfect-focus/

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