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Webb space telescope nears its destination almost a million miles from Earth, ready for critical mirror alignment - CBS News
Jan 22, 2022 2 mins, 13 secs

Thirty days outbound from Earth, the James Webb Space Telescope will slip into its parking orbit nearly a million miles away on Monday, an ideal spot to scan the heavens in search of faint infrared light from the first generation of stars and galaxies.

Scientists and engineers now have to turn the $10 billion Webb into a functioning telescope, precisely aligning its 18 primary mirror segments so they work together as a single 21.3-foot-wide mirror, by far the largest ever launched.

Earlier this week, engineers remotely completed a multi-day process to raise each segment, and the telescope's 2.4-foot-wide secondary mirror, a half-inch out of the launch locks that held them firmly in place during the observatory's Christmas Day climb to space atop a European Ariane 5 rocket.

"Our primary mirror is segmented, and those segments need to be aligned to a fraction of a wavelength of light," said Lee Feinberg, optical telescope element manager at NASA's Goddard Space Flight Center.

Each mirror segment was ground to a prescription that takes into account the deforming effects of gravity on Earth and their expected shrinkage in the ultra-low-temperatures of space.

But If Webb was aimed at a bright star today, the result would be 18 separate images "and they're going to look terrible, they're going to be very blurry," Feinberg said in an interview, "because the primary mirror segments aren't aligned yet.".

That's the next major hurdle for the Webb team, mapping out and then tilting each segment in tiny increments, merging those 18 images to form a single exactly focused point of light.

Each 4.3-foot-wide hexagonal primary mirror segment features six mechanical actuators in a "hexapod" arrangement on the back side, allowing movement in six directions.

"The big thing is getting the 18 primary mirror segments pointing in a similar way so that their images are about the same size," Feinberg said.

The goal is to tilt the segments as required to minimize the size of the defocused images and then to move the multiple reflections to the same point at the center of the telescope's optical axis, all of them stacked on top of each other to produce a single beam of sharply focused light.

It is a process of tilting the primary mirror segments so that the images fall on top of each other.".

The procedures were tested before launch using a sub-scale model of the telescope and Feinberg said he's confident the alignment process will work as planned.

"We want to make sure that the first images that the world sees, that humanity see, do justice to this $10 billion telescope and are not those of, you know, hey look, a star," said Jane Rigby, Webb operations project scientist at Goddard

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