Engineers inspect one of the first two flight mirrors to arrive at NASA Goddard.

Flight mirror canisters stored at Goddard.

Here the flight telescope structure is lifted in the cleanroom at NASA Goddard.

The flight telescope structure sits in the assembly stand at NASA Goddard, ready for mirror assembly.

The last mirror was installed in February of 2016. Not long after, the protective covers were removed, and the full mirror was revealed.

The Uncovered Mirrors

 

 

 

Once the mirrors were completed, the science instruments were integrated into the telescope. While at Goddard, the telescope also underwent environmental testing - both acoustic and vibration - to ensure it will be able to withstand the rigors of launch. That successfully completed, the telescope was sent off to NASA Johnson in Houston, Texas, for tests of the optics and instruments at cryogenic temperatures. NASA Johnson's Chamber A is the only thermal vacuum chamber NASA has that is large enough for Webb!

Aligning The Mirrors On Earth And In Space

Once the telescope is in orbit, Engineers on Earth will need to make corrections to the positioning of the Webb telescope's primary mirror segments to bring them into alignment - ensuring they will produce sharp, focused images.

These corrections are made through a process called wavefront sensing and control, which aligns the mirrors to within tens of nanometers. During this process, a wavefront sensor (NIRCam in this case) measures any imperfections in the alignment of the mirror segments that prevent them from acting like a single, 6.5-meter (21.3-foot) mirror. Engineers will use NIRCam to take 18 out-of-focus images of a star - one from each mirror segment. The engineers then use computer algorithms to determine the overall shape of the primary mirror from those individual images, and to determine how they must move the mirrors to align them.

Engineers tested this alignment process in the cryogenic, vacuum environment of Chamber A at NASA's Johnson Space Center during about 100 days of cryogenic testing. The environment of the chamber simulates the frigid space environment where Webb will operate, and where it will collect data of never-before-observed portions of the universe. Inside the chamber, engineers fed laser light into and out of the telescope, acting like a source of artificial stars. The test verified the entire telescope, including its optics and instruments, worked correctly in this cold environment and ensured the telescope will work correctly in space.

Webb sitting inside Chamber A after it completed cryogenic testing.

Having passed its tests at NASA Johnson, Webb and its mirrors have moved to Northrop Grumman, where the telescope will be mated with the sunshield and spacecraft bus.

Quelle: NASA

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NASA’s Webb Telescope Reaches Major Milestone as Mirror Unfolds

NASA’s James Webb Space Telescope team fully deployed its 21-foot, gold-coated primary mirror, successfully completing the final stage of all major spacecraft deployments to prepare for science operations.

A joint effort with the European Space Agency (ESA) and Canadian Space Agency, the Webb mission will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe.

“Today, NASA achieved another engineering milestone decades in the making. While the journey is not complete, I join the Webb team in breathing a little easier and imagining the future breakthroughs bound to inspire the world,” said NASA Administrator Bill Nelson. “The James Webb Space Telescope is an unprecedented mission that is on the precipice of seeing the light from the first galaxies and discovering the mysteries of our universe. Each feat already achieved and future accomplishment is a testament to the thousands of innovators who poured their life’s passion into this mission.”

The two wings of Webb’s primary mirror had been folded to fit inside the nose cone of an Arianespace Ariane 5 rocket prior to launch. After more than a week of other critical spacecraft deployments, the Webb team began remotely unfolding the hexagonal segments of the primary mirror, the largest ever launched into space. This was a multi-day process, with the first side deployed Jan. 7 and the second Jan. 8.

Mission Operations Center ground control at the Space Telescope Science Institute in Baltimore began deploying the second side panel of the mirror at 8:53 a.m. EST. Once it extended and latched into position at 1:17 p.m. EST, the team declared all major deployments successfully completed.

The world’s largest and most complex space science telescope will now begin moving its 18 primary mirror segments to align the telescope optics. The ground team will command 126 actuators on the backsides of the segments to flex each mirror – an alignment that will take months to complete. Then the team will calibrate the science instruments prior to delivering Webb’s first images this summer.

“I am so proud of the team – spanning continents and decades – that delivered this first-of-its kind achievement,” said Thomas Zurbuchen, associate administrator for the Science Mission Directorate in NASA Headquarters in Washington. “Webb’s successful deployment exemplifies the best of what NASA has to offer: the willingness to attempt bold and challenging things in the name of discoveries still unknown.”

Soon, Webb will also undergo a third mid-course correction burn – one of three planned to place the telescope precisely in orbit around the second Lagrange point, commonly known as L2, nearly 1 million miles from Earth. This is Webb’s final orbital position, where its sunshield will protect it from light from the Sun, Earth, and Moon that could interfere with observations of infrared light. Webb is designed to peer back over 13.5 billion years to capture infrared light from celestial objects, with much higher resolution than ever before, and to study our own solar system as well as distant worlds.

“The successful completion of all of the Webb Space Telescope’s deployments is historic,” said Gregory L. Robinson, Webb program director at NASA Headquarters. “This is the first time a NASA-led mission has ever attempted to complete a complex sequence to unfold an observatory in space – a remarkable feat for our team, NASA, and the world.”

NASA’s Science Mission Directorate oversees the mission. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the project for the agency and oversees the Space Telescope Science Institute, Northrop Grumman, and other mission partners. In addition to Goddard, several NASA centers contributed to the project, including Johnson Space Center in Houston, the Jet Propulsion Laboratory in Pasadena, Marshall Space Flight Center in Huntsville, Alabama, Ames Research Center in Silicon Valley, and others.

Quelle: NASA

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Update: 11.01.2022

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All hail the Ariane 5 rocket, which doubled the Webb telescope’s lifetime

"It would have been criminal not to do it."

There were two stunningly good pieces of news about the James Webb Space Telescope this past weekend. One was widely reported—that after an intricate, two-week process, the telescope completed its deployment without any difficulties. The next steps toward science operations are more conventional.

The other piece of news, less well-covered but still important, emerged during a news conference on Saturday. NASA's Mission Systems Engineer for the Webb telescope, Mike Menzel, said the agency had completed its analysis of how much "extra" fuel remained on board the telescope. Roughly speaking, Menzel said, Webb has enough propellant on board for 20 years of life.

This is twice the conservative pre-launch estimate for Webb's lifetime of a decade, and it largely comes down to the performance of the European Ariane 5 rocket that launched Webb on a precise trajectory on Christmas Day.

Prior to launch, the telescope was fueled with 240 liters of hydrazine fuel and dinitrogen tetroxide oxidizer. Some of this fuel was needed for course adjustments along the journey to the point in space, about 1.5 million km from Earth, where Webb will conduct science observations. The remainder will be used at Webb's final orbit around the L2 Lagrange point for station-keeping and to maintain its orbit.

So every kilogram of fuel saved on Webb's journey to the Lagrange point could be used to extend its life there. Because ten years seemed like a fairly short operational period for such an expensive and capable space telescope, NASA had already been contemplating a costly and risky robotic refueling mission. But now that should not be necessary, as Webb has at least two decades of life.

A lot of this comes down to the performance of the venerable Ariane 5 rocket. NASA and the European Space Agency reached an agreement more than a decade ago by which Europe would use its reliable Ariane 5 rocket to lift the telescope into space, and in exchange, European scientists would get time to use the telescope.

During an interview with The Interplanetary Podcast, Ariane 5 program manager Rudiger Albat explained how European rocket scientists approached the Webb launch. Each Ariane 5 vehicle is interchangeable, but engineers and technicians involved in the production of the rocket know which components are going on which rocket. So when they were building a part of Webb, an engineer might say, "I'll take a second look" to make sure the piece was the best it could be.

The Ariane 5 program also selected the best components for Webb based upon pre-flight testing. For example, for the Webb-designated rocket, the program used a main engine that had been especially precise during testing. "It was one of the best Vulcain engines that we've ever built," Albat said. "It has very precise performance. It would have been criminal not to do it."

A similar attitude was taken toward other components, including the solid rocket motors that were used to build the Ariane 5 that launched two weeks ago.

Albat admitted that the days prior to launch were exhausting and nerve-wracking. But soon after the launch, Albat said he and the entire European space community could take pride as Webb took flight and began to unfurl its wings. Now, he said, "I feel totally relaxed." The same can be said for a lot of scientists who have been watching Webb's development for two decades.

Quelle: arsTechnica

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Update: 16.01.2022

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What will the James Webb Space Telescope look at first?