Webb Telescope deployments wrap up as side mirrors fall into place
A pallet containing three of the 18 hexagonal mirror segments from the James Webb Space Telescope rotated into position and locked in place on Saturday, filling the observatory’s 21.3-foot-wide primary mirror to wrap up the most complicated set of deployments spacecraft never attempted.
Fourteen days after launch on Christmas Day and now 665,000 miles from Earth, the right “wing” of Webb’s iconic segmented mirror fell into place at 10:28 a.m. EST, eliciting cheers and applause from enthusiastic scientists and engineers of the Baltimore Institute of Science space telescope.
“We now have a fully deployed telescope,” an engineer calmly reported to the team.
It took several hours to finish locking the pallet in place, which was completed just before 2 p.m.
Considering the need to successfully deploy Webb’s fragile tennis court-sized sunshade and the precision required to deploy its optical components, heaters and other critical equipment, “that has arguably been the program. most difficult deployment ever made by NASA, ”said the systems engineer. Mike Menzel.
The heads of mission were delighted with the results.
“I just want to thank everyone, congratulate them on a safe mirror move,” project manager Bill Ochs told the operations team. “The past two weeks have been totally amazing. Thousands of people have worked on JWST to this point to bring us here.… Every day I am honored and humbled to be associated with this team.”
At a cost of nearly $ 10 billion, Webb is the most expensive science spacecraft ever built and by far the most powerful space telescope, 100 times more sensitive than the 31-year-old Hubble, the observatory he will eventually replace.
It is also one of the most difficult to deploy, with success relying on the flawless functioning of 178 trigger mechanisms which all had to work perfectly to complete 50 major deployments to unfold the telescope after it was packed in. the nose cone of a European Space Agency. -supplied Ariane 5 rocket.
En route to orbit the sun a million miles from Earth, Webb is already well beyond the reach of any predictable astronaut repair crew. His complex, multi-step metamorphosis, requiring all of these non-redundant mechanisms to work exactly as intended, just had to work.
And he did.
“I’m moved about it,” said NASA chief scientist Thomas Zurbuchen. “What an incredible milestone. One hundred and seventy-eight out of 178 of those actuators that must have tripped the right way, I’m so amazed and impressed with this team.”
Next, for Webb, now that his structural deployments are complete: precisely aligning the 18 segments of his main mirror to achieve extremely sharp focus. At the same time, its scientific instruments need to be checked and calibrated, while waiting for the telescope to cool down to near absolute zero.
The first scientific images are expected in about six months.
“We start with the mirrors offset by a few millimeters, and we lead them to be aligned to less than the size of a coronavirus, like tens of nanometers,” said Jane Rigby, scientist for the Webb Operations project. “It’s this very deliberate process that takes time.”
Rather than showing initially blurry “first light” images over the next few weeks, “we want to make sure that the first images the world sees … do this $ 10 billion telescope justice,” she said. declared. “So we are planning a series of ‘wow’ images to be released at the end of commissioning.”
Since its launch on December 25, Webb has successfully deployed its critical solar panel, the high gain antenna that it will use to send data back to Earth, a stabilizing “pulse flap” to counter the effects of the solar wind. and radiators to dissipate excess heat.
But radiators alone were not enough.
Webb was designed to capture light from the first stars and galaxies to form after the Big Bang, radiation that was extended into the infrared region of the spectrum by the expansion of space itself over the course of 13.8 billion years.
To register this low heat, Webb must be cooled to less than 50 degrees absolute zero, or to about 370 degrees below zero Fahrenheit.
In the riskiest deployment procedure of all, two unfolded paddles and five layers of hair-thin Kapton were removed to form a tennis court-sized sun visor using 90 motorized cables running through by dozens of pulleys.
As the layers were slowly stretched, they were lifted and pulled apart to create a space between each one, allowing the heat to reflect off the sides. As the layer facing the sun will experience temperatures of up to 290 degrees, the telescope will be cooled to unprecedented levels to record infrared light from early galaxies.
Halfway through the sunshade deployment, a tower was extended, elevating the main mirror and instruments 4 feet above the shield to provide space for membrane tension and to further remove the optics from the shield. heat generated by the electronic equipment of the spacecraft.
After the sunshade deployment was complete, engineers sent out commands to deploy Webb’s 2.4-foot-wide secondary mirror on top of an articulated tripod consisting of three 25-foot-long arrows. An instrument heater was then deployed to help dissipate the heat generated by Webb’s science instruments.
This set the stage for the last two deployments of the telescope’s initial commissioning.
Webb’s segmented primary mirror was too large to fit into the nose cone of an existing rocket. Thus, six of its 18 segments, three on each side, were folded onto hinged pallets. The left pallet was rotated into position on Friday and the right pallet followed suit on Saturday.
“This is an important step to complete all deployments,” said Greg Robinson, Webb mission director. “We still have a long way to go, but it’s certainly great to have this part behind us.”
Once the deployments are complete, flight controllers will now begin work to precisely align the 18 segments so that they act as a single 21.3-foot-wide mirror.
Each segment has six mechanical actuators allowing movement in six directions. A seventh actuator can push or pull on the center of a segment to slightly deform its shape if necessary.
Before alignment, the 18 segments will produce 18 distinct images. Using Webb’s infrared camera, engineers will map the alignment of each segment and send commands to adjust orientation and curvature as needed to produce a single, crisp image. The process should take several months.
“This telescope is not ready for use,” said Rigby. “The first few pictures are going to be ugly. It’s going to be blurry, 18 of these little pictures all over the sky.… It’s like we have 18 mirrors that are little prima donnas right now, all doing their own thing. . and we have to make them work as a choir. It’s a methodical and painstaking process. “
But at the end of commissioning in about six months, images will be unveiled “which are designed to show what this telescope can do and … really wow everyone.”
Webb was designed to operate for five to 10 years, a lifespan based on the amount of propellant available on board to maintain the telescope’s orientation. But thanks to the precision of its launch and two subsequent course correction maneuvers, Menzel said it should be able to operate for around 20 years.