|The James Webb teams have successfully aligned their mirrors, and commissioning is continuing|
James Webb teams mirror aligned successfully, commissioning continues
After a historic launch in December 2021 and an incredible arrival at Lagrange Point 2 (L2) in January, James Webb Space Telescope teams have worked hard to prepare the telescope for its first observations this summer. On March 16, NASA announced that one of the most important steps in the commissioning process had been completed – the alignment of all 18 individual mirrors on James Webb’s primary mirror.
Meanwhile, as the optics team was working on aligning the mirrors, instrument teams began to bring the instruments online as James Webb’s temperature continues to drop to expected operating levels.
“We’ve perfectly aligned and focused the telescope on a star, and the performance is beating specifications. We’re excited about what this means for science. Now we know we’ve built the right telescope, Said Ritva Kesky-Kuha, James Webb’s deputy optical telescope element manager at NASA’s Goddard Space Flight Center.
James Webb’s massive 6.5-meter primary mirror is the largest mirror ever flown in space, and thus makes it one of the most complex – if not the most complex – ever flown. Since its launch in late December, optics teams have been working round the clock to align not only the primary mirror, but other optics systems at the observatory as well.
Due to the sheer size of James Webb’s mirror, it could not be sent into fully positioned space. In order to fit inside the fairing of the Ariane 5 rocket, the mirrors had to be folded inward on the observatory’s port and starboard side, forming “wings”. Once in space and en route to L2, the James Webb teams successfully unfold these “wings”, bringing the iconic primary mirror to its final form.
James Webb’s primary mirror consists of 18 individual hexagonal mirror segments, each covered with beryllium and gold. Each mirror segment is connected to a small motor, allowing the optics team to precisely align each mirror in nanometer increments and “focus” the entire primary mirror.
This fine process of moving each mirror segment to align the primary mirror is what James Webb’s optics team has been working on throughout the commissioning process so far.
On March 11, the optics teams successfully completed one of the final procedures required for alignment. This step is called “fine phasing”. With fine phasing complete, every optical system at James Web that has been tested and tested should operate at or above their expectations. Fortunately, the optics team found no major problems with the mirror and confirmed that there was no contamination or blockage in any of the observatory’s optical systems.
With fine phasing complete and the primary mirror aligned, the team took an image of the star 2MASS J17554042+6551277 using the NIRCam (Near-Infrared Camera) instrument and a red filter to optimize visual contrast. The purpose of the image is to confirm that the light collected by the mirror is being transferred correctly to the observatory’s instruments.
The successful alignment and focus of the primary mirror comes after weeks of work by the optics team to align the image. After the wings of the primary mirror were folded, the teams first had to confirm that each of the motors attached to the 18 mirror segments were working. After confirming that each mirror segment could be moved, the teams began a three-month process of aligning the mirror segments with each other.
The teams began the alignment process by pointing James Webb at a star and aligning each individual mirror at it. Additionally, the teams aligned the mirrors to the shape of the primary mirror. The image used to confirm this work showed 18 separate images of the same star, all 18 images aligned to the shape of the primary mirror.
Once each mirror was aligned with the star, the optics teams focused the star in each mirror using a secondary mirror located on the end of the Secondary Mirror Support Structure (SMSS) tripod. After the mirror segments were focused, the image of each segment was stacked on top of the other, creating the image of only one star.
After the stack of images was completed in late February, the teams worked to fine-tune the image and make it progressively sharper. Once completed, the last step by step process above took place.
Although the mirrors and equipment are perfectly aligned, several steps still need to be completed before James Webb’s all-optical system is fully operational. These final steps are scheduled to be completed over the next six weeks and include aligning the observatory with NIRSPC (Near-Infrared Spectrograph), MIRI (Mid-Infrared Instrument), and FGS/NIRISS (Fine Guidance). The working optics team will be involved. sensor/near infrared imager and slitless spectrograph) equipment. Currently, Webb is only aligned with NIRCam (Near-Infrared Camera) equipment.
While the observatory is being aligned with other instruments, teams will evaluate the performance of each instrument, which will then allow the instrument and optics teams to decide on final improvements that need to be made before the mirror alignment process is completed. the wanted. The final step in the alignment process will be followed by improvements made to the equipment, with the Web team adjusting any errors in the positioning of the mirrors.
Currently, James Webb teams are on track to finish the mirror alignment process in early May, if not sooner. Once mirror alignment is complete, instrument teams will take two months to prepare their respective instruments for science operations, which are set to begin this summer.
All four of James Webb’s instruments were operated successfully in late January, and are being tested and tested by instrument teams to confirm that they are working properly at L2 after launch.
However, James Webb is still cooling down to its operating temperature, which is about six Kelvin. Some instruments, notably the MIRI instrument, require the observatory to be at a certain temperature to operate, so Webb teams will need to continue to watch the observatory’s temperature to make sure the cooling system is working properly.