JWST entering the “final stretch” of start-up

WASHINGTON – The James Webb Space Telescope is operating better than expected as the spacecraft enters the final stages of commissioning, project officials said May 9.

In a call with reporters, scientists and mission managers said they have completed the alignment of the telescope’s optics with all of its instruments and are now preparing the instruments for science operations, the final step in a commissioning process. which began shortly after the installation of the telescope. release on Christmas Day last year.

“The performance is even better than we expected,” said Michael McElwain, project scientist for the JWST observatory at NASA’s Goddard Space Flight Center. “We have basically achieved a perfect alignment of the telescope. There are no adjustments to the telescope’s optics that would make material improvements to our scientific performance.”

When asked later to quantify that “better than expected” performance, he said that a parameter known as static wavefront error is “significantly better” than planned. “What that means is that we got the telescope mirrors into position more accurately and precisely than we had budgeted for, so we’re doing much better than the requirements.” That reduced error, she said, improved both the sensitivity and resolution of the instruments.

Marcia Rieke, principal investigator for one of JWST’s instruments, the Near Infrared Camera (NIRCam), said images taken by the instrument show that the telescope’s resolution is diffraction limited at key wavelengths, meaning that its images are as sharp as possible according to the laws of physics “It’s amazing that the image quality is so excellent, and that will help our science a lot,” he said.

With the telescope alignment complete, the project is moving into the final phases of commissioning, which includes preparing the instruments for science operations. “It’s time to do all the necessary checks and calibrations before starting the science,” McElwain said.

“I would also call this the home stretch,” he added. “We have planned about 1,000 activities for the entire launch, and there are only about 200 activities left to complete.”

That process will take about two months. The mission will wrap up that start-up with the public release of what it calls “early launch observations,” an initial set of images designed to showcase the telescope’s capabilities.

“Its goal is to demonstrate, at the end of the startup, to the world and to the public, that the Webb is fully operational and producing excellent results,” said Klaus Pontoppidan, JWST project scientist at the Space Telescope Science Institute. Formal science operations through an observations program called Cycle 1 will begin after the first observations are made public, which he said is tentatively scheduled for mid-July.

Those early launch observations will involve all four science instruments and cover a variety of objects. Pontoppidan said a committee developed a classified list of objects to include among early release observations, but he declined to say which objects are included in that list. One reason, he said, is that the selected objects could change depending on when observations can be scheduled. Plus, he added, “we’d really like to be a surprise.”

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