Friday’s first images from the James Webb Space Telescope’s James Webb Space Telescope were revealed. A “selfie” of the observatory’s primary mirror measuring 21.3 feet wide and a mosaic showing multiple images a nondescript stars was used to align the 18 segments.
Although the images are blurry and misaligned might be disappointing to the uninitiated they are nearly exactly what engineers expected at this stage in the complex commissioning of the observatory, 48 days after its Christmas Day launch .
Lee Feinberg, manager of Webb optical elements, stated that “this amazing telescope has not just spread its wings but has also opened its eyes.”
NASA is currently aligning 18 hexagonal segments of Webb’s large main mirror. They are carefully setting the tilt of each segment in small increments to align multiple reflections of target star into one beam, similar to a one-piece mirror.
Feinberg stated that the tedious work so far has been remarkably smooth with no major setbacks or problems.
He said, “The only thing that I want to warn you about is that it’s still very young.” We don’t yet have detailed evaluations for everything. However, our initial evaluations show that everything matches the models exactly as we would expect them to at this point.
Webb spent the first three weeks of his life in space deploying its solar array, high-speed antenna and secondary mirror. Six of its 18 segments were removed for launch. Webb also extended a tennis court-size shade to block out the heat and light from the sun, Earth, and moon.
On January 25, Webb arrived at its operational destination , one month after launch. It orbited around Lagrange Point 2,, a million miles from Earth. From there, it will circle the sun in gravitational sync with Earth.
It went without a hitch. Engineers have been closely monitoring the telescope’s instruments and optics as they cool to ultra-low temperatures, near-absolute zero temperatures, in order to register faint light emitted by the first stars and galaxies that formed after the Big Bang.
Low temperatures are necessary because space has expanded over the 13.8 billion year period since the birth of the universe, extending that initial light into an infrared spectrum. Webb must be cooler than the environment to “see” these objects, which are so far away in time and space.
Mirror segments are still not at uniform temperatures. The segment temperatures varied from a “high”, of minus 349 Fahrenheit near the sunshade, to a “low” of minus 375 degrees further away. Engineers expect a temperature range of less than 10 degrees Fahrenheit after cooling is complete.
Ground controllers have pointed the telescope at HD 84406 (242 light years distant) in order to align the mirror segments. The team started mapping the reflections of each of the 18 primary mirror sections using one of Webb’s four instruments, the Near Infrared Camera or NIRCam.
Feinberg stated, “We pointed the telescope at an isolated bright star and found 18 spots that correspond to the 18 primary mirror segments.” “At this point we have been able analyze multiple engineering images which help us understand the mirror alignments.
“And we don’t see any concern. This is the first time that we have data on mirrors at zero gravity using starlight to illuminate their primary mirrors. Again, the data matches our expectations and models.
Marshall Perrin (Webb deputy telescope scientist) said that engineers had expected that the mirror segments would be misaligned by as much as a millimeter before the alignment process began. More than 1500 images were taken across a large area of the sky to ensure they found the target star within each segment.
It turned out that all 18 images were located within the first 10 percent of the search area. This indicates that the telescope launched with a good coarse alignment.
Perrin said, “That was just an amazing moment. There were lots of tears and excitement from everyone in the room.” “The mirrors were already aligned because we found them all so close together and in the same search area.
Marcia Rieke (principal investigator, University of Arizona, Tucson) said that NIRCam was a great success story.
She said, “My team has worked on NIRCam since over 20 years.” “And it was hard to describe the joy of finally seeing some light through the telescope onto NIRCam detectors.
“This place was a huge celebration because the light made it, and we were super happy. … We were able to capture beautiful images, or at least beautiful for someone who has worked with NIRCam long enough.
The segments will be aimed, checked, and re-aimed over the next few weeks in an iterative process. This will move the reflected beams towards the center of Webb’s optical axis. From there, they will be stacked or merged into one beam. This will give Webb’s science instruments precisely focused light.
In June, the first science images will be available.
The mirror segments, instruments, and detectors will continue cooling down in the meantime. The mirror’s average temperature will be about minus 370 degrees. Webb’s three near infrared instruments will reach 388 degrees below zero Fahrenheit when they are mounted behind the primary mirror.
The Mid-Infrared Instrument (or MIRI) is the fourth instrument. It must be colder than that to allow its detectors work as intended. The high-tech gaseous hydrogen refrigerator will cool it down to minus 447 degrees. This is just 7 degrees higher than absolute zero.
