Damage The James Webb Telescope’s primary mirror from a micrometeorite impact in May is worse than first thought, according to new images emerging in a new report.
An article published on Tuesday arxiv.org academic print server Details of Webb’s performance during the telescope’s commissioning revealed that most micrometeorite impacts on Webb’s large mirror resulted in minor damage, but an impact in mid-May even left the telescope with permanent damage.
“The single micrometeorite impact that occurred between May 22 and 24, 2022 exceeded pre-launch expectations of damage for a single micrometeoroid, prompting further investigation and modeling by the JWST Project,” he said.
Unlike the Hubble Space Telescope, which includes a primary mirror that the telescope uses to collect light and focus light onto science instruments in a cylindrical housing, Webb’s 6.5-meter-diameter segmented mirror is exposed to space. But given by Webb orbit Around Lagrangian point 2, or L2, a region of space about 1 million miles from Earth, scientists expected Webb to encounter potentially dangerous micrometeorites only once a month.
During the commissioning period from late January to June, the primary mirror sustained six total micrometeorite impacts as ground controllers calibrated, aligned and tested Webb’s mirrors and instruments.
Five of those impacts did little damage, causing a root-mean-square (RMS) wavefront error of less than 1 nanometer, a technical way of describing how much the Webb mirror distorts the starlight it collects from the mirror. Most of the distortion added by these five strokes can be corrected outside the mirror, as the 18 hexagonal segments that make up its face can be individually and finely adjusted.
But the sixth impact, which hit the mirror segment labeled C3, caused more damage that was fully repairable. That micrometeorite impact adjusted the segment, increasing the segment’s wavefront error from 56 nanometers to 178 nanometers after correction.
According to the report, since each mirror segment is adjustable, damage to the C3 segment can be compensated and does not compromise the resolution of Webb’s primary mirror as a whole. Due to the shock, the total wavefront error for the entire mirror increased by about 9 nanometers.
“It is not yet clear whether the May 2022 C3 segment impact was a rare event (that is, an unfortunate early impact by a high-kinetic-energy micrometeoroid that occurs statistically only once every few years)” or whether the telescope predicted before its launch. may be more sensitive to micrometeoroid damage than modeling.
The report notes that the Webb project team is considering actions to mitigate future micrometeorite impacts, such as limiting the telescope’s mirror orientation in directions known to expose it to a higher probability of micrometeorite impacts.
Preserving the long-term health of the Webb telescope is a high priority NASA and astronomers everywhere.
After more than 20 years and $10 billion in development, the space telescope launched on an Ariane 5 rocket on Christmas Day. The launch was more accurate than expected, saving Webb a significant amount of fuel that would have been used to correct its course after launch, and almost doubling the observatory’s projected lifetime — as long as space rocks don’t damage its optics.
“Prior to launch, JWST was required to carry fuel for at least 10.5 years of mission life,” the report said. “Now that JWST is in orbit around L2, it is clear that the remaining fuel will last more than 20 years over the life of the mission.”
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