New images revealed in a new report show that the damage to the main mirror of the James Webb Telescope from a small meteor strike in May is worse than initially thought.
Paper published on Tuesday Academic Prepress Server arxiv.org He revealed in detail about Webb’s performance while the telescope was operating that most of the micro-meteorite strikes on the large Webb mirror caused minor damage, but the strike in mid-May left the telescope with permanent damage.
“The impact of a single minor meteorite that occurred from May 22-24, 2022 UT exceeded previous staging predictions for damage caused by a single minor meteorite leading to further investigation and modeling by the JWST Project,” the report states.
Unlike the Hubble Space Telescope, which encloses the primary mirror the telescope uses to collect light and focus light on scientific instruments in a cylindrical shell, the Webb’s 6.5-meter split mirror is space-exposed. But looking at Webb’s orbit around Lagrange Point 2, or L2, a region of space about a million miles from Earth, scientists only expected Webb to encounter a small, potentially dangerous meteor once a month.
During the commissioning period from late January to June, during which ground controllers calibrated, aligned, and tested Webb’s mirrors and instruments, the primary mirror was subjected to six precise meteor strikes.
Of those, five did little damage, causing less than 1 nm of root mean square (RMS) wavefront error, which is a technical way of describing how much a Webb mirror distorts the starlight the mirror collects. Most of the distortion added by those five strokes outside the mirror can be corrected, as the 18 hex segments that make up its face can be adjusted individually and precisely.
But the sixth hit, hitting a mirror clip called C3, did more damage that could be fully rectified. This micro-meteor strike raised the wavefront error of the sector from 56 nm to 178 nm after correction by modulating the section.
Since each mirror clip is adjustable, the damage to the C3 segment can be compensated and did not affect the accuracy of the underlying Webb mirror as a whole, according to the report. The overall wavefront error of the whole mirror increased by about 9 nm due to the hit.
“It is not yet clear whether the May 2022 hit of Section C3 is a rare event (i.e. an early unlucky strike by a small, high-kinetic meteor that may statistically occur only once every several years),” the report reads. The telescope is more susceptible to damage by micrometeorites than previous launch modeling.”
The report goes on to note that the Webb project team is considering measures to mitigate future micrometeorite strikes, such as determining how long the telescope can be pointed in known directions to expose the mirror to a greater likelihood of micrometeorite strikes.
Maintaining the long-term health of the Webb Telescope is a top priority for NASA and astronomers everywhere.
After more than 20 years and $10 billion in development, the space telescope was launched atop an Ariane 5 rocket on Christmas Day. This launch was more accurate than expected, providing ample motivation for Webb that he would use to correct its trajectory after launch, and nearly doubled the observatory’s expected operational life—as long as space rocks didn’t spoil its optics.
“Before launch, the JWST was required to carry a thruster for a minimum of 10.5 years of mission life,” the report read. “Now that JWST is in orbit around L2, it’s clear that the remaining propellant will last more than 20 years of the mission’s life.”
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