Damage to the main mirror of the James Webb Telescope from a micrometeorite impact in May is worse than previously thought, according to new images revealed in a new report.
An article published Tuesday in the academic preprint server arxiv.org detailing Webb’s performance during the telescope’s start-up revealed that most micrometeorite impacts on Webb’s large mirror resulted in negligible damage, but one impact that occurred in mid-May even left the telescope with permanent damage.
“The single micrometeorite impact that occurred between May 22 and 24, 2022 UT exceeded pre-damage release expectations for a single micrometeorite, prompting further investigation and modeling by the JWST Project,” it reads in the report.
Unlike the Hubble Space Telescope, which encases the main mirror that the telescope uses to collect light and focus it on science instruments in a cylindrical housing, Webb’s 6.5-meter-diameter segmented mirror is exposed to space. But given Webb’s orbit Around Lagrange Point 2, or L2, a region of space about 1 million miles from Earth, scientists only expected Webb to find potentially dangerous micrometeorites once a month.
During the start-up period from late January through June, while ground controllers calibrated, aligned, and tested Webb’s mirrors and instruments, the primary mirror suffered a total of six micrometeorite impacts.
Of those hits, five did little damage, causing less than 1 nanometer of root mean square (RMS) wavefront error, a technical way of describing how much Webb’s mirror distorts the starlight the mirror collects. Most of the distortion added by those five bumps can be corrected out of the mirror, as the 18 hexagonal segments that make up its face can be individually and precisely adjusted.
But the sixth hit, hitting a mirror segment labeled C3, caused more damage than can be fully corrected. That micrometeorite impact raised the segment wavefront error from 56 nanometers to 178 nanometers after correction by segment adjustment.
However, because each mirror segment is adjustable, the damage to the C3 segment could be compensated for and did not compromise the resolution of Webb’s main mirror as a whole, according to the report. The total wavefront error for the entire mirror increased by about 9 nanometers due to the impact.
“It is not yet clear whether the May 2022 impact on segment C3 was a rare event (i.e., an unfortunate early impact of a high-kinetic-energy micrometeoroid that could statistically occur only once in several years),” the report read. report, “or whether the telescope may be more susceptible to micrometeoroid damage than the pre-launch model predicted.”
The report goes on to note that the Webb project team is considering actions to mitigate future micrometeorite impacts, such as limiting how long the telescope can be pointed in known directions to expose the mirror to a higher probability of micrometeorite impacts.
Preserving the long-term health of the Webb telescope is a high priority for POT and astronomers everywhere.
After more than 20 years and $10 billion spent on development, the space telescope launched on an Ariane 5 rocket on Christmas Day. That launch was more precise than expected, saving Webb a considerable amount of propellant that he would have used to correct his course after launch and nearly doubling the observatory’s projected operational lifespan, provided space rocks don’t mess up its optics. .
“Prior to launch, the JWST was required to carry propellant for at least 10.5 years of mission life,” the report reads. “Now that JWST is in orbit around L2, it is clear that the remaining booster will last more than 20 years of mission life.”
