NASA: Micrometeoroid Causes Significant Uncorrectable Damage To James Webb Space Telescope
SPACE - NASA has reported that Micrometeoroids have hit the new James Webb space telescope that was launched on December 25th, 2021, and caused "significant uncorrectable" damage to the C3 mirror, which is one of its 18 gold plated primary mirror panels.
The James Webb Telescope sensors have detected six deformations on the telescope's primary mirror panels that NASA says were caused by Micrometeoroid strikes. One such strike was reported to have occurred between May 22nd, 2022, and May 24th, 2022.
A least 19 micrometeoroids have hit the telescope, but one, in particular, caused noticeable damage to one of its gold-plated mirrors. The impact however does not seem to have damaged the telescope's ability to perform any of its tasks. Rather, the telescope is exceeding expectations "almost all across the board".
A micrometeoroid is a small particle of rock that usually does not weigh more than a gram and travels at high speeds through space. It is often confused with a micrometeorite, which is also a small particle of rock that, but one that has survived traveling through the earth's atmosphere and reached the surface.
A report released by three space agencies stated that "The effect was small at the full telescope level because only a small portion of the telescope area was affected. After two subsequent realignment steps, the telescope was aligned to a minimum of 59 nm RMS, which is about 5-10 nm RMS above the previous best wavefront error RMS value."
The report also said that "Each micrometeoroid caused degradation in the wavefront of the impacted mirror segment, as measured during regular wavefront sensing".
A report released by NASA on June 8th stated, "Micrometeoroid strikes are an unavoidable aspect of operating any spacecraft, which routinely sustain many impacts over the course of long and productive science missions in space. Between May 23 and 25, NASA’s James Webb Space Telescope sustained an impact to one of its primary mirror segments."
The report went on to say, "After initial assessments, the team found the telescope is still performing at a level that exceeds all mission requirements despite a marginally detectable effect in the data. Thorough analysis and measurements are ongoing.
Impacts will continue to occur throughout the entirety of Webb’s lifetime in space; such events were anticipated when building and testing the mirror on the ground. After a successful launch, deployment, and telescope alignment, Webb’s beginning-of-life performance is still well above expectations, and the observatory is fully capable of performing the science it was designed to achieve.
Webb’s mirror was engineered to withstand bombardment from the micrometeoroid environment at its orbit around Sun-Earth L2 of dust-sized particles flying at extreme velocities. While the telescope was being built, engineers used a mixture of simulations and actual test impacts on mirror samples to get a clearer idea of how to fortify the observatory for operation in orbit. This most recent impact was larger than was modeled, and beyond what the team could have tested on the ground.
"We always knew that Webb would have to weather the space environment, which includes harsh ultraviolet light and charged particles from the Sun, cosmic rays from exotic sources in the galaxy, and occasional strikes by micrometeoroids within our solar system," said Paul Geithner, technical deputy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. "We designed and built Webb with performance margin – optical, thermal, electrical, mechanical – to ensure it can perform its ambitious science mission even after many years in space." For example, due to careful work by the launch site teams, Webb’s optics were kept cleaner than required while on the ground; their pristine cleanliness improves the overall reflectivity and throughput, thereby improving total sensitivity. This and other performance margins make Webb’s science capabilities robust to potential degradations over time.
Furthermore, Webb’s capability to sense and adjust mirror positions enables partial correction for the result of impacts. By adjusting the position of the affected segment, engineers can cancel out a portion of the distortion. This minimizes the effect of any impact, although not all of the degradation can be canceled out this way. Engineers have already performed the first such adjustment for the recently affected segment C3, and additional planned mirror adjustments will continue to fine-tune this correction. These steps will be repeated when needed in response to future events as part of the monitoring and maintenance of the telescope throughout the mission.
To protect Webb in orbit, flight teams can use protective maneuvers that intentionally turn the optics away from known meteor showers before they are set to occur. This most recent hit was not a result of a meteor shower and is currently considered an unavoidable chance event. As a result of this impact, a specialized team of engineers has been formed to look at ways to mitigate the effects of further micrometeoroid hits of this scale. Over time, the team will collect invaluable data and work with micrometeoroid prediction experts at NASA’s Marshall Space Flight Center to be able to better predict how performance may change, bearing in mind that the telescope’s initial performance is better than expected. Webb’s tremendous size and sensitivity make it a highly sensitive detector of micrometeorites; over time Webb will help improve knowledge of the solar system dust particle environment at L2, for this and future missions.
“With Webb’s mirrors exposed to space, we expected that occasional micrometeoroid impacts would gracefully degrade telescope performance over time,” said Lee Feinberg, Webb's optical telescope element manager at NASA Goddard. “Since launch, we have had four smaller measurable micrometeoroid strikes that were consistent with expectations and this one more recently that is larger than our degradation predictions assumed. We will use this flight data to update our analysis of performance over time and also develop operational approaches to assure we maximize the imaging performance of Webb to the best extent possible for many years to come.”
This recent impact caused no change to Webb’s operations schedule, as the team continues to check out the science instruments’ observing modes and prepares for the release of Webb’s first images and the start of science operations." — Thaddeus Cesari, NASA Goddard.
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