A micrometeoroid struck the James Webb Space Telescope between May 22 and 24, impacting one of the observatory’s 18 hexagonal gold mirrors. NASA disclosed the micrometeoroid impact in June and noted that the debris was larger than pre-launch modeling had estimated. Now, scientists on the mission have shared an image showing the severity of the impact in a report (opens in a new tab) released July 12 that describes what scientists on the mission learned about using the observatory during its first six months in space. Fortunately, in this case the overall effect on Webb was small. That said, the report describes the research and modeling engineers are undertaking to assess the long-term effects of micrometeroids on Webb. Based on fuel usage, the telescope should last 20 years in space. But scientists aren’t sure how much of an effect the micrometer-sized bumps will have on its functions, the report’s authors said. Micrometroids are a known hazard of space operations, and dealing with them is nothing new to scientists. the International Space Station and the Hubble Space Telescope are among the long-running programs that continue to operate despite occasional space rock impacts. However, Webb’s orbit at Lagrange Point 2 about 1 million miles (1.5 million kilometers) from Earth may change the risk profile significantly. Webb engineers first detected distortions in the primary mirror during the start-up period during the alignment (or wavefront detection) phase, which put the 18 hexagonal mirror segments in the best position to capture light. Those first six strikes met pre-release rate expectations, coming in at a once-a-month pace, the report said. Additionally, some of the resulting distortions can be corrected through mirror rearrangements. But it’s the size of one of those six bumps that caused the most concern, the paper noted, as it caused a significant blemish in a section known as C3. The strike at the end of May “caused a significant non-corrective change in the overall numbers of this department,” the report said. In this case, however, the overall impact on the mission is small “because only a small part of the telescope area was affected.” Seventeen mirror sections remain intact, and engineers were able to realign Webb’s sections to account for most of the damage.
Jupiter and its moon Europa, left, are seen through the 2.12 micron filter of the James Webb Space Telescope’s NIRCam instrument. (Image credit: NASA, ESA, CSA and B. Holler and J. Stansberry (STScI)) Engineers are still modeling how often such events will occur. “It is not yet clear whether the May 2022 success in the C3 segment was a rare event,” the team wrote. “Rarely,” they said, they are likely to have a high-energy impact that should statistically only happen once every few years. Alternatively, Webb may be “more susceptible to micrometeoroid damage than pre-launch modeling predicted,” the team wrote. Modeling is ongoing to estimate the hazardous population of micrometeoroids and to find solutions such as limiting pointing direction. One solution could be to minimize the time that Webb points directly in its orbital direction, “which has statistically higher micrometeor rates and energies,” the team wrote. The primary mirror’s performance is rated by how much it distorts starlight, according to the journal Astronomy (opens in new tab), and is measured using what scientists call root-mean-square wavefront error. When Webb’s mission began, the affected C3 segment had a wavefront error of 56 nanometers rms (root mean square), which was consistent with the other 17 mirror segments. However, after impact, the error increased to 258 nm rms, but realignments to the mirror sections as a whole reduced the total impact to just 59 nm rms. For now, the team wrote, Webb’s alignment is well within the performance limits, as the aligned mirror sections are “about 5-10 nm rms above the previous best rms wavefront error values.” For now, engineers are keeping an eye on possible future dust-creating events, such as 2023 and 2024, when Webb is expected to fly through particles left behind by Halley’s Comet, according to Nature (opens in new tab). NASA’s Meteor Environment Office at Marshall Space Flight Center in Huntsville, Alabama is modeling the Webb impact risk associated with Halley. NASA officials also emphasized during recent media briefings that the matter of micrometroids has their full attention, Nature added. Follow Elizabeth Howell on Twitter @howellspace (opens in new tab). Follow us on Twitter @Spacedotcom (opens in new tab) and Facebook (opens in new tab).
