by A small space rock has been shown to have a major impact on NASA’s recently operational space telescope.
A micrometeoroid hit the James Webb Space Telescope between May 22 and 24, and hit one of the observatory’s 18 hexagonal golden mirrors. NASA had uncovered the micrometeoroid attack in June and noted that the debris was larger than modeling before launch had accounted for. Now, researchers on the mission have shared a picture that shows the severity of the blow in a report (opens in new tab) published on July 12, which describes what scientists on the mission learned about the use of the observatory during the first six months of space.
Fortunately, the overall effect on Webb was small in this case. That said, the report outlines the survey and modeling that engineers are conducting to assess the long-term effects of micrometeroids on Webb.
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Based on fuel consumption, the telescope will last for 20 years in space. But researchers are not sure how much effect micrometeroid attacks will have on the operations, the report’s authors said.
Micrometeroids are a known danger to space operations, and meeting them is by no means new to scientists; the International Space Station and the Hubble Space Telescope are among long-standing programs that are still operational despite occasional space rocket attacks. However, Web’s orbit at Lagrange Point 2, approximately 1 million miles (1.5 million kilometers) away from Earth, can change the risk profile considerably.
Web engineers first discovered deformations on the primary mirror during the commissioning period during the alignment phase (or wavefront sensing), which put the 18 segments of the hexagonal mirror in the best position to capture light.
These first six strikes met expectations for speed before launch when they came in at a rate of once a month, the report said. In addition, some of the resulting deformations can be corrected through mirror adjustments. But it is the extent of one of these six strikes that caused more concern, the newspaper noted, as it caused a significant flaw in a segment known as C3. The strike at the end of May “caused a significant irreparable change in the total number for that segment,” 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 segments remain spotless and engineers were able to adjust Web segments to account for most of the damage.
Engineers continue to model how often such incidents will occur. “It is not yet clear whether the May 2022 hit to segment C3 was a rare occurrence,” the team wrote. By “rare” they said that it is possible that they happened to have a high-energy impact that statistically should only happen once every couple of years.
Alternatively, Webb may be “more prone to micrometeoroid damage than pre-launch modeling predicted,” the team wrote. Modeling is underway to estimate the dangerous population of micrometeoroids and find solutions, such as limiting the pointing direction.
One means could be to minimize the time Webb points directly into its orbit, “which statistically has higher micrometeoroid velocities and energies,” the team wrote.
The main mirror performance is assessed based on how much it deforms starlight, according to the magazine Astronomy (opens in new tab), and measured using what researchers call wavefront error root mean square. When Webb’s mission began, the affected C3 segment had a wavefront error of 56 nanometers rms (root mean square), which was in line with the other 17 mirror parts.
After shock, however, the error increased to 258 nm rms, but readjustments of the mirror segments as a whole reduced the overall effect to only 59 nm rms. So far, the team wrote that Web’s adjustment is well within the performance limits, as the readjusted mirror segments are “approximately 5-10 nm rms above the previous best rms values for wavefront errors.”
For now, engineers are keeping an eye on potential future dust-generating events such as in 2023 and 2024, when Webb is expected to fly through particles left by Halley’s comet, according to Nature (opens in new tab).
NASA’s meteoroid environmental office at the Marshall Space Flight Center in Huntsville, Alabama is modeling the impact impact of Webb associated with Halley. NASA officials have also stressed during recent media briefings that the micrometeroid problem has its full attention, Nature added.
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