A small space rock has been shown to have a large effect on NASA’s newly operational deep space telescope.
A micrometroid hit the James Webb Space Telescope between May 22 and 24, impacting one of the observatory’s 18 hexagonal gold mirrors. NASA revealed the micrometeoroid attack in June and noted that the debris was more important than the pre-launch model had assumed. Now, mission scientists have shared an image showing the severity of the blow in a report (opens a new tab) posted on July 12 that describes what mission scientists learned about using the observatory during his 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 that engineers are conducting to assess the long-term effects of micrometeroids on Webb.
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Depending on fuel consumption, the telescope should last 20 years in space. But scientists are unsure of the effect micrometeroid blows will have on their operations, the report’s authors said.
Micrometroids are a known danger of space operations, and tackling them is not at all new to scientists; the International Space Station and the Hubble Space Telescope are among the long-running programs that are still operational despite occasional space rock accidents. However, Webb’s orbit at Lagrange 2 point one million miles (1.5 million kilometers) away from Earth can change the risk profile considerably.
Webb engineers first detected deformations in the primary mirror during the start-up period during the alignment phase (or wavefront detection), which put the 18 segments of the hexagonal mirror in the best position for capture light.
These first six strikes met pre-launch speed expectations as they reached a rate of once a month, according to the report. In addition, some of the resulting deformations are correctable by mirror realignments. But it is the magnitude of one of these six attacks that caused the most concern, the document noted, as it caused a major stain in a segment known as C3. The strike in late May “caused a significant incorrigible change in the overall figure for this segment,” the report states.
In this case, however, the overall impact on the mission is small “because only a small part of the telescope’s area was affected.” Seventeen mirror segments remain spotless and engineers were able to realign Webb segments to account for most of the damage.
Jupiter and its moon Europa, on the 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 these events will occur. “It is still unclear whether the May 2022 coup in the C3 segment was a rare event,” the team wrote. For “rare,” they said they may have a high-energy impact that statistically should 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 underway to estimate the dangerous micrometeoroid population and find remedies, such as restricting the target direction.
One remedy could be to minimize the amount of time Webb points directly at its orbital direction, “which statistically has higher micrometeoroid rates and energies,” the team wrote.
The performance of the main mirror is evaluated by how much it deforms starlight, according to Astronomy magazine (opens in a new tab) and is measured using what scientists call the average square root of wavefront error . When Webb’s mission began, the affected C3 segment had a wavefront error of 56 nanometers rms (average square root), which was in line with the other 17 parts of the mirror.
After impact, however, the error increased to 258 nm rms, but realignments of the mirror segments as a whole reduced the overall impact to only 59 nm rms. For now, the team wrote that Webb’s alignment is within performance limits, as the realigned mirror segments are “about 5-10 nm rms above the best rms values of front-end error.” previous wave “.
For now, engineers are watching for possible future dust-generating events, such as 2023 and 2024, when Webb is expected to fly through particles left by Comet Halley, according to Nature (opens in a new tab ).
NASA’s meteorological environment office at the Marshall Space Flight Center in Huntsville, Alabama is modeling the impact risk for Halb-associated Webb. NASA officials have also stressed during recent media conferences that the micrometeroid problem has its full attention, Nature added.
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