A small space pebble has had a large impact on NASA’s newly operating deep-space telescope. Between May 22 and 24, a micrometeoroid damaged the James Webb Space Telescope, damaging one of the observatory’s 18 hexagonal golden mirrors. NASA announced the micrometeoroid strike in June, stating that the debris was larger than pre-launch modeling had predicted. In a report released on July 12 explaining what scientists on the project learned about operating the observatory during its first six months in space, experts on the expedition have shared an image that emphasizes the gravity of the blow.
Fortunately, the total impact on Webb was minimal in this situation. Nonetheless, the study details the research and modeling that engineers are conducting to examine the long-term impacts of micrometeroids on Webb. Based on fuel consumption, the telescope should last in orbit for 20 years. But scientists aren’t sure how much of an effect micrometeroid strikes will have upon its operations, the report authors stated.
Micrometeroids are a well-known risk to space operations, and scientists are used to dealing with them; the International Space Station and the Hubble Space Telescope are two long-running missions that continue to operate despite periodic space rock attacks. However, Webb’s orbit at Lagrange Point 2 about 1 million miles (1.5 million kilometers) away from the Earth may change the risk profile considerably.
NASA is unsure how much of an effect space rock will have on Webb’s lifetime after the event ‘exceeded pre-launch expectations of damage.’
During the commissioning process, Webb engineers first observed deformations on the primary mirror during the alignment (or wavefront sensing) phase, which put the hexagonal mirror’s 18 segments in the ideal position to gather light.
According to the research, the first six strikes met pre-launch rate projections, coming in at a rate of once per month. Furthermore, some of the ensuing deformations can be corrected by mirror realignments. The size of one of these six strikes, however, prompted the most anxiety, according to the paper, as it produced a substantial imperfection to a piece designated as C3. According to the report, the strike in late May “generated a significant uncorrectable change in the total number of that section.”
In this case, however, the overall impact to the mission is small “because only a small portion of the telescope area was affected.” Seventeen mirror segments remain unblemished and engineers were able to realign Webb’s segments to account for most of the damage.
Engineers are still modeling how frequently such events will occur. “It is not yet clear whether the May 2022 hit to segment C3 was a rare event,” the team wrote. By “rare,” they said it is possible that they happened to get a high-energy impact that should statistically happen only once every few years.
Alternatively, it may be that Webb is “more susceptible to damage by micrometeoroids than pre-launch modeling predicted,” the team wrote. Modeling is ongoing to estimate the hazardous population of micrometeoroids and to figure out remedies, such as restricting pointing direction.
One remedy could be minimizing the amount of time Webb points directly into its orbital direction, “which statistically has higher micrometeoroid rates and energies,” the team wrote.
Main mirror performance is assessed by how much it deforms starlight, according to Astronomy magazine(opens in new tab), and measured using what scientists 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 17 other mirror portions.
Post-impact, however, the error increased to 258 nm rms, but realignments to the mirror segments as a whole reduced the overall impact to just 59 nm rms. For the time being, the team wrote Webb’s alignment is well within performance limits, as the realigned mirror segments are “about 5-10 nm rms above the previous best wavefront error rms values.”
For the time being, engineers are focusing on probable future dust-generating events, such as those in 2023 and 2024, when Webb is scheduled to fly over particles left behind by Halley’s Comet, according to Nature.
The impact danger associated with Halley is being modeled by NASA’s meteoroid environment office at the Marshall Space Flight Center in Huntsville, Alabama. NASA officials have also stated in recent media briefings that the micrometeoroid issue has their complete attention, according to Nature.
