The May micrometeoroid impact on Webb’s mirror
In a detailed report [pdf] of Webb’s overall excellent operational status following its in-space commissioning, the science team also included an analysis of the May 2022 micrometeoriod impact on one segment of Webb’s mirror.
The image to the right, taken from figure 3 of the report, shows the remaining alignment error of Webb’s entire mirror, after alignment. Except for that one bright spot in the segment to the lower right, all of the segments show excellent alignment, well within the range predicted before launch. The bright spot however is from the impact, and suggests that one mirror segment is significantly damaged. From the report:
The micrometeoroid which hit segment C3 in the period 22—24 May 2022 UT caused significant uncorrectable change in the overall figure of that segment. However, 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 values 7 . It should be noted that the drifts and stability levels of the telescope mean that science observations will typically see telescope contribution between 60 nm rms (minimum) and 80 nm rms (where WF control will typically be performed). Further, the telescope WFE combines with the science instrument WFE to yield total observatory levels in the range 70-130 nm (see Table 2), so the slight increase to telescope WFE from this strike has a relatively smaller effect on total observatory WFE.
In plain English, the impact while damaging has not seriously reduced the telescope’s predicted capabilities.
However, to be hit with this size impact so soon after launch is very worrisome, especially because Webb’s mirror is not housed in any protective tube like Hubble or most telescopes. From the report:
It is not yet clear whether the May 2022 hit to segment C3 was a rare event (i.e. an unlucky early strike by a high kinetic energy micrometeoroid that statistically might occur only once in several years), or whether the telescope may be more susceptible to damage by micrometeoroids than pre-launch modeling predicted.
The science team is presently trying to anticipate what might happen if the impact rate turns out to be much higher than expected, and what can be done to mitigate the degradation of the mirror should more impacts occur.
In a detailed report [pdf] of Webb’s overall excellent operational status following its in-space commissioning, the science team also included an analysis of the May 2022 micrometeoriod impact on one segment of Webb’s mirror.
The image to the right, taken from figure 3 of the report, shows the remaining alignment error of Webb’s entire mirror, after alignment. Except for that one bright spot in the segment to the lower right, all of the segments show excellent alignment, well within the range predicted before launch. The bright spot however is from the impact, and suggests that one mirror segment is significantly damaged. From the report:
The micrometeoroid which hit segment C3 in the period 22—24 May 2022 UT caused significant uncorrectable change in the overall figure of that segment. However, 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 values 7 . It should be noted that the drifts and stability levels of the telescope mean that science observations will typically see telescope contribution between 60 nm rms (minimum) and 80 nm rms (where WF control will typically be performed). Further, the telescope WFE combines with the science instrument WFE to yield total observatory levels in the range 70-130 nm (see Table 2), so the slight increase to telescope WFE from this strike has a relatively smaller effect on total observatory WFE.
In plain English, the impact while damaging has not seriously reduced the telescope’s predicted capabilities.
However, to be hit with this size impact so soon after launch is very worrisome, especially because Webb’s mirror is not housed in any protective tube like Hubble or most telescopes. From the report:
It is not yet clear whether the May 2022 hit to segment C3 was a rare event (i.e. an unlucky early strike by a high kinetic energy micrometeoroid that statistically might occur only once in several years), or whether the telescope may be more susceptible to damage by micrometeoroids than pre-launch modeling predicted.
The science team is presently trying to anticipate what might happen if the impact rate turns out to be much higher than expected, and what can be done to mitigate the degradation of the mirror should more impacts occur.