The telescope has been struck at least five times by small objects, with one strike by an object that was larger than what pre-launch models suggested.
One of the primary mirror segments had a noticeable effect on the mirror segment's performance between May 23 and May 25. Despite a slight effect in the data, the telescope is still performing at a level that surpasses all mission requirements.
Lee Feinberg, the manager of the optical telescope element at NASA, said that they expected the occasional impacts to degrade the telescope performance. Since launch, we have had four smaller measurable micrometeoroid strikes that were consistent with expectations, and this one more recently that is larger than we assumed. We will use this flight data to update our analysis of performance over time and also develop operational approaches to assure we maximize the image performance of Webb for many years to come.
The team said that the most recent hit was not caused by a shower, but an unavoidable chance event. The size of the object is not known according to Mark McCaughrean, the European Space Agency's senior advisor for science and exploration. It is hard to know the size without knowing the speed. Small bits of dust are not rocks.
The telescope team has known for a long time that there will be meteorite impacts in space. Feinberg said that webb will be hit by many different sizes with a 25 square meter primary mirror and large sun shield. We built it with large margins.
The mirror segments were designed to resist bombardment from the known micrometeoroid environment. Engineers used simulations and test impacts on mirror samples to figure out how to fortify the observatory for operation in space.
One thing other space telescopes don't have is the ability to adjust the mirror segments. With the ability to sense and adjust mirror positions, partial correction can be achieved.
The position of the affected segment can be adjusted to cancel out some of the distortion. Not all of the degradation can be canceled out this way. Engineers have already done a first mirror adjustment for segment C3 and more will be done in the near future. As part of the monitoring and maintenance of the telescope throughout the mission, these steps will be repeated when necessary.
The flight team has the ability to perform maneuvers that will keep the meteorites away from the eye. As a result of this impact, a specialized team of engineers has been formed to look at ways to mitigate the effects. Over time, the team will be able to better predict such impacts and how they will affect the telescope's performance, as well as getting a handle on the dust particle environment at L2. They are working with experts at NASA.
As an outside observer, it's hard to see how frequently JWST will be impacted. After all the worries about the telescope's launch, and all the delicate operations that had to go perfectly for the telescope's deployment and alignment, it hits home. The observatory is capable of performing the science it was designed to achieve, as the team reassured. The first observational images are due to be released in July.
The first fully functional telescope will be commissioned before the end of the year. When each mode has been verified, you can follow along at NASA's deployment explorer website. The order in which the modes are being commissioned is not available, but the team at the Association of Universities for Research in Astronomy has put together a JWST Bingo sheet to see all the steps required
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