However, because spacecraft lack a protective bubble of atmosphere, it is nearly impossible to avoid these hits.
The team is continuing to analyze and assess what happened and how it may affect the telescope’s performance. It’s also likely the first of many such experiences that Webb will have over its time in space.
When the telescope and its massive mirror were being built and tested on Earth, engineers made sure that the mirror could survive the micrometeoroid environment the spacecraft would experience in its orbit about a million miles from Earth at a point called L2, where dust particles are accelerated to extreme velocities.
Preparing for impact
A micrometeoroid is a space particle no larger than a grain of sand. According to NASA, millions of meteoroids and micrometeoroids hit the Earth’s atmosphere on a regular basis, however the majority of them are incinerated.
The Webb telescope sustained such an impact between May 23 and 25, but “the telescope is still performing at a level that exceeds all mission requirements despite a marginally detectable effect in the data,” according to the Webb team.
Webb was put through its paces while on Earth, and the team used both simulations and test impacts on mirror samples to understand what it would face.
The May impact event was larger than anything the team tested or would have been able to model while Webb was still on the ground.
“We always knew that Webb would have to weather the space environment, which includes harsh ultraviolet light and charged particles from the Sun, cosmic rays from exotic sources in the galaxy, and occasional strikes by micrometeoroids within our solar system,” said Paul Geithner, technical deputy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement. “We designed and built Webb with performance margin — optical, thermal, electrical, mechanical — to ensure it can perform its ambitious science mission even after many years in space.”
Fortunately, each hexagonal mirror segment is fully adjustable, and the impacted segment has already been adjusted to lessen some of the distortion. This is something engineers can continue to do in the future as they monitor Webb’s mirror for any signs of degradation in the space environment. Webb’s flight team already turns the spacecraft’s mirror away from known events, like meteor showers, to protect the telescope’s optics. But this impact, which wasn’t part of a meteor shower, was unforeseen and “an unavoidable chance event,” according to NASA.
“As a result of this impact, a specialized team of engineers has been formed to look at ways to mitigate the effects of further micrometeoroid hits of this scale,” according to a release from the agency. Looking ahead
“Since launch, we have had four smaller measurable micrometeoroid strikes that were consistent with expectations and this one more recently that is larger than our degradation predictions 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 imaging performance of Webb to the best extent possible for many years to come.” Webb has already exceeded expectations since launching in December, and the telescope is preparing for the beginning of science operations.
“With Webb’s mirrors exposed to space, we expected that occasional micrometeoroid impacts would gracefully degrade telescope performance over time,” said Lee Feinberg, Webb optical telescope element manager at NASA Goddard, in a statement. The Webb team will work closely with micrometeoroid prediction experts at NASA’s Marshall Space Flight Center in Huntsville, Alabama. And Webb will be able to help NASA scientists learn more about the dust environment of the solar system at this orbit point, which can assist with preparing for future missions.