Micrometeoroid impacts are an unavoidable aspect of the life of any spacecraft, routinely sustaining many impacts over the course of long and productive scientific missions in space.
Between May 23 and 25, NASA’s James Webb Space Telescope suffered an impact on one of its primary mirror segments. After initial evaluations, the team found that the telescope still performs at a level that exceeds all mission requirements despite a minimally detectable effect on the data. Comprehensive analyzes and measurements are underway.
Impacts will continue to occur throughout Webb’s lifetime in space; such events were already anticipated by building and testing the mirror on the surface of our planet. After a successful launch, deployment, and alignment of the telescope, Webb’s initial performance is still well above expectations, and the observatory is fully capable of conducting the scientific research for which it was designed.
The Webb’s mirror was designed to resist the bombardment of micrometeoroids in its environment (in its L2 orbit, around the Sun-Earth), particles the size of dust that fly at extreme speeds. While the telescope was being built, engineers used a combination of simulations and actual test impacts on mirror samples to get a better idea of how to harden the observatory to work while in orbit. This most recent impact was larger than modeled and beyond what the team might have tested on the surface.
“We always knew that Webb would have to weather the space environment, which includes strong ultraviolet light, charged particles from the Sun, cosmic rays from exotic sources in the galaxy, and occasional impacts from micrometeoroids located within our solar system,” he said. Paul Geithner, deputy technical director for projects at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We designed and built the Webb with performance headroom (optical, thermal, electrical, mechanical) to ensure it can perform its ambitious science mission even following many years in space.” For example, due to the careful work of the launch site teams, Webb’s optics were kept cleaner than necessary while on the ground; its pristine cleanliness improves reflectivity and overall performance, thus improving overall sensitivity. This and other performance margins make Webb’s science capabilities robust once morest potential degradation over time.
In addition, the Webb’s ability to detect and adjust the positions of the mirrors allows partial correction of the impact result. By adjusting the position of the affected segment, engineers can cancel out some of the distortion. This minimizes the effect of any hits, although not all degradation can be canceled this way. Engineers have already made a first-of-its-kind adjustment for the recently affected C3 segment, and future planned mirror adjustments will continue to fine-tune this correction. These steps will be repeated as necessary in response to future events as part of monitoring and maintaining the telescope throughout the mission.
To protect Webb in orbit, flight crews can use protective maneuvers that intentionally move the optics away from known meteor showers before they occur. This most recent impact was not the result of a meteor shower and is currently considered an unavoidable chance event. As a result of this impact, a specialized team of engineers was assembled to look for ways to mitigate the effects of further micrometeorite impacts of this scale. Over time, the team will collect data and work with micrometeoroid prediction experts at NASA’s Marshall Space Flight Center to better predict how performance may vary, given that the telescope’s performance is better than initially expected. The tremendous size and sensitivity of the Webb make it a highly sensitive detector for micrometeoroids; Over time, Webb will help improve understanding of the solar system’s dust particle environment at L2 for this and future missions.
“With Webb’s mirrors exposed to space, we expected that occasional micrometeoroid impacts would degrade the telescope’s performance over time,” said Lee Feinberg, manager of optical elements for the Webb telescope at Goddard. “Since launch, we have measured four smaller micrometeorite impacts that were consistent with expectations, and this most recent one is larger than our degradation predictions assumed. We will use this flight data to update our performance analysis over time and also develop operational approaches to ensure that we maximize Webb’s imaging performance to the best of our ability for many years to come.”
This recent impact did not cause any changes to the Webb’s operations schedule, as the team continues revising the observation modes of scientific instruments and prepares for the launch of the first images of the Webb and the start of science operations.
Editing: R. Castro.
