The mirror for Webb was designed to withstand the intense bombardment of dust-sized particles flying at extreme speeds over the micrometeor environment in its Sun-Earth L2 orbit.
A segment of the 6.5-meter primary mirror of the James Webb Space Telescope suffered a fortuitous and larger-than-expected micrometeor impact 1.5 million kilometers from Earth. The impact happened between May 23 and 25. Following initial evaluations, the telescope is still performing well beyond mission requirements despite a marginally detectable effect on the data. Extensive testing and measurements are underway. Over the course of long and productive missions in space, any spacecraft will suffer numerous impacts from micrometeoroids. This is an unavoidable aspect of operation in space.
A though mirror
The mirror for Webb was designed to withstand the intense bombardment of dust-sized particles (micrometeoroids) flying at extreme speeds over the micrometeor environment in its Sun-Earth L2 orbit. For a better understanding of how to harden the observatory to work in orbit, engineers combined simulations with actual impact tests on mirror samples. According to NASA, the latest impact was much larger than the team could have modeled and tested on the ground. According to Paul Geithner, deputy technical director for projects at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, Webb had to cope with strong ultraviolet light and charged particles from the Sun, cosmic rays from exotic sources in the galaxy, and occasional micrometeoroid impacts within our solar system.
“To ensure Webb can perform its ambitious scientific mission even after many years in space, experts designed and built it with performance margins (optical, thermal, electrical, mechanical). Webb’s optics were kept cleaner than necessary on the ground because of the diligent work of the launch site teams; it improves reflectivity and performance, improving overall sensitivity. With this margin and others, Webb’s scientific capabilities are resilient to degradation of its scientific capabilities over time. In addition, Webb’s ability to sense mirror positions and adjust them allows it to partially correct impact results. It is possible to cancel out a portion of the distortion by adjusting the position of the affected segment.
By doing so, any impact is minimized, but not all degradation is neutralized. This first-of-its-kind adjustment has already been made to fix the recently affected segment of C3, and more mirror adjustments are planned. In response to future events, these steps will be repeated as needed as part of telescope monitoring and maintenance. A protected maneuver may be used to protect Webb while it is in orbit. In this maneuver, the flight team intentionally moves optics away from known meteor showers before they occur. Since this most recent impact had nothing to do with a meteor shower, it is now considered to be an unavoidable chance event.
Mitigating future impacts
In response to this impact, an engineering team was formed to find ways to mitigate future impacts caused by micrometeorite fragments. Since the telescope’s initial performance has been better than expected, the team will be collecting invaluable data over time and working with NASA’s Marshall Space Flight Center micrometeorite forecasting experts to make better predictions about future performance. . Webb’s tremendous size and sensitivity make it a highly sensitive detector of micrometeorites; Eventually, Webb will provide a better understanding of L2’s dust particle environment for future missions as well.
Webb’s operations schedule was not affected by the recent impact as the team continues to review instrument observing modes and prepare for the launch of new Webb images and science operations.