After a few hits, NASA’s newest space telescope will adjust its observing strategy to avoid hitting its mirror with small space rocks.
The James Webb Space Telescope (Webb or JWST) has yet to celebrate its launch anniversary, but in recent months 14 dust-sized micrometeoroids have hit its gold mirror, which is 6.5 meters wide. The view from the observatory remains stunning, but mission personnel have decided to modify the telescope’s operation to avoid directly confronting what experts have identified as “micrometeoroid avoidance zones.”
“Micrometeoroids impacting the mirror head-on have twice the relative velocity and four times the kinetic energy, so avoiding this direction whenever possible will help prolong the outstanding optical performance for decades,” said Lee Feinberg, Webb optical telescope element manager at NASA’s Goddard Space Flight Center in Maryland, said in a pronunciation.
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JWST planners knew to expect micrometeoroid impacts, and the telescope was designed to withstand the kinds of strikes scientists expected. However, afterwards an impact at the end of May caused more damage than the models predicted, mission personnel began studying ways to mitigate the impact.
Webb is extremely vulnerable because his mirror is huge and exposed directly to space – unlike, say, the Hubble Space Telescope‘s mirror, which is smaller and shielded by a protective casing. But for JWST, shrinking or shielding the mirror would have reduced the telescope’s power.
A team of experts gathered to analyze the May impact determined that the event was an unfortunate breakthrough because an unusually high-energy micrometeoroid happened to strike a more vulnerable part of the mirror. Still, the scientists determined it was worth adjusting JWST’s observations to further reduce the likelihood of another such impact on the vast light-gathering surface.
JWST orbits what scientists call a Lagrange point, where gravity tugs evenly pull out to create “parking lots” that spacecraft can use to reduce the fuel and maneuvers required to stay in position. JWST’s specific Lagrange point is nearly 1.5 million kilometers away Soilon the side of our planet opposite the Sun.
Other spacecraft have previously been stationed here, allowing scientists to model how many tiny micrometeoroids the observatory might encounter, and after analyzing the May event, experts identified “micrometeoroid avoidance zones” of particular risk along the telescope’s path through space.
Starting next summer, as JWST enters its second year of science operations, the telescope will try to avoid focusing its mirror on these zones during observations. Instead, JWST personnel will schedule those sightings for a different time of year when the threat of micrometeoroids is lower in the necessary direction. The adjustment won’t block any science, although it will complicate observatory planning, NASA officials have said.
Time-sensitive observations, also of objects within the solar systemcan still occur in avoidance zones.
The announcement comes as the Space Telescope Science Institute in Maryland, which operates JWST, has begun accepting proposals from scientists who want to use the facility during its second year of scientific work, called Cycle 2.