Webb gets its first large micrometeoroid impact
In a carefully worded press release this week, NASA revealed that one segment of the primary mirror of the James Webb Space Telescope had been hit by a micrometeoroid.
Between May 23 and 25, NASA’s James Webb Space Telescope sustained an impact to one of its primary mirror segments. After initial assessments, the team found the telescope is still performing at a level that exceeds all mission requirements despite a marginally detectable effect in the data. Thorough analysis and measurements are ongoing. Impacts will continue to occur throughout the entirety of Webb’s lifetime in space; such events were anticipated when building and testing the mirror on the ground.
The reason such events were expected is because — unlike most telescopes (including Hubble) — Webb’s mirrors are not enclosed in a tube for protection. To do so would have made the telescope far too expensive to build or launch.
After describing in great detail all the work done prior to launch to anticipate such hits and deal with them, the press release then mentioned this fact almost as an aside:
This most recent impact was larger than was modeled, and beyond what the team could have tested on the ground.
Localized damage to the primary mirror of any telescope is not unusual. With ground-based telescopes such issues are not infrequent and easily worked around. The same applies to Webb. The engineers will calculate how to calibrate this particular segment to minimize distortion from the impact.
However, that the telescope experienced a hit larger than ever modeled, so soon after launch, suggests that those models were wrong, and that larger and more frequent hits can be expected. If so, this could be very worrisome, as over the long run it could shorten the telescope’s life in space significantly.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
In a carefully worded press release this week, NASA revealed that one segment of the primary mirror of the James Webb Space Telescope had been hit by a micrometeoroid.
Between May 23 and 25, NASA’s James Webb Space Telescope sustained an impact to one of its primary mirror segments. After initial assessments, the team found the telescope is still performing at a level that exceeds all mission requirements despite a marginally detectable effect in the data. Thorough analysis and measurements are ongoing. Impacts will continue to occur throughout the entirety of Webb’s lifetime in space; such events were anticipated when building and testing the mirror on the ground.
The reason such events were expected is because — unlike most telescopes (including Hubble) — Webb’s mirrors are not enclosed in a tube for protection. To do so would have made the telescope far too expensive to build or launch.
After describing in great detail all the work done prior to launch to anticipate such hits and deal with them, the press release then mentioned this fact almost as an aside:
This most recent impact was larger than was modeled, and beyond what the team could have tested on the ground.
Localized damage to the primary mirror of any telescope is not unusual. With ground-based telescopes such issues are not infrequent and easily worked around. The same applies to Webb. The engineers will calculate how to calibrate this particular segment to minimize distortion from the impact.
However, that the telescope experienced a hit larger than ever modeled, so soon after launch, suggests that those models were wrong, and that larger and more frequent hits can be expected. If so, this could be very worrisome, as over the long run it could shorten the telescope’s life in space significantly.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
You should remove “First” from your post title. Quoting from a NASA blog post at https://blogs.nasa.gov/webb/2022/06/08/webb-engineered-to-endure-micrometeoroid-impacts/ (edit: that’s the same post you linked!) “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.”
David Eastman: You are correct. I have edited the headline.
This is VERY unfortunate.
We are going to have to go up add a shield around it and replace the mirrors that are damaged.
At this rate the thing will not last 5 years.
Obviously this is disappointing, but as noted we have to expect this and in the end it will give us a lot more good data on the topic. And that is in fact necessary because as Bob has noted the future for all advanced astronomy has to be in space and this is a fact of life and we need to learn to deal with. And the data will apply equally well to the risk assessment and design considerations for future space suits, lunar habitats, and everything else we build to operate in the vacuum of space.
It would be interesting to know more about their model and how many/how often/how big/ how impactful they expect these events to be. Are 4 events this early into the mission outside the model too? How large do they expect these events to be? How much larger was this than expected? Etc.
In the end though I expect the implications to science will be pretty miniscule. Taking the 4 events so far as a baseline we’re looking at roughly 1 per month, and assuming a 10 year operating life (2X the mission plan) we can expect a lifetime total of 120 or so. And presumably these only create defects on the order of a few square millimeters each (a number I recall from reports on space shuttle window incidents).. So assuming 4mm sq each you’re looking at about 500mm sq. of damaged mirror by the end of the mission and given that Webb has 26,300,000mm sq of polished mirror area we’re only looking at the loss of 0.002% of the mirror surface.
Will that impact some science? Sure. But it seems hardly a serious impediment to lots of interesting work regardless so long as the instrumentation remains healthy.
MHO
Remember-a km diameter Earth Trojan was found not long ago. A wider target….spallation off which may be what we see here.
It shows we have a lot to learn about interplanetary space. Ironic that we find this out not by using a purpose built collector but from a device designed to observe the edge of the universe. Ouch!
That article on BehindTheBlack about how our Earth might have been exposed to the inter stellar medium also blew my mind.
Computer models are great after they’ve been validated and verified. Good news everybody, after Webb, the models will be spot on regarding the micrometeorite environment at L2.
Don’t Lagrange points “collect” junk? I know L3 and L4 do (hence the Jupiter Trojan asteroids). Are L1 and L2 different, being in such a drastically different position?
markedup2 asked: “Don’t Lagrange points “collect” junk? I know L3 and L4 do (hence the Jupiter Trojan asteroids). Are L1 and L2 different, being in such a drastically different position?”
None of them is very stable, even L4 and L5 are iffy, where even some of Jupiter’s Trojan asteroids sometimes pop out of their L4 or L5. positions.
https://en.wikipedia.org/wiki/Lagrange_point
Although L4 and L5 can be visualized as shallow “bowls” (sort of kidney shaped), where objects have to “roll uphill” to escape (thus they are considered to be stable), L1, L2, and L3 are visualized as saddles, where any deviation or perturbation from the exact balance point results in the object eventually “rolling away.” Thus, the halo orbit that Webb is in “around” the L2 point is unstable and Webb would need to perform the occasional stationkeeping maneuver if it wants to stay there for many years.
https://upload.wikimedia.org/wikipedia/commons/d/d0/Lagrangian_points_equipotential.gif
The Lagrange points orbit the Earth along with the Moon, but the gravitational influences of the Moon make the L1, L2, and L3 orbits relatively stable despite the violation of fundamental equations of orbital mechanics.