Any satellite in space is exposed to meteoroids and space debris, and this can cause problems during the operation of a spacecraft.

Does JWST have any protection against these problems on its sun shield and/or in it mirror?

  • $\begingroup$ This is a great question! There's a potentially a duplicate from way back in 2014; it certainly has another good (and thorough, and well-sourced) answer! Aren't the mirrors of the James Webb Space Telescope too unprotected? (emphasis added) $\endgroup$
    – uhoh
    Dec 29, 2021 at 9:11
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    $\begingroup$ Hi! I am new to the forum and i didn't know this answer. What should I do? Answer my own question linking this question? $\endgroup$
    – iamfran
    Dec 29, 2021 at 20:46
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    $\begingroup$ Oh you don't have to do anything right now. My comment is for both you and all readers. You can just check there for additional information. Welcome to Stack Exchange! $\endgroup$
    – uhoh
    Dec 29, 2021 at 22:06
  • $\begingroup$ Of course! It has this lazer gun that will zzap any... NO! There is no human space debris at L2. And any rare micrometeorite would only make an irrelevant microscopic hole in the sunshield. And a hole in one of the mirrors doesn't matter much, you could shoot at it with a gun and still go on: astroanecdotes.com/2015/03/26/… $\endgroup$
    – LocalFluff
    Dec 30, 2021 at 12:43

3 Answers 3


There is some information on the NASA site about the sun shield.

See here: The Sunshield Webb/NASA.

In the paragraph on "Special Seaming" it states that there are reinforcing strips about every six feet or so forming a grid pattern of "rip-stops". This limits the damage from a small hole from a meteorite strike and prevents it from tearing the whole shield.

I suggest reading the whole article for more information.


This has already been answered but here are some additions:

On a personal note, if you have ever dealt with, or worn, military clothing in the last few decades (and now general outdoor gear), 'ripstop' was a standard term encountered. Basically if you get your clothing ripped or torn, although that could not have been prevented, it will not be made any bigger, due to a combination of materials that are woven into a square pattern, with extra threads that are placed within the weave at certain increments, the extra thread strength is what stops a tear or rip from continuing beyond the first square, thus the name 'ripstop'.

The spacing and number of layers of the sunshield reminded me of spaced armor, a technique used by the Germans on their tanks in WW2: multiple layers of armor plating with space inbetween, idea being to reduce the penetration power of both kinetic energy and high explosive anti-tank projectiles when penetrating the first layer and lose their effectiveness completely when contacting the main body of the tank.

  • this also obviously forms the basis of its primary purpose of protection.

These coatings and Sunshield geometry work together to reduce the 250, 000 watts of the sun’s energy that hits the first sun facing layer to less than 1 watt by the time it works its way to the fifth and last layer.

Imagine sunglasses that can withstand the severe cold and heat of space, a barrage of radiation and high-speed impacts from small space debris.

Hypervelocity impact tests up to 12 kilometers per second (7.4 miles/second) of meteoroid-like sand particles were performed on tensioned, irradiated membrane material at extreme hot and cold temperatures at Auburn University’s Hypervelocity Impact Facility.


Q: Once Webb is in orbit, how susceptible will it be to micrometeoroid strikes? For example, what would happen if one of Webb’s primary mirror segments or the sunshield got struck?

Paul: Although space is mostly empty, there is some debris. In the inner Solar System where Webb will orbit, we have a good understanding of what the population of meteoroids is like from years of observations and research. It’s mostly dust and very small particles, with the majority being sparsely distributed and tinier than grains of sand. There are some pebbles, rocks, and boulders, but they are very sparse and very rare. At Webb’s orbit at L2, the debris is all natural and the environment is not as hazardous as it is much closer to Earth, where there is a fair amount of human-generated “space junk.”

We know Webb will get struck by micrometeoroids during its lifetime, and we have taken that into account in its design and construction. We sized Webb’s main mirror so that even after years of little impacts it will still have the reflective surface area and quality necessary to do the science. We even did tests on the ground that emulated micrometeoroid impacts to demonstrate what will happen to the mirrors in space.

Similarly, part of the reason the sunshield has five layers is so it can tolerate more than the number of expected small holes, and even some tears, and still work as it should.

Also, almost all of Webb’s sensitive components (besides the mirrors and sunshield) are protected behind “micrometeoroid armor.” When micrometeoroids do strike, most are so small that they totally disintegrate upon impact, even when they hit something thin like thermal blankets or a sunshield membrane. Critical wires and electronics are shielded behind even more robust metal “armor” or inside metal boxes.


JWST's backplane is the large structure that holds and supports the big hexagonal mirrors of the telescope. The backplane has an important job as it must carry not only the 6.5 meter (over 21 foot) diameter primary mirror plus other telescope optics but also the entire module of scientific instruments. All told, the backplane carries more than 2400kg (2 1/2 tons) of hardware.

This structure is also designed to provide unprecedented thermal stability performance at temperatures colder than -400°F (-240°C). At these temperatures, the backplane was engineered to be steady down to 32 nanometers.

Northrop Grumman was responsible for the development of advanced graphite composite materials mated to titanium and invar fittings and interfaces.


No, it's all part of the plan; “What you see is what you get”

NASA relies on probability to make it without serious damage, but minor damage seems likely to occur over its lifetime.

From Futurism's NASA Says Space Debris will Definitely Slam Into the James Webb Space Telescope; It's All Part of the Plan.:

But the massive space observatory isn’t out of the woods just yet. As it spins around the Sun in a chaotic orbit, it will likely encounter plenty of space debris along the way — and an impact, its team says, is likely inevitable.

“Some small impacts from micrometeorites will happen,” NASA Goddard Space Flight Center scientist Michelle Thaller said during a livestream over the weekend. “You know, over the lifetime of the mission there will be some damage to the mirrors of the telescope.”

The telescope itself is indeed vulnerable, but the team says it’s likely it’ll be able to survive some damage.

“Let’s say a piece of debris hits it,” said Julie Van Campen, a NASA engineer, during the stream. “And then we had a problem like that broke a mirror.”

In terms of protection, there’s “not much,” she explained. “What you see is what you get.”

However, Van Campen said, if a micrometeor were to rip a tear into the telescope’s protective sunshield there would be at least four more layers to keep the shield together.

“It was part of our lifetime calculations,” she added.

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    $\begingroup$ Do you have a reference that backs up your claim? $\endgroup$ Dec 29, 2021 at 4:14
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    $\begingroup$ I just thought about this the other day as I watched the deployment video. I once saw a quote the average density of particles per square kilometre was about 300 atoms but this was from an Issac Arthur video I may be wrong. Heres a ref but it has different values, however the density is always very low. hypertextbook.com/facts/2000/DaWeiCai.shtml $\endgroup$
    – Joseph
    Dec 29, 2021 at 4:36
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    $\begingroup$ Actually, there are reinforcements on the shield to limit the effects of meteorite damage. So they are not just relying nothing happening. $\endgroup$
    – rghome
    Dec 30, 2021 at 15:42
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    $\begingroup$ @uhoh I am not the downvoter $\endgroup$ Jan 12, 2022 at 13:07
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    $\begingroup$ @OrganicMarble Oh, I just wanted to let you know your helpful comment was taken seriously by someone, and I thought you might be interested in the quote itself :-) $\endgroup$
    – uhoh
    Jan 12, 2022 at 13:27

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