<p>As I am unable to comment, this answer is in regards to the 7,000 moving parts claim, but also contains links to articles that address the question.</p>
<p>From The Universe Today's <a href="https://www.universetoday.com/153863/still-nervous-about-jwst-friday-and-saturdays-sunshield-deployments-will-be-nail-biters/" rel="nofollow noreferrer">Still Nervous about JWST? Friday and Saturday’s Sunshield Deployments will be Nail-biters</a>:</p>
<blockquote>
<p>This complicated deployment involves around 7,000 parts, including 400 pulleys, numerous cables and eight motors.</p>
</blockquote>
<p>From <a href="https://www.northropgrumman.com/space/james-webb-space-telescope/game-changer-part-ii-northrop-grumman-and-the-james-webb-space-telescopes-confounding-sunshield" rel="nofollow noreferrer">Game Changer Part II: Northrop Grumman and the James Webb Space Telescope’s Confounding Sunshield</a> (of a three part series By David Larter):</p>
<blockquote>
<p>When you want to survive launch, you want to make the telescope really stiff so it doesn’t move around and tear itself up as it’s getting to space&quot;, Levi recalled from his Space Park office in Redondo Beach. “And when you want to it to be deployable, you need to have gaps, hinges, and other things like that which are going to vibrate and potentially break during launch. And then when you want to operate at cryogenic temperatures you have you have to use soft materials that can expand in predictable ways.</p>
</blockquote>
<p>All those requirements compete with each other, Levi said, and that made the design incredibly complex.</p>

CC BY-SA 4.0
2024-12-25T03:57:25.217Z
2024-12-26T22:47:48.170Z
2024-12-26T22:47:48.170Z
Just a guy
<p>Just an add-on for the other answers.</p>
<p>Because the sunshield is so thin and so complex in design, it have repeatedly got minor damages during assembly and testing.</p>
<p><a href="https://newatlas.com/space/nasa-james-webb-space-telescope-sunshield/#:%7E:text=During%20an%20earlier%20test%20the,had%20delayed%20progress%20towards%20launch." rel="noreferrer">Tears of the fabric:</a></p>
<blockquote>
<p>During an earlier test the sunshield had been damaged during deployment, suffering a number of tears that, along with other issues had delayed progress towards launch.</p>
</blockquote>
<p><a href="https://spaceflightnow.com/2018/05/08/jwst-beset-by-another-problem-as-northrop-grumman-revamps-training/" rel="noreferrer">The fasteners getting loose.</a></p>
<p>Many authors write about &quot;organisation mishap&quot; by Northrop Grumman, the manufacturer of the sunshield. But honestly, I think it was really challenging to &quot;organise in the right way&quot; the development of such complex, fragile, labor-intensive and unique-designed item.</p>

CC BY-SA 4.0
2024-12-25T08:08:10.513Z
2024-12-25T08:08:10.513Z
Heopps
<p>It's got to be big.</p>
<p>It's got to be light.</p>
<p>It's got to be super effective.</p>
<p>It's got to fit inside a rocket.</p>
<p>It's got to work. First time, no do-overs.</p>
<p>The sun shield has to be the size of a tennis court, but must weigh as little as possible, So it has to be thin: 0.05 of a millimetre. The hot side of the sun shield is about 300 degrees C hotter than the cold side.  That's a big temperature difference to maintain.</p>
<p>And it has to fold up and fit in a rocket. To make that possible there are ~7000 parts, with hundreds of them moving. These have to survive being shaken in a rocket launch, then it must unfold in zero-gravity with nobody around to tweak things if something gets caught.</p>
<p>The technical challenge is the extremely tight tolerances on its manufacture and the requirement that it must work right the first time. There was no way to have a trial run and work out the problems practically.</p>
<p>(<a href="https://science.nasa.gov/mission/webb/webbs-sunshield/" rel="noreferrer">main source</a>)</p>

CC BY-SA 4.0
2024-12-25T06:51:38.057Z
Do you have a defintion of "moving part" beyond "a part that moves"?
James K
CC BY-SA 4.0
2024-12-25T07:02:15.410Z
same question to uhoh, typically I consider springs, bearings, pulleys to be moving parts, since they are used in things that move.
justhalf
CC BY-SA 4.0
2024-12-25T07:43:34.107Z
I don't understand why the sunshields have to be too thin (even less than a paper). I thought the weight of the sunshields are negligible compared to other parts of the telescope, why they have to be too light?
Amir reza Riahi
CC BY-SA 4.0
2024-12-25T08:45:45.827Z
That's actually an interesting question.  They are light, in comparison, but that is by design. A Heavier shield could be delivered by a more powerful rocket. I think they need to be super thin because they have to fit inside a rocket. Try folding a piece of  paper and you'll see how it quickly becomes thick, the sunshield has to fold up small.  Space on the rocket is strictly limited. A thicker sunshield means a smaller telescope, so thinner is better.
James K
CC BY-SA 4.0
2024-12-25T10:22:02.883Z
@AmirrezaRiahi That is a good question, and since that's a spaceflight rather than an Astronomy question, you can certainly ask it in [Space Exploration SE](https://space.stackexchange.com/). As an example, see [Why is the sunny side of JWST's sunshield purple and covered with silicon?](https://space.stackexchange.com/q/58536/12102)
uhoh
CC BY-SA 4.0
2024-12-25T10:28:56.623Z
@uhoh fair point! I concede.
justhalf
CC BY-SA 4.0
2024-12-25T12:32:33.877Z
I really don't care that much. The edit button is there, do thine worst
James K
CC BY-SA 4.0
2024-12-25T13:31:16.980Z
[Ni!](https://youtu.be/US49fI5AzzE)
uhoh
CC BY-SA 4.0
2024-12-25T19:25:44.003Z
Good answer, but additionally:  It has to operate at zero-g and vacuum, but has to be built and tested on the earth.
Adam
CC BY-SA 4.0
2024-12-26T15:52:18.860Z
@AmirrezaRiahi Space flight is all about trade-offs. Every payload launched into space has very strict weight, volume, and dimensional limits depending on the rocket design. After launch, you can free up the dimensional constraints, but you're still limited by the weight and volume constraints. So every gram and cubic centimeter given to one part is a gram and cubic centimeter less for other parts.
David S
CC BY-SA 4.0
2024-12-28T11:43:18.387Z
@JamesK in case you or anyone else is interested in the number of moving parts: "[The unfolding and tensioning of the sunshield involved 139 of Webb’s 178 release mechanisms, 70 hinge assemblies, eight deployment motors, roughly 400 pulleys, and 90 individual cables](https://www.nasa.gov/news-release/sunshield-successfully-deploys-on-nasas-next-flagship-telescope/)" found [here](https://space.stackexchange.com/questions/67577/how-many-of-jwsts-single-point-failure-issues-were-related-to-sunshield-deploym?noredirect=1#comment228093_67577)
uhoh
CC BY-SA 4.0
2024-12-24T20:15:51.037Z
2024-12-26T14:53:48.527Z
2024-12-26T14:53:48.527Z
James K
<p>The Webb telescope is an infrared telescope, therefore heat from sun can cause noise and even damage its super sensitive sensors (If I'm wrong please correct me, I'm not expert).
So the telescope should be kept away from sun light. But I have heard that creating sunshield for Web telescope was an engineering challenge. I can not understand the technical difficulties of creating a sunshield which blocks sunlight to reach the telescope.</p>
<p>Can someone explain it to me?</p>

CC BY-SA 4.0
2024-12-26T13:48:07.557Z
This is probably the most detailed video about the shield, from Smarter Every Day, his dad worked on it: https://www.youtube.com/watch?v=Pu97IiO_yDI
Greg Miller
<space-telescope><james-webb-space-telescope><infrared>
Why was creating sunshields for Webb telescope challenging?
Amir reza Riahi
# Why was creating sunshields for Webb telescope challenging?

(Asked by: username_0 on 2024-12-24)

The Webb telescope is an infrared telescope, therefore heat from sun can cause noise and even damage its super sensitive sensors (If I'm wrong please correct me, I'm not expert).
So the telescope should be kept away from sun light. But I have heard that creating sunshield for Web telescope was an engineering challenge. I can not understand the technical difficulties of creating a sunshield which blocks sunlight to reach the telescope.

Can someone explain it to me?

**Tags:** space-telescope, james-webb-space-telescope, infrared

> **Comments:**
> **username_1**: This is probably the most detailed video about the shield, from Smarter Every Day, his dad worked on it: https://www.youtube.com/watch?v=Pu97IiO_yDI  

---

## 3 answers

### Answer by username_4 on 2024-12-24. Score: 31 | Accepted answer

It's got to be big.

It's got to be light.

It's got to be super effective.

It's got to fit inside a rocket.

It's got to work. First time, no do-overs.

The sun shield has to be the size of a tennis court, but must weigh as little as possible, So it has to be thin: 0.05 of a millimetre. The hot side of the sun shield is about 300 degrees C hotter than the cold side. That's a big temperature difference to maintain.

And it has to fold up and fit in a rocket. To make that possible there are ~7000 parts, with hundreds of them moving. These have to survive being shaken in a rocket launch, then it must unfold in zero-gravity with nobody around to tweak things if something gets caught.

The technical challenge is the extremely tight tolerances on its manufacture and the requirement that it must work right the first time. There was no way to have a trial run and work out the problems practically.

([main source](https://science.nasa.gov/mission/webb/webbs-sunshield/))

> **Comments:**
> **username_4**: Do you have a defintion of "moving part" beyond "a part that moves"?  
> **username_5**: same question to username_6, typically I consider springs, bearings, pulleys to be moving parts, since they are used in things that move.  
> **username_0**: I don't understand why the sunshields have to be too thin (even less than a paper). I thought the weight of the sunshields are negligible compared to other parts of the telescope, why they have to be too light?  
> **username_4**: That's actually an interesting question.  They are light, in comparison, but that is by design. A Heavier shield could be delivered by a more powerful rocket. I think they need to be super thin because they have to fit inside a rocket. Try folding a piece of  paper and you'll see how it quickly becomes thick, the sunshield has to fold up small.  Space on the rocket is strictly limited. A thicker sunshield means a smaller telescope, so thinner is better.  
> **username_6**: @username_0 That is a good question, and since that's a spaceflight rather than an Astronomy question, you can certainly ask it in [Space Exploration SE](https://space.stackexchange.com/). As an example, see [Why is the sunny side of JWST's sunshield purple and covered with silicon?](https://space.stackexchange.com/q/58536/12102)  
> **username_5**: @username_6 fair point! I concede.  
> **username_4**: I really don't care that much. The edit button is there, do thine worst  
> **username_6**: [Ni!](https://youtu.be/US49fI5AzzE)  
> **username_7**: Good answer, but additionally:  It has to operate at zero-g and vacuum, but has to be built and tested on the earth.  
> **username_8**: @username_0 Space flight is all about trade-offs. Every payload launched into space has very strict weight, volume, and dimensional limits depending on the rocket design. After launch, you can free up the dimensional constraints, but you're still limited by the weight and volume constraints. So every gram and cubic centimeter given to one part is a gram and cubic centimeter less for other parts.  
> **username_6**: @username_4 in case you or anyone else is interested in the number of moving parts: "[The unfolding and tensioning of the sunshield involved 139 of Webb’s 178 release mechanisms, 70 hinge assemblies, eight deployment motors, roughly 400 pulleys, and 90 individual cables](https://www.nasa.gov/news-release/sunshield-successfully-deploys-on-nasas-next-flagship-telescope/)" found [here](https://space.stackexchange.com/questions/67577/how-many-of-jwsts-single-point-failure-issues-were-related-to-sunshield-deploym?noredirect=1#comment228093_67577)  

---

### Answer by username_2 on 2024-12-25. Score: 7

As I am unable to comment, this answer is in regards to the 7,000 moving parts claim, but also contains links to articles that address the question.

From The Universe Today's [Still Nervous about JWST? Friday and Saturday’s Sunshield Deployments will be Nail-biters](https://www.universetoday.com/153863/still-nervous-about-jwst-friday-and-saturdays-sunshield-deployments-will-be-nail-biters/):

> This complicated deployment involves around 7,000 parts, including 400 pulleys, numerous cables and eight motors.

From [Game Changer Part II: Northrop Grumman and the username_4 Webb Space Telescope’s Confounding Sunshield](https://www.northropgrumman.com/space/username_4-webb-space-telescope/game-changer-part-ii-northrop-grumman-and-the-username_4-webb-space-telescopes-confounding-sunshield) (of a three part series By username_8 Larter):

> When you want to survive launch, you want to make the telescope really stiff so it doesn’t move around and tear itself up as it’s getting to space", Levi recalled from his Space Park office in Redondo Beach. “And when you want to it to be deployable, you need to have gaps, hinges, and other things like that which are going to vibrate and potentially break during launch. And then when you want to operate at cryogenic temperatures you have you have to use soft materials that can expand in predictable ways.

All those requirements compete with each other, Levi said, and that made the design incredibly complex.


---

### Answer by username_3 on 2024-12-25. Score: 5

username_2 an add-on for the other answers.

Because the sunshield is so thin and so complex in design, it have repeatedly got minor damages during assembly and testing.

[Tears of the fabric:](https://newatlas.com/space/nasa-username_4-webb-space-telescope-sunshield/#:%7E:text=During%20an%20earlier%20test%20the,had%20delayed%20progress%20towards%20launch.)

> During an earlier test the sunshield had been damaged during deployment, suffering a number of tears that, along with other issues had delayed progress towards launch.

[The fasteners getting loose.](https://spaceflightnow.com/2018/05/08/jwst-beset-by-another-problem-as-northrop-grumman-revamps-training/)

Many authors write about "organisation mishap" by Northrop Grumman, the manufacturer of the sunshield. But honestly, I think it was really challenging to "organise in the right way" the development of such complex, fragile, labor-intensive and unique-designed item.


---

