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James Webb Telescope

The cold side temperatures have dropped considerably

Primary Mirror: -88°C (down from -44°C yesterday)
Instrument Radiator: -183°C (down from -144°C yesterday)

The sunshield is having the desired effect
 
I had a pessimistic thought that bothered me about the sun shield. If there’s a hole or a rip in it would they be able to know? Nobody can see it directly anymore. They just have whatever the sensors can detect. Eventually it would become evident because the cold side wouldn’t get as cold as it’s supposed to be.
 
Puppycow said:
I had a pessimistic thought that bothered me about the sun shield. If there’s a hole or a rip in it would they be able to know? Nobody can see it directly anymore. They just have whatever the sensors can detect. Eventually it would become evident because the cold side wouldn’t get as cold as it’s supposed to be.
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https://webb.nasa.gov/content/observatory/sunshield.html

"Special Seaming

The membrane material is tough, but if it gets a small tear or hole, the hole could become much larger. So, there is a special process called a Thermal Spot Bond (TSB) - areas where each layer are melted together. In addition, reinforcing strips of membrane material are Thermal Spot Bonded to the parent membrane about every 6 feet or so, forming a grid pattern of "rip-stops."

"This has been shown through testing to arrest a tear and keep it from extending outside of a given grid area," said Cooper. So, if a hole occurs in a layer of the sunshield from a meteoroid, or small meteor, the size of the damage is limited. These are not intended to stop a meteoroid, but rather to contain the area of damage."​
 
Puppycow said:
I had a pessimistic thought that bothered me about the sun shield. If there’s a hole or a rip in it would they be able to know? Nobody can see it directly anymore. They just have whatever the sensors can detect. Eventually it would become evident because the cold side wouldn’t get as cold as it’s supposed to be.
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smartcooky said:
https://webb.nasa.gov/content/observatory/sunshield.html

"Special Seaming

The membrane material is tough, but if it gets a small tear or hole, the hole could become much larger. So, there is a special process called a Thermal Spot Bond (TSB) - areas where each layer are melted together. In addition, reinforcing strips of membrane material are Thermal Spot Bonded to the parent membrane about every 6 feet or so, forming a grid pattern of "rip-stops."

"This has been shown through testing to arrest a tear and keep it from extending outside of a given grid area," said Cooper. So, if a hole occurs in a layer of the sunshield from a meteoroid, or small meteor, the size of the damage is limited. These are not intended to stop a meteoroid, but rather to contain the area of damage."​
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Seems that the NASA professionals have already anticipated (and hopefully solved) any problem that us amateurs here can come up with :D
 
Steve said:
Seems that the NASA professionals have already anticipated (and hopefully solved) any problem that us amateurs here can come up with :D
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Well, they've had around 25 years to work things out.

After spending $10 Bil or so, the extra cost of a few GoPro's so we could see what 's goin on would've been a good idea ;)
 
ynot said:
Well, they've had around 25 years to work things out.

After spending $10 Bil or so, the extra cost of a few GoPro's so we could see what 's goin on would've been a good idea ;)
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I know you are kidding, but that is also a serious question; one that quite a few people have asked. It seems that the addition of cameras to watch adds an extra heat load that the telescope would have to compensate for to operate at its target temperature of around 7°K (-266°C)

And in any case, they don't need cameras to see what is going on because this spacecraft has sensors for Africa! As each step is carried out, they know exactly what data they should see from an array of sensors all over the spacecraft. They can pretty detect anything that goes wrong during the deployment from analysis of that sensor data.

For example, yesterday sensors indicated that the activation of the switches which released the sun-shield covers did not take place when it was supposed to, which if true, means they might not have rolled up correctly. This needed to happen before the mid-booms were extended otherwise there would be a risk of tearing the shield. However, they were able to determine that the cover did indeed roll up from looking at two secondary pieces of sensor data

1. Data from temperature sensors showed a drop in temperature from a sensor that had to have been blocked by the cover rolling up, and

2. Data from sensors attached to a gyroscope indicated motion consistent with the sun-shield cover release devices being activated.
 
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The latest from NASA's mission blog:

https://blogs.nasa.gov/webb/

Work on the deployment of Webb’s sunshield mid-booms went late into the night yesterday. Webb mission management decided this morning to pause deployment activities for today and allow the team to rest and prepare to begin Webb’s sunshield tensioning tomorrow, Sunday, Jan. 2. That deployment is still expected to take place over at least two days.

This will likely affect the full timeline for Webb’s deployment. The timeline will be updated as major deployments resume.
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Extending the booms did take longer than anticipated, but nevertheless appears to have been successful. So they called it a day and decided to begin the tensioning process Sunday.

While the deployments took longer than expected today, that was due to the operations team moving forward with caution and according to the protocols they laid out for dealing with unpredictable situations.

“Today is an example of why we continue to say that we don’t think our deployment schedule might change, but that we expect it to change,” Parrish said. “The team did what we had rehearsed for this kind of situation – stop, assess, and move forward methodically with a plan. We still have a long way to go with this whole deployment process.”
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ynot said:
Well, they've had around 25 years to work things out.

After spending $10 Bil or so, the extra cost of a few GoPro's so we could see what 's goin on would've been a good idea ;)
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Aside from the mentioned problem of added heat load, the other factor arguing against this is, what good would it do? Suppose there's a rip, and we see it with the camera. What then? There's no way to do anything about the rip. It can't be repaired. So how does seeing it help? It really doesn't.
 
I suspect if they were designing and building the telescope now, they would put a camera on it. It probably wouldn't have much practical use. But, GoPro type cameras are now inexpensive, low-power, reliable, and able to produce highly-compressed video streams, so they might have added one just because they could.

Back when the JWST was being designed, though, adding a camera just to give us a view of the spacecraft would have been a much larger and expensive endeavor.
 
jadebox said:
I suspect if they were designing and building the telescope now, they would put a camera on it. It probably wouldn't have much practical use. But, GoPro type cameras are now inexpensive, low-power, reliable, and able to produce highly-compressed video streams, so they might have added one just because they could.
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The cost of the camera isn't the issue. This is a multi-billion dollar project, even 20 years ago a camera wouldn't have cost much.

But on a project like this, you don't put an ounce of weight on the thing if you don't have a damn good reason to. A camera would have been more weight, it would have been increased thermal transfer, and it would have offered no actual benefit to mission control.
 
Uh, yeah, the cost of the camera is nothing compared to the $2,500 cost of launching it into space. And launch cost is just the tip of the ice berg. I'd expect the dominant cost is all the one off engineering making sure everything is going to work well together.
 
An aside while we await more deployment action . . .

If JWST or subsequent technologies every find really good evidence of some forms of life on other planets, would that pose a problem/threat to current religious beliefs? I think it would have to, but when I asked a “DIY” Christian friend recently he quickly said “No, of course not”. When I bombarded him with a barrage of “what about” and “yeah but” examples of how and why it should, he just hand-waved them all away with silly “God works in mysterious ways” and “We can’t understand the mind and workings of God” type dodges.
 
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Ziggurat said:
The cost of the camera isn't the issue. This is a multi-billion dollar project, even 20 years ago a camera wouldn't have cost much.

But on a project like this, you don't put an ounce of weight on the thing if you don't have a damn good reason to. A camera would have been more weight, it would have been increased thermal transfer, and it would have offered no actual benefit to mission control.
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All true. The other issue is with outgassing of commercial parts. The first space GPS receivers in LEO lasted hours, not days or years, due to commercial parts failures.
 
RecoveringYuppy said:
Uh, yeah, the cost of the camera is nothing compared to the $2,500 cost of launching it into space. And launch cost is just the tip of the ice berg. I'd expect the dominant cost is all the one off engineering making sure everything is going to work well together.
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Crikey! - I might be able to afford to send something to L2!
 
Tensioning of the sunshield has been delayed until tomorrow. Instead they have decided to focus today on optimizing Webb’s power systems while learning more about how the observatory behaves in space.

Cold side temperatures have continued to fall.

Primary Mirror: -116°C (down from -88°C yesterday)
Instrument Radiator: -192°C (down from -183°C yesterday)
 
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