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The James Webb Space Telescope and stuff


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3 hours ago, sgt_flyer said:

You would see yes, but mostly by occultation. not very useful for checking if there's wrinkles in the sunshield with a camera. 

you can see how much light earth atmosphere is diffusing - even in the shadow, while iss parts are seen by occultation. (Outside of the few parts  that receive some light from earth itself)

And according to the comments, the series of photo for the vid below has 1.6s exposure time...

 

earth is in frame... 

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8 hours ago, sgt_flyer said:

ISS EVAs videos, you'll see quickly how dark it is with cameras in space when iss is in earth's shadow

I have seen it.  Now I'm wondering if it is a problem with the camera tech or whether the Mark 1 Eyeball would be similarly affected... 

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Having a longer exposure time for dim objects is not a problem when using a fixed camera to image an object that is not moving relative to the frame. I have a feeling the JWST team are more than qualified to figure out how to do that considering that that's exactly how the James Webb telescope is meant to capture its images anyway. That's their expertise.

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17 hours ago, sgt_flyer said:


Well, on the cold side, you won't have  light outside the stars, so any camera would need to have a way to illuminate the parts to have a chance to see them - which would be likely to disturb the instruments (between the heat from cabling resistance, etc) - and you'll need cameras able to resist to the extreme cold.

on the hot side, outside of the antenna, flap, solar arry and external sunshield, you don't really have anything to look for that couldn't be easily tested.

antenna and solar array are pretty straightforward, if they didn't deploy you wouldnt have power or high speed communications. (Easy to test)

outside of reading motor values, basic detectors on the latches can check if the various parts reached their intended positions. And i guess they could measure the angular moments  the spacecraft was submitted to from deploying the parts from the gyroscopes, so you can know if the parts moved accordingly too :)

The more or less only 'unknown' would be the sunshield's layers, and i guess they can check from the pulley system if there's abnormal forces from the motors to detect anomalies.

 

 

the purpose of such cameras would just be to provide engineers on the ground with some useful troubleshooting data when things go wrong, or to help the deployment process. they would be shut down for when the telescope starts telescoping.  to deal with the cold you could do fiber optic camera, with the camera itself being in the equipment bay. of course a simple resistive heater with the camera in a small pressurized dome could work, you wouldn't need much heat. i like the idea of a tentacle camera that perhaps comes out the side of the boom and can bend to look at either the top or bottom, and simply put one on each side.  muscle wire can provide the actuation, such a system could inspect all the layers of the sun shield.

technology has changed a lot since webb was built. years in the hanger didnt help. and then there is about the 10 or so years it takes to rad hard off the shelf components. ive only started seeing tiny cameras in parts catalogs for a couple years.  cameras from when webb was build were significantly larger. from around a centimeter cube to something a couple mm square. they are intended for use as inspection cams, for medical and industrial applications. webb might be too old to use these technologies, but next time we launch something equally as complex if not more, you might see them in use. 

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Tensioning delayed: power systems being looked at. 

https://www.google.com/amp/s/www.space.com/amp/james-webb-space-telescope-sunshield-tension-delay

 

Webb team is spending Sunday (Jan. 2) studying the observatory's power subsystem, NASA announced.

"Nothing we can learn from simulations on the ground is as good as analyzing the observatory when it's up and running," Bill Ochs, Webb project manager at NASA’s Goddard Space Flight Center (GSFC) in Maryland, said in an agency statement released Sunday (Jan. 2). "Now is the time to take the opportunity to learn everything we can about its baseline operations. Then we will take the next steps."

Edited by JoeSchmuckatelli
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A bit more detail on the delay and assess:

Quote

 

the team paused work to confirm that the sunshield cover had fully rolled up as the final preparatory step before the mid-boom deployment.

Switches that should have indicated that the cover rolled up did not trigger when they were supposed to. However, secondary and tertiary sources offered confirmation that it had. Temperature data seemed to show that the sunshield cover unrolled to block sunlight from a sensor, and gyroscope sensors indicated motion consistent with the sunshield cover release devices being activated.

 

First of Two Sunshield Mid-Booms Deploys – James Webb Space Telescope (nasa.gov)

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The completion of the sunshield cover and mid-boom deployments over the past two days marks a critical milestone for Webb: all 107 membrane release devices associated with the sunshield deployment — every single one of which had to work in order for the sunshield to deploy — have now successfully released. Webb has 178 of these ‘non-explosive actuators’ in all; 107 were used to keep the sunshield safe and folded prior to deployment.

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“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.”

Quote

Webb’s engineers will begin with the bottom layer – the largest and flattest layer, which is closest to the Sun and will reach the highest temperatures. They will proceed sequentially to the fifth and smallest layer, closest to the primary mirror. Tensioning the layers involves sending commands to activate several motors to reel in a total of 90 cables through numerous pulleys and cable management devices. Sunshield tensioning will take at least two days but may take longer, due to the complexity of the process

James Webb Space Telescope (nasa.gov)

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Today, at 3:48 pm EST, the Webb team finished tensioning the first layer of the observatory’s sunshield– that is, tightening it into its final, completely taut position. This is the first of five layers that will each be tightened in turn over the next two to three days, until the observatory’s sunshield is fully deployed. The process began around 10 am EST.

This layer is the largest of the five, and the one that will experience the brunt of the heat from the Sun. The tennis-court-sized sunshield helps keep the telescope cold enough to detect the infrared light it was built to observe.

The team has now begun tensioning the second layer.

 

 

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7 minutes ago, Brotoro said:

I'm very happy to see that the tensioning is going well, since it was the step I was most worried about.

Me too, but that fear the the complex stuff will be fine and the simplest last deployment, the radiator will fail is hard to ignore... or worst, the insertion burn... everytime something complex is done, the next simple thing became as scary as it can be since NOTHING can go wrong (I guess)

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18 minutes ago, Brotoro said:

I'm very happy to see that the tensioning is going well, since it was the step I was most worried about.

I'd agree, except I'm still terrified of all the other stuff that needs to happen. I'd fully exhale once the first pictures come in. 

 

I'd say something positive, but I don't want to magically jinx this! :confused:

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There has been a lot of talk about how expensive Webb is.  The live broadcast is shedding a bit of light on this - aside from showing the numbers of people who worked on it, they did things like retrofit the cryo chamber at Johnson (developed for the Appolo Missions) and conducted over 100 days of cryo testing to confirm the systems work at ridiculously low Temps and in vacuum. 

 

Cool stuff! 

Edit - between Sunshield deployment and observatory deployment are a 'bunch of deployments we don't often talk about' - radiators and the like.  

Mirror section deployments are "... later in the week". 

Later still, they will free up and test the 18 individual mirror segments (could take 24 hours to release and a week to test) 

Edited by JoeSchmuckatelli
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3 minutes ago, JoeSchmuckatelli said:

retrofit the cryo chamber at Johnson (developed for the Appolo Missions) and conducted over 100 days of cryo testing to confirm the systems work at ridiculously low Temps and in vacuum. 

They even mentioned testing in some sort of rapid-depressurization chamber to make sure that the sea-level pressure air could escape during launch without damaging the sunshield. I hadn't even thought of that.

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Last note on the live feed (fascinating, but I have to get to work);  it's amazingly well done. 

I've watched a lot of Astronomy 'science shows'... And the live stream seems almost post production quality - they have lots of of info graphics, animations and other things that explain what and why so very well. 

Contrast this with good streams like we see for SX launches - enthusiastic amateurs watching space (lots of fun banter and speculation) or a company sharing the launch (straight forward information and self congratulation) - and this 'stream' has the feel of a full production NOVA program.  Serious kudos to the production team and selection of the narrator Dr. Michelle Thaller. 

https://en.m.wikipedia.org/wiki/Michelle_Thaller

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I've seen Dr. Thaller involved in a number of NASA projects, like I remember her asking questions in person for one of the rover/lander missions a year+ ago. 

8 minutes ago, JoeSchmuckatelli said:

I've watched a lot of Astronomy 'science shows'... And the live stream seems almost post production quality - they have lots of of info graphics, animations and other things that explain what and why so very well. 

I'm glad JWST is getting this much effort and production put into its deployment. I guess all those billions of tax dollars went to things beyond extensive testing and development ;D

I was somewhat worried how it would be promoted, since there aren't actually any cameras, or anything to "see" beyond whatever photos it takes. So having 3d animations and graphics and high quality resources to help keep track of what is going on is very nice :)

 

 

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28 minutes ago, VaPaL said:
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With all five layers of sunshield tensioning complete, about 75% of our 344 single-point failures have been retired!

So there are 86 left. Glad most of them are gone.

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Today's livestream is for the secondary mirror:

At the moment they're confirming that there aren't any cameras to watch the deployment because it would be too dark and cold.

Edited by HebaruSan
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