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The James Webb Space Telescope and stuff


Streetwind
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The L2 point.

1959:
The 2nd fleet of the Deep Space Bombardment Forces should be drifting at L2 for 25 years, rotating the crew every 6 months.
The Orion battleships with 200 W-56 x 1.5 Mt each.

2021.
A 6 t telescope is finally launched to L2 after many year delays to work there for (2 years?), to everyone's amusement.

The space era.
Expectations...
Reality...

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4 minutes ago, Gargamel said:

I foresee an Evergreen-esque thread in the works.   JWST, It’s stuck!   It’s not stuck!   Oh it’s stuck again!    Ok it’s unstuck! 

I mean, they got the swiveling camera unstuck on...was it Cassini or Voyager? by wiggling it back and forth...so I bet there's some parts of this that they could fix if they went wrong. I think they can at least do the insertion burn with the thing unfolded like it is.

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17 minutes ago, cubinator said:

I mean, they got the swiveling camera unstuck on...was it Cassini or Voyager? by wiggling it back and forth...so I bet there's some parts of this that they could fix if they went wrong. I think they can at least do the insertion burn with the thing unfolded like it is.

Thought they bounced it off mars on the way by........

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42 minutes ago, cubinator said:

I bet there's some parts of this that they could fix if they went wrong.

The FAQ comes close to saying so outright:

Quote

Is there flexibility built into the planned deployments?

NASA has a detailed plan to deploy the Webb Space Telescope over a roughly two-week period. The process involves hundreds of individual deployments. The team will be monitoring telemetry in real-time and may pause the nominal deployment timeline to assess data received. The deployment process is not an automatic hands-off sequence like the Mars rover; it is human-controlled. This means that the deployments may not occur exactly in the order or times depicted in the animated deployment videos.

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I'm going to hazard the guess that even partial sunshield deployment is a good thing - that 'tensioned' is a 'nice to have' (optimal) rather than a 'need to have'.

Pure guess on my part - but for the money, you would expect some flexibility built into the design.

 

So - this begs a question: at the operating temps on the cold side: what lubricants can they use?  Graphite only - or are there other 'super cold' lubricants?

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On 12/30/2021 at 10:38 PM, HebaruSan said:

The sunshield covers are now released.

https://jwst.nasa.gov/content/webbLaunch/assets/video/deploymentSteps/1k/WEBB_allCovers_1280_30fps_h264.mp4

Next up, the start of the unfurling!

"All hands, to the lines, haul away! Raise the sheets, from the jibs to the driver, courses to royals! Steady now, all together lads, pull like you're getting paid for it!"

Edited by grungar3x7
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9 hours ago, JoeSchmuckatelli said:

I'm going to hazard the guess that even partial sunshield deployment is a good thing - that 'tensioned' is a 'nice to have' (optimal) rather than a 'need to have'.

Pure guess on my part - but for the money, you would expect some flexibility built into the design.

 

So - this begs a question: at the operating temps on the cold side: what lubricants can they use?  Graphite only - or are there other 'super cold' lubricants?

I don't know, if the instruments are emitting infrared thermal radiation to any significant degree they can't be used at all.

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are there any engineering cameras on the webb at all? now that you can get a camera the size of a grain of rice i expect to see them plastered all over space probes in the near future. the webb was in the  hanger too long for that to happen here, but there has to be at least one or two. 

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24 minutes ago, Nuke said:

are there any engineering cameras on the webb at all? now that you can get a camera the size of a grain of rice i expect to see them plastered all over space probes in the near future. the webb was in the  hanger too long for that to happen here, but there has to be at least one or two. 

Spoiler

How, do you think, it can publish in instragram the sky photos? They have put an array of webcams looking at that mirror, that's how it works.

The screen which is being deployed right now, is a background skybox.

Spoiler

Hope, they didn't attach the palms on a beach instead of stars and galaxies...

 

 

Edited by kerbiloid
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2 hours ago, Nuke said:

are there any engineering cameras on the webb at all? now that you can get a camera the size of a grain of rice i expect to see them plastered all over space probes in the near future. the webb was in the  hanger too long for that to happen here, but there has to be at least one or two. 

Ive heard several times that there are none, thats why the video of the solar panel deployment is the last we will see of the telescope itself.

Edited by Elthy
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3 hours ago, Nuke said:

are there any engineering cameras on the webb at all? now that you can get a camera the size of a grain of rice i expect to see them plastered all over space probes in the near future. the webb was in the  hanger too long for that to happen here, but there has to be at least one or two. 


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.

 

 

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6 minutes ago, sgt_flyer said:

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

Why would that be?  I've been out in the deep desert many times on moonless nights and seen by starlight... Am I wrong to presume that the same would be true 'out there'?

8 minutes ago, sgt_flyer said:

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.

This part here is why I think there's no cameras; no real need for them

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I believe they baselined 25.5m/s for observations, and that would be sufficient for 10 years of observations in random directions (fuel can be saved by momentum-conserving manoeuvres).

https://www.reddit.com/r/spacex/comments/r616aw/comment/hqq67z3/

66.5 m/s were reserved for the first couple of mid-course corrections. Of this budget they've managed to conserve ~38m/s so far. This would imply a life on the order of 25 years, bar any fuel saving exercises.

If JWST has 93-150m/s in total then there could be up to another 57m/s available additional (+~20y). Some of this may be consumed in commissioning exercises, but even so this is very good.

Initial estimates of 5y life appear to have been extremely conservative!

 

 

Edited by RCgothic
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7 hours ago, JoeSchmuckatelli said:

Why would that be?  I've been out in the deep desert many times on moonless nights and seen by starlight... Am I wrong to presume that the same would be true 'out there'?

This part here is why I think there's no cameras; no real need for them

On earth, atmosphere scatters a lot of light and reflects / deflects some of it, even during the night without clouds or moon (light pollution is a thing) :), the same way they can bounce radio waves against the atmosphere.
 

in vacuum, they would need a lot of exposure time per frame to get enough light on the cold side to see anything (even then, you would mostly only be able to see through stars occultation) without also having projectors (light or IR)

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

 

 

 

Edited by sgt_flyer
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No, it would be possible to see by starlight. Just as you would on a desert.

The reason why it's generally not possible on a spacecraft is because of the presence of very bright sunlit objects in the frame of the camera. Dynamic range is an issue.

But on a spacecraft entirely shaded by a sunshield that wouldn't be a problem. You could see by starlight just fine.

Edited by RCgothic
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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...

 

Edited by sgt_flyer
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