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the james webb telescope


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I’m surprised that it’s unfolding during…ascent.  Not sure why it surprised me, it’s not like there’s wind resistance and aerodynamic considerations.  
 

so initially I was thinking they’d have to wait for it to arrive at L2 and then unfold and THEN figure out if it’s working. But I guess they’ll know in a month?

Can they turn it around for near earth orbit repairs if not?

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4 hours ago, Pato del Muerto said:

 

Can they turn it around for near earth orbit repairs if not?

This is from NASA

 

Quote

The James Webb Space Telescope is launched on a direct path to an orbit around the second Sun-Earth Lagrange Point (L2), but it needs to make its own mid-course thrust correction maneuvers to get there. This is by design, because if Webb gets too much thrust from the Ariane rocket, it can’t turn around to thrust back toward Earth because that would directly expose its telescope optics and structure to the Sun, overheating them and aborting the science mission before it can even begin.

 

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9 hours ago, Pato del Muerto said:

I’m surprised that it’s unfolding during…ascent.  Not sure why it surprised me, it’s not like there’s wind resistance and aerodynamic considerations.  
so initially I was thinking they’d have to wait for it to arrive at L2 and then unfold and THEN figure out if it’s working. But I guess they’ll know in a month?
Can they turn it around for near earth orbit repairs if not?

There would be structural shaking considerations during 'ascent', meaning when the rocket is accelerating the ship, so you dont want to unfold too soon, but the 'ascent' is mostly done now. The main remaining burn (MCC-1a) is happening about now (fingers crossed), and the only thing unfolded so far is the solar panel which let the telescope stop draining the battery. Once the MCC-1a burn (and another smaller MCC-1b) is done, it basically coasts into place. It just takes some days to get there.

And there is no chance for repair if something goes wrong. The telescope is on its way to L2 and is not coming back.

Edited by pantone159
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And MCC-1a is done, all seems fine. Nothing left in the deployment is time critical, so ground crew can monitor the spacecraft and tweak the unfolding process if needed.

https://blogs.nasa.gov/webb/2021/12/25/the-first-mid-course-correction-burn/

The next step is putting the good antenna into place, then one more smaller burn to be right on track for L2. Merry Christmas, and thanks Santa!

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The NASA blog is really good for following along as this gets unwrapped. It sounds like the first 'glitch' has happened and has been overcome: After releasing the covers for the sunscreen, some of the contact switches did not trigger, which could have meant that the release did not work properly. But after checking things, it seemed that the release was ok, the switches just did not signal right. So NASA took it slow in extending the sunshield booms, but that all worked fine, so all seems to be good still.

https://blogs.nasa.gov/webb/2021/12/31/with-webbs-mid-booms-extended-sunshield-takes-shape/

 

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Posted (edited)

Am I misremembering, or is the sun shield tensioning already lowering the high temperature? I thought that temp had reached 170F+, but now reads 136F.

Edited to share:

Material Make-Up 

The sunshield consists of five layers of a material called Kapton. Each layer is coated with aluminum, and the sun-facing side of the two hottest layers (designated Layer 1 and Layer 2) also have a "doped-silicon" (or treated silicon) coating to reflect the sun's heat back into space. The sunshield is a critical part of the Webb telescope because the infrared cameras and instruments aboard must be kept very cold and out of the sun's heat and light to function properly.

Kapton is a polyimide film that was developed by DuPont in the late 1960s. It has high heat-resistance and remains stable across a wide range of temperatures from minus 269 to plus 400 Celsius (minus 452 to plus 752 degrees Fahrenheit). It does not melt or burn at the highest of these temperatures. On Earth, Kapton polyimide film can be used in a variety of electrical and electronic insulation applications.

The sunshield layers are also coated with aluminum and doped-silicon for their optical properties and longevity in the space environment. Doping is a process where a small amount of another material is mixed in during the Silicon coating process so that the coating is electrically conductive. The coating needs to be electrically conductive so that the Membranes can be electrically grounded to the rest of JWST and will not build up a static electric charge across their surface. Silicon has a high emissivity, which means it emits the most heat and light and acts to block the sun's heat from reaching the infrared instruments that will be located underneath it. The highly-reflective aluminum surfaces also bounce the remaining energy out of the gaps at the sunshield layer's edges.

Edited by Willfully Horn
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willfully plaintext:

Material Make-Up 

The sunshield consists of five layers of a material called Kapton. Each layer is coated with aluminum, and the sun-facing side of the two hottest layers (designated Layer 1 and Layer 2) also have a "doped-silicon" (or treated silicon) coating to reflect the sun's heat back into space. The sunshield is a critical part of the Webb telescope because the infrared cameras and instruments aboard must be kept very cold and out of the sun's heat and light to function properly.

Kapton is a polyimide film that was developed by DuPont in the late 1960s. It has high heat-resistance and remains stable across a wide range of temperatures from minus 269 to plus 400 Celsius (minus 452 to plus 752 degrees Fahrenheit). It does not melt or burn at the highest of these temperatures. On Earth, Kapton polyimide film can be used in a variety of electrical and electronic insulation applications.

The sunshield layers are also coated with aluminum and doped-silicon for their optical properties and longevity in the space environment. Doping is a process where a small amount of another material is mixed in during the Silicon coating process so that the coating is electrically conductive. The coating needs to be electrically conductive so that the Membranes can be electrically grounded to the rest of JWST and will not build up a static electric charge across their surface. Silicon has a high emissivity, which means it emits the most heat and light and acts to block the sun's heat from reaching the infrared instruments that will be located underneath it. The highly-reflective aluminum surfaces also bounce the remaining energy out of the gaps at the sunshield layer's edges.

Edited 5 hours ago by Willfully Horn

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Craziness

 

Temperatures on the Sun/hot side of the sunshield will reach a maximum of approximately 383K or approximately 230 degrees F and on the cold mirror/instruments side of the sunshield, a minimum of approximately 36K or around -394 degrees F. Due to the engineering of the sunshield, this incredible transition takes place across a distance of approximately six feet.”

 

 

Can I get that foil at HEB (assuming they’re open)?

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1 hour ago, UTexasFight said:

Craziness

 

Temperatures on the Sun/hot side of the sunshield will reach a maximum of approximately 383K or approximately 230 degrees F and on the cold mirror/instruments side of the sunshield, a minimum of approximately 36K or around -394 degrees F. Due to the engineering of the sunshield, this incredible transition takes place across a distance of approximately six feet.”

 

 

Can I get that foil at HEB (assuming they’re open)?

I have a tiny piece of Kapton from the Apollo 11 command module that I got for Christmas this year /csb

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Posted (edited)
8 hours ago, Elvis said:

Can they point the Hubble at it?

yes, they can point hubble at it, but hubble couldn't see it for anything useful.  hubble can resolve 1/20 of an arcsecond, or 1/72,000th of a degree.  at 900,000 miles, that's about a fifth of a mile.  so, webb, big as it is, is too small for hubble to resolve.  and that's before you get into webb moving across hubble's field of view at a pretty high angular rate (though galaxies are obviously moving much faster, the apparent motion is very low).

Edited by elfenix
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https://www.nasa.gov/sites/default/files/thumbnails/image/hubble_mwayjet_composite_annotated.jpg

this is the black hole at the center of our galaxy rendered using data from alma, chandra, hubble and the vla

webb *should* be able to improve this image by "orders of magnitude"..... 2 is plural and would be a 100x improvement, 3 would mean a 1000x improvement.....

the zen master says...... we shall see....

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