JWST Countdown To Terror 😳

[Floater]

Phew! Just found this on spacepolicyonline.com and feeling a bit better.

Mike Menzel, Mission Systems Engineer at NASA’s Goddard Space Flight Center, which manages the program, told reporters today that just 49 single point failures remain. They are common to most spacecraft, such as the propulsion system, and will remain throughout the lifetime of the telescope.

Edited January 9, 2022 by Floater

[Macavity]

Maybe my less than serious reflection re. Apollo 11 vs. Luna 15! 🙃
https://en.wikipedia.org/wiki/Luna_15 (Space is still a big place).
Interesting, the Russians "revealed the flight plan", at that time. 😎

The shape of things to come? Fortunately L2 is "self-cleaning"...
https://en.wikipedia.org/wiki/Collision_avoidance_(spacecraft)
 

[jock1958]

I like a bit of Lego, this years Christmas pressie maybe 🤔 

[kirkster501]

I think they are going to commence with the mirror positioning today now that the shaded side has dropped low enough in temperature.

[maw lod qan]

I can just imagine the person who gets to squeeze the shutter button the first time, standing in the back asking,

"How long is this going to take??"

[Stu]

33 minutes ago, maw lod qan said:

I can just imagine the person who gets to squeeze the shutter button the first time, standing in the back asking,

"How long is this going to take??"

They did remove the lens cap (secondary cover) didn’t they? 😱🤣.

 

[Swoop1]

As long as no one installs security lighting and a patio heater, they should be OK?

[Stu]

18 minutes ago, Swoop1 said:

As long as no one installs security lighting and a patio heater, they should be OK?

And the Bluetooth shutter release works…

[Swoop1]

At leas they won't need to worry about polar alignment.

[kirkster501]

There are still a lot of moving parts to getting this thing deployed yet, despite the success so far.

The mirrors themselves have to be "unlocked" (they were locked to prevent the launch vibrations wrecking them). The unlocking moves the mirrors - the entire mirror segment -  forward by about one cm.   Do that 18 times.  But then, amazingly, they can be moved to nanometer precision with respect to each other.  How can any motor have the granularity to do that?  As an engineer myself I find that fascinating.  Even a motor focus that many of us use on our home telescopes can move the focuser to micron accuracy.  But to nanometer accuracy, in those extreme cold temperatures after surviving the stresses of launch?  It is quite incredible.

You can see why this thing cost $10billion.

Edited January 11, 2022 by kirkster501

[kirkster501]

7 minutes ago, Swoop1 said:

At leas they won't need to worry about polar alignment.

They still need very long exposures though.  If you take a 30 minute exposure to image extremely distant objects in the depths of the early universe, even the orbit of the telescope around the sun during that 30 minutes will blur the image.  The imaging sensor has to be moved very slightly with either the entire telescope or the fine guiding mirror to compensate for that orbital motion and the amount of movement is dependent on where in the sky it is imaging.

The more you think about it the more amazing this telescope and its engineering becomes.

[tomato]

I’m pretty sure it’s not done by worm gear reduction.😊

[Stu]

1 hour ago, kirkster501 said:

There are still a lot of moving parts to getting this thing deployed yet, despite the success so far.

The mirrors themselves have to be "unlocked" (they were locked to prevent the launch vibrations wrecking them). The unlocking moves the mirrors - the entire mirror segment -  forward by about one cm.   Do that 18 times.  But then, amazingly, they can be moved to nanometer precision with respect to each other.  How can any motor have the granularity to do that?  As an engineer myself I find that fascinating.  Even a motor focus that many of us use on our home telescopes can move the focuser to micron accuracy.  But to nanometer accuracy, in those extreme cold temperatures after surviving the stresses of launch?  It is quite incredible.

You can see why this thing cost $10billion.

Agreed! It’s not just having the adjustment though, it’s knowing what to do with it! Each mirror has seven adjustments, a centre (which adjusts the curve as I understand it) and six others to position it relative to the others. With 18 mirrors that’s a heck of a lot of very fine adjustment, which must have taken years to perfect the methodology to get them aligned perfectly. 
 

https://www.nasa.gov/feature/goddard/2017/aligning-the-primary-mirror-segments-of-nasa-s-james-webb-space-telescope-with-light

[900SL]

It's a phenomenal engineering achievement.

Just the materials science alone.. getting all those components to operate on the dark side with operational temperatures at -200C or more, thermal gradients of 300+C, it's remarkable. It's a welcome demonstration of what we can achieve when we put our minds to it, and a refreshing counterbalance to Covid et al.

 

 

[gilesco]

2 hours ago, Stu said:

With 18 mirrors that’s a heck of a lot of very fine adjustment

It's going to be like collimating 18 telescopes based on the stack of images received from all?

[Stu]

27 minutes ago, gilesco said:

It's going to be like collimating 18 telescopes based on the stack of images received from all?

Yes, but much more so as they can adjust the shape of each segment as well.

[tomato]

I’m assuming the algorithms have all been coded in based on image feedback so a large part of the operation does not require manual intervention?

[Tomatobro]

I think I read somewhere that the light from each segment is only combined at the very end of the light path so if one segment is out the scope can still function.

[maw lod qan]

I just hope none of my distant Klingon brethren come by and mistake it for another piece of that human space trash!

[AstroKeith]

1 hour ago, Tomatobro said:

I think I read somewhere that the light from each segment is only combined at the very end of the light path so if one segment is out the scope can still function.

No, the segments act as one single  large mirror, but if they have a problem with a segment they would steer its output well away from the collection optics.

[kirkster501]

1 hour ago, Stu said:

Yes, but much more so as they can adjust the shape of each segment as well.

Remember the collimation of even one segment will be orders of magnitude better than what we can do with our 12" Dobs.  But furthermore, they have to do that with respect to each other as well.  Each mirror must match the others with incredible accuracy.  How would they see the airy disk????   It is beyond incredible!

Edited January 11, 2022 by kirkster501

[kirkster501]

8 minutes ago, AstroKeith said:

No, the segments act as one single  large mirror, but if they have a problem with a segment they would steer its output well away from the collection optics.

Yes, assuming they *can* steer it Keith.  What if one mirror is a complete (or becomes a complete) duffer over the lifetime of the mission so that its movement is impeded or stops working completely?  There must be ways whereby they can subtract that mirror's input to the composite optical image, maybe electronically.

Edited January 11, 2022 by kirkster501

[AstroKeith]

1 hour ago, kirkster501 said:

Yes, assuming they *can* steer it Keith.  What if one mirror is a complete (or becomes a complete) duffer over the lifetime of the mission so that its movement is impeded or stops working completely?  There must be ways whereby they can subtract that mirror's input to the composite optical image, maybe electronically.

Once you're past the secondary mirror there is no way to 'subtract' one segment. Each segment has multiple motors so your worse case scenario is (hopefully) extremely unlikely to occur. Plus they will have planned for it!

[Rusted]

2 hours ago, maw lod qan said:

I just hope none of my distant Klingon brethren come by and mistake it for another piece of that human space trash!

Who are you calling trash?

The Borg would probably upgrade it. 👾

[Ags]

4 hours ago, maw lod qan said:

I just hope none of my distant Klingon brethren come by and mistake it for another piece of that human space trash!

I would be more worried about a passing Ferengi shutle claiming salvage rights on the gold mirror!