James Webb Telescope.

[Screwdriver]

Well the actual mirror bodies are made out of gold "plated" beryllium but I can't get the filament to load in my ancient Ender3 so they're PETG.

Having said that, I tried 24 carat gold leaf but the polishing requirements are onerus (the design allows for disassembly for mirror polishing!). Here's the best I could do with the primary mirror.



That was using home made "size" which also added to the crappy surface finish. The gold leaf is only a few hundred atoms thick....

So I'll be sticking on some gold coloured thing and be done with it. I'm not happy with this particular tape so the end result will be more mirror like.



Still working on the telescopic boom arms. Some progress made.



That's a "print in place" telescoping tube at 4mm. Getting that to stay rigid when extended was tricky but I'm happy with the final result.

Next big issue will be the giant screen. Won't be small even on this model and there will be five of them or I'll be damned. The five screen version will not fold. I would need to find a 40:1 scale version of 0.025mm Kapton tape and that would be as thin as that bloody gold foil!

[Screwdriver]

[Mr. Dazzle]

Well the actual mirror bodies are made out of gold "plated" beryllium

Beryllium is an amazing material. Its a shame its so expensive and hard to work with, otherwise you'd see it more often. Its banned in F1 now, ostensibly cause its expensive and toxic but actually more like because only a couple of teams could figure out how to work with it.

Pretty much all metal has the same stiffness/density ratio. Steel is roughly three times denser than aluminium but is also three times stiffer. Titanium is about twice as dense but about twice as stiff and so on. Its uncanny, nearly every metal is 25,000Pa per kg per cubic metre.

What that boils down to is, if you swap a steel part for an aluminium one the weight saving of the ally is exactly cancelled out by the fact you need more metal to achieve the same stiffness.*

Every metal except Beryllium, which has a way way higher stiffness/density ratio.

Tis also the main reason carbon fibre is a thing, thats also off the chart on stiffness/density compared to metals.

*Obviously there's load more to it when you start thinking about strength, manufacturing, geometry blah blah blah but you get the idea

[Screwdriver]

Materials science is an amazing subject in its own right. Almost any substance has some extraordinary strangeness or peculiarity somewhere in the range of temperature you can work with it. Then the addition of even the tiniest alloy can drastically change the material behaviour almost to the point where it becomes unrecognisable.

In addition to the above characteristics of beryllium, I understand it is also extremely stable at low temperature, the -200ºC (or so) that the mirrors have to operate at. Bit like an F1 car, the machine has been built to operate within a particular temperature range, outside that range, at "normal" earthly temperatures when they made it, each and every part would be substantially larger than it needs to be since it will of course shrink in the extreme cold of space.

For the pedants out there, space itself is not "cold". There's "nothing" in it (except a ton of radiation and quantum "foam"). Instead, you might think of anything you put there being hot with the ability to radiate that heat (in the infra red!) until it is in equilibrium with whatever incoming radiation might end to warm it up.

If you were standing there orbiting the L2 point, you would feel the blast of the suns radiation (unprotected by earths magnetic shield) and your backside would freeze solid. The JWST sun shield is another extraordinary system. Each of the five stacked layers is slightly angled so that radiation bounces between the layers until it bounces out from between the edges and dissipates into the void.

It is the most impressive single item of engineering I have witnessed to date. Right up there with whatever those crazy boffins are doing at CERN. And they managed to package it into an unfeasibly small compartment at the top of a rocket. fire it into space where it can be deployed remotely in an amazing ballet of unfolding.

Makes me proud to feel human.

[Screwdriver]

[Kneerly Down]

It is somewhat reminiscent of the Hoth Radar Lasers!

[Horse]

https://www.forbes.com/sites/jamiecarte ... -and-when/

When you spend $10 billion on a space telescope you have to justify it. It’s also something of a tradition for astronomers to celebrate the start of science operations on a new telescope with a selection of images to showcase exactly what it can do.

That’s exactly what NASA will do when the James Webb Space Telescope—or Webb, for short—is ready for science.

“We are planning a series of “wow” images to be released at the end of commissioning when we start normal science operations that are designed to showcase what this telescope can do,” said Jane Rigby, Webb Operations Project Scientist, NASA Goddard Space Flight Center at a press briefing in January. “They will showcase all four science instruments and they will really knock everybody’s socks off.”

[slowsider]

I'll have a 'P' please, Bob

[Yambo]

Arrived at L2!

[Bwana]

Posted on a website in far away galaxy

I live near JSC and have inside sources of information there. The good news of full deployment recently announced isn’t the whole story and NASA management is right now desperately trying to find a way to admit the existence of a severe and embarrassing mistake on par with Hubble’s mis-ground mirror. An internal investigation has been underway for weeks and last week news of the problem came to the attention of Congress. A major scandal is about to erupt and it could not come at a worse time for NASA or the country in general.

My inside source is a member of an elite team of PhD level engineers and scientists working to understand how it happened and what, if anything, can be done to salvage the mission. They are in a very preliminary phase of what will likely be an investigation every bit as broad and meticulous as those that followed the two Shuttle disasters.

The basic facts of the situation are not in dispute and the root causes are becoming more and more clear as the engineer/scientist team follow the tracks of what will be a giant embarrassment to NASA and disappointment to a nation of already depressed, angry people.

The chain of events leading to this have an unexpected origin connected to the fact that across the entire federal workforce NASA employees have, and have had for decades, the highest job satisfaction numbers by large margins; NASA, it seems, is just a great place to work. A little known privilege accorded at most of the centers is allowing support animals to be in most areas of most buildings (Langley being the exception after the never reported poodle-in-the wind-tunnel incident). Before the pandemic I had a visitors pass that I used to pick up my anonymous friend on days his old geeky BMW from college was in the shop and the sight of all those dogs, cats, chickens and armadillos, along with miniature horses, cows, and one tiny little camel heading to the parking lots, helping their harried owners home at the end of a hard day of rocket science, is the image of the JSC family that will always be nearest my heart.

The vacuum chamber shown above has been as JSC since the beginning. It’s big enough for an entire Apollo Command/Service Module spacecraft to be placed in it. It was used for mission simulations lasting for days where astronauts operated the spacecraft while it was in a hard vacuum with realistic thermal conditions. Since the Apollo program the chamber has been used for testing spacecraft components and materials in a realistic space-like environment. In June of 2017 the Webb was brought to JSC and placed in the chamber for one last systems check before the final folding before flight. While there a tremendous failure unfolded unseen.


One of those pet-supported people whose image has stuck with me is that of Senior Engineer Chester Poindexter. An Apollo alumni, Dr. Chitty (he has a PhD in EE), as he’s known to his friends and grandchildren, began in backroom support at Mission Control and rose up through the ranks to be eventually put in charge of space toilet development for both the Shuttle and International Space Station. It was an absolutely essential task that, nevertheless, subjected Dr. Poindexter to an endless series of micro-aggressions; the first letter of his nickname was changed and he once attended a meeting where a toilet seat had been place on his assigned chair. Being a consummate professional, he took these insults in stride and went on to oversee the successful development of a system without which human exploration of space would be completely obstructed.

When his role as what he called ‘the space plumber’ ended, he was rewarded with the more respectable, less demanding but equally important job of overseeing the big vacuum chamber in building 32. It was in this role that I remember him dressed in all black carrying his briefcase with his cat Flumpy riding on his shoulder as he walked to his VW bus painted up to look like the Shuttle. On chilly days he wore a cape.

In early June of 2017 preparations to receive the Webb into the big vacuum chamber began in earnest and Dr Poindexter’s meticulous oversight often required that he work all night. He began to sleep in his office and have his wife ‘Missy’ bring him clean clothes and various feline supplies for his ever supportive cat, Flumpy. As the testing proceeded the work hours increased and Flumpy often remained in the office.

When the tests were completed, close out teams from JPL and Goddard were brought in to place the Webb into the fairing which would protect it during launch. With the completion of this operation it was loaded onto the Super Guppy and flown to the Cape.

During this time, Flumpy was absent from Dr. Poindexter’s office, but was assumed to be in one of his many hiding spots amid the chamber’s many pumps, pipes and valves, but since locating the cat wasn’t part of the official checklist, this wasn’t checked. You can see where this is going — Flumpy was launched.


The first paw prints were detected during the unfolding operation — over three hundred have been identified so far. The primary aperture is 25% obstructed by what is believed to be mostly gakk and fur, with other components being referred to as FSWC (feline solid waste contamination) an acronym NASA never expected to use. Flumpy is assumed to be deceased, but his legacy will remain as the most expensive cat funeral since the time of the Pharaohs. This is about to come out. NASA does’t have enough litter to keep it covered up.

Some of the pet species should have been omitted.

[Screwdriver]

I am remodelling already. I want to include the four major instrument packages because they look so pretty.



Getting there.



Everything modelled from scratch (in Sketchup) at 40th scale. I have a working prototype with the DTA skeletised now with the correct structure (took days) and the ISIM which houses the instrument modules. NIRCAM and NIRSPEC look ok (they need work) and I am still amazed that the Ender can print such tiny framework, 2mm sections with 1.2mm locating holes! Alas, such a path leads me towards modelling the entire backplane properly.

That's this lot:



Yikes! Looks complicated but that's because it is.

What a magnificent machine the JWST is though. I literally cannot stop admiring the millions of pictures out there. It is such a fantastic accomplishment for humankind (lets just hope it works after its all cooled down and setup )

[MingtheMerciless]

Have a read on it’s reaction wheels system to reduce the use of point and steer thrusters (as well as the momentum flap).

[Screwdriver]

Have a read on it’s reaction wheels system to reduce the use of point and steer thrusters (as well as the momentum flap).

I am familiar with those systems. Which aspect do you find compelling? TBH, while reaction wheels are hardly "old hat" they are as old as space exploration itself being fitted to all spacecraft and satellites.

Interestingly, the JWST has a fine steering mirror which mitigates the need for reaction wheels to constantly keep the thing pointing in the right direction.

I find the whole thing so overwhelming, I think I might be having an episode.

I spent AGES trying to find good intel on the dimension for some of those extraordinary instruments. The sheer level of technical information is gargantuan. So much technology packed into one thing. Bizarrely, my favourite part is still the secondary mirror folding arm. I can't stop playing with it, it's such a delightfully simple engineering solution.

I bet @Mr. Dazzle is having similar issues with the composite materials they created to allow this thing to survive launch forces.

Another curious phenomena (obvious when you think about it I suppose) is that the model I am making, which mimics the design of the composite backplane, is itself, a surprisingly stiff structure even in thin PETG.

[Mr. Dazzle]

I bet they're actually using fairly mainstream composites for this. High performance, for sure, but not novel. I doubt there's much to he had which doesn't already exists so you'd go with known technologies. That's just a guess though.

AFAIK weight isn't a huge problem here (its about half the mass of hubble I believe).

Composites in cryogenics are well established. Pretty much every MRI scanner uses a glass and carbon fibre support structure for the cryostat - the really really cold bit. MRI scanners get down to 4K, colder even than JWST. The support structures were one of our (my last job) core products.

The same sort of technology is used anywhere else where you're holding up really cold stuff. The LHC for example or anywhere else you see superconducting magnets.

[MingtheMerciless]

Have a read on it’s reaction wheels system to reduce the use of point and steer thrusters (as well as the momentum flap).

I am familiar with those systems. Which aspect do you find compelling? TBH, while reaction wheels are hardly "old hat" they are as old as space exploration itself being fitted to all spacecraft and satellites.

I never realised they used them, always thought is was done with thrusters. It’s fascinating that something “spiny” and mechanical can last for so long in a really harsh environment. Apparently two of the Hubble’s wheels were swapped out after electrical anomalies and the wheels lube was found to be in excellent condition after 7 years in space. Different I know but the lube in my MTB bottom bracket bearings is shot after 3 months of winter riding.

[Mr. Dazzle]

'They' use a combination of reaction wheels and gyroscopes. You can get a control torque from a gyroscope by taking advantage of precession. I don't think JWST has gyros too though.

That's something else we used to make - carbon flywheels that spin incredibly fast.

JWST also has a fourth and final 'fine steering mirror' which is completely flat. Its only job is to 'jiggle about' and relfect the image in such a way as to cancel out jiggles in the spacecraft.

[Screwdriver]

I bet they're actually using fairly mainstream composites for this. High performance, for sure, but not novel. I doubt there's much to he had which doesn't already exists so you'd go with known technologies. That's just a guess though.

AFAIK weight isn't a huge problem here (its about half the mass of hubble I believe).

Composites in cryogenics are well established. Pretty much every MRI scanner uses a glass and carbon fibre support structure for the cryostat - the really really cold bit. MRI scanners get down to 4K, colder even than JWST. The support structures were one of our (my last job) core products.

The same sort of technology is used anywhere else where you're holding up really cold stuff. The LHC for example or anywhere else you see superconducting magnets.

Yes I think you're right. Plenty of ultra high precision manufacture and of course cryogenic conditioning and other super high tech stuff but reading between the lines, they went with the best available, nothing extraordinary or novel.

The weight is "not a problem" per se, but being a six and a half metre ton of ultra high precision (nanometer scale) mirror assembly, it needed a LOT of extraordinary design features. Virtually everything is stowed away into load bearing support structures and has to be deployed after launch. That includes some hilariously complex hinge mechanisms and of course the mirror segments themselves. Then the whole thing pushes itself apart on the huge central tower (the deployable tower assembly).

Interesting fact about MRI scanners, cheers. I might go look into that. The cryogenic heat pump on the JWST is a novel invention I think, operating on the thermoacoustic principle which is a new one on me...

[Mr. Dazzle]

The "new technology" on JWST had to be taken with a grain of salt i think. I doubt there's anything totally new per se, but there will be plenty of "first large scale applications" of emerging ideas. Acoustic heat pumps have existed for decades for example.

That's not doing NASA a disservice. They're smart enough to know you wouldn't put something completely brand new just invented on such a critical task. In fact NASA invented the idea of a Technology Readiness Level (TRL) as far as I know. All the stuff on Webb would have been TRL 1 at some point (as has everything else in the world) before JWST was built...although I bet they did a lot of work bringing stuff up the TRL scale for JWST's benefit.

There will be loads of stuff currently at TRL 1-6 sort of levels which doesn't even have a specific mission in mind yet. Some will be the work of NASA, other bits at Unis and so on.

[Screwdriver]

Almost done, just the sunshield problem to solve.



Folds up, DTA can be lowered into base (on a hidden screw mechanism), boom arms telescope fully into the spaceship body, primary mirro folds, fwd/aft pallets hinge etc.



I should do a video I suppose and I might consider a kickstarter to see if I can turn this into a production model.



Should look a lot better once it's fully decorated with more shiny and some decals for the Ariane 5.

[Screwdriver]

Well the actual mirror bodies are made out of gold "plated" beryllium

Beryllium is an amazing material. Its a shame its so expensive and hard to work with, otherwise you'd see it more often. Its banned in F1 now, ostensibly cause its expensive and toxic but actually more like because only a couple of teams could figure out how to work with it.

Pretty much all metal has the same stiffness/density ratio. Steel is roughly three times denser than aluminium but is also three times stiffer. Titanium is about twice as dense but about twice as stiff and so on. Its uncanny, nearly every metal is 25,000Pa per kg per cubic metre.

What that boils down to is, if you swap a steel part for an aluminium one the weight saving of the ally is exactly cancelled out by the fact you need more metal to achieve the same stiffness.*

Every metal except Beryllium, which has a way way higher stiffness/density ratio.

Tis also the main reason carbon fibre is a thing, thats also off the chart on stiffness/density compared to metals.

*Obviously there's load more to it when you start thinking about strength, manufacturing, geometry blah blah blah but you get the idea

Only just had the chance to really look at this curious phenomena which I found here: https://en.wikipedia.org/wiki/Specific_modulus

Not only do those metals you refer to hover around the same properties, it's almost the same for balsa! That's nuts.