The James Webb Space Telescope

[Jimmy Higgins]

Speaking of the mouse on the Moon. It is certainly capable of that because it is cold enough to be sensitive to 1 photon per second rates.

And another interesting thing is that it has basically ordinary refrigerator on board, unlike previous telescopes which used liquid gases as coolant which were limited resource. The only thing which limits the telescope is fuel for thrusters, but it seems NASA thinks about refueling it. So it can last much longer than 10 years.

And I agree, future telescopes should be assembled in space (remotely)
It should be cheaper that this insane engineering.

I think that 10 year thing is more accounting than anything else. Otherwise, the price tag would scared the pants off people.

 

[Jimmy Higgins]

NASA on Twitter: "NOW: @NASAWebb experts summarize the space telescope’s first week of deployments and the next steps as we #UnfoldTheUniverse: (links)" / Twitter
NASA had a press conference:
Media Briefing: Webb Telescope Week One Deployments Update - YouTube

They found that some of the motors and pulleys had become a little bit too hot, so they tilted the spacecraft to cool them down.

They also said that once the sunshield is deployed, then the deployment process will be past 70 - 75% of the failure points of the process.

Yes, but the remaining 25% represents 75% of the potential problems.

 

[lpetrich]

Deployment Explorer Webb/NASA - deployed parts' dates updated to actual dates, undeployed parts' dates now TBD.

Turning to JWST detailed deployment schedule it is evident that deployment is now 2 days behind its original schedule. That allows me to estimate when the next deployments are.

• Wed Jan 5: Deployable Radiator Shade Assembly (DRSA), Star Tracker Support Assembly
• Thu Jan 6: Secondary Mirror Support Structure (SMSS), Secondary Mirror Assembly (SMA)
• Fri Jan 7: Aft Deployed Instrument Radiator (ADIR) on the back of the ISIR
• Sat Jan 8: Primary Mirror Backplane Assembly (PMBA) Wing 1 (port)
• Sun Jan 9: Primary Mirror Backplane Assembly (PMBA) Wing 2 (starboard)

Moving the mirrors should start a few days later.

 

[lpetrich]

NASA on Twitter: "Listen in as @NASAWebb experts give an update following today’s successful deployment of the 5-layer, tennis-court-size sunshield in space: (link)

~75% of 344 potential single-point failures are now behind us on the telescope's journey to #UnfoldTheUniverse. (pic link)" / Twitter
noting
Webb Sunshield Tensioning Telecon Recording 1 4 21 - YouTube

The tensioning phase fit very well with predictions from tests on the ground; it went better than they had hoped. Tests like of how much electric current went through the motors and what length of cable was pulled by the motors. These motors' job is now done, and they will never be run again.

A JWST team member joked that an ideal deployment would make them completely bored.

There was a bit of trouble with the sunshield covers, but they had extra evidence, and they decided that the covers deployed correctly.

Then which is the most difficult. Mechanically, the sunshield. Another team member considered the solar array the most important, because without power, one can't do much.

As to solar radiation pressure and solar-wind pressure, it has been within the team's modeling, and the spacecraft has an additional resource: the aft momentum flap, for rotating the JWST with that pressure.

Then the mirror deployments. The primary-mirror wing deployment will happen after the star-tracker deployment, and will likely be done over the weekend. Tonight, heating the motors for the secondary mirror, and over the next two days, heating the motors for the primary mirror wings.

Staff members are rested on a rotating schedule, so they don't have too many back-to-back 12-hour shifts.

 

[lpetrich]

They bumped it up a day, so it's now only one day behind.
Secondary Mirror Deployment Begins Tomorrow – James Webb Space Telescope

NASA Webb Telescope on Twitter: "We just finished deploying ..." / Twitter

We just finished deploying our sunshield today, but wait, there's more!

#NASAWebb's secondary mirror is planned to be unfolded tomorrow, Jan. 5th, in the morning (Eastern time). Read more at the blog: (link) #UnfoldTheUniverse (pic link)

Note: We will have LIVE coverage of the secondary mirror deployment on (link) starting at approximately 9:45 a.m. EST (subject to change based on Webb’s operations).

NASA Live | NASA

The picture was an animated GIF showing the folding out of the secondary-mirror assembly.

 

[lpetrich]

MIRI Instrument Marks a First Milestone in Space – James Webb Space Telescope - the Mid-Infrared Instrument

Its contamination-control cover was unlocked, though it will stay closed until the telescope cools further, to reduce the chance of contamination. Later on, it will be opened. So they haven't forgotten about their lens cap.

NASA on Twitter: "Watch live coverage starting at ~10:20am ET (15:20 UTC) from @NASAWebb mission control as teams deploy its tripod-like secondary mirror structure. The mirror will help reflect light to #UnfoldTheUniverse: (link)

Have questions? Drop them below. (pic link)" / Twitter
The picture: a closeup of the secondary-mirror holder.

NASA Webb Telescope on Twitter: "LIVE NOW: ..." / Twitter

NASA Webb Telescope on Twitter: "LIVE NOW: Today we’re deploying #NASAWebb’s secondary mirror structure, a tripod that helps the mirror reflect light to our instruments. Watch as we unfold the mirror that’s second on paper but tied for first in our hearts #UnfoldTheUniverse

: (links)

Let's show some for #NASAWebb's tertiary and fine steering mirrors too, which direct light from the secondary mirror to the science instruments! Together Webb's mirrors are a mighty light-reflecting super team that will help astronomers worldwide #UnfoldTheUniverse! (pic link)

With a 3D-model animation of the structure unfolding, and also an animation of the light path through the telescope: bouncing off of four mirrors before it goes into the telescope instruments. Incoming light bounces off of the primary mirror and is focused onto the secondary mirror. It in turn bounces light into the black tube in the middle of the primary mirror, and it bounces off of a third and forth mirror. The third mirror bounces light back toward the secondary mirror, and the fourth mirror bounces it back toward the instruments.

Historical curiosity: the first reflecting telescopes had mirrors made out of metal. Metal-coated glass mirrors became practical in the 19th cy., and they are very commonly used. The JWST reverts to the original sort of material by using all-metal mirrors -- beryllium coated with gold.

NASA on Twitter: "LIVE NOW: Teams deploy @NASAWebb’s secondary mirror, a tripod-like structure that will help the space telescope #UnfoldTheUniverse. Have questions? Use #AskNASA! (link)" / Twitter

NASA Webb Telescope on Twitter: " Secondary mirror deployed! ..." / Twitter

NASA Webb Telescope on Twitter: " Secondary mirror deployed!

But there's little time to pause and reflect. Teams will ensure @NASAWebb's tripod structure is latched before beginning its final major milestone this week: full deployment of the space telescope's honeycomb-shaped primary mirror. (pic link)

CONFIRMED: “The world’s most sophisticated tripod” has not only deployed but also latched!

Each of the struts for this tripod, which helps #NASAWebb’s secondary mirror direct light into the instruments, is about 25 feet long (7.6 m)! (link) #UnfoldTheUniverse (pic link)

The pictures show the JWST on its side with the secondary-mirror structure deployed. Yes, the spacecraft was tested on its sides as well as in its "normal" orientation, to get an idea of how the deployment of its parts would work in microgravity -- tested with different directions of gravity relative to it.

 

[bilby]

Just think how much more NASA could achieve if they put their best brains onto tasks such as mission planning and design, instead of having them brainstorm a more impressive way of saying 'lens cap'.

 

[Elixir]

Just think how much more NASA could achieve if they put their best brains onto tasks such as mission planning and design, instead of having them brainstorm a more impressive way of saying 'lens cap'.

“Contamination Control Covers” are what lens caps become when you put remote controlled locks on them.

 

[Loren Pechtel]

A JWST team member joked that an ideal deployment would make them completely bored.

That's always how it is. Once a bird launches the ideal mission is total boredom other than from whatever it discovers.

 

[Jimmy Higgins]

Just think how much more NASA could achieve if they put their best brains onto tasks such as mission planning and design, instead of having them brainstorm a more impressive way of saying 'lens cap'.

Gotta give English Lit majors something to do.

 

[lpetrich]

Deployment Explorer Webb/NASA has an updated schedule for the remainder of the deployment.

• Thu Jan 6: Aft Deployed Instrument Radiator (ADIR)
• Fri Jan 7: Port Wing of Primary Mirror
• Sat Jan 8: Starboard Wing of Primary Mirror

Secondary Mirror Deployment Confirmed – James Webb Space Telescope

The deployment process began at approximately 9:52 a.m. EST, and the secondary mirror finished moving into its extended position at about 11:28 a.m. EST. The secondary mirror support structure was then latched at about 11:51 a.m. EST. At approximately 12:23 p.m. EST, engineers confirmed that the structure was fully secured and locked into place and the deployment was complete.

“The world’s most sophisticated tripod has deployed,” said Lee Feinberg, optical telescope element manager for Webb at Goddard. “That’s really the way one can think of it. Webb’s secondary mirror had to deploy in microgravity, and in extremely cold temperatures, and it ultimately had to work the first time without error. It also had to deploy, position, and lock itself into place to a tolerance of about one and a half millimeters, and then it has to stay extremely stable while the telescope points to different places in the sky – and that’s all for a secondary mirror support structure that is over 7 meters in length.”

The ADIR is next.

 

[lpetrich]

NASA on Twitter: "Like a latch made in heaven, @NASAWebb’s secondary mirror is now fully deployed and locked!

The team remains focused as they work toward the final major milestone this week – deployment of the iconic honeycomb-shaped mirror. Details: (link) #UnfoldTheUniverse (pic link)" / Twitter
With an animation of the deployment. The secondary mirror is on three struts, one upside and two downside. The upside one has a hinge in the middle of it. In the assembly's stowed position, the downside struts pointed upward and the upside one was bent in the middle. For deployment, the secondary mirror moved outward and downward, and the upside strut became straightened. It is now latched in place with a latch in its middle hinge.


NASA Webb Telescope on Twitter: "Don’t lose your chill — helium is the coolest element. (It's got the lowest boiling point!) Apply pressure, and it gets even cooler.

Find out how pressurized helium helps keep the cryocooler of Webb’s MIRI instrument about 7 degrees Kelvin (-448 degrees F, or -266 degrees C)! (vid link)" / Twitter
then
NASA Webb Telescope on Twitter: "Speaking of Webb's Mid-Infrared Instrument (MIRI), how's it doing

We recently unlocked MIRI's Contamination Control Cover! Here's how that worked: (links)" / Twitter

 

[lpetrich]

Elements of Webb series:

#1: Au
NASA Webb Telescope on Twitter: "Yes, that's real gold on our mirrors. And it's not just stunning to look at — it's functional, too!

Learn why going for gold means giving Webb its best shot to #UnfoldTheUniverse. Watch the first episode of "Elements of Webb" below (vid link)" / Twitter
Gold is a noble metal, very chemically unreactive, and it is a good reflector of infrared light. Gold gets its yellow color from not reflecting blue light very well.

#2: Au
NASA Webb Telescope on Twitter: "Get this: all the gold we’ve found on Earth can fit in just 3 Olympic-size pools.

The Webb telescope's gold-coated mirrors are dazzling, but why is gold so rare on Earth? Find out in our latest “Elements of Webb” episode (vid link)" / Twitter
Then an overview of its formation in merging neutron stars: the r-process, adding neutrons very fast. The s-process is adding neutrons slowly, and the p-process is adding protons.

#3: Be
NASA Webb Telescope on Twitter: "Which element is six times stiffer than steel yet lighter than aluminum?

It’s beryllium! And here’s why we’re using it for the James Webb Space Telescope's mirrors (vid link)" / Twitter
It also expands relatively little with temperature. But it's hard to machine.

#4 Be
NASA Webb Telescope on Twitter: "What did it take to build the Webb telescope's beryllium mirrors? Millions of pounds of rock

Dig deep into how beryllium is mined with host Sophia Roberts in our latest “Elements of Webb” episode.

Credit: NASA's Goddard Space Flight Center (vid link)" / Twitter
Most of our beryllium comes from a mine in Utah with an ore that is only 0.25% Be. Ore that is buried under a lot of other rock that must be removed to get at it.

#5 Be
NASA Webb Telescope on Twitter: "#NASAWebb's mirrors are made of beryllium, and most of the world's beryllium is buried in volcanic rock. But where does beryllium *really* come from? To explain its rare beginnings, we have to talk about the cosmic origins of most elements. Watch our latest “Elements of Webb” (vid link)" / Twitter
Nucleosynthesis in the cores of stars: makes most elements heavier than helium. But helium-3, lithium, beryllium, and boron are made by cosmic-ray spallation, explaining their great rarity.

 

[lpetrich]

More Elements of Webb:

#6 Kapton - (C22H10N2O5)x
NASA Webb Telescope on Twitter: "What is Kapton? And how does material only 1/1000th of an inch thick keep #NASAWebb super chill?

Find out in this episode of Elements of Webb: A Tennis Court of Carbon. (vid link)" / Twitter
A plastic that's much like Mylar.

#7 C
NASA Webb Telescope on Twitter: "Carbon is the backbone of life — and the "backbone" of the Webb telescope! Watch how engineers incorporated this material to make Webb strong and lightweight in the latest episode of Elements of Webb.

Credit: NASA's Goddard Space Flight Center (vid link)" / Twitter
Much of the JWST's structure is made of carbon composites: carbon fibers bonded together with glue.

#8 Si
NASA Webb Telescope on Twitter: "Silicon is the go-to chip and sensor material for a reason — it works! Learn about the semi-conductor properties that make this element the right choice for #NASAWebb, in the newest episode of Elements of Webb. #UnfoldTheUniverse (vid link)" / Twitter

#9 He
NASA Webb Telescope on Twitter: "Don’t lose your chill — helium is the coolest element. (It's got the lowest boiling point!) Apply pressure, and it gets even cooler.

Find out how pressurized helium helps keep the cryocooler of Webb’s MIRI instrument about 7 degrees Kelvin (-448 degrees F, or -266 degrees C)! (vid link)" / Twitter
Not explained as well as I want, I must note. While most of the instruments of JWST are passively cooled, MIRI has an additional refrigerator, its "cryocooler", that uses liquid helium as its refrigerant. It is used because it is the only material to be gaseous at 7 K without being at super low pressures.

 

[lpetrich]

Cryocooler Webb/NASA for MIRI - it uses arsenic-doped silicon detectors that are chilled to 7 K, colder than the telescope's other detectors: 40 K.

The Webb MIRI cryocooler is basically a sophisticated refrigerator with its pieces distributed throughout the observatory. The primary piece is the Cryocooler Compressor Assembly (CCA). It is a heat pump consisting of a precooler that generates about 1/4 Watt of cooling power at about 14 kelvin (using helium gas as a working fluid), and a high-efficiency pump that circulates refrigerant (also helium gas) cooled by conduction with the precooler, to MIRI. The precooler features a two-cylinder horizontally-opposed pump and cools helium gas using pulse tubes, which exchange heat with a regenerator acoustically. The high-efficiency pump is another two-cylinder horizontally-opposed piston device that circulates a different batch of helium gas separate from the precooler's helium.

 Pulse tube refrigerator -  Thermoacoustics

It notes
How Cold Can You Go? Cooler Tested for NASA Telescope | NASA

To avoid excess heat and vibrations affecting MIRI, the Webb telescope's designers had to place the majority of the cooler behind the telescope's massive sunshield. Webb's telescope and main instrument module are protected from the heat of the sun by a shade about as big as a tennis court. With the pumping portion of the cooler on the other side of the shield, a pair of refrigerant lines -- one feed line and one return line, each roughly one-sixteenth of an inch in diameter -- are used to connect it to MIRI. In total, the cooling system involves roughly 67 feet (20 meters) worth of the thin tubing that snakes delicately throughout the observatory, carrying the recirculating helium coolant.

"There's nothing quite like this," said Kalyani Sukhatme, the instrument's U.S. project manager at JPL. "One of the complexities of this system is how distributed it is."

The MIRI cooling system has four stages, chilling gas down successively to lower and lower temperatures. The first three stages make up the majority of the cooler and take place in the cold compressor assembly -- the largest portion of the cooler. That compressor, as well as its controlling electronics, recently passed cold and vibration tests at JPL. Engineers first fitted the compressor and their electronics into a special cold chamber and tested it, then they vibrated the compressor to mimic the effects of a rocket launch, and finally tested it once again in the cold chamber, checking-out its full range of performance.

The results showed that the device is twice as efficient as required. "If a lot of extra unanticipated heat is generated by the telescope, we can take care of it," said Sukhatme.

 

[lpetrich]

Then this cutesy tweet:
NASA Webb Telescope on Twitter: "Sorry for the shade, @NASASun, @NASAMoon & @NASAEarth! But you're just not cool enough

Now fully deployed, our sunshield blocks your heat & light so that our mirrors will be able to detect faint heat signals in the universe: (link) #UnfoldTheUniverse (pix link)" / Twitter
Showing a picture of NASASun's Twitter page being blocked, NASAMoon's and NASAEarth's pages.

 

[lpetrich]

Webb’s Specialized Heat Radiator Deployed Successfully – James Webb Space Telescope

At about 8:48 a.m. EST, a specialized radiator assembly necessary for Webb’s science instruments to reach their required low and stable operating temperatures deployed successfully. The Aft Deployable Instrument Radiator, or ADIR, is a large, rectangular, 4 by 8-foot panel, consisting of high-purity aluminum subpanels covered in painted honeycomb cells to create an ultra-black surface. The ADIR, which swings away from the backside of the telescope like a trap door on hinges, is connected to the instruments via flexible straps made of high-purity aluminum foil. The radiator draws heat out of the instruments and dumps it overboard to the extreme cold background of deep space.

The deployment of the ADIR – a process that released a lock to allow the panel to spring into position – took about 15 minutes.

Right on schedule. The two primary-mirror wings are scheduled to be deployed on Jan 7 and Jan 8.

Why Doesn’t Webb Have Deployment Cameras? – James Webb Space Telescope
It was something that JWST's designers considered, but decided against. A lot of extra electronics without much gained, since the JWST has plenty of mechanical, thermal, and electrical sensors. Also, the telescope proper is in darkness, and one would have to have some light for it, meaning even more electronics. The cameras will also have to survive the great cold that they would be in: some 74 - 109 K.

 

[lpetrich]

Where Is Webb? NASA/Webb - 70% of the distance to L2, almost 2 2/3 the distance to the Moon, right now moving at 440 m/s relative to the Earth-Moon system, only 4/3 of the speed of sound in air.

Here is a very simple calculation of Newtonian-gravity motion in some special cases.. Simple if you've taken first-year calculus -- what Isaac Newton himself had to invent. The differential equation for motion:

\( \displaystyle{ \frac{d^2 {\vec r}}{dt^2} = - \frac{GM}{r^3} {\vec r} } \)

GM = gravitational constant * central-body mass. r is the radius vector.

Circular motion:

\( \displaystyle{ \frac{d {\vec r}}{dt} = {\vec\omega} \times {\vec r} ;\ {\vec\omega} \cdot {\vec r} = 0 ;\ \omega^2 = \frac{GM}{r^3} } \)

where ω is the angular-velocity vector. It points to an orbit pole.

Radial motion:
\( \displaystyle{ \frac{d^2 r}{dt^2} = - \frac{GM}{r^2} } \)

One can solve this equation with an ansatz or a guessed solution:

\( r = r_0 t^p \)

One finds

\( p(p-1) (r_0)^3 t^{3p - 2} = - GM \)

This gives us p = 2/3 and

\( \displaystyle{ r_0 = \left( \frac{9}{2} GM \right)^{1/3} } \)

I won't derive more general solutions unless anyone wants me to.

This calculation is for one object with locally-dominant gravity. But where the JWST is, the Sun's differential gravity is comparable in size to the Earth's gravity. Differential gravity meaning difference between gravity on JWST and gravity on the Earth -- the tidal force.

 

[lpetrich]

NASA Webb Telescope on Twitter: "Space telescope radiators: they’re instrumental!

Our “trap door” is now open: the ADIR (Aft Deployable Instrument Radiator) has swung out from the back of the telescope to radiate heat from our science instruments into space. (link) #UnfoldTheUniverse (pic link)" / Twitter


NASA Webb Telescope on Twitter: "We've been hearing you loud and clear: ..." / Twitter

We've been hearing you loud and clear: Why doesn't Webb have cameras for its journey to #UnfoldTheUniverse? It sounds like a no-brainer, but there's more to it than meets the lens. Thread (pic link)

1. Light

Our gold-coated mirrors were photogenic on Earth, but the mirror side of Webb is pitch dark in space. Meanwhile, the other, Sun-facing side of Webb is so shiny that cameras there would have glare & contrast issues.

2. Power

We would have to run cables and power out to cameras on Webb, and the power balance on the cold side of Webb is especially delicate. More cables adds more of a threat of heat and vibration transfer through the wires, which could impact image quality.

3. Temperature

A camera that would work at the cryogenic temperatures on the cold side of the sunshield would have to be specially designed. Plastics fall apart, shrink, and crack, and glues don’t hold together.

4. Complexity

Webb is big and changes configuration during deployments. Where do you put cameras? How many? Narrow-field ones add complexity; wide-field ones don’t give detailed information.

So how *do* we know a deployment is successful? Our spacecraft has mechanical, thermal, and electrical sensors, which provide telemetry to our ground teams. Mission control at @SpaceTelescope also has a special visualization tool to check the status of the telescope. (pic link)

Everything clicking? Read more about the considerations behind why we don’t have engineering cameras onboard here: (link) #UnfoldTheUniverse

And as for the telescope itself — don’t worry, we removed the “lens cap”:

From half a year ago:
NASA Webb Telescope on Twitter: "
Tower stowed
Lens cap removed
Sunshield pallets stowed
3 more testing milestones have been completed for #NASAWebb! The world’s most complex & powerful space telescope is making big progress for its launch & million-mile journey later this year. (links)" / Twitter

 

[lpetrich]

ESA Webb Telescope on Twitter: "#Webb has just crossed the 1 million km mark, having now completed 2/3 of the distance.

If you want to go fast, go alone. If you want to go far, go together. @NASA / @esa / @csa_asc

#WebbSeesFarther
Animation: @NASAGoddard (vid link)" / Twitter
That animation video showed only the Sun and it seemed to show the JWST going toward the Sun. Or else it was from a viewpoint that overtook the JWST.

In any case, it got right that the telescope proper is in darkness, shaded from the Sun.

NASA on Twitter: "Get ready for @NASAWebb's final unfolding!

We'll have live coverage on social media and NASA TV as Webb deploys its second and final primary mirror wing, with our broadcast beginning no earlier than 9am ET (14:00 UTC) Sat., Jan. 8: (link)

#UnfoldTheUniverse (pic link)" / Twitter
noting
NASA to Host Coverage, Briefing for Webb Telescope’s Final Unfolding | NASA

Avonord on Twitter: "@NASA @NASAWebb Second primary mirror wing on Saturday. So, the first primary mirror wing tomorrow?" / Twitter

NASA on Twitter: "@Avonord @NASAWebb That's right! The second deployment will mirror the first one.
Here's our timeline: (link)" / Twitter


James Webb Space Telescope Testing Progress Continues | NASA
From half a year ago. The removal of its lens cap:

AOS (Aft Optics Subsystem) Cover: Removed

Webb’s “lens cap” has been removed! A technician can be seen carefully removing what’s known as Webb’s aft optics subsystem cover. This important piece of protective equipment has kept the observatory’s instruments clean, contaminant-free, and safe from stray light while it was assembled and fully prepared for flight. Now that launch is so close, the cover has been removed to allow engineers freedom to continue packing up the rest of the observatory into its flight-like formation.