terramex

Final optical instruments were integrated in 2014, proposed launch date at the time was 2018. There was not enough time to think about any upgrades and cost was ballooning anyway.

NIRCam has quantum efficiency of 70 to 90% depending on light frequency. https://jwst-docs.stsci.edu/files/97978241/97978242/1/159607...

MIRI has average efficiency of about 50%. https://jwst-docs.stsci.edu/files/97977640/97977649/1/159607...

Internal noise of electronics is not significant compared to thermal noise at operating temperature of MIRI (7 Kelvin).

Further small improvements might be possible in the future but no 'orders of magnitude' can be expected without going into even colder temperatures, that would require total redesign.

At the end of the day, efficiency can be offset by simply taking longer exposures so it is nice to have but does not have to be super optimised. Achieving diffraction limit is much more important and JWST's camera do that.

https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam... https://jwst-docs.stsci.edu/jwst-mid-infrared-instrument/mir...

No, cameras' resolution is limited by diffraction that is a function of mirror size. JWST achieves that diffraction limit in range between 2 to 28.5 micron where most of it observations will be performed. As for sensitivity, installed instruments are state of the art, finding any improvements would necessitate multi-year research programs.

CPU it uses is RAD750, pretty standard radiation-hardened CPU for spacecrafts. https://en.wikipedia.org/wiki/RAD750

More powerful and modern CPU would not enable any more science to be gathered and only increase chance of failure. Maybe some power saving could be achieved, but that CPU requires only 5W from 2000W produced by solar panel anyway.

> As an additional challenge, the JWST observation schedule in the next 21-day period will not be known at the time of SK [station keeping] maneuver planning. A planned observation schedule one week ahead will be available, but the actual observation schedule will be event-driven. If a ‘target of opportunity’ arises then the schedule can be changed within 48 hours to point at the new target.

https://ntrs.nasa.gov/api/citations/20140007519/downloads/20...

Momentum flap will bring average CoP closer to CoM but CoP will shift as JWST is rotated to point at different targets. Unwanted torque can be minimised by carefully choosing observations targets so it mostly cancels out but it cannot be done perfectly.

> That's a fixable design problem.

You are right, it is fixable. It was fixed by adding active station keeping to the telescope.

> Or you can rotate the telescope.

There are limits on its rotation with respect to the Sun, dark side must be kept away from sunlight at all times. It can rotate 5 degrees "pitch down" toward the Sun and 45 degrees "pitch up". Gimballed antenna has enough authority so that it can communicate with Earth at whatever valid rotation telescope is so that science operations are not interrupted for transmitting data.

> The earth and the moon are nearby anyway. What about that reflected light? And heck, what about the sun limiting its field of view?

That light is reflected back by sunshield as all 3 bodies are behind it. Sun is limiting field of view but area of exclusion changes as telescope orbits and it can image every point in the sky at least every 6 months and 39% of the sky at any given moment.

Here is a paper detailing metal reaction wheels failure modes going into detail on how charge was built up and solar influence on this process: https://www.esmats.eu/esmatspapers/pastpapers/pdfs/2017/bial...

I cannot find primary source for JWST using ceramic bearings right now, but I know they are manufactured by Rockwell Collins Deutchland and have good track record: https://jwst.nasa.gov/content/forScientists/faqScientists.ht...

TELDIX (today owned by Rockwell Collins Deutchland) invented use of ceramic bearing in reaction wheels for spacecraft use in 1978: https://patents.google.com/patent/DE3027209A1/en

so it would make sense that JWST uses ceramic bearings. Other manufacturers (ITHACO) have switched to ceramic too.

> Some high priority scientific observations (GTO & GO) with the JWST are likely to be carried out during the commissioning period, since it is clearly desirable to begin to take science data as early as is technically feasible.

> Early Release Observations (EROs) will be taken by JWST during both the commissioning and post-commissioning phases of operation. These observations will be chosen to have wide public appeal and are designed to demonstrate the capabilities of the JWST instruments. Publication or reporting in any form of results of these observations is embargoed until the EROs are released.

https://jwst-docs.stsci.edu/jwst-opportunities-and-policies/...

There is a chance for first images to be released before commissioning is complete, but no dates announced so far.

There are no plans at the moment because it is not even clear how long will current fuel supply last. NASA engineer today said "maybe 20 years, roughly speaking", my back-of-napkin math says that it could be up to 30 if everything goes great. It will depend on exact schedule of observations, number of unexpected transient observations and solar activity. Computer simulations of its orbit and solar wind pressure have some error bars that will be corrected once we get solid data. It also has funding for only 5 years of ground operations right now. Once the mission get extended and we have solid understanding of how it behaves in space we could think of designing refuelling mission. It has fuel port so it is possible in principle, but I don't expect any concrete plans within 10 years.

> Some high priority scientific observations (GTO & GO) with the JWST are likely to be carried out during the commissioning period, since it is clearly desirable to begin to take science data as early as is technically feasible.

> Early Release Observations (EROs) will be taken by JWST during both the commissioning and post-commissioning phases of operation. These observations will be chosen to have wide public appeal and are designed to demonstrate the capabilities of the JWST instruments. Publication or reporting in any form of results of these observations is embargoed until the EROs are released.

https://jwst-docs.stsci.edu/jwst-opportunities-and-policies/...

There is a chance for first images to be released before commissioning is complete.

Actually LUVOIR will most likely have smaller 6 meter mirror to reduce cost and use lessons from JWST construction. It will be simpler design than JWST as it will use only 2 or 3 layer sunshield and no cryocooler (creating equipment that can work at 5 Kelvin was massive issue for JWST). Its main science goal will be examining atmospheres of exoplanets, plus general observations like Hubble.

It will observe in UV/visible/near-IR so its resolution will be higher than JWST's as shorter wavelengths are easier to focus (diffraction limit is a function of wavelength) but it will not be able to see objects at the very end of observable universe as it cannot image in mid-IR or longer wavelengths. There is still plenty of interesting stuff closer to us and it will be "true" successor to Hubble.

> It's like saying if you invent the first microscope, and discover bacteria, why bother with another one?

Exactly, why bother with discovering millions of bacterias with 20 copies of the same microscope if for the same cost can build 5 different microscopes allowing discoveries of thousands of fungi, viruses, protozoans, algae, plankton etc.

In astronomy there are multiple bands to observe - gamma rays, x-rays, EUV, UV, visible light, near-IR, far-IR, short/medium/long radio waves. There are also gravitational wave observatories and special instruments like spectrographs and coronagraphs for imaging exoplanets. Every of those observations needs highly specialised instrument but brings a lot of new insight about what is happening in the universe.

Most of Hubble's groundbreaking discoveries came in first 10 years of its operation. Less in next 10 years. Even less in third decade. In fact its final service mission had been cancelled once but was reinstated once it was clear that JWST will be massively delayed and risky. For combined cost of Compton (gamma/high x-rays), Chandra (low x-rays) and Spitzer (infrared) we most likely could have built and launched another Hubble, but there was no point as those 3 generated much more valuable science than another Hubble ever would.

> The reason Kepler ran out of fuel when it did was that it was expending more maneuvering fuel for attitude control because two of its four reaction wheels failed. Hubble and the ISS also had similar failures.

And to calm down anyone afraid of JWST sharing the same fate - construction of reaction wheels have been changed some time ago to make them significantly more reliable. The source of issues on Hubble, Kepler, FUSE, Hayabusa, Dawn and TIMED was electrical arcing between metal parts of reaction wheels. Static charge was building up like when you rub a ballon against your head. That charge caused arcing that in turn caused metal pitting and increased friction leading to failures. That failure mode was understood only in late 2007, when Kepler was already fully build and ready for launch.

JWSt uses new generation ceramic bearing in its reaction wheels, they have been used in spacecrafts since 2010 with great performance.

It matters a lot, L2 is unstable point so if it ventures beyond L2 there would be no way to bring it back and it would enter a heliocentric orbit. Communication between Earth and telescope would become impossible after some time as gimballed antenna can only rotate so far and stray light reflected from Earth would limit its field of view.

Due to that JWST will always be on 'close side of L2' and technically in slow freefall back to Earth and boosted up periodically, but always a bit short of passing to the other side.

It will surely take plenty of engineering and calibration photos during that time. I don't think they will be published instantly because telescope operators want to make a 'wow' effect with first photos from JWST.

Here is first technical image from Hubble, before its mirror's flaw was discovered: https://stsci-opo.org/STScI-01EVTBEME0059ASGX8X3DFWZMX.jpg

There is a bit of exaggeration, for example non-explosive actuators that needed to be released for sunshield to deploy have two redundant electric circuits for their deployment but are considered 'single points of failure' as compound part. Propulsion system is also considered SPoF but there is some redundancy built in, like there are two independent sets of thrusters feeded from one fuel tank.

Some other parts don't and cannot have redundancy due to design.

Pressure from solar wind will constantly put some torque onto telescope as its center of pressure is offset from center of mass. This torque will be counteracted by reaction wheels but they have maximum rotation speed and need to be unloaded using thrusters periodically.

Similar question was just asked during press conference and the answer was "telescope is cooling a bit faster than we simulated but it is not a significant difference, it might be ready one or two days ahead of current estimation".

Current timeline is for getting all 4 cameras to work, but I think only one needs cryogenic cooling, other 3 could work with just sunshield. In another answer one of the engineers said that first images will be released once telescope is fully operational (aka all 4 instruments cooled down).

> Mike Menzel: 49 of the 344 single point failures remain and will remain throughout the mission. They are the same types of things on every mission, like propulsion. 15 are related to the instruments.

https://twitter.com/SpcPlcyOnline/status/1479900221131964421

I've read that optical tracking/docking markers were added around mating ring that connected JWST to Ariane upper stage. It does not mean that docking to it will be easy but it was at least considered.

It does use helium only as refrigeration fluid in closed cycle, it does not get depleted. Building a cryocooler capable of achieving so low temperatures without boiling helium off was a major hurdle in JWST development.

Hubble needed to hide mirror because it is passing from sunlight into shadow every 47 minutes and mirror has to be protected from thermal stress. Also Earth emits some light even on night side that would interfere with observations.

JWST's mirror is always in shadow and stray light from sides will not be a problem at L2.

Not an IR astronomer, but enthusiast astrophotographer. As I understand it there is a bit of leeway in the sunshield. They added strips of "duct tape" going across layers to prevent potential tears from spreading and telescope can still achieve full science power with few tears in the sunshield, depending on their location and sizes. With bigger tears it might be possible to still carry out observations in visible spectrum and near-IR but not in mid-IR as thermal radiation would crush the signal. Mission would still be considered failure in that case.

It has a docking ring for potential service mission.

An article clearing it up a bit: https://www.autocar.co.uk/car-news/new-cars/renault-zoe-give...

Matthew Avery, Euro NCAP board member and chief research and strategy officer at Thatcham, told Autocar: “Every few years, Euro NCAP raises the bar by introducing new tests which either exploit new technologies or lift the hurdle to make manufacturers do better. If everyone is five-star, we need to lift the barrier."

As a result of these alterations, he explained: “When we first tested the Zoe, it did reasonably well and had all the elements you needed back then to get a reasonable score. But if you've still got the same design 10 years later, you aren't going to score as well.”

"The Zoe was launched in 2013 and received 5 stars with Euro NCAP protocol at that time. The Euro NCAP protocol has since 2013 undergone five changes. With the same equipment, a model can lose up to two stars in each protocol change.

I was not aware how quickly and dramatically the tests change, it makes comparison between different models almost useless unless you read through entire test protocols.

> On M1 Air there is pwm flickering which makes impossible to work with it

According to table you linked M1 Air has PWM frequency of almost 120 kHz, which very high and well above headache and eye strain inducing frequencies.

I'll add one idea to the list: tracking moving objects using IBIS.

Like when you shoot moving car or flying bird - use existing autofocus to detect the object and then track it over exposure time to keep it free from motion blur but get nice, blurred background. Pentax have simple version of that for tracking stars mentioned in the article but I hope some company figures out how to do it for arbitrary, fast moving objects in real-time.

Sony a9 series already got rid of blackout during shooting so it is technically possible to get image data in realtime, have continuous autofocus and save full size RAW files at the same time: https://www.youtube.com/watch?v=_ZXFI-eIXk8

Etsy is 404 too: https://www.etsy.com

Seems to be a bigger issue.

edit: Nest is down too: http://nest.com

Fitbit.com is 404 too: https://www.fitbit.com

Big GCP issue?

edit2: Downdetector.com shows multiple website and services as down, including Pokemon GO or Rocket League.

GCP status page is still green all over the board: https://status.cloud.google.com

19:10 CET update: Some websites are coming back, including spotify.com, but their app still does not work for me.

information about outage just added to GCP status page, direct link: https://status.cloud.google.com/incidents/6PM5mNd43NbMqjCZ5R...

Description: We are experiencing an issue with Cloud Networking beginning at Tuesday, 2021-11-16 09:53 US/Pacific.

Our engineering team continues to investigate the issue.

We will provide an update by Tuesday, 2021-11-16 10:40 US/Pacific with current details.

We apologize to all who are affected by the disruption.

19:20 CET update:

Description: We believe the issue with Cloud Networking is partially resolved.

Customers will be unable to apply changes to their load balancers until the issue is fully resolved.

We do not have an ETA for full resolution at this point.

We will provide an update by Tuesday, 2021-11-16 11:28 US/Pacific with current details.

Spotify desktop app still not working for me.

19:45 CET: Spotify app is back online for me.

I tried again got it working this time. I turns out that in versions below 12 the way to set up mirroring of only 2 out of 3 displays is: "Press and hold the Option key and drag one display icon onto another display icon to mirror those two displays.". 10 years of using Mac every day and never knew it was possible.

It is pretty buggy though, "Arrangement" tabs stops working and I cannot change relative screen positions anymore, so to get it kinda working I had to set my real and dummy displays to the same lower resolution before dragging one onto the other and then I could set my desired resolution on dummy screen and it got mirrored onto physical screen.

Is this a macOS 12 feature? I am stuck on 11 for now and I do not see any Main/Extended setting.

Is there a way to keep using internal screen? When I turn mirroring on, internal display starts mirroring virtual screen too. Readme says "Your internal screen will be available as an extended space on a MacBook" but I do not know how to do it.