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James Webb Space Telescope launch media kit [pdf] (esa.int)
194 points by kloch 10 days ago | hide | past | favorite | 127 comments

I find that a sense of scale is important to appreciate the Webb. Here are some of my favorite photos,


One of the taller people in there is 6'4. :)

Here's one with a human for scale standing near the mirror,


With the folded assembly,


The JWST going in for testing,


With the sun-shield unfurled,


It is important to remember that the sunshade teared during a test: https://www.inverse.com/article/42894-sunshield-rips-keep-ja... and a small detail like that, fibers from the sunshade, affected another space telescope mission, ESA's GAIA: https://en.wikipedia.org/wiki/Gaia_(spacecraft)#Stray_light_...

Putting this instrument operational at the right place is probably an unprecedented mission in terms of automated complexity.

I really really really hope JWST successfully launches and deploys. It's been almost 3 decades, countless people worked on it and billions of dollars are invested in this project. Not to mention how much it will improve our understanding of the universe. Fingers crossed.

While I agree on an emotional level that this would be a tragedy if it fails I have serious concerns about the fact that we've invested so much in this one instrument. I wonder, if the launch or the satellite was to fail would we end up firmly accepting that this was a bad idea and instead of spending 10 billion on 1 really amazing telescope we should have spent 1 billion on 10 telescopes of 500m on 20 telescopes.

I definitely don't want the JWST to fail. I've never seen an image which endears such an existential crisis as the hubble deep field.

I simply, paradoxically, wonder what good might come if this does fail.

How much of the money was spent on the James Webb itself, as opposed to research, testing, etc. that we can use on future telescopes?

Isn't that exactly the point of saying we should deploy more, cheaper per unit, devices?

Sure some of the money went to R&D but the question is not can be it be used on a future telescope, it's will it be used?

I suspect if someone wants to launch another telescope today they would look at JWST and largely say they need to start over because it doesn't make sense to start with a 20-year-old design.

Well maybe the point is that it's simply not possible to even design a telescope like this without a huge activation energy of R&D costs. If we had deployed more, cheaper devices, it might be the case that those devices, even taken together, would not have given us the information that JWST will.

Take the sunshield - the huge tarp-looking thing that you always see below the telescope itself. My understanding is that this is critical for JWST to see in the deep infrared, since otherwise heat will interfere with the imaging. Probably a lot of money was spent on the development of this. But if that money had just been spent on 20 other telescopes, none of them would have been able to capture that part of the infrared spectrum that JWST will.

The original sin is the lack of will to make the Webb nuclear powered. Since it is solar powered, it has to be in the sun. Since it has to be in the sun, it needs a huge shield. Since it is solar powered, it must be passively cooled to save power. Since it is passively cooled, it needs the science experiment - 5 layer shield deployed with 50 different pulleys, cables, telescoping poles and who knows what else.

The power limit also requires that science data be downloaded with an experimental 26Ghz radio that only the three 100' diameter Deep Space Network dishes can receive. The projected science data download will require using the DSN for 8 hours a day, everyday for 5-10 years.

They should have started over using nuclear power and then they would have had a chance.

The need to be in the sun isn't about power. Wherever JWST is, it has to be exposed to either the sun or to a planetary body that's shielding it.

At the low temperatures involved, Earth's night side puts out enough infrared radiation from its own heat to cause problems. JWST is all the way out at Sun-Earth L2 not for power reasons, but so that it will never be in a position where it needs to keep off heat from two different directions.

Nuclear does not help with this. In fact, by having a nearby penetrating radiation source and a high-temperature core mechanically connected to the spacecraft, it may be worse from a thermal perspective.

JWST is a strange spacecraft with very strange design constraints. Your intuitions about planetary/Earth-science or higher-frequency astronomy will not serve you well here.

I am not sure how you know what my intuitions are. My insights come from reading the "design trades" papers about Webb published over the last 20 years.

Here is a good place to start: https://www.spiedigitallibrary.org/journals/Journal-of-Astro...

Yes, insulating an RTG from the IR sensors would have been a challenge, but one that could be completely and accurately tested on earth. The lack of sufficient power directly drove the passive cooling requirement. Which in turn drove the fraught 5 layer shield requirement - which has never been and can't be "Test as you fly" tested on earth.

The lack of power also drove the decision to use the experimental 26 Ghz Ka band downlink radio instead of a higher power and more robust X band radio.

This is good thinking. However, it seems that Earth doesn't quite eclipse the sun from L2, so it might have been complicated anyway.

My calculations tell me this is not true for Mars though. The next time we do this, we should send it to the L2 of Mars.

> The original sin is the lack of will to make the Webb nuclear powered.

There is a broader point about space exploration in general here. The science that can be delivered by nuclear powered probes is well beyond that of solar ones. Higher instrument power, better comms, longer life, more predictable power supply. It's just better. There's one place in America that makes the plutonium for RTGs.

Plutonium is the ideal RTG fuel from an engineering point of view. But controlling and securing it jacks up the costs. What we need is lots of research into less-politically-fraught fuels. Americium is looking really promising.


Arguably, this thing should have been installed on the far side of the Moon, with a relay orbiter to get data back to Earth. Then it could be serviced.

(Of course the "dark side" isn't actually dark when the Sun hits it, so that would limit the available observing time.)

The near and far side of the moon spent the same amount of time in darkness, so there's no advantage gained by putting it on the far side.

Edit: I just realized this idea comes from radio telescopes. Those would actually benefit from sitting on the far side of the moon, because that way they'd be shielded from the radio emissions of human civilization. That concept doesn't transfer to visible light or IR telescopes though.

The moon is tidally-locked, so the near side always faces Earth. It'd be a good place for a spy satellite, maybe, but less desirable for any kind of sensitive astronomical instrument.

The Earth might as well be as big as the Sun from the perspective of the IR instrumentation on JWT. They'd prefer to keep it entirely out of their field of view, which is why it's being positioned at L2. Placing the telescope on the far side of the moon would have the same effect at least part of the time, and we'd potentially be able to carry out maintenance and upgrades in the future.

> Since it has to be in the sun, it needs a huge shield.

I don't think there's any place in the solar system you can put things so that they won't be in the sun. If you're going to be in the sun anyway, better use it.

Lagrange Points can offer deployment in the shadow, or by using orbits with long times spent in the shadow while being sun synchronous.

I thought it is already designed to be at L2? But because of diffraction it still cannot stay perfectly in the darkness. It also requires propellant to stay at L2, so it’s actually only designed to be operational for 5-10 years. It’s kinda sad to see some gadgets going out faster than it takes to build it.

You can hide behind a planet

That really depends on the configuration and architecture used for the future telescopes.

The thing about telescopes is that bigger is always better, and bigger is always more expensive. 10 small telescopes will do less useful science than one large telescope. The optical capabilities of a telescope are a function of the mirror diameter.

That isn't always true, for longer wavelength in particular it's very feasible to use many smaller telescopes with interferometry to reach effective aperture sizes we could never reach with a single telescope.

However in regards to JWT I expect that a lot of its missions will collect miniscule amounts of light, making interferometry infeasible.

Why don't we just build several identical copies of things like this during development? Surely most of the cost is in the engineering, the added cost of fabricating a few of everything must not be that high. Then if it does fail for some reason, we can just try again.

This is in fact done (effectively). All components have a "flight spare", which is just a second copy. It can be swapped should any component fail before take-off. It doesn't get assembled into the whole thing though.

Other uses include debugging already-launched kit with the easily accessible copy, reusing in other projects, and ultimately, museum artifacts.

It is also worth saying that producing anything, from mirrors and cameras, to boring screws and nuts, that end up going into space, is no small endeavour. It's not the case that you can just mill something out of aluminium, then do it N more times. Here's a nice video about it: https://www.youtube.com/watch?v=QlASewYMDsg (in fact in the specific context of JWST)

Setting aside the question of whether one telescope-sized duck is more formidable than ten duck-sized telescopes, is it really plausible that the funding and management processes that produced the JWST might learn from past mistakes and evolve toward more efficient use of time and money? If we're going to make that shift at all, I personally think sending ~$10B up in smoke will hurt rather than help. We're arguably already on a good trajectory (heh) with increased competition in the launch services market threatening to break up the pork party, and that kind of loss would be a big PR blow for NASA.

>> that the funding and management processes that produced the JWST might learn from past mistakes and evolve toward more efficient use of time and money?

Nope. This is a generational project. At all levels, but more so at the top, the people involved have spent significant blocks of their working lives on this project. Many have begun and ended decade-spanning carriers totally within this one program. It has taken so long that few will be around to contribute to the next. The institutional knowledge will have all retired or moved on by the time we are ready to fund the next epic telescope.

This problem has parallels other programs such as the F-35. Nobody lives/works long enough to see the project from beginning to end. Everyone at the start moves on/up/out. Those present at the end joined in the middle after major decisions were already set in stone. Priorities shift. Deadlines measured in decades start to seem unreal. Everything slips into bloat and delay because so few expect to still be around on D-day. It's a problem with no good solution.

If JWST was designed today, with F9 reusable and Starship on the horizon, would/could it have been cheaper to have multiple launches and assembly on orbit, rather than the super complex unfolding system and all-eggs-in-one-basket launch?

>> cheaper to have multiple launches and assembly on orbit

This has only been done a handful of times outside of Kerbal. Apollo was one of the very few times that two spacecraft launched separately and then continued onto another orbit (as opposed to space stations that are built and stay where they are). Connecting two objects and then blasting them into a transfer orbit ... even Apollo didn't do that. I don't think it has ever been done. It would mean strong docking hardware and deep structural analysis to handle flexing while under even moderate thrust, something far more than aligning a couple docking ports.

Getting a delicate craft to escape velocity would require multiple burns over multiple orbits, necessitating engines that could relight many times. Electric drives could work, but they lack the thrust for a final definitive escape towards an L point.

I think it would be very valuable for humanity to start learning how to do assembly in orbit, I think china is planning to do that for their next space station. not sure if that will actually happen, but it would be cool if that sparked a new space race. I think you would be a bit disadvantaged as a superpower when the other superpower can build stuff in orbit while you can't.

Once we build the first large, pressurised hangar in space, then we will be able to start assembling stuff up there far more easily. That's the kind of space station I'm looking forward to. I'm sure assembling a spacecraft while wearing T-shirts in 0G will be far easier than working in 1G.

If only building a large, pressurised hangar in space was easy!

I have to imagine it must. Perfect practice make perfect. Another comment mentions the mission has hundreds of single-point failures, and JWST is known to have had testing hiccups on Earth.

How much better would the program run overall if it were comprised of a series of increasing-stakes missions, like Apollo? Build a dummy instrument just to test the heat shield. Send a satellite up to L2 with no optics just to test the 26Ghz link. Heck, even just one "dress rehearsal" launch and deployment would inform so much.

> Hadden : First rule in government spending: why build one when you can have two at twice the price? - Contact

This is a pretty strong claim to make without any arguments to back it up. Do you have scientific arguments as to how 10 telescopes at 1/10 the cost would have been better?

At this scale and level of tech, projects such as this are employment and research programs just as much as they are a means to get a nice telescope at the end.

Will it cost 10 billion to build it again?

I feel the same way, and I'm reminded of a quote from Elon Musk recently when discussing Starship's Raptor engine:

"It's 10-100x more difficult to design the production system than the engine itself"

So what we really need is to invest and innovate in the production of complex telescopes/probes/etc such that it doesn't cost $10 Billion and 20 years to build, and the loss of one wouldn't hinder the overall production.


I largely agree, even though you're being downvoted.

What we really need is to standardize as much of the telescope as possible.

Communications? Don't need to be bespoke per satellite. Guidance/Navigation? Doesn't need to be bespoke.

Ultimately only the actual optical payload really needs to be bespoke. Commonality of components and design can drive down prices and reduce time-to-launch.

The problem is that if you can't really just standardize every subsystem unless you're willing to give compromise your mission in the name of a one-sizw-fits-all approach. Presumably the people who built JWST passed on of-the-shelf busses for a reason. Imagine if you to tried to force JWST's bus onto every satellite:

people who don't care about pointing accuracy end up spending zillions of dollars so they can have fraction of an arc-second precision

satellites that are in Earth orbit have different thermal needs than one in L2

satellites that are less weight sensitive waste money on carbon fiber

an instrument that needs to be cooled down to 50K doesn't need a JWST-tier cryocooler, etc.

You could try having a range of things, e.g. small, medium, and large bus with a handful of interchangeable subsystems. But you're still asking designers to sacrifice their precious size, weight & power requirements

The cost doesn't come from a lack of production efficiency. A significant fraction of the cost is for testing/validation of the spacecraft, which must be done for every unit you produce. Simulating operating conditions on Earth is extremely expensive and time consuming.

It's the same reason SpaceX is eating Boeing's lunch with their space program. One uses an iterative build process, and the other uses the more historical waterfall method. That's not to say waterfall didn't or doesn't have merit here, just that it seems like technology has advanced to a place where hopefully in the future we can build these things much faster and cheaper, such that the stakes aren't so high for a single unit.

I don't disagree with your point re: Boeing v SpaceX, but precision scientific instrumentation is a very, very different domain where "move fast and break things" cannot be naively applied. The sensitivity to failure is so ridiculously high that you need 6 to 7 sigmas of reliability for each of ten thousand critical components in order to even have just a 90% chance of mission success. Something as simple as an instrument bring slightly out of tolerance, faulty rad-hardening on a CPU, the sun shield having a minor tear, are all enough to completely jeopardize the entire mission. As a fully integrated system, JWST is at least an order of magnitude more complex than Starship, whose main design goals (launch, orbit, land, don't explode) tend to favor a more iterative approach.

Pretty sure this argument could have been levied against rocketry. For scientific telescopes most likely a frame shift would be needed to break out of this mindset that would be analogous but distinct from the one applied to rocketry.

There are two key differences between rockets and space telescopes (any space-faring probe, really) which prohibits "iterate to failure" as a development technique:

1. Forensics difficulty. You need extensive data to debug issues for complex systems. You can collect so much more data from terrestrial testing, which allows you to do the extensive forensic analysis required to achieve the required component reliability. Once you put a telescope in space, you can't inspect it anymore. A lot of the sensitive components which might fail on JWST have to be inspected to microscopic precision in order to perform adequate failure analysis.

2. Design requirements are far, far more precise. Many failures in deep space are effectively impossible to correct in later iterations due to point 1. Telemetry and sensor data is enough to debug rockets, but for JWST you would need to ship so much extra data/sensor infrastructure alongside the telescope that the whole project becomes recursively intractable.

The system complexity is so high that you absolutely must have the ability to make arbitrary system corrections because the chance of "building everything correctly the first time" is effectively zero, even with perfect hindsight! Essentially, any time you build the thing from scratch, you will always find mission-ending statistical deviations. The objective of on-ground testing is to identify and correct those specific deviations, until the whole system is within design tolerances. If you were to totally rebuild it, the next iteration will have a totally different set of statistical deviations which will need to be corrected. This process of development involves "hardening" the entire system through extensive testing, because it impossible to build a fully-hardened system to start with, even after "learning" from previous attempts.

I’m not arguing that the frame shift is identical to rockets, just that assumption breaking probably is a way to avoid such risk laden events like this launch. For example, finding a way to create a flywheel to drive costs down, or a way to take smaller steps, or a way to incentivize more disposable missions that will build on each other but can tolerate some failures. I’m not an expert but the reason rocketry is moving forward again isn’t because of “move fast and break things” per se but from a rethinking of foundational assumptions in general about how rockets “must” be developed that led to that methodology being discovered as a useful one.

I do agree with this. Most systems have significant basis in unnecessary or outdated methodologies. I think with the JWST project (with partial hindsight), we probably could have benefited from having a "stepping stone" optical telescope after Hubble which we could have used to proof out some of the hard parts of JWST. We learn quite a lot from just running missions beginning-to-end, and extremely long cycle times sacrifice this learning opportunity. It also means that we focus less on developing extensible "platforms" in favor of one-of-a-kind systems which have somewhat less carryover knowledge for the next project. Shorter mission timelines mean that you can better leverage state-of-the-art technology, rather than being forced into a design which constrains you to decade-old technology.

Maybe it's cheaper to launch 10 not so perfect telescopes and have 9 fail and 1 work.

Kind of like in computing, where we moved from a single ultra reliable mainframe to tens of commodity hardware.

No, it's actually more expensive because you don't get anything done. Precision equipment either works or it doesn't.

Commercial software development practices might be relevant where you can fix things overnight, but this is hard science instrumentation made of atoms, you ship things that must work as expected because the whole point of all this is making better measurements as the field evolves and there's a scientific case for doing it. It is not about selling production versions of the experiment to potential customers.

Then we need to design precision equipment differently. More redundant parts. More wiggle room. More fuzz testing. Find out where precision actually matters, and not just overbuild everything. And iterate more.

Sure, "move fast and break things" can't be naively applied but that doesn't mean it can't be applied.

Instead of sending up 1 super precise super accurate super reliable telescope let's send up 1000 mostly POS telescopes and combine the results using AI of the 900 which actually make it to orbit and return useful images.

I'm hardly saying that's a 100% working plan, but, I think that kind of paradigm shift which is required.

Sounds impossible to park 900 satellites on the same L2 Lagrange point. Hope you realize this telescope is to be positioned on an infinitesimally small and unstable point in empty space, on the "far side of Earth" from the Sun. Because that's the spot with the best view, apparently.

They don't park them right on L2, JWST will orbit L2 thousands of kilometers away from the exact point.

But how are you going to validate your scientific discoveries if all the images are coming through the pipeline: "POS telescope > AI upscale"?

The AI would lack training data.

If you can produce them cheaply but not test them cheaply, the solution is really simple, just don't test them. Send them to space, see what happens.

It's not like space telescopes need any of the valuable orbit space, and even if they did it's easy to put thrusters on board that can de-orbit them or move them to a graveyard orbit (depending on their operational orbit) in the case of failure.

I addressed this in another comment: https://news.ycombinator.com/item?id=28452001

To summarize, you have to have the ability to correct statistical aberrations after manufacture via extensive validation and testing, as opposed to design aberrations which can largely be eliminated through destructive iteration. Without the former process, you'll launch a million telescopes and not a single one will work.

When you build 20 scopes you can use the fail fast approach to better iterate on the next versions. It's okay if the first few fail.

Except after the second failure you have a REALLY hard time to get funding out of politicians...

Its about setting proper expectations. Its not a failure if its expected. Get the politicians to commit to all 20 launches in advanced.

This is not a device that will be produced in an assembly line. Efforts to improve its production would be nullified by the fact that every unit is itself a prototype.

I wonder about that. Hubble, after all, could have been looked at the same way from the outside, but it was essentially a proof of concept for a constellation of top secret satellites still in use today.

The opposite is true. Hubble is a stripped down version of a Keyhole spy satellite that was already in production. One of the major repairs (replace solar panels) was required because of long duration exposures used in astronomy that are not used in spying.

Remember that Hubble was essentially useless until heroically repaired the first time by Story Musgrave. Many subsequent repairs were required to get the best pictures from it - like the deep field, long duration picture.

There's another way to think of this. Let's use Starlink as an example, which is ~1300 today growing to 40k satellites in LEO.

If each of these had a high-grade commercial camera lens pointed towards earth, you could have real-time viewing of the entire planet with just a little bit of math. With a bit more fun (and for each click of optics improvements), you could "Bullet Time" view a great number of things...

If each of these had a high-grade commercial lens pointing outwards, what could that be used to capture? At scale, it seems like doing diff's against all the images would reveal a huge number of previously unidentified asteroids and other near-earth objects.

What if you put "very good" optics on them? Or a radio antenna pointed out? Could you make earth sized optical or radio telescopes? Seems like you could.

It's increasingly looking like the assumption each one needs to drive the state of the art, and each one needs to be "space grade at 100x the cost" is a fallacy simply because launching was historically so expensive.

Very frequently in this type of conversations a layman suggests "just make a constellation of low/average quality telescopes that acts like one big telescope". Presumably because they have heard of "long baseline telescopes"[1]. No, that does not work in the optical and infrared because you can not keep the signals from different telescopes coherent with one another (the technology to do that is science fiction today and it would be crazy expensive the first time realized). This is not to say there is no merit in the idea that many cheap telescopes can be useful in some other (non-visible-or-IR-spectrum) way, but the typical bombastic suggestions are simply wrong and are a disservice to an otherwise interesting idea. We will continue needing big-mirror optical and IR telescopes for quite a while if we want to continue studying the universe.

[1]: https://en.wikipedia.org/wiki/Very-long-baseline_interferome...

For the cameras facing earth, you wouldn't need fantastic resolution for it to be useful. With a resolution of 50 meters, you could track suezmax ships. With a resolution of 5 meters, you could track commercial aircraft. Not great, but it would help with a Malaysia Airlines Flight 370 like incident.

Biggest issue is that the efficiency of telescopes at detecting faint point sources scales as (mirror diameter)^4th power -- strongly favors large telescopes over arrays of small ones.

With asteroids, you don't need to diff telescopes at different locations; you can just diff the image taken at one location, 15 minutes apart.

I am so nervous about this. We get one shot for everything to go right, with no chance of fixing it.

I really hope they will be able to get spectrographs of exo-planet atmospheres, but there is almost no chance that the Webb telescope will deliver meaningful science. The Project leaders are already starting to telegraph that message:


This should have been cancelled 3 or 4 years ago when the sunk costs were only $8B. Instead we dumped another $2B into this almost sure failure

Just like the US should have cancelled all those air-craft carriers that cost as much or more? This is pennies compared to the defense budget.

Are you trying to imply that the JWT is not fit for its mission to deliver meaningful science? Because that's not at all what the article you linked says. It just says Zurbuchen admits that there's a lot that could go wrong.

Nothing, to me, indicates "almost sure failure." Just a realistic overview of the risks.

That's kinda what it's implying though. You can't outright say "yeah this thing is doomed from the start" (unless you are Elon). But you have to shape the audience's expectations. "There's a lot that can go wrong" "high risk" "many single-point failure events that have to go off perfectly" etc.

I'm not getting "there is almost no chance that the Webb telescope will deliver meaningful science" from your linked article. Can you elaborate on what you mean by this, and what statements from the project lead(s) lead you to this conclusion?

I have been following this project for years and it has had one embarrassing mis-step after another. Here is the last independent review board assessment from 2018 where they found over 300 single points of failure that would doom the telescope:


To name a couple other problem spots: They have trouble getting the shield to deploy on earth: https://arstechnica.com/science/2018/02/analysis-finds-james...

The IR detectors were replaced in 2015 because they were deteriorating in storge. Now the new detectors are 6 years old: https://optics.org/news/6/2/35

Even the 26Ghz downlink radio that can only be received the the 3 huge Deep Space Network dishes on earth is an experiment.

I really REALLY want the Webb to work, but I would take 10:1 action against.

I will make my offer concrete.

You will pay me $250 if NIRCam returns one scientifically useful observation (i.e. photograph). I will pay you $25 if it does not. If the only observations are of debatable scientific value (e.g. somewhat blurry), then the wager is off.

There are three analogous wagers for NIRSpec, for MIRI, and for NIRISS (for a total of $1000/$100).

The deadline is when all four wagers are resolved in my favor, or when it is obvious that they will be resolved in your favor (i.e. loss of vehicle), or December 31st, 2023, whichever comes first.

In the event of a dispute, we will attempt to find a JWST team member, instrument team member, or active professional astronomer to resolve the dispute via a public social media post. In the event that this does not resolve the dispute, that wager is off.

My real name is Nils Enevoldsen. You can find a $10,000 wager I have accepted with Robin Hanson at https://twitter.com/robinhanson/status/1390439816148525058.

Do you accept?

Yes I accept, but how about a definition of delivering a picture better than what is currently available?

I really want the Webb to work and would like this bet to somehow hedge my happiness. I would be happy to pay $1000 if it somehow contributed to future missions like this one being successful. Is there somewhere that money would do some good? Likewise $100 is not going to move the needle off the peg of how disappointed I will be.

What do you think about the money going to: https://www.planetary.org/ In the winners name?

I don't know enough about each of the four instruments to know that they each produce something "better than what is currently available". How about substituting the text "one scientific observation (i.e. photograph) that is either within instrument specifications or is better than what is currently available"?

I am, to be honest, substantially more interested in money going to me than in money going to someone else. However in the interest of compromise I would offer a 50/50 split with the Planetary Society (which is an excellent choice of charity). In other words, if the mission fails entirely, I will pay you $50 and also donate the Planetary Society $50 in your name. If the mission succeeds entirely, you will pay me $500 and also donate the Planetary Society $500 in my name.

Are these terms acceptable? If they are, please also let me know your real identity so that we can both be held accountable.

Every finger and toe on my body will be crossed for a month straight between launch and deployment.

I would probably take this wager, but I'd need a clearer definition of "working". What do you propose?

I have not gotten any offers to take the other side of my 10:1 offer...

I was surprised to find that it's not on any of the obvious prediction markets.

Anyway, I'm a bit of a JWST pessimist too, but I don't find any of your arguments very convincing. It feels like you're cherrypicking bad things about the program without doing a very good job quantifying why they're supposed to matter in the big picture of absolute risk.

The problem comes down to diffuse leadership. The mars lander sky crane was a crazy idea. The head of JPL raised his hand in one of the early design reviews and said so, then drilled down into why it was a reasonable solution and how they would "Test Like You Fly".

The sunshield is a crazy idea and no one challenged it. Even worse, it is impossible to test it on earth. Just about every (partial) test of the shield has revealed problems that have been patched instead of starting over. If they had made the Webb telescope nuclear powered, many problems would go away - including deploying a 5 layer, experimental sun shield.

It's also interesting to see that James Webb the administrator who took nasa from NACA to the moon is getting some attention. At the end of the day, he made the moon program work, and was made a political scapegoat at the end of it.

I think that people are also going to look at the transformation that NASA went under the last 4 years, with the rise of SpaceX, and think that this was the second most disruptive time. In both cases, the administration was run by a administrator, not a scientist.

This is also interesting — "FAQ For Scientists":


Strangely, observing the universe curving back on itself is not listed.. j/k

Hey, your https://bsrender.io/ is really really awesome! The very large generated images are mind boggling.

Thanks! I'm a total amateur (coder && astronomer) but I'm having a lot of fun with it. I started it because I wanted to see what the galaxy looked like from outside perspectives. Unfortunately the uncertainty (noise) in the Gaia parallax data makes things look weird as soon as you move the camera a short distance from the sun.

Interesting! I didn't know the telescope started to unfold en route to L2. I thought it would start unfolding after reaching L2. Are there any significant acceleration events needed to enter L2, one that might add stress to the unfolded sections?

“A trajectory can be fashioned so that JWST ‘falls into orbit’ about L2 rather than having to forcibly inject itself into a set orbit using its propulsion subsystem; this saves propellant and makes for simpler orbit maintenance.”

Quote from the JWST’s user documentation: https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-o...

So no significant acceleration event is expected as they enter an orbit around L2.

Furthermore they will have to keep doing orbit maintenance burns every 21 day while there, so they must have designed the structure with that in mind.

Found an even better source!


This paper discussed the Monte Carlo method they implemented to plan and control the orbital insertion.

At page 16 they discuss nominal burn times. The MCC-2 burn has an associated deltaV of 0.712m/s. (That is the first of many burns which happen in the unfolded state) Of course the real value will depend on how accurate the previous burns happens to be, but it provides a rough estimate of what we can expect.

I wonder how many years worth of fuel they have to maintain orbit, and what happens when orbit fails. Does it settle into the L point instead of orbiting it? Does it fly off?

It's like a hilltop, without propellent to keep it near L2 it will roll off into solar orbit.

I would assume these are well known concerns to the Webb team: if they are planning to begin unpacking prior to reaching L2, it must be because the forces involved with finalizing the orbit are well within the tolerances of the fully expanded craft.

They would not risk damage to the telescope if the processes involved weren't already rigorously tested and safe. There's a lot of eyes and quite a lot of money riding on this project.

Okay that doesn't really answer the question

Perhaps I missed it in the launch kit, but here's a link to the first cycle of approved proposals for time on the telescope, in case you're interested:


> STScI announces the selected JWST General Observer programs for Cycle 1. This follows the review of submitted proposals by the JWST Telescope Allocation Committee, which made recommendations to the STScI Director, who approved the final selection. The selection is scientifically balanced, with a distribution of science categories that broadly matches the submitted proposals. More detailed information about the approved proposals is now available.

> The Cycle 1 GO program includes 266 proposals for approximately 6,000 hours of JWST prime time and up to 1,231 hours of parallel time, as well as 15 archival and 5 theory proposals. This milestone completes the definition of the first year of JWST science, as envisioned by a broad, worldwide community of observers. The selected proposals were prepared by more than 2,200 unique investigators from 41 countries, including 43 US states and territories, 19 ESA member states, and 4 Canadian provinces.

Sometimes, I wish there was an anti-spoiler extension to block JWST until it either succeeds or fails to deploy. Headline of this project has been a reoccuring source of mild anxiety for almost a decade.

I was a little surprised (but, as a European, chuffed!) that this is launching on Ariane 5. I would have thought that Falcon 9 would be cheaper, and Atlas V would be preferred as a way of keeping it in-house. I believe they both have the capacity needed. Maybe Falcon 9 wasn't sufficiently proven when the deal was done, and Atlas V was more expensive?

Ariane 5 has a really good track record, with no failed launches since the early 2000's and only a partial failure in 2018: https://en.wikipedia.org/wiki/Ariane_5#Launch_statistics

The two launches in 2020 saw excessive vibrations on the payload after fairing separation though, which would be pretty terrible for JWST.

ESA launching their satellite on their own launch platform and on their own launch pad isn't really all that surprising, is it?

In my head, JWST was a NASA project (James Webb was an early director of NASA, during its formative years). I had completely blanked the fact that it's an international project, sorry!

Can this detect planet 9? It's supposed to be more easily seen with infrared.

Maybe, if it exists. Remember that it's only hypothetical, even if that hypothesis is a well-founded one.

It would be so crazy to discover another planet in the solar system after all these years... space is vast and dark.

Will the JWST downlink be unencrypted?

Most likely, but you'll need to find a 23GHz receiver with an insanely low SNR and a very good dish to receive properly.

China could.

The plan is to use the big dishes of the Deep Space Network to receive the signals, so regardless of encryption, you're probably not going to be able to receive its signals.

“Webb observes near infrared to mid infrared light”

Interesting. I thought all the fuss was because it would be in the visible spectrum (i.e. nice magazine photos and desktop backgrounds)

Disclaimer: I know very little about astrophotography

Almost all colour astrophotographs you see are made up of a composite of many bands, like UV, IR, X-ray, etc (and visible), with colours mapped to the different wavelengths. The instruments collect many wavelengths because it allows us to see through certain things, as well as recognise certain elements and phenomena from their spectrum.


Almost all images you see from space probes are false color - they approximate what it might look like or what might look pleasing to the human eye. There will be plenty of awesome images coming out of this bad boy.

This would be a good quick hack project-- a program that accurately blueshifts JWST images.

You can see the list of NIRCam filters here: http://ircamera.as.arizona.edu/nircam/in_filters.php#wavelen...

Only F070W is partly human-visible, everything else is off into infrared, as you'd expect.

Oh neat a picture of nothing

Because the universe is expanding the older and farther away light is the redder it looks to us. So by collecting this infrared light we can see farther back in time than we could with any other instrument before.

Here's a band comparison between UV+visible and infrared (from the JWST Wikipedia page) that I thought was fitting given the question:


It’s a good range for a wide variety of science, especially above the atmosphere.

Also a good range to sniff the atmospheres of earth sized planets for chemical composition, if everything works just right.

In theory Webb might be able to sniff out a water/nitrogen/oxygen atmosphere, some thought to most likely come from plant life.

Glad to see it's actually (finally) close to launch. I got a chance to see it in the factory (NG) a few years ago.

I didn't know it was possible to make a PDF file clickable. But thinking it again, the TOCs of PDF files have always been clickable, so I should have assumed that there were also other uses.

Actually pretty easy to do with latex and hyperref. Has been fairly standard for scientific preprints on arxiv for a decade or more.

Is there a target date for the launch? The Ariane 5 timeline mentions 2021, but nothing more specific.

When will it be shipped to French Guiana?

In July, NASA said they are targeting the launch for Oct 31, 2021.


Really well done.

where’s the interactive version?

This is the interactive version. Almost every page has links you can click to watch videos and read more about a topic.

Slide/page 3 has clickable icons to take you to those pages. I guess thats what they mean by "interactive".

Oh wow, I didn't realize those were links, looks like there are a handful scattered around.

Most of them can't be found unless you hover your cursor over the box, which is less than ideal to say the least.

Hopefully ESA doesn't mess up like they did with the Schiaparelli EDM lander.

We're so far along now that this must mean the attempts to cancel James Webb and get the name changed failed.



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