the post is really not very long and I would suggest getting it straight from the horse's mouth, but for those not willing to devote a click here are arguably the most relevant bits!
"deployment surveillance cameras would not add significant information of value for engineering teams commanding the spacecraft from the ground."
"Webb’s built-in sense of ‘touch’ (for example, switches and various mechanical, electrical, and temperature sensors) provides much more useful information than mere surveillance cameras can," said Geithner. "We instrumented Webb like we do many other one-of-a-kind spacecraft, to provide all the specific information necessary to inform engineers on Earth about the observatory’s health and status during all activities."
One thing they mentioned that kinda sends it home to me is that the telescope is aimed at the dark and away from the sun, and the other side is especially reflective[0]. In other words, one side is too dark to see, and the other is too bright to see.
It seems to me that that isn't quite right. "Dark" just means no visible light, but an infrared or thermal camera could see stuff. The article above mentions this possibility and the problems, which are harnessing and operating at cryogenic temperatures.
The point of the telescope is to capture IR light from space, if the telescope itself were generating IR light itself it would disrupt the sensor and data that it collects. Part of why its going to take so long for it to begin operating is that it needs to cool down to ultra cold temperatures before beginning operation.
Who said anything about generating infrared light? And I don't know what your last sentence is in reference to. Yes, it needs to cool down. Why is that relevant to this discussion other than what's already mentioned about that being a downside to operating cameras?
From the article so people can just debate NASA's own reporting:
> Although infrared or thermal-imaging cameras on the cold side could obviate the need for illumination, they would still present the same harnessing disadvantages. Furthermore, cameras on the cold side would have to work at very cold cryogenic temperatures.
The JWST has an extremely sensitive IR camera. And it is going to cool down to near absolute zero so that the IR sensors don't get flooded with radiation from the rest of the telescope. Because it will get so cold, it is not going to be emitting much IR (I think this is what the GP said when they said "generating"). Your typical deployment observation IR camera's won't be of much help in that case.
That makes sense, and I got thrown off (by maybe misreading the comment) thinking they meant the camera or something else would generate additional IR to illuminate the telescope, which I got confused by. It makes sense now that the comment was meaning that the cool down was to reduce as much telescope generated IR noise as possible.
I think that article is leaving out some of the other problems (which is understandable, it already covers plenty of downsides). The whole point of keeping the cold side cold is so that it doesn't emit any IR radiation (otherwise the JWST couldn't work). So by design it's "dark" to an IR or thermal camera in the same way it's dark to a visible light camera. Certainly you can build a camera to see it anyway (without extra lights), but the question then becomes how big that camera has to be, and I would assume it's way to big to be realistic.
First it’s possible to send up a camera that would be sensitive enough to use starlight to capture images on the dark side. However, those things aren’t light and would come at the cost of less propellant for minimal gain. Adding a tiny camera and a tiny light at the same time would also be possible but there really isn’t anything worth looking at via a single camera.
As to using infra red camera, they simply don’t work on objects the same temperature as the camera. NASA could have sent one up with a cooling system to look at the cold side of the sunshade, but again weight and pointlessness means it’s just wasteful.
It's probably not practical for JWST, but starlight is actually fairly bright. If you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight. At the South Pole on a clear night we would walk out to the dark sector (where the telescopes are) with our headlamps off because it just wasn't necessary. The only illumination sources outside were red safety lights[1] and we'd normally turn those off for long exposure photography. You do need a fast lens though, and that inevitably means lots of glass.
Whether the telescope is reflective enough to get a good photo is another matter - I would guess not, it's designed to minimise stray light.
As for IR, the telescope is probably bright compared to the background at least for now. The main issue though is whether you'd need to actively cool the engineering camera. Cooling stuff in space is difficult because you can only really dump heat via radiation. It's probably not worth the weight to carry a separate cryocooler just for that. The inability to conduct heat is partly why it takes so long to cool down, aside from minimising thermal stress on the infrastructure.
[1] The main reason they exist is so that you have a point of reference when walking about outside, particularly on foggy or cloud days. The meteo folks also use them as visibility markers in winter - e.g. IceCube is something like 1km from the station by line-of-sight. Turning them off for a brief period is usually fine and we'd notify the station before we did it. On a clear night though you don't need them at all.
If you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight
This reminds me... I need to experience this firsthand at some point. Thank you!
Question: how much (if any) of that light is due to atmospheric scattering? ie, the sun's light hitting the daytime side of the earth, being scattered in our atmosphere, and faintly illuminating the night side of our planet? Would the same be true in the zero-atmosphere environment of space?
Plenty of places around the world offer dark enough conditions (but make sure it’s a new moon) - in the US you just need to get out to Arizona or Joshua Tree (or similar empty places). In Europe and elsewhere look for International Dark Sky Reserves. In general go visit places where telescopes are built.
Possible that some of it is from scattering and then if course you wouldn't get that in space as there's no atmosphere to scatter from! Scattering is incredibly faint though, even compared to starlight.
See also gegenschein and the Zodiacal light - both are backscatter effects.
Slight addendum - actually you often want satellites to be reflective. Dark means good radiator, but also good absorber and a black spacecraft is about as bad as you can get for thermal management if you point it in the wrong direction. For an Earth orbiting craft that means it’ll overheat in sunlight and then dump everything in shadow - lots of thermal stress and not good for instruments that like a constant temperature. That’s why you often see sats covered in polymide foil.
Actually JWST orbits around L2 at appreciable altitude. The unique aspect of the orbit is that it is never in the shadow of the Earth or moon. It guarantees consistent solar power and thermal load.
One of the fascinating bits is how much engineering has gone into keeping the detectors cold. Because JWST is (primarily?) taking images in the mid-IR region, it is crucially important to keep the detectors cool otherwise you'd just be swamped in background noise. Keeping things cold in space is despite it being a cold place actually extremely difficult, because you can't use convective cooling. If something sits in the sun "all-day" it gets warm, so the whole reason for the sunshield is to keep the instruments cool. On top of that they are using active cooling for the (IIRC) first time on a satellite. I saw a presentation from one of the engineers two years ago and it's absolutely fascinating stuff.
My first thought is, "Why didn't they eschew solar power entirely and 'simply' park it in the shade?"
Surely they considered that, and the wins would have been massive -- no sunshields needed. So I'm sure the downsides must have been massive as well. Not enough plutonium fuel, or perhaps it just wouldn't provide enough power over the life of the mission. And of course the radioactive fuel would generate its own heat as well.
Now I need to find out more about that decision....
edit: Another commenter mentioned, "The earth's shadow never reaches L2 anyhow - it's only penumbra at that distance since the angular size of the earth is smaller then the angular size of the Sun." If that's correct, then there was never truly an option of "parking it in the shade" anyway.
The dark side of the Earth is very bright in IR. Getting far away from the Earth and moon makes them dimmer. Also, going for L2 makes sure the Earth, moon, and Sun are all always in the same direction, so the sun shield will block all significant IR sources.
Given that this does not really give the orbit any real significance in terms of being shaded by the Earth from the Sun, is there another reason it's there?
I guess it gives you a very stable position for observations, but why not just put it in solar orbit then? Then again this is kind of a solar orbit that happens to stay close to the Earth at all times so that's a plus for comms.
That's exactly what L2 is. Otherwise the orbits of JWST and Earth would have different periods. It's handy to be able to have constant high speed communications and not need large antennas with blackouts.
It also is handy to keep the closest IR sources (Earth and moon) in the same direction as the sun at all times so there is never a point where you have a significant IR source above the sun shield.
JW does indeed circle that Lagrange point, but it is definitely not in Earth’s shadow.
The JW orbit semi major axis (about the L2 point) is order of 500,000 km. The radius of Earth is about 6500 km. Thus, the shadow of the Earth is extremely small compared with the excursions of JW.
The earth's shadow never reaches L2 anyhow - it's only penumbra at that distance since the angular size of the earth is smaller then the angular size of the Sun
Besides the sun being so stupendously large that the L2 point isn't in the direct shade cone anymore. At the orbit it is in full sunshine as though the Earth isn't there.
We're talking about "see the faintest light from stars millions of lightyears away"-dark (for that reason you also can't shine a light on it), with our sun in the background. To see something on that side, you'd basically need the vision capabilities the telescope itself has and that's obviously not going to happen.
It has a selfie 'lens': NIRcam has extra optics that can be swung in that allows the camera to focus on the primary mirror instead of out in the great infinity.
So in this sense webb is already a camera which can photograph itself!
This capability exists for mirror alignment: They'll point webb at an isolated star, switch to focusing on the primary mirror, swap in optics that cause small phase differences to result in diffraction patterns, and then they can use the resulting images to fine tune the positioning of the mirror segments to a small fraction of the wavelength of light that they're using.
> to see something on that side, you'd basically need the vision capabilities the telescope itself
I'm not sure if that's correct - there's a lot of photons hitting the telescope (the night sky), and night vision systems can work off of a relatively small number of photons
Yes, I get all of that, but they still missed an excellent PR opportunity. NASA really could have built some engagement showing images of the deployment process, even if the images wouldn't have direct scientific benefit. Good PR leads to improved funding which leads to more science.
Your position is that they should have added significant complexity to a maneuver that was already the most complex of its kind. A maneuver with $10 billion and two decades of work on the line. In order to make the first 30 days of a 10+ year mission marginally more entertaining.
You propose this while fully aware that the "entertainment" in question consists of things unfolding in extremely slow motion, in total darkness.
I mean, okay.
(Thought experiment: when you think about the Hubble, do you think about the day they shoved it out of the shuttle's cargo bay, or do you think about those groundbreaking images it captured during its multidecade mission?)
NASA has often added video or image capability with low scientific value to increase public engagement, despite the associated risk and cost. They made a call not to do it this time. My only point is that it would have been a nice PR opportunity if they could have found a way to make it work within their mission parameters. I apologize if making such a simple and obvious point has offended you in some way.
Nope. In the category of probes/satellites, NASA doesn't put cameras that aren't needed. Probes on Mars get cameras, but that's because they're in a dynamic environment. They then use those cameras in fun, engaging ways.
As the aforelinked blog post explains, the extreme environment of the JWST makes this more challenging than it would be for missions like the Mars rovers.
The dark side of the JWST (where all the instruments are) will be operating very close to absolute zero and in near-absolute darkness which, of course, is the entire point of the mission.
A selfie camera there would need to function in that environment, while also somehow not polluting the instruments on that side of the camera with heat.
It's surely do-able, but it's a more complex engineering task (and would therefore require more tradeoffs) than operating a camera in the relatively balmy environment of Mars, where heat pollution is of no concern because of the different nature of the mission.
Keep in mind that doing this on the JWST also need to have been accomplished with decades-old technology, given the extremely long design and engineering lifecycle of a complex space mission.
Not really. There are no "selfies" of voyagers, Dawn, New Horizons, Juno etc. T There ARE pictures/data from what these have produced. JWST will be no different.
Even Hubble didnt really have any of that that I am aware of. Most of the pictures of hubble itself are from servicing missions.
Sure you have some rover selfies on Mars, but thats not the sole purpose of the instruments, quite the contrary really.
How much electrical power do you want to devote to this feel-good PR selfie camera?
According to the mission director SmarterEveryDay interviewed on his YouTube channel recently, the James Webb Space Telescope is so sensitive it could detect the heat signature of a bumblebee at the distance of the moon.
I’m pretty sure if you asked the astronomers if you could put a 5 Watt webcam on the dark side of their sun shield for the social media clicks, they’d tell you to fuck right off to L3…
It’s designed to see things very very far away, which are all severely redshifted. It’s mostly an infrared camera. In the human visual range of light frequencies, is camera sensors only go up to orange.
Well it can allegedly make photos of Jupiter that would be comparable of doing them during a close flyby, but that's likely not good enough for something of that sort. You'd have to see things through kilometers of ice.
I'm wondering if there is a correlation between the level of bowing to media hype by including cameras and the actual scientific value of the mission?
The recent filming of EDL of the Perseverance rover was spectacular, but a significant aim of that mission and indeed most of the recent mars rovers has been to inspire an interest in exploration and science in the public, a significant part of that is getting happy snaps of events as they happen. The pictures taken were also of significant interest to the engineers involved as they showed events that were extremely dynamic, video being one of the best methods to gain information about the events without impacting the operation.
Web is more aimed at direct science, the products of which will, as happened with Hubble be used to make pretty pictures, which in themselves have limited scientific value, but are of enormous value in engaging the public. This combined with the difficulty and risk of capturing meaningful images given the environment makes live video a non starter.
I see you haven't read NASA's aforelinked blog post where they explicitly detail the sorts of complexity it would add.
Since you've indicated an unwillingness to read the blog post I'll summarize briefly:
A camera on the "light" side of JWST would need its own heat shielding and wouldn't show us any of the instruments.
A camera on the "dark" side of JWST would need to function at temperatures close to absolute zero. It would somehow need to do this without disturbing the ultrasensitive instruments on the JWST.
This would have been needed to be accomplished with, essentially, 10-30 year old technology as the designs for spacecraft like this need to be locked in far ahead of time due to the incredible complexity of deep space launches.
In both cases the cameras would need power and data cable routing, and given the various harsh constraints involved (complexity, budget, liftoff weight, size) would have involved compromises in some other area.
There is no reason to use the camera while the telescope is telescoping. From what is being requested in this subthread it doesn’t even need to survive past the initial unfolding, just get a pic or two and be done with it.
I’ve read the article and I’m not criticising NASA’s decision. I’m just pointing out that a cam wouldn’t need to bring significant complexity, not in the insane context of this project.
That 10 billion was funded by taxpayers, and the assertion that at the very least there should have been a possibility of those taxpayers seeing the fruits of their money through pictures instead of some intractable telemetry is a fair one.
What if the public funded it and tolerated the cost overruns, and the numerous delays because they wanted the "circus aspect" photography? Looking at you Juno and thanks for the swirling ocean photos on Jupiter. I bet the majority of the public did! YMMV
But the JWST will be returning some spectacular images: it's a telescope.
That's why I don't understand this debate. You'll be getting lots of spectacular images from the earliest moments of the universe. Is that clear? We are getting a time machine here. We're just not getting selfies.
What if the public funded it and tolerated
the cost overruns
OK. Let's assume unlimited budget. The public (or, at least, Congress) has already tolerated plenty of them on this project. So that's a very reasonable "what if."
You'd still face the hard payload constraints of the launch vehicle itself. Every kilogram and centimeter devoted to this camera system (and the associated power and shielding requirements) would represent kilograms and centimeters that would need to be chopped elsewhere. You'd need to compromise or eliminate other aspects of the spacecraft, and/or tolerate the increased complexity and risk resulting from the inclusion of a zero-science-value selfie camera.
I would expect HN readers, of all folks, to be really familiar with the concept of the harsh realities of engineering solutions for resource-constrained environments.
Anyway, the armchair spacecraft designers among us clamoring for a selfie camera might as well go full armchair spacecraft designer. Tell us which of the JWST's instruments you would have compromised or scrapped in order to accommodate the selfie camera.
The excellent PR opportunity is going to be the spectacular images it produces in 3-6 months time. I have a feeling some dark grainy photos of tin foil unrolling will pale in comparison to what the device will actually product
For the sake of correctness, Tranquility Base is not where the museum is built upon in Futurama S01E02; you must be misremembering. In fact, the moon landing site is considered lost at the beginning of that episode.
When it's later found in the episode, it's found with the lunar ascent module still attached. Because the astronauts ascended in this module, only the descent modules should be there, so you might at first think that this is a blatant mistake on the part of the writing staff and you might hope someone was fired for that blunder[1]. However, if you pay close attention, there's a plaque behind Leela while she's in the ascent module that states "Lander returned to this site by the Historical Stickler's Society."[2]
Sadly one of the the problems is, it's dark where it is. The mirror side is in complete darkness (because of the sunshield), and the sun side is blazingly bright (because of the reflective sunshield).
This is the unfortunate reality of space: The images we see from the Hubble, et al, are exposed for minutes if not hours, and processed to bring out colors invisible to the human eye. An astronaut flying to see the Webb, or one of many other "well known" astronomical landmarks would see either nothing or a faint smudge without a telescope or other enhancements.
The aforementioned NASA blog post goes into the many other reasons this wasn't practical.
Yeah, scientists are point-missing dummies who think that the images that telescope will produce are of no value next to images of the telescope unfolding. Far better to have internet randos who surely aren't dummies running things.
When you think of the Hubble, do you think of "product porn" shots of the telescope itself, or the spectacular images and science it produced?
Likewise, for Voyager/Cassini/Huygens/etc? Don't remember any selfies from those. We merely had to settle for the spectacular, never-before-seen images of other worlds. Guess they were failures. :-(
Nothing could have been seen: on the bright side, a smudge of light. On the dark side, nothing. The mirror is currently at -172° C and further cooling down toward absolute zero temperature; even with infrared it's hard to see anything at this point.
What are the reasons? I'm sorry ~ I'm ignorant on the topic, but I'd love to learn more. Why/what are the reasons?