[HN Gopher] Decoding James Webb Space Telescope
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Decoding James Webb Space Telescope
Author : gaius_baltar
Score : 156 points
Date : 2021-12-27 17:31 UTC (5 hours ago)
(HTM) web link (destevez.net)
(TXT) w3m dump (destevez.net)
| rodiger wrote:
| Does anyone know offhand when we should receive the first images?
| manquer wrote:
| Many other posters have said 6 months, but it will likely be
| much earlier to get the _first_ images.
|
| 6 Months is the time frame for regular science operations. It
| is likely NASA will share some images _well before_ that from
| the calibration phase as part of mission PR.
|
| As regular joe's on the internet we are only interested in
| those PR images, regular science operations are more important
| for astronomers applying for time on the telescope.
|
| Beyond those initial PR images, we can perhaps expect some PR
| worthy research papers (i.e. kind of papers that will get
| posted here) maybe a year from now, given the first projects
| will get access 6 months from now.
| pacha-- wrote:
| Six months if I recall correctly
| gjsman-1000 wrote:
| ~6 months.
|
| https://webbtelescope.org/quick-facts/mission-launch-quick-f...
| [deleted]
| shagie wrote:
| About six months.
|
| https://webbtelescope.org/quick-facts/mission-launch-quick-f...
|
| > After reaching its orbit, Webb undergoes science and
| calibration testing. Then, regular science operations and
| images will begin to arrive, approximately six months after
| launch. However, it is normal to also take a series of "first
| light" images that may arrive slightly earlier.
|
| It will take about a month for it to get out to the Sun-Earth
| L2 point which is 1.5M km (0.01 AU) from the Earth. For
| comparison, the Moon is 384k km away. The telescope will be 4x
| further away from the Earth than the Moon is.
| monocasa wrote:
| We'll probably get the calibration images before the six
| months from now when regular science missions start if they
| go according to plan as it's great press. Also there's a
| chance that there's a delay on the science mission images to
| allow for academic publishing.
| pp19dd wrote:
| Of some interest, this is the proposed imaging breakdown by
| time: 2.0 % observation calibration 4.9
| % instrument calibration 7.9 % solar system (comets,
| asteroids, kuiper belt objects, etc) 16.1 % exoplanets
| 17.2 % nearby galaxies 20.4 % galactic (debris disks,
| etc) 31.5 % distant galaxies and cosmology
|
| There's a whole huge breakdown of what instrumentation
| calibration entails: https://www.stsci.edu/jwst/about-
| jwst/history/science-operat...
|
| This doc was drafted in 2012, and so this might've already
| changed or will be:
| https://www.stsci.edu/jwst/about/history/science-operations-...
| [deleted]
| Beltiras wrote:
| I'm a bit shocked at how low bandwith was allocated. 421
| Megabytes per day is the theoretical upper limit. 16 Terabytes
| for the entire mission. I have more bulk storage in my desktop.
| TedDoesntTalk wrote:
| That's insane. Where did you read that?
| jandrese wrote:
| It's in the article, but the OP was confused because this
| isn't the imaging data. It's the telemetry, things like
| thruster temps, gyro speeds, etc... The metadata that NASA
| uses to make sure the spacecraft is healthy, not the mission
| payload.
| smccully wrote:
| Astronomical Images are calculated in Hours, and I have no
| idea how long the average image will be for NIRCam on JWST,
| but your average Space Photo from Ground Telescopes is
| usually a combination of 5 to 15 minutes images, with a total
| imaging time from 10 - 40 hours.
| semi-extrinsic wrote:
| The instruments aren't really high bandwidth. If you take
| NIRCam as an example, it's 40 megapixels with an observation
| time per image that is from 4 minutes up to 3 hours.
| boardwaalk wrote:
| This is just the telemetry data. They deployed the high data
| rate antenna yesterday which can do many GB per day.
| Animats wrote:
| Oh, good, that unfolding worked.
|
| The amount of unpacking involved as this thing deploys is
| insane.
|
| On the data rate thing, satellites usually have a low data
| rate system with omnidirectional antennas, used for command
| and positioning. Then they have a high data rate system with
| directional antennas for whatever it is they do.
|
| (The USAF used to have a strict separation between the two.
| This reflects the USAF's pilot-oriented mentality. The USAF
| is pilots, and then everybody else. The low data rate system
| belonged to the piloting operation, which used to be in the
| Blue Cube in Sunnyvale CA and is now at Schriever Space Force
| Base, formerly Falcon AFB, in Colorado Springs CO. They
| "drive the bus", managing orbital insertion and station
| keeping. The high data rate system belonged to the payload,
| and once the piloting operation had it turned on and aimed,
| it was turned over to the agency that owned the payload.
| Private satellite operators usually don't make that
| distinction.)
| foobarian wrote:
| And according to this chart it's about to pass the Moon in
| distance in a few hours.
| https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html
| cfraenkel wrote:
| There are completely practical reasons.... The omni-
| directional antenna typically doesn't have the gain, or
| bandwidth, or power of the high bandwidth antenna, but does
| have the useful property of being usable when the vehicle
| might be tumbling.
| Animats wrote:
| Right, but didn't want to go into that much detail.
| [deleted]
| halfdan wrote:
| You have to take into account that it was originally scheduled
| to launch in 2007, then in 2014. Development began as early as
| 1996.
| Yes_and wrote:
| Yes, please provide a source! Based on this [0], with the High-
| Gain antenna (Ka-band), they can do 3.5 Mbyte/sec (28
| Mbit/sec), which is about 295 Gbyte/day. Even if only assuming
| 16 hours/downlink/day, that is ~200 Gbytes/day. Also, with the
| S-Band Medium gain antenna, JWST is capable of accomplishing
| true duplex communication, which means they can uplink on the
| S-band and simultaneously downlink on Ka-band.
|
| For reference, MRO is capable of downlinking at up to 5
| Gbit/sec with a 3.0-meter HGA [1].
|
| [0] https://jwst-docs.stsci.edu/jwst-observatory-
| hardware/jwst-s... [1]
| https://descanso.jpl.nasa.gov/DPSummary/MRO_092106.pdf, table
| 4-7
| gjsman-1000 wrote:
| One would _wish_ that for budget-exponentially-overrun taxpayer-
| funded infrastructure, there would be open-source decoding
| information available.
| pkaye wrote:
| There are lots of interesting tools and information on the
| Space Telescope Institute website to browse through. I'm
| guessing you can get the decoded data as its received.
|
| https://www.stsci.edu/jwst/science-execution/data-analysis-t...
| andruby wrote:
| I actually don't know if they want to protect the data. I can
| imagine they might not want China or other countries listening
| in and potentially sending commands to the craft.
|
| Does anyone know if there is typically encryption on the
| downlink? How about uplink commands? I guess we want those to
| be secured so only authenticated control can send commands
| gjsman-1000 wrote:
| There would have to be some sort of encryption or passkey or
| digital signature on commands, for sure. Otherwise some
| hobbyist in the middle of the Ocean on his yacht could be
| messing with the craft and taking pictures and there'd be no
| easy way to shut him down.
| dylan604 wrote:
| "Torpedo in the water!" would probably be sufficient.
| dividedbyzero wrote:
| The US government being able to discreetly torpedo
| everyone everywhere within what would have to be a few
| minutes at most, that would be pretty pretty scary.
| Imagine the number of drones they'd need to have deployed
| and armed at all times, and the potential for abuse.
| manquer wrote:
| It is not necessary really.
|
| There is unlikely any non-state actors[1] that has the
| ability to _transmit_ signals to L2 . Just _receiving_
| signals even now (only 2 out of 30 days to l2) the OP used
| a 6 meter dish. Most of interplanetary mission signals are
| handled by the DSN.
|
| Any sort of encryption will add both b/w requirements and
| compute requirements . The CPU/network budgets on such
| missions are very very limited. Every bit and cycle counts.
|
| Finally standard encryption libraries, algorithms et al,
| are not likely suitable . I am no expert, but I have not
| read of any modern algorithms with very low network
| overhead + compute requirements designed for these kind of
| use cases, that is also _secure_ from brute force or other
| attacks.
|
| Mission risk is also a factor, even handshake failures can
| jeopardize the mission. It is one thing a website did not
| load because of TLS negotiation failures and $10 B mission
| overshot its orbit because handshake failures on the
| encryption layer.
|
| [1] Threats from state actors for science missions is
| different category of concern, harder to quantify and with
| not much history of actual attacks. Collateral risks like
| from the ASAT Russian test to ISS, or in dual use missions
| would perhaps not apply here .Usually science teams
| collaborate well even if there is lot of tension in
| political sphere.
| Sporktacular wrote:
| "It is not necessary really."
|
| Authentication of commands to satellites is very, very
| necessary
| manquer wrote:
| Encryption !=authentication. OP was talking about
| encryption.
|
| You could do authentication over plain text. For popular
| example http basic auth.
|
| It is not recommended for regular use cases, but is not
| out of realm of possibility in satelite given the
| constraints.
| iszomer wrote:
| I'd imagine the specs are rated and hardened for
| radiation first, as seen on all previous NASA satellite
| and probe missions before getting into the weeds of
| overhead and encryption.
| cycomanic wrote:
| I highly suspect that China (and almost every other country)
| are not the issue. Chinese and the whole international
| scientific community will profit immensely from the data
| coming from James Webb, so I don't think the Chinese have any
| interest in sabotaging the project. More dangerous would be
| some average joe, somewhere who would try to mess with it for
| the lulz.
| foobiekr wrote:
| Embarrassing the US is high value.
| wongarsu wrote:
| If somebody like China is caught sabotaging JWST the
| fallout could be immense. They would be accused of trying
| to hold back human progress, and I could easily imagine
| high profile Chinese scientists leaving the country and
| science institutions boycotting China. It's not worth the
| risk.
| leephillips wrote:
| I also don't think they would want to do this, but I
| think you're overestimating the risk. Genocide, stealing
| the entire South China Sea, and threatening the
| sovereignty of other nations haven't inspired such
| boycotts.
| iszomer wrote:
| Or frame the average Joe for the lulz for political points.
|
| (sorry, I'm just now reading into the drama with the fbi
| and gov. whitmer..)
| TedDoesntTalk wrote:
| Or terrorist organizations with tech skills
| ixfo wrote:
| Yes, CCSDS Magenta and Blue reference books mandate
| AES-256-GCM as a minimum for data encryption and mandate that
| encryption and authentication should be used, particularly
| for commands/uplink. Sliding scale of requirements based on
| application of course - your cubesat's imaging system is less
| critical than the flight termination system on a manned
| mission, for instance.
| xxpor wrote:
| Fwiw, sat c&c is the one thing you're allowed to use
| encryption on the Amateur radio bands for.
| adgjlsfhk1 wrote:
| how is that enforceable? you can't determine what the
| encrypted communication is.
| monocasa wrote:
| Same as anything in amateur radio. There'll be a lot of
| hints at what you're doing from the shape of your
| broadcasts, and there's a lot of amateur radio
| enthusiasts that'll call the feds on you if they get a
| hint that you aren't following the rules.
| jcims wrote:
| I don't have any inside information but in my experience
| lurking in the amateur radio community the answer is 'it
| depends' and there is a lot of downlink that is not
| encrypted. This will get you into the graph:
|
| https://twitter.com/usa_satcom
|
| https://twitter.com/uhf_satcom
|
| https://twitter.com/r2x0t
| mhh__ wrote:
| Science in general still basically operates on the "NASA
| invented xyz while going to the moon"-model from the 20th
| century. Things get developed and then trickle into industry
| via back-channels (or people moving) but the idea of open-
| source is still both culturally alien and legally suspect.
|
| Even in CS papers directly dealing with a piece of software
| there is no obligation to publish code.
| ufmace wrote:
| After seeing plenty of code and projects by people who
| weren't professional software engineers used to working on
| teams, part of the problem is likely that code written for
| this sort of thing often depends on a ton of dependencies and
| system-specific configuration bits that are documented poorly
| or not at all. Getting such projects to a state where a
| random person could git pull it and make sense of it and use
| it is a whole project unto itself that usually the core
| contributors are poorly equipped to take on. How many really
| understand the pain of onboarding into a poorly-documented
| repo and how to use the right tools to make it a smooth
| process?
| Twisol wrote:
| On top of that, missions are heavily incentivized (in a
| "our success depends on this" way) to solve only the
| problems they absolutely need to solve, due to constraints
| on time, budget, and manpower. It's an incredible feat to
| achieve what they do, but reuse and non-specialist use are
| non-goals.
| colechristensen wrote:
| This is just telemetry data which doesn't have much general or
| scientific interest, i guess they could publish the protocol
| spec (honestly it probably is aquirable) but most of the fun
| for the kinds of people who want this data is going to be doing
| this reverse engineering themselves.
|
| The real imaging data would require a much more significant
| dish to even receive (i can't immediately find what it's going
| to use, but I'm guessing something like a 40 meter dish) so
| there are approximately zero amateurs who could use such open
| source information.
| Twisol wrote:
| Most of the public specifications are distributed freely by
| the CCSDS (Consultative Committee for Space Data Systems):
| https://public.ccsds.org/Publications/BlueBooks.aspx
|
| The mission-specific parameters ("managed parameters") used
| by any given mission are usually more tightly controlled, as
| are the payload specifications for each telemetry channel.
|
| > This is just telemetry data which doesn't have much general
| or scientific interest
|
| My understanding is that "telemetry" and "telecommand" stand
| for the downlink and uplink directions of a space link. I
| mostly worked upstream of telecommand, but I understood
| "telemetry" to refer to received data of any kind -- e.g. in
| CCSDS 130.1-G-3, an informational report on the design of the
| CCSDS telemetry system.
| https://public.ccsds.org/Pubs/130x1g3.pdf
|
| By the by, I've been continually impressed with the quality
| of the CCSDS' documents. The "green books" (informational
| reports, like the one above) are extremely approachable and
| well-written.
| astroflask wrote:
| Gonna chime in here to comment that most NASA missions (and
| ESA too) provide the scientific data for download free of
| charge, under Public Domain or CC licenses. If it's for
| scientific purposes, it's not just good manners, but rather
| a requirement to cite the proper dataset (that also gives
| you the bonus of citing a respected source, so it's a win-
| win). Thing is that many people doesn't even know where to
| look for!
|
| And it doesn't help that some missions manage their own
| archives differently, and there's a lot of terminology to
| learn on your own. One of the complete opposites of that,
| which was a joy, was the New Horizons archive which, at one
| point, you could download from a torrent! For example, if
| you wanted to see V3 of the Arrokoth encounter from 2019,
| you'd go to: https://pdssbn.astro.umd.edu/holdings/nh-a-
| lorri-3-kem1-v3.0...
|
| Again, New Horizons is a bit of a rare case in which they
| went for super accessible data for everyone. PDS itself is
| a great system, but many missions will just upload a bit of
| data to PDS and then manage the rest some other way
| (Cassini for example has only a couple of instruments on
| PDS, and you have to go to some other URL if you want
| uncalibrated but automatically processed images on JPEG
| format[0], but yet another place (to which I've lost the
| link to and I can't find on mobile) for the full, science-
| grade dataset).
|
| A great resource is OPUS[1] too, however I find it's UI a
| bit difficult, and in the end I prefer to download full
| datasets and just explore them on my own rather than going
| with those online browsers. For example, if you wanted to
| check the Voyager images of Neptune, you'd go to this
| massive URL[2]. Quick tip: once you've configured the
| filter you want to apply, the Search button is on the top
| left -- this is the kind of usability thing I mentioned,
| buttons and links aren't quite where you'd expect them. Oh
| and there's a limit to how many things you can select for
| download at once. And it's all dynamically loaded, and on
| and on and on. Which is why, as I said before, I generally
| prefer to just download the full GB sized dataset and
| explore it on my own.
|
| [0] https://solarsystem.nasa.gov/raw-images/raw-image-
| viewer/?or...
|
| [1] https://opus.pds-rings.seti.org/opus/
|
| [2] https://opus.pds-
| rings.seti.org/opus/#/instrument=Voyager+IS...
| dylan604 wrote:
| Aren't they using the Deep Space Network for this?
| jacquesm wrote:
| Yes, all communications are routed through DSN.
| londons_explore wrote:
| But in a really open project, the design of the whole lot
| would be on the web, and the data sent back would be sitting
| on an FTP server somewhere for anyone to download and use.
|
| In many ways, an open project is cheaper to do than a behind-
| closed-doors project where every new contractor needs to get
| access to only the bits of the project they need access to,
| and misunderstandings happen because not everyone has enough
| of the big picture.
|
| The only bit that needs to be secret is one private key used
| to sign the commands sent to the satellite, just so one
| random Mallory can't 'steal' it.
| coldpie wrote:
| You're assuming it's secret, but the more likely case is it
| just isn't anyone's job to make it public.
| semi-extrinsic wrote:
| > the data sent back would be sitting on an FTP server
| somewhere for anyone to download and use
|
| I'm sure they could actually do that without too much fuss.
| But it would require significant amounts of scientist time
| to document those datasets to enable others to use them
| _for any arbitrary dataset_. I 'm sure we'll see fully open
| data sets from JWST appear, but lots of the stuff it
| collects isn't going to be interesting enough that it's
| reasonable to spend scientist time documenting it.
| jandrese wrote:
| It seems like it should all be automated. Some scientist
| generates a mission request for the JWST techs. If
| accepted the mission is added to the timeline with all of
| the metadata the original scientists had in their
| proposal. Stuff like the area being imaged, the sensors
| in use, duration of capture, etc...
|
| Once the data is collected and downloaded it is added to
| the catalog with all of that metadata attached. Then it's
| a matter of opening up that catalog to the public,
| although I'm guessing the downloads will be quite
| sizeable so the bandwidth could be an issue.
|
| The trick to making this work is to integrate the
| publishing into the workflow so it doesn't require any
| additional effort on the part of anyone.
| xioxox wrote:
| The data from the mission will be made public after
| proprietary periods [1]. They have an archive [2]. I
| don't expect that the raw telemetry will be made
| available, but the raw science data in FITS format
| appears will be available.
|
| [1] https://jwst-docs.stsci.edu/jwst-opportunities-and-
| policies/... [2] https://archive.stsci.edu/missions-and-
| data/jwst
| londons_explore wrote:
| I think there needs to be a distinction between something
| that a project "publishes", and something that is "made
| available".
|
| Something published has been checked by a few team
| members, written with care, and represents the opinion of
| the authors and project.
|
| Something made available has no guarantees of
| correctness, might not represent the projects opinion,
| and might just be random matlab scripts made by a JWST
| scientist in their lunchtime that they thought was fun.
|
| In the open source world, what is 'published' is probably
| the projects homepage, and code. What is 'made available'
| is random chatter on their discord or IRC channel.
|
| I hope that more government projects 'make available'
| everything done by all the workers - every file saved on
| every PC, with the understanding that there is no
| guarantee of correctness.
|
| I guess it's the same idea as being able to see into the
| kitchen from a restaurant. You might see the chef making
| mistakes or juggling the saucepans, but you'll also see
| the work being done as it's done, and being able to view
| doesn't delay the chefs work.
| dividedbyzero wrote:
| That's a pretty bad idea IMO. Putting people in a
| panopticon has a strong chilling effect, no matter what
| disclaimer you put on the recordings. Creative, deep work
| needs space to make blunders in private, scientists are
| no exception. They'll just use their personal laptops or
| document every experiment and mistake and script to
| death, getting done a lot less actual research.
|
| Plus, it will be pretty much useless im practice since
| you'd have to be an expert in that niche yourself to know
| what's correct (you're not getting any extra docs or
| context) and probably most of it will be some kind of
| incorrect, possibly very subtly. The only people who
| could profit tremendously are the competition who aim to
| snipe that particular paper. Science is pretty dirty and
| ruthless often as not, I totally could see this happen.
| aunty_helen wrote:
| From: https://ntrs.nasa.gov/api/citations/20080030196/downloa
| ds/20...
|
| >To keep up with the high downlink, the recorder data gets
| sent directly to the Ka-band transmitter
|
| Currently aws groundstation doesn't support KA band so no
| luck there. It's apparently going to do a transmission once a
| day so you would need to time it right with the ground
| station.
| Thorentis wrote:
| Groundststion as a Service. I had no idea this existed. I
| am continuously amazed at how many things Amazon churns out
| "as a service".
| hayanno wrote:
| Nice link, very informative, here's a funny excerpt : "It
| [JSWT] is currently planned to be launched in 2013 from
| French Guiana aboard an Ariane 5 launch vehicle".
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