[HN Gopher] Webb placed on top of Ariane 5 ___________________________________________________________________ Webb placed on top of Ariane 5 Author : _Microft Score : 235 points Date : 2021-12-14 16:40 UTC (6 hours ago) (HTM) web link (www.esa.int) (TXT) w3m dump (www.esa.int) | YossarianFrPrez wrote: | I keep reading about how there are ~350 single points of failure | once Webb is successfully launched. Can someone with expertise | and chime in about why the telescope wasn't designed with more | built-in deployment redundancies? It would seem to be good | engineering practice to ensure that there are back-up systems, | etc. | bumby wrote: | Redundancy is only one way to increase reliability. For | example, having redundant elements can allow you to use cheaper | components and meet the same level of reliability as a single, | more expensive component but at the cost of mass (or vice | versa). Most often, there are reliability requirements that are | defined at a very high level, and a reliability engineer helps | determine the right tradeoffs to meet those requirements. In | addition, some of the points of failure don't lend themselves | well to redundancy, like release mechanisms. | | For certain risks, like human-rated spaceflight, they may just | have requirements like "no single-point failures", which means | redundancy is a must. | evgen wrote: | Redundancy costs mass and there are a lot of deployment steps | that simply cannot be made redundant. The trick is folding | everything to fit into the constraints of the payload fairing. | Good engineering is to design within these limits and but if | you make it too safe you end up with something that is not | worth launching. | hollander wrote: | Plus you don't get to send a Space Shuttle to L2 in case the | mirrors are malfunctioning. | pelagicAustral wrote: | Talking about Ariane 5, it's been interesting reading parts of | its history. Particularly: | | "Ariane 5's first test flight (Ariane 5 Flight 501) on 4 June | 1996 failed, with the rocket self-destructing 37 seconds after | launch because of a malfunction in the control software. A data | conversion from 64-bit floating point value to 16-bit signed | integer value to be stored in a variable representing horizontal | bias caused a processor trap (operand error)because the floating | point value was too large to be represented by a 16-bit signed | integer. The software was originally written for the Ariane 4 | where efficiency considerations (the computer running the | software had an 80% maximum workload requirement) led to four | variables being protected with a handler while three others, | including the horizontal bias variable, were left unprotected | because it was thought that they were "physically limited or that | there was a large margin of safety". The software, written in | Ada, was included in the Ariane 5 through the reuse of an entire | Ariane 4 subsystem despite the fact that the particular software | containing the bug, which was just a part of the subsystem, was | not required by the Ariane 5 because it has a different | preparation sequence than the Ariane 4" | | I wouldn't want any part on something as mission critical as | getting a rocket to deliver something into orbit. | Eikon wrote: | Video of the incident: | https://www.youtube.com/watch?v=gp_D8r-2hwk | jlengrand wrote: | I still remember that one, I was at school 80 kms away when it | blew up. Quite the boom given the distance, but nobody scared, | just heard a large bang. | | Most launches were at night, and we could watch the trail of | flames pass by but 501 was launched during the day. Impressive | to watch how wrong it went, how fast. There's even still the | dude saying "all parameters and trajectory normal" literally as | the thing explodes. | | Good times and nice memories. | barkingcat wrote: | That part about the saying "well, it's not rocket science" | | In this case, it _is_ rocket science. | colechristensen wrote: | Eh, aerospace involves a lot more testing and specification and | generally being careful in engineering practices and still | failure for new products is expected. | | You launch your first few rockets _expecting_ them to explode | because even with all of the care, it 's just not reasonable to | expect that you got everything right in simulation, test, and | design. | | This is why the public response to "failures" from SpaceX, | NASA, etc. etc. are so frustrating, people don't understand the | nature of product testing. You don't get to see a washing | machine or microchip or car or whatever else do its equivalent | of exploding on the pad, but they all do and much worse. | | The first flight of a rocket _not_ exploding is like spending | days writing code, compiling it once without errors and running | it in production with no issues. It 's basically unimaginable | and when it does happen you sit and wonder what's actually | going wrong that you don't know about yet. | | Once you do get a working configuration, you don't change it or | make only very safe changes. You rely on what's worked before | because things are actually exactly the same, not constantly | changing like so much software today. This leads to a lot of | conservatism that people don't understand (why is military | hardware using X, it's so outdated!) | bumby wrote: | I think this is a fair take when you're talking about | failures of nascent designs because of unknown failure modes. | But it's frustrating when there are failures from known | failure modes that just had process escapes. A couple | examples: | | - CST-100 was sent into orbit with _software mapped to valves | incorrectly_. There is no credible reason this shouldn 't | have been tested thoroughly on the ground first. | | - Falcon 9 had a failure due to a tank support strut that had | strength characteristics a fraction of its design spec. Good | supplier quality control should have vetted the material | prior to its use. (SpaceX has since added material tests). | | Finding unknown causes of failures help us learn more about | the science of the industry. But not catching known failure | modes due to lack of process control is a different animal. | hn_throwaway_99 wrote: | > But not catching known failure modes due to lack of | process control is a different animal. | | I agree, but for any complicated product like a rocket | launch there are probably many many tens of | thousands/hundreds of thousands/millions of things like | this where one small uncaught error can cause mission | failure. At some point it's just statistics, you'd expect | to see some catastrophic failures across some percentage of | products early in their lifecycle, regardless of how good | your process control is. | bumby wrote: | Yes, there is reliability analysis involved which invokes | probability. However, that's not the case with the items | I mentioned above. | | It would be one thing if SpaceX tested the material | coupon and found it within specs, but by sheer | probability, the strut had a portion of its material | structure that was anomalous. That's what you're talking | about. What I'm talking about is there are specific | process steps that would have caught those mistakes | above, and those processes were just not performed. | Neither of the cases mentioned above are the result of | "We did everything right, but the probability gods were | just not on our side." | hn_throwaway_99 wrote: | > It would be one thing if SpaceX tested the material | coupon and found it within specs, but by sheer | probability, the strut had a portion of its material | structure that was anomalous. That's what you're talking | about. | | Actually, that's not what I'm talking about. What I'm | talking about is lessons from QA processes and the chance | that any particular bug escapes from one QA process to | the next. | | The idea being, suppose you have: | | * one million different "components" in a system | | * each of those components have, say, 10 possible failure | modes | | * There are 100 of these new complex products a year. | | Obviously the numbers above are all made up, but the idea | would be in that example you'd have a billion (1,000,000 | X 10 X 100) possible failure modes. Any QA filter, might | be expected to catch, say, 95% of remaining bugs. | | So you run as many filters as you can, but at some point | you're still left with the small probability for new | bugs, and they only way to remediate those bugs is to | figure out what went wrong after the fact. | bumby wrote: | Not every bug creates a failure, so there's not | necessarily a need to be completely bug-free. The point | is to focus efforts on the bugs that _can_ cause failure | and design mitigations for them. If your system has a | billion potential software failure modes, my hope is that | a project manager will say the software is too complex | and needs to be redesigned. I think this is where some in | the software crowd get it wrong in their understanding of | how software reliability in safety-critical applications | is performed. There are a lot of project managers who | deliberately avoid using software as a mitigation because | of the complexity issue (see the 737Max use of software | as a mitigation for a good example of where this practice | can go wrong). | | So take the software example from above on CST-100. The | valve mapping error should have been a known failure mode | ("We command valve A and it doesn't respond." or "We | command valve X and valve A responds"). Those failures | are very straightforward to test for with simulations on | the ground, yet somehow those errors made it into a | flight configuration. Arguably, the software timer issue | on that flight falls into a similar category, but the | mitigations there are a bit more complex. | buran77 wrote: | > there are specific process steps that would have caught | those mistakes above | | Overestimating the risks can bury a project just as | quickly as underestimating them. If you test for every | possible failure mode you may never get off the ground. | There's always a test or check that can catch something | before the risk is realized. Every nut and bolt can be | X-rayed, every line of code and possible combination can | be tested, it's just a balancing act. Sometimes the risk | doesn't justify all the tests, sometimes a test is | accidentally omitted, or poorly defined because someone | made a mistake or misunderstood the explanations behind | it, or someone misread the result, or the risk was | considered avoided because the code was tried and tested | tech on Ariane 4. | | Rockets are so complex that there are millions of | situations where a mistake can be made and later | amplified. | bumby wrote: | I agree that there needs to be a balance between testing | and cost. One one side, QA managers can become chicken | littles who define the only acceptable level of risk as | zero. On the other are project managers who let cognitive | biases help them rationalize the answer they want in | order to avoid cost overruns. | | But the issues above aren't that. I can think of very | little reason that _valve command mappings on a human- | rated rocket_ were not adequately tested. The larger | point is there needs to be good testing on credible | risks, not that risk needs to be driven to zero. | | I would say someone who thinks "the risk was considered | avoided because the code was tried and tested tech on | Ariane 4." doesn't actually know the nature of the risk | in order to determine if it's credible. The risk was not | mitigated because changing configuration added an | untested interaction risk. | buran77 wrote: | > I can think of very little reason that valve command | mappings on a human-rated rocket were not adequately | tested | | The procedure and checks were probably repeated multiple | times during earlier preparations with no issues. God | only knows how many potentially critical problems exist | in every system on a code path never taken, or with a | component that's never used. It's one thing to test | everything for the design of the system and call it | complete, and another to test everything for operations. | Human error caused an operational misconfiguration on a | system that was otherwise validated. | | Think of aviation where the entire plane design and the | technology used are fully tested and known to meet all | the requirements. But every time you operate that plane | you have a shorter pre-flight check to confirm | operational worthiness. Some things that can cause a | disaster won't be covered, and some items on the the | checklist will be mistakenly marked as OK, which may or | may not cause a problem. | | I'm not saying it's normal just that statistically | speaking at some point you'll miss something for one | reason or another, and eventually the proper conditions | will be met for a disastrous outcome. Might as ell be a | valve control check. | [deleted] | dylan604 wrote: | >I wouldn't want any part on something as mission critical as | getting a rocket to deliver something into orbit. | | I hear there's a need for 3rd party libraries to log data. | Stevvo wrote: | I find it interesting that bug is so normal, like it's exactly | the type of bug we encounter all the time in terrestrial | software. Yet the stakes are so much higher. | jollybean wrote: | Amazing. I wonder if given the large advances in computing | power, that we might develop something like Ada+Rust for such | systems where we can eliminate all sorts of error classes. | acomjean wrote: | I worked on radars. We used Ada. The knock on it is that its | slow, and didn't have a huge ecosystem. but 20 years later at | least slow is not really much of a problem. You kinda got | used to the fact if the software compiled it probably would | run. It had some neat features (like constraining values, eg | this variable will be between 0 and 10. Of course you'd have | to deal with things when you ended up outside that range.. ). | Really quite reliable. | | https://learn.adacore.com/courses/intro-to- | ada/chapters/stro... | | They tested a lot (some of the testing was delivered with the | software even, to run anytime...). | jollybean wrote: | I interned in IT on Space Systems and looking back I'm | basically amazed we ever put 'software' in space. | | There were some organizational attempts to control for such | issues, but there were no real solutions other than a bunch | of guidelines. | | Some of the code written for the space station was done in | long, sleepless 'power-coding' binges. I thought that was | 'cool' now I think it's 'insane'. | | I do remember learning a bit about Ada, but it's been so | long, and it's probably out of the range for most things | today. | | Even Rust is a bridge to far for most projects, I really | wish there were ways to 'back off' from Rusts ultra-hard | principled approach because I think what most projects need | is '65% Rust', not '100%' which is the only current option. | MayeulC wrote: | > were left unprotected because it was thought that they were | "physically limited or that there was a large margin of safety | | You didn't mention it, but IIRC what made the overflow possible | was the increased performance of Ariane 5. Such values couldn't | physically be reached with Ariane 4. | | Now, the real irony is that indeed that computation and whole | subsystem wasn't needed. It tells you something about removing | unneeded parts. On the other hand, the aerospace sector is | traditionally very conservative and reluctant to change things. | Have a look at the superstition surrounding launch processes: | http://stevenjohnfuchs.com/soyuzblue/yes-they-pee-on-the-tir... | | I can picture code being included whole for fear of breaking | something by mistake. | pkaye wrote: | Looks like 95.5% success rate. I don't know if there is | anything better with that much payload capacity and as long a | track record. | | https://en.wikipedia.org/wiki/Ariane_5 | ceejayoz wrote: | https://en.wikipedia.org/wiki/Delta_IV and | https://en.wikipedia.org/wiki/Atlas_V have essentially | perfect records. The IV had a lower-than-expected orbit on a | non-payload test flight, and the V had a lower-than-expected | orbit that the payload was able to fix. | wumpus wrote: | NROL-30 on Atlas 5 apparently had a shorter lifetime after | the "fix", and that is normally considered a "partial | failure". | colechristensen wrote: | You have to take statistics like this with a grain of salt. | Sometimes less than perfect reliability is by design, | sometimes development details (like how different the "new" | rocket that earned that name is from previous designs) hide | failures in earlier rockets with different names. | ceejayoz wrote: | Sure, but if anything, Ariane 5 is a good example of | that; it blew up because of reused software from the | Ariane 4. | wumpus wrote: | SpaceX F9 has 106 successful launches after their last | failure. | | Ariane 5 has 106 launches since their last full failure. (1 | partial failure in there.) | | Of course, F9 is a little smaller, everything other than | Delta IV Heavy is a little smaller, so your statement | including "with that much payload capacity" is true by | construction. | shakezula wrote: | Wow, that's a much better continuous success rate than I | would've guessed on either account. | richardwhiuk wrote: | Success rate isn't very interesting. If a random 1/20 rockets | fail, then that's very bad. If your first 10 rockets failed, | and then you next 190 succeed, that's likely to be a much | better rocket. | qwertyuiop_ wrote: | I hope it works up there. They dropped it | | https://blogs.nasa.gov/webb/2021/11/22/nasa-provides-update-... | findalex wrote: | > caused a vibration throughout the observatory. | | I hope there won't be vibrations during the launch of the | rocket. | zamadatix wrote: | One means you felt something else have an bad day, the other | means you had a bad day. | mort1merp0 wrote: | The launch vibrations and their resonance frequency are | accounted for in the design. | | The unplanned vibrations due to this mishap was not planned | for. | | I understand they ran some tests and calculations after the | accident and believe that the instruments are good to go. | [deleted] | kingcharles wrote: | After checking, it was fine. | redis_mlc wrote: | From your link, it doesn't sound like they dropped it. | | A clamp band "released" causing vibration, but that is not the | as a 1g fall to the hard floor. | | This is one of the few NASA projects to actually care about, | since the Shuttle and the ISS were flaming moneypits. Virtually | no science has ever been done on the ISS, even compressing it's | entire history into a single year - it's that worthless. | (Another HN reader confirmed that by reading NASA's junk PR | releases about ISS.) | ceejayoz wrote: | Could've been worse. | https://en.wikipedia.org/wiki/NOAA-19#Damage_during_manufact... | nabla9 wrote: | Super exiting. | | - JWST costs $8.8B USD, about the same as aircraft carrier, or | Large Hadron Collider and it goes into a rocket! | | - JWST has 344 single-point-of-failures, 80% of them related to | deployment. Mars landers have significantly less If I remember | correctly. | | If each single-point failure has 0.0001 failure probability, the | mission fails with 3.4% probability. | | If each single-point failure has 0.0002 failure probability, the | mission fails with 6.6% probability. | ashton314 wrote: | The launch is super scary, but the deployment seems even worse. | When will we know whether or not all is working? | | I don't know if I could handle that much pressure to launch that | thing. | danielodievich wrote: | I am there with you. I've been watching this unfold for half of | my life, and seems like EVERYTHING must go right for it to | happen. The unfold is scary complex. I really, really, really, | really want it to go right and worry. | | On other hand, NASA has done this amazing thing with landing | rovers on Mars flawlessly and those were incredibly complex | processes with sophisticated pieces of engineering. | | _biting my nails here_ | edoceo wrote: | How about Cassini? (sp?) threw this little sensor disk to | Saturn for information - what a cool project. | Rebelgecko wrote: | All the scary stuff that can go catastrophically long is within | the next 40 days or so. However it'll take months to go through | the calibration process, tweak the mirror positions, check out | optics, etc | jessriedel wrote: | Yea, I'm having trouble finding a detailed schedule, but it | looks like the main mechanical components are all deployed in | the first 15 days | | https://upload.wikimedia.org/wikipedia/commons/6/6a/JWSTDepl. | .. | | https://webbtelescope.org/contents/media/images/4180-Image | | After that they still need to a do a ton of checks, wait for | outgassing, etc. The first "science-quality images" are | expected by the end of the third month. | michielt wrote: | Are there any onboard cams to watch the deployment after it | reaches L2? | pgen wrote: | Deployment sequence: https://www.youtube.com/watch?v=RzGLKQ7_KZQ | NikolaNovak wrote: | I could be wrong, but I feel SpaceX has mastered how to add | pizazz to such videos :-) | [deleted] | davesque wrote: | I've found that there's a weird internal psychology I have with | any news relating to Webb. I'm just as excited and hopeful as | everyone else. But somehow the whole story underscores the perils | of singular hope. It also seems to underscore the inherent issues | with massive, carefully planned, "vertically" scaled science | projects a la 20th century NASA. I've carved out a little nook in | my psyche to cope with the outcome that something goes wrong | during the Webb's incredibly complicated launch process and all | those years of effort come to nothing. | | It's also made me wonder if there's a way for humanity to pivot | to more "horizontally" scaled science. I'm imagining a kind of | science conducted by aggregating the data collected by many | cheap, easily produced instruments instead of a few incredibly | fragile, extremely difficult to build contraptions. I have an | intuition that we'll increasingly run up against practical | limitations in undertaking ever more complex projects of this | kind in the coming years. | mwattsun wrote: | I can't even follow the news because I know how disappointed | I'll be if the launch crashes. Wake me up when it's over. | bumby wrote: | I think these are large vertical projects because of the nature | of the problem. I.e., the data we're after is inherently | obfuscated by our earthly dwelling so we need to get our | instruments a long ways "out-there". And to do so incurs a lot | of risk and, generally speaking, the only institutions large | enough to incur a risk that large without much profit upside | are governments. | | Now maybe we'll find clever ways to get different data cheaply | that meets similar ends, but that seems to be hinged on hope at | the moment. | natch wrote: | On the ESA web page... 4 likes. Come on, world! We can do better | than that. | lainga wrote: | I can't find an answer to this anywhere: is there a backup JWST | (or parts thereof) if this one fails to launch? | kilroy123 wrote: | No, and I think they should have made two of them. | [deleted] | crate_barre wrote: | Makes me wonder if it would have been smarter to build it in a | modular way with different pieces being sent up one at a time, | assembled on the ISS, then launched in the direction it needed | to go. | dekhn wrote: | humanity has a lot of experience building reliable one-offs, | actually a lot more experience and a lot better experience | than with modularity and bits and pieces. I'm a software | engineer by trade but every time I look into industry (ship | building, skyscrapers, etc) you realize: that aphorism about | software engineers, woodpeckers and civilization was | absolutely right. | Something1234 wrote: | "If builders built buildings the way programmers wrote | programs, then the first woodpecker that came along would | destroy civilization." ~ Gerald Weinberg. | | For those who don't know what the quote is. I found it | here[1]. | | [1]: | http://www.ganssle.com/articles/programmingquotations.htm | bumby wrote: | Can you explain the colloquialism a bit? Is it a knock on | modular design? | | Having worked both in construction and software, modular | design seems fairly common in both. | jandrese wrote: | Then you have multiplied your launch risk by the number of | launches it would take to get it up there, plus there is the | difficulty of assembling it in orbit. The only other project | built like that was the ISS, and it took decades and a launch | vehicle that no longer flies. | | The biggest problem would be that it would be in the ISS | orbit, which would require a lot of delta-V to get it to its | final orbit. | jbay808 wrote: | An advantage of assembling it in ISS orbit is that you have | DEXTRE and a team of spacewalking astronauts available to | do the unpacking and assembly! | echelon wrote: | Or an altogether different design: thousands of cheap, | totally fungible sensors in an array at the L2 point. | | Not only would they be replaceable, but we could increase | capacity in the future. | petschge wrote: | Except that interferometry at IR is still extremely hard. | findalex wrote: | Imagine having the replacement gold reflector dish in storage | somewhere. | echelon wrote: | This is our only shot. They didn't replicate the build. | | https://www.quora.com/What-would-happen-if-the-James-Webb-Sp... | [deleted] | [deleted] | mikepurvis wrote: | Relatedly, I'd be curious to know what the split has been of | the $10B "program cost" in terms of development vs | manufacturing. | | I assume that like with most things, the vast majority of the | cost has been in the design and documentation over its 30 years | of development. At the same time, there's obviously a ton of | extremely high precision bespoke components in there, so | "building another one" would definitely not be trivial. | 0_____0 wrote: | If it's anything like the hardware engineering programs I've | been involved in, at qty=1 the cost is almost all R&D. That | includes development of processes to build something like | 1.3m wide ultraprecise beryllium mirror segments... | bumby wrote: | Aerospace isn't necessarily like that for a number of | reasons. A large driver of cost is quality control. For | example, when a custom part is manufactured it needs to go | through a number of tests, some of the raw material needs | to be kept and tracked for future testing, etc. When they | get shipped they have to be be tracked and handled | differently, sometimes accelerometers are placed on the | cargo to measure any shocks, etc. They need to be stored in | a bonded warehouse, often climate controlled throughout its | life. All of that control, testing and documentation adds | to the cost even after R&D is a sunk cost. | mikepurvis wrote: | Oh absolutely, but I still wouldn't be surprised if the | cost for unit 2 was still another half a billion dollars. | It would be fascinating to know. | dgrin91 wrote: | The answer is no for mainly two reasons: | | 1. Prohibitive costs. Its extremely expensive (both in money | and time) to manufacture many of the parts of the telescopes, | such as the reflector dishes. Its even more expensive to do all | the testing & certification of the manufactured parts. | | 2. Its all outdated anyways. The JWST project has been ongoing | for literally decades (starting in '96 if I remember). If we | were to start from scratch today we would make a lot of | different design choices based on more recent technological | developments | gibbonsrcool wrote: | I would love to see a video where one of the engineers on the | project talked about what would be different if Webb was | started today. Materials, software, processes, everything! | p_l wrote: | A huge design issue that might - or might not - be pushed | would be the power system. | | Solar panels require that JWST stays in the sun while | conducting observations, while at the same time being | critically dependant on the observing equipment to be cool | - and being unable to just keep it inside bigger structure | like with Hubble. | | This means that there's a huge problematic sun shade | structure which is considerable part of the SPOFs still | endangering JWST even if it is inserted into orbit | correctly. | dotnet00 wrote: | It's worth considering that nowadays we don't really do backup | copies of satellites/probes because launch is pretty reliable | by now, especially on rockets that have been flying for a while | (which is pretty much a requirement to be chosen to launch a | flagship project like JWST). | | Ariane 5 has a long flight record with very few failures and | the design has been further carefully reviewed specifically for | JWST, with the previous two launches having served as | verification for any fixes that needed to be made prior to | flying this mission. | | Basically, the chance of JWST being lost due to a rocket issue | is much lower compared to the chance of it being lost due to | design issues with the telescope itself. | ufmace wrote: | Nope. Wouldn't be a good use of money anyways. If it fails, it | might be because of a design or manufacturing flaw. Better to | make the new one after we have some idea what went wrong. | BurningFrog wrote: | To me, this is a major dysfunction of the NASA model. | | Why wasn't 5 Hubble telescopes launched? The marginal cost for | the other 4 must have been vastly smaller than the first. | Observation time on the original Hubble is _still_ , after 30+ | years a scarce resource. With 5 of them, we could have gotten | vastly more science done at smaller cost. | | I don't have a fully fleshed out theory for why, but part of it | is that NASA as a government organization is ultimately a | political endeavour, and it will have to optimize for what | makes politicians look good in the press, rather than what | gives the most science bang per buck. | giantrobot wrote: | > Why wasn't 5 Hubble telescopes launched? The marginal cost | for the other 4 must have been vastly smaller than the first. | | Economies of scale only apply at, well, scale. Five Hubbles | would cost 5x one Hubble to construct. There's very little in | the way of savings because most parts are custom fabricated. | The parts need to be tested, integrated, then tested after | integration. The testing and verification of each subsystem | takes the same number of person-hours. So testing 5x the | systems requires 5x the time. | | You can't just accept a high failure rate of something the | size of Hubble just because you've built five of them. If you | launched a Hubble and it failed in some Loss of Vehicle | fashion after inserted into orbit you've got a big | uncontrollable mass of telescope flying around the Earth. | | Even if we still had the Space Shuttle (or a fantasy version | of the SpaceX Starship) flying an uncontrollable Hubble | couldn't necessarily be retrieved. If it wasn't accepting | commands and was spinning on some axis it would be too | dangerous to approach with another vehicle. Even an unmanned | vehicle couldn't necessarily approach it without a collision | that causes even more problems. See the recent idiotic | Russian ASAT test for an object lesson in what could happen. | | This is all to say you don't want some large satellite in a | long lived orbit to fail. So there's no savings on testing | and verification. Even though at launch Hubble's mirror had | problems the satellite itself was fully under control and | operable. | | Something like Starlink is very different. All the satellites | in a given block are functionally identical and fungible. If | one fails it's easily replaced by another. They also deploy | to a low unstable orbit. If a Starlink satellite fails and is | uncontrollable it will de orbit by itself quickly. They | _must_ be functional to enable the onboard engines that get | them to a stable intended orbit. A Starlink satellite then | needs far less testing and verification than a Hubble or | JWST, not that they can be poor quality but they don 't need | to function Or Else Bad Things. | mbfg wrote: | Is that really true? I'm guessing a big part of the cost is | figuring out how to actually invent stuff needed for the | project. That knowledge is now known. That cost is now 0. | giantrobot wrote: | > I'm guessing a big part of the cost is figuring out how | to actually invent stuff needed for the project. | | We're talking about marginal costs, not development | costs. So the cost to invent a component is already out | of the equation. The high production cost of something | like Hubble comes from testing and validation more than | materials or fabrication. | | The failure modes for something big in space can be | extremely dangerous. Even a tiny "cheap" cubesat requires | a lot of relatively expensive testing so there's a | reasonable assurance it won't fail in some catastrophic | fashion and destroy the entire rocket. | | Testing space hardware is additionally difficult because | you can only _just_ approximate the hardware 's operating | environment on the ground. Space hardware also can't be | easily repaired or repaired at all once launched. So | you've got to test actual flight hardware and if it fails | possibly rebuild it from scratch testing and validating | the entire way. | | Developing space hardware and high precision science | instruments is expensive and difficult. But it's just a | small portion of the overall mission cost for something | like Hubble or JWST. | bumby wrote: | > _There 's very little in the way of savings because | most parts are custom fabricated. The parts need to be | tested, integrated, then tested after integration._ | | To piggy back on the the GP's point, the fabrication | research is only one small cost center. Quality control | costs much more in aerospace than many people realize. | The reason why a bolt may cost $150 is because it has to | be tracked, material coupons kept/tracked/tested, held in | bonded storage etc. and not because we had to figure out | how to make a bolt. Those costs don't come down as much | with scale as, say, raw material. | | If it were all about knowledge costs, many designs today | would be dramatically cheaper because many use technology | (and even refurbished rockets) from 50 years ago. | Quenty wrote: | Just because the knowledge exists in the world doesn't | mean that you know it. Consolidating knowledge is a non- | trivial exercise. | [deleted] | p_l wrote: | NASA was trying to get some form of series production for | base system bus for long distance probes in late 1980s. | | What happened was that pretty soon the budget got slashed, | and the out of the prototype two units they barely scrambled | to have one of them flown, with very complex process to | balance the budget in face of constant attempts to cut it by | Congress. | | Maybe if NASA's budget was allocated in different process, | things would be different. As it is now, the people | controlling the purse strings care about their reelection so | they will at best jerk projects around to send money to their | states, or to place their own spin on things, etc. | spyspy wrote: | Even in high school robotics we built a main chassis and a | 1:1 spare for testing and hot swapping parts. | kevin_thibedeau wrote: | That would require staffing up for the production run and | then firing them when the contract was finished. There is a | limited volume of sporadic work available for contractors to | bid on. Increasing production capacity doesn't increase | demand. At the end of the day public investment into science | is always a jobs program first. | WorldMaker wrote: | I'd expect the largest part of why is that the marginal costs | of launches to space unfortunately don't go down. Each launch | is nearly as expensive as the first. The marginal cost on the | ground is one thing, and it sounds like Nasa often builds | things in triplicate or more on the ground, but then uses the | parts in training exercises or for debugging purposes. Nasa | probably made three or four equivalents to Hubble. Probably | plenty more than that to do all the underwater training on | the incredible repair missions for Hubble that extended its | lifetime from a projected 5, then a sad "failed mission", | then finally the 30+ years we should be grateful to have | gotten at all. | | They just have never had the budget in launch costs to ever | launch more than one. | Rebelgecko wrote: | Even in the Hubble days, launch costs were a relatively | small piece of the pie compared to the costs of actually | building the thing. I think for Hubble it was less than 10% | (depending on how you count the servicing missions). For | Webb it's significantly lower. | JumpCrisscross wrote: | > _the marginal costs of launches to space unfortunately | don 't go down_ | | Until recently, neither launch nor satellites had economies | of scale. With reusability, launch does. And with common | platforms and constellations, satellites are beginning to. | bumby wrote: | > _marginal costs of launches to space unfortunately don 't | go down._ | | Some aspects certainly do, like ground-support-equipment | and basic launch infrastructure. | sho_hn wrote: | There was. Sort of. | | https://en.wikipedia.org/wiki/KH-11_KENNEN | | In particular some of the manufacturing tooling for the | mirrors were shared, leading to the HST mirror being | downsized to 2.4 meters. | thereddaikon wrote: | Its surprising how many people don't know this all these | years later. Hubble is repurposed spy satellite. The main | cost of the vehicle isn't in the spacecraft itself though | its the optics which are different from those used on | KH-11. What is good for looking at Russian military bases | doesn't directly translate to looking at galaxies. | ceejayoz wrote: | In fact, the NRO donated two Hubble-like KH-11s in 2012, | on the condition that they not be used to observe Earth. | | https://en.wikipedia.org/wiki/2012_National_Reconnaissanc | e_O... | | One of them forms the base of https://en.wikipedia.org/wi | ki/Nancy_Grace_Roman_Space_Telesc.... | NikolaeVarius wrote: | no | Zealotux wrote: | I'm wondering why is that, which part of the effort was | dedicated to research and how much time and money would it | cost to build a new JWST? | throwaway64643 wrote: | I'd imagine they just cannot fabricate the mirrors as many | as they want. The mirrors, arguably the most important | parts of any telescope or optical instrument, need delicate | manufacture due to the required precision. At the end of | the day, this is not automobile industry. | guerrilla wrote: | The reasoning that I heard (and I hope I'm relaying this | right) was that if it doesn't work then it will most likely | be because of something that needs to be redesigned, so | there's no point in producing an exact replica. | cbm-vic-20 wrote: | It's also going out pretty far (the L2 Lagrange point on | the other side of the moon), so they also won't be able | to perform any manned post-launch repair missions like | they did with Hubble. | messe wrote: | > so they also won't be able to perform any manned post- | launch repair missions like they did with Hubble. | | In terms of hardware that's readily or soon to be | available, it is _technically possible_. Starship, _if it | gets off the ground_ , is the obvious choice. Orion could | do it, but it would mean dumping another two billion into | JWST. | | If it really came down to it, Falcon Heavy launched with | a Crew Dragon sitting on top of it could probably reach | it, although it might need an additional kick stage (I | haven't done the maths), and it would need to be crew | rated first (and SpaceX don't currently have an interest | in doing that). | bumby wrote: | If you consider the human to be part of that hardware, | it's over 4x the distance that a human has ever | travelled. There would still be a lot of technical | problems to be figured out. | gaius_baltar wrote: | Having a ship and a launcher capable of reaching the | telescope is a bit different of being able to service it. | I understand that just planning and preparing a mission | on this scale, with current technology and processes, | would take more time than the service life of the | telescope itself. | | Also, AFAIK, Crew Dragon does not have airlocks or other | resources for EVAs. Not sure it the capsule can be | evacuated for that too. But I would like more information | in this issue ... could not find too much from reliable | sources for now. | messe wrote: | > Having a ship and a launcher capable of reaching the | telescope is a bit different of being able to service it. | | True. But generally when people bring up the statement | that we can't service it, they usually back that up by | citing the distance. There would still be a lot of | hurdles to overcome, but none are insurmountable with | relatively small investment. | | All of that said, if Starship works, then the economics | change drastically anyway. You could probably launch an | entire fleet of less reliable, but much cheaper | telescopes, for less than the cost of servicing. | guerrilla wrote: | Actually I have a question about this. What happens if it | fails at L2? Is that position like occupied or more | difficult to deal with from then on? | huntsman wrote: | The L2 point is unstable do energy needs to be expended | to maintain position there. | Out_of_Characte wrote: | Solar wind will push it out of L2 and into an orbit | around the sun. This is already going to happen once JWT | runs out of fuel to maintain its position. | bewaretheirs wrote: | Webb is going to the Sun-Earth L2 (about 1.5 million km | from Earth), not the Earth-Moon L2 (which is about 61,000 | km from the Moon and 445,000 km from the Earth. | | https://webb.nasa.gov/content/about/orbit.html | mikepurvis wrote: | I think this assumes a successful launch and some kind of | issue with the deployment. | | The other concern is, of course, what happens if it blows | up on the launchpad. | guerrilla wrote: | Presumably they've actually quantified these | probabilities and think that the chance of that is | relatively very low compared to the chance of something | going wrong in the design. These things are not cheap, so | it makes sense not to have to make three if the launch | succeeds and design fails. | Kaibeezy wrote: | Ariane 5 appears to have 96% mean reliability. Source: | _2021 Space Launch Report - Launch Vehicle by Success | Rate (spacelaunchreport.com)_ - | https://www.spacelaunchreport.com/log2021.html#rate | | https://news.ycombinator.com/item?id=29554274 | JumpCrisscross wrote: | The footnote about Lewis Point Estimates is super | interesting. | | "Lewis Point Estimate Determined as Follows. | Maximum Liklihood Estimate (MLE)= x/n where | x=success, n=tries For MLE<=0.5, use Wilson Method | = (x+2)/(n+4) For MLE Between 0.5 and 0.9, use MLE | = x/n For MLE>=0.9, use Laplace Method = | (x+1)/(n+2) Lewis, J. & Lauro, J., "Improving | the Accuracy of Small-Sample Estimates of | Completion Rates", Journal of Usability Studies, | Issue 3, Vol. 1, May 2006, pp. 136-150." | Kaibeezy wrote: | Concur. You have to see this thread on it in the NASA | Spaceflight forum - | https://forum.nasaspaceflight.com/index.php?topic=39928.0 | mikepurvis wrote: | Oh yes, I totally agree-- this is a very proven rocket, | and the deployment sequence is very, very much _not_ | proven. So it absolutely makes sense to have gone this | way. | CamperBob2 wrote: | That's assuming that anything that goes wrong in the | deployment sequence necessitates a clean-sheet redesign | of the whole thing. No reason to think that. | mikepurvis wrote: | But with so many things that _could_ go wrong in such a | tightly integrated system, it 's impossible to predict | which components or assemblies may be affected by a | partial redesign. | CamperBob2 wrote: | If you say so. | sho_hn wrote: | I think OP means "what if the rocket fails". | | The answer is that building another telescope specimen | would be quite expensive, even without any changes to the | design. The supply chains aren't set up for volume and | integration and testing is very involved. I can't put a | number on "the second telescope would be x% cheaper", but | it would be very disappointing. | revax wrote: | Also Ariane 5 is one of the most reliable rocket capable | of launching JWST on the correct orbit. | _joel wrote: | I've never been so nervous for a launch in my life. | Mountain_Skies wrote: | I'm more nervous about the deployment. There are so many things | that can go wrong after the launch but before it is fully | operational. | fortysixdegrees wrote: | Although I guess once it's in orbit, and major problems could | be sorted out over the following years with manned repair | missions, like they did with hubble | FourHand451 wrote: | Not really, unfortunately. Webb will be much further from | Earth than Hubble is, so as far as I'm aware a human | mission to go repair it isn't really considered an option. | | https://www.nasa.gov/topics/universe/features/webb-l2.html | ravi-delia wrote: | If Starship delivers on its deltaV and economic promises, | it's at least feasible, although that's a big if. | Besides, if you can boost something the mass of the | telescope with twice the volume and much less money, why | would you bother fixing the one you have? | BbzzbB wrote: | They've worked on the design for over 20 years AFAICT. | Even tho Starship will enable bigger and better | telescopes, if there's a repairable problem and it is | within reach, would be odd to just bail on JWST when the | whole design/build process of the next gen will likely be | a very long endeavor. | | https://en.wikipedia.org/wiki/James_Webb_Space_Telescope# | His... | ravi-delia wrote: | I think it's fair to say that with lower stakes you can | definitely take less time on each telescope. The Webb is | a miracle of engineering, but a lot of that miracle goes | towards squeezing it into a pretty narrow fairing. | BbzzbB wrote: | Sure, I'd also expect (as an outsider) that new | iterations will be quicker from this new knowledge base | and a 9m x 18m payload rocket, I'm just saying if there | is a way to fix broken JWST I see no reason to not even | try and wait out the next gen. They are not mutually | exclusive. | NobodyNada wrote: | > major problems could be sorted out over the following | years with manned repair missions, like they did with | hubble | | Not anytime soon. The Hubble is in low-earth orbit at an | altitude of 540 Km, whereas JWST is at the Earth-Sun L2 | point at an altitude range of 370 Mm to 1.5 Gm; further | than the Moon. No spacecraft capable of carrying humans | beyond LEO has been built since the Apollo missions. | | Starship and SLS will change the game, but both are still | years away from manned flights. | retrac wrote: | Even then, it's quite possible a human mission beyond LEO | to repair the JWST would end up costing more than just | building a replacement telescope. | _joel wrote: | 178 things! | bumby wrote: | Ohh, you optimist :-) | | > _" There are 344 single-point-of-failure items on | average," Menzel said about the Webb mission, adding that | "approximately 80% of those are associated with the | deployment _ | | https://www.space.com/james-webb-space-telescope- | deployment-... | Ostrogodsky wrote: | step 138: npm run | baggy_trough wrote: | I never thought the Mars rover sky crane would work, but it | did! | _joel wrote: | I think most of the engineers on the project didn't either, | what did Adam Steltzner, something like "It was the least | worst option out of a lot of bad options". | | I'm sure there's a commentary there on modern life, but sod | that, this far cooler than any addage :) | remram wrote: | When's the launch date? I couldn't find a definitive answer, as | both December 18 and December 22 are listed. | _Microft wrote: | December 22, delays are always possible but it's not going to | launch earlier than that ("no earlier than" is often | abbreviated "NET" in that context). | | https://jwst.nasa.gov/content/webbLaunch/countdown.html | stanmancan wrote: | December 22nd; they were aiming for the 18th but there was a | small issue that required a bit of additional testing so they | pushed it back to the 22nd. | gizmo385 wrote: | Wasn't the most recent 18 -> 22 delay because they dropped | it? | progbits wrote: | They didn't drop it but a clamp released unexpectedly | during some operation and it caused vibrations in the | telescope. At that time they didn't have sensors attached | that would be able to confirm if the vibration was within | specified tolerances so manual inspection of sensitive | components had to be done again. | | Glad to hear it went well and we are back on track! | gdecaso wrote: | Yep. ___________________________________________________________________ (page generated 2021-12-14 23:00 UTC)