[HN Gopher] Akin's Laws of Spacecraft Design ___________________________________________________________________ Akin's Laws of Spacecraft Design Author : filiph Score : 97 points Date : 2023-08-09 09:45 UTC (13 hours ago) (HTM) web link (spacecraft.ssl.umd.edu) (TXT) w3m dump (spacecraft.ssl.umd.edu) | karaterobot wrote: | I have a subset of these printed out and tacked to a cork board | in my office, and I refer to this website a few times a year. | Very, very good stuff. | | This one in particular was a big influence on me when I moved | from engineering to design. It expressed what I'd felt but hadn't | put into words. Not just the look, but nearly every aspect of a | project is _de facto_ path dependent, so you want to be as far | upstream as possible. It 's also why I volunteer to write a lot | of documents I'm not strictly responsible for: | | > 30. (von Tiesenhausen's Law of Engineering Design) If you want | to have a maximum effect on the design of a new engineering | system, learn to draw. Engineers always wind up designing the | vehicle to look like the initial artist's concept. | AnimalMuppet wrote: | > 8. In nature, the optimum is almost always in the middle | somewhere. Distrust assertions that the optimum is at an extreme | point. | | This rings true in politics as well. | firewolf34 wrote: | More succinctly stated as "Only the Sith deal in absolutes." | pdhborges wrote: | Isn't a Pareto optimal solution always at the edge of the | feasible space? | GlenTheMachine wrote: | Hi. I'm Henshaw of Rule 37. AMA. | starkparker wrote: | Who doesn't love grapplers? | carabiner wrote: | What work are you doing these days? | Rebelgecko wrote: | What's the backstory, was there a situation where you were the | blamee (or the blamer?) | mmaunder wrote: | Thanks for the clear line of blame. | aredox wrote: | Well, you can tell us about the event/project that led you to | coin that rule and how it panned out... | xNeil wrote: | What's a line of blame? | innrautha wrote: | I took it to mean clearly delineated responsibilities (i.e. | who gets blamed when a part / aspect doesn't work). | | If there are unclear boundaries between responsibilities, | things will fall through the gaps when one group assumes | another will take care of something. | firewolf34 wrote: | Furthermore, when people are held responsible for quality | completion of a task, they are often more driven to achieve | the task at-quality. This must be balanced with not over- | taxing them, but that's a given. | e40 wrote: | I take it to mean when blame is being aimed you are not in | the line of fire. | Eduard wrote: | interesting - I understand it differently, namely as in: | | "at a project's beginning, define rules such as 'if | component X explodes, it is team ABC's fault'". | | context: | | > 37. (Henshaw's Law) One key to success in a mission is | establishing clear lines of blame. | jameshart wrote: | I don't feel like a field that has in its entire history only | produced a handful of actual successful designs at all can | possibly rate this kind of 'world weary cynicism' style of | writing. | | Nobody has the experience or ability to be able to say 'trust me | I've built a few spaceships, this is the hard won truth of how it | is'. There are exactly _nine_ spacecraft that humans have ever | flown in. Only the Mercury /Gemini/Apollo programs really | accumulated any kind of experience and that experience was | extremely specific to a particular place and time and | organization. | | So sure, some general engineering truisms in here have the ring | of wisdom to them and us non-spacecraft engineers can nod at them | and quote them with the cachet they get from being associated | with NASA. | | But 'trust me I have been teaching people to design spacecraft | for decades' doesn't really count for much when during those | decades no new spacecraft designs were actually getting made and | launched. | firewolf34 wrote: | In Shute Norway's autobiography, _Slide Rule_ , he describes the | design and construction of the | [R100](https://en.m.wikipedia.org/wiki/R100), an airship of which | he was one of the leading engineers. | | The R100 design was "competing" with the design for the R101; | both design teams were simultaneously tasked with constructing a | viable airship to make a long-range trip (in the case of R100, | crossing the Atlantic in 78 hours, which was a remarkable | achievement for the time). The difference was that the R101 | project was state-owned whereas the R100 was privately-owned. | | R101 crashed and burned in France, en route to India on 5th of | October, 1930, likely due to structural issues damaging the | airships gasbags, of which the only survivors were those lucky | enough to be in the engine cars. | | In the autobiography, Norway describes how the difference in | program management led to the disaster. There are a lot of | factors that led to the crash, as you might imagine, but one of | the points he makes is that the publically-owned project was not | held to strict requirements in its design process. The privately- | owned R101 had a strict contract that they needed to complete, | with a tight budget to complete it. They had _constraints_. | Whereas the public-sector project was allowed to continually | revise their design as they went, making many successive rewrites | and changes without much structure. In particular, they cut the | ship in half and rebuilt it at one point in it 's development. | And when they arrived at the end of their development cycle, they | had no leeway to maneuver because they had a lot of public money | wrapped up in the project, along with a lot of public visibility | and responsibility, pressuring them into rushing the launch | without complete trust in their design, and into terrible weather | conditions. | | *13. Design is based on requirements. There's no justification | for designing something one bit "better" than the requirements | dictate.* | | Decide/envision your outcome, and set your constraints | correspondingly early on in development, aligned with realistic | expectations of resources, folks. | | To underline my point, here's a quote from the Wikipedia page. | | "Shortly before R101's flights in June 1930, the Cardington | [R101] engineers tentatively suggested that the long flights to | Canada and India might be postponed until 1931 on the grounds | that neither of the two airships was fit to make a lengthy flight | at their current developmental stage. The R100 team replied that | their airship was perfectly capable of flying to Canada, _and | that the Canadian flight was a part of their contract._ " | | R101 did not have a contractual obligation to meet, but did not | want to outright state they needed more time, lest admit defeat. | R100 had requirements that they needed to meet, which they were | ready to meet, as they had them written from the start in clear. | R100 launched successfully. R101 was forced to launch to compete | before it was ready, due to this "spontaneous requirement". R101 | burned for it. | freitzkriesler2 wrote: | > 3. Design is an iterative process. The necessary number of | iterations is one more than the number you have currently done. | This is true at any point in time. | | I'm going to agilely build a space craft! /S | carabiner wrote: | Funny thing is SpaceX is known for applying Agile to its | aerospace engineering workflows. Boeing etc. are much slower | because they use waterfall. | Balooga wrote: | Oh, I'm pretty sure someone(s) manages a massive GANTT chart | over on the SpaceX side. | datadrivenangel wrote: | It's the only way a spacecraft has ever really been built! | avmich wrote: | This is definitely the wisdom of ages, but some points do show | some age. 39. (alternate formulation) The three | keys to keeping a new human space program affordable and | on schedule: 1) No new launch vehicles. 2) | No new launch vehicles. 3) Whatever you do, don't | develop any new launch vehicles. | | Recent SpaceX developments, Starship in particular, put some | doubts on this one. | idlewords wrote: | Let's put this comment in the comment cellar for a few years, | to fully develop the tannins, and then see how it has aged. | Starship progress is a little ways away from proving this adage | wrong. | bryanlarsen wrote: | It could be argued that Dragon has already proven this wrong. | Falcon 9 was developed in the form it was specifically to | launch Dragon. SpaceX's original next rocket was going to be | a Falcon 5 until they got the Dragon contract from NASA. Yes, | the original Dragon was a cargo vehicle rather than a human | spaceflight vehicle, but both Falcon 9 and Dragon were | developed with the intention of eventually human rating. | inamberclad wrote: | Both were late, and I wouldn't say that Falcon was built | expressly for humans. It spent a decade proving itself | before it flew with people. That's not a _new_ launch | vehicle. | bryanlarsen wrote: | A decade is a short period of time by human-rated- | spaceflight standards. | hannasanarion wrote: | So? Falcon wasn't a human spaceflight program during that | time, and it was also over-schedule and over-budget | anyway. | | The advice isn't "no new launch vehicles should ever be | invented ever", it's "if you want your human spaceflight | program to be on time and on budget, don't include a new | launch vehicle in the plan" | avmich wrote: | > Both were late | | What was the "determined" date to have them ready? How do | you know they were late? Judging by Elon's estimates? | | > I wouldn't say that Falcon was built expressly for | humans | | You know of course that requirements for the rocket to | launch people are different from the rocket to launch | only cargo? There were cases when non-human-rated rocket | became human rated (at least Proton), but these days it's | better to plan ahead, like teams working on Arian-5 (and | also Dream Chaser, not a rocket) do. I'd assume Flacon-9 | developed from the beginning in such a way so at least | human-rating would be possible - if not built-in already. | | > It spent a decade proving itself before it flew with | people. That's not a _new_ launch vehicle. | | I'd agree regarding Falcon-9. Starship is another story. | inamberclad wrote: | > What was the "determined" date to have them ready? How | do you know they were late? Judging by Elon's estimates? | | Crew Dragon was approximately 3 years late, from the | original planned launch date of 2017 to the actual date | of 2020. Given that the contract for the missions were | awarded in 2014, it's a miracle that things have | proceeded at the pace they have. | | > You know of course that requirements for the rocket to | launch people are different from the rocket to launch | only cargo? | | I'm well aware of the differences. I work in this | industry. That said, SpaceX made the wise decision to cut | their teeth and prove their design on cargo first. That's | not a new launch vehicle by definition. They were | launching rockets regularly for years before they put | people on the pointy end. Most other human-rated rockets | in recent history have _only_ launched humans. I'm | neglecting older, converted ICBMs like Redstone and | Titan. The only standout from this list is probably Soyuz | (the R-7 derivative launch vehicle), which has been kept | going through sheer inertia. | | > I'd agree regarding Falcon-9. Starship is another | story. | | I suspect that Starship will be years behind schedule | before it even launches cargo. I suspect that it will | miss NASA's planned lunar landing date, but it won't be | at fault because other parts of the program will suffer | even worse schedule slips. I understand that people are | hopeful that this really will revolutionize spaceflight, | and I count myself in that group too! Reality has a way | of intruding eventually though. I want SpaceX to build, | fly, and trash as many unmanned Starships as it takes to | make it reliable. That will cause some level of delay | because they'll find something new in the testflights | that will necessitate a redesign before it kills someone. | dylan604 wrote: | >I suspect that it will miss NASA's planned lunar landing | date, but it won't be at fault because other parts of the | program will suffer even worse schedule slips. | | Could you imagine if NASA mandated that SpaceX be the | launch platform for Boeing's capsule? | bryanlarsen wrote: | Congress didn't pay SpaceX the agreed upon amounts for | the first 3 years of the contract, and Crew Dragon was 3 | years late. Coincidence? | Zandikar wrote: | Err, what? Keyword there: "New". | | SpaceX still faces large costs and delays in developing new | launch vehicles, including starship, which is delayed and | unfinished btw, so no matter how you try to spin it, Starship | is not (currently) a good example of SpaceX being an exception | to the adage. Artermis 3 isn't exactly cheap afterall, and if | you don't know what that is but know what Starship is, that | proves the adage this one is refering to: | | > 39[a]. Any exploration program which "just happens" to | include a new launch vehicle is, de facto, a launch vehicle | program. | | The whole point of these two adages is that reusing an existing | design is better than a new one. SpaceX's REUSABLE rockets are | great for a number of reasons yes, but by definition, those are | not NEW launch vehicles. And when they were new, well, lots of | delays and setbacks and costs as they kept accidentallying | rockets trying to land them. Not a slight against SpaceX btw, | that's part of rocket science and innovation, but again, not | cheap or quick. | | If anything, SpaceX's entire business model is EMBRACING that | adage, not disproving it or an exception to it. | | EDIT: clarified | avmich wrote: | > The whole point of these two adages is that reusing an | existing design is better than a new one. | | Yes, and that's put in doubt. Starship aims to improve on | previous designs - in terms of affordability, that is, making | human flights cheaper. This cheapness can't be realized with | existing designs, so a new design becomes better in that | regard. | | > SpaceX's REUSABLE rockets are great for a number of reasons | yes, but by definition, those are not NEW launch vehicles. | | I don't know how good definition can exclude reusable rockets | from being new. Was Shuttle ever new? Delta Clipper? Reusable | Falcon-9? Falcon Heavy? I think this is not a good | definition, if, according to it, reusable rockets can't be | new. | | > And when they were new, well, lots of delays and setbacks | and costs as they kept accidentallying rockets trying to land | them. | | Do you know the difference between designing and using? In | software it's rather clear, and nobody would expect a half- | written program to function according to specs. Neither it's | the case in aerospace - while Falcon reusability was being | designed and tested, nobody should expect it to perform | flawlessly as when used "in production". Not cheap, agree | (actually, quite cheap by aerospace standards, but still not | some typical household-sized money), but I'd argue that was | rather quick - just a few years to put reusable first stage | into production starting from announcing the idea and | building the first "Grasshopper". So, while 39[a] may stand | here, your comment doesn't provide a good justification to | it. | | > If anything, SpaceX's entire business model is EMBRACING | that adage, not disproving it or an exception to it. | | SpaceX benefited immensely from using proven solutions, but | the results they are showing are still disproving the idea of | this law. The ambitions of SpaceX are high compared to the | rest of the world launching industry, but so are the results, | and we also have genuine "firsts", like putting the reusable | first stage into production, or flying reusable spacecrafts | to space station, TKSes and Shuttles notwithstanding. | | Let me try to explain again my main point: SpaceX aims to | make human spaceflight significantly cheaper, and the opinion | is that it can't be done without radical redesign from | scratch. It was attempted several times in the past, with | e.g. Shuttle and Energiya, and it still isn't done today, but | if you want to risk being put on the "you're currently here" | list of SpaceX achievements(1), which were doubted and then | happened, I'd at least propose you to think from the basic | assumptions and find out why SpaceX won't actually achieve | cheaper human spaceflight this time. | | (1) In Russian that list looked like this before reusable | Falcon: | https://meduza.io/impro/0ZWeCgCXA4nsWv7dj7CHbSIrsURgOh- | qpiUh... | singleshot_ wrote: | > In software it's rather clear | | In software, I perceive there to be almost no separation | whatsoever between design and use. I'm using windows 11 | right now, and sometime in the next few days it will | silently download software patches that were designed over | the last few days to address situations not considered in | the original design of windows 11. Software goes back and | forth from the design process to active use pretty much | continuously these days. | | Just an alternate perspective to think about. | Alupis wrote: | None of this is put in doubt though. Your points about | SpaceX's potential for future cost savings and efficiencies | are hardly realized today - particularly when considering | the length of time that has been spent without a capable | manned vehicle. If, fast forward a decade or two and SpaceX | is still using today's designs (albeit, upgraded) and | actually realized massive savings - then we can talk. | However, I'd bet they're going to re-design and build brand | new models along the way... | | There's a reason military aircraft tend to have extreme | service lives. It's far cheaper and effective to upgrade | and refit/improve existing airframes with modern technology | than it is to start from scratch - every single time. | | Look at the F-35 program. It's not exactly fair because the | design goals are vastly different - but upgrading aging | F-15's has kept them on the battlefield for 47 years[1], | and today they're still a seriously potent air superiority | fighter. The F-15's of today are only similar in shape to | the originals, however. | | [1] | https://en.wikipedia.org/wiki/McDonnell_Douglas_F-15_Eagle | Swizec wrote: | The "No new launch vehicles" adage reads to me as "Don't | develop a new browser when you make a website" | | That doesn't mean we never need or want a new browser. It | just means that developing a browser is a separate project | and if your fancy websites requires a new browser, it is in | fact a browser development project, not a website project. | inamberclad wrote: | That's still going to be late and over-budget. | avmich wrote: | Late comparing to what? Maybe SpaceX will not make it ready | for NASA's return to the Moon flights as it was planned. | However those dates don't look too serious to me - what's the | justification for them? I suspect they were specified fully | understanding they can easily slip right. | | Over-budget - what's the planned budget? I suspect Elon Musk | himself doesn't have pre-approved specific budget to develop | Starship, which makes sense, as e.g. it's rather hard to | pinpont. As for the overall idea for how much Starship | development would cost - how do you know it's missed already | or going to be missed? | [deleted] | bryananderson wrote: | Falcon 9 (plus Dragon) is the definitive counterexample. The | jury on Starship remains out. | avmich wrote: | I'd consider development of Crew Dragon to be rather fast - | because, in the condition of a private development, it wasn't | done before. Comparing to other spacecraft developments, in | late 1950-s there was a race, USA vs. USSR, to put a man in | space "soonest", and it took Soviets ~3.5 years from the | launch of the Sputnik to send Gagarin to orbit. So, just a | few short years... and a large government backing. | | Still, given that Crew Dragon was developed by a private | company and is quite modern judging by performance, I think | it's a good result. | dylan604 wrote: | Compare the budget of SpaceX to NASA's up to and through | Mercury. NASA's experience was one of something never | having been done before compared to the experience of | SpaceX seeing many others doing it just needing to tweak | the formula to make it affordable. Also, without NASA's | burden of being a government pork/jobs program rather than | being a streamlined process | vannevar wrote: | Far from being a counterexample, Falcon 9 is a great example | of the adage's truth. It flew for 10 years before being used | for human missions. | filiph wrote: | I knew #36 and have used it in the context of software | engineering. But much of the rest is similarly applicable. | | > #36 Any run-of-the-mill engineer can design something which is | elegant. A good engineer designs systems to be efficient. A | _great_ engineer designs them to be effective. | belter wrote: | Good rules, despite the page background choice going against | rule 20: "...A good design with a bad presentation is doomed | immediately..." | Eduard wrote: | how is this rule meaningful beyond platitude? | | "boss, I have finished the task. But this time, I activated | _great engineer mode_ , hence the result is not only elegant, | but efficient and effective." | wmanley wrote: | I think you've misunderstood the quote. The solution that the | great engineer produces is effective, but may not be | efficient nor elegant if it doesn't need to be. The point is | that solving the problem (and maybe stopping there) is more | important than producing something that is fast or beautiful | that doesn't solve the problem. | | I think there's some overlap with: | | > 13. Design is based on requirements. There's no | justification for designing something one bit "better" than | the requirements dictate. | dakr wrote: | I take this progression to mean that the novice will design a | part or subsystem that is good by itself. The more | experienced engineer is thinking bigger by taking into | account the effect of the larger design on the portion they | are working on. The great engineer is thinking holistically | and so also considers how the part affects the whole design. | | The same thing applies, I think, to anyone who works on a | team. The beginner thinks of the problem by itself. The more | experienced member thinks of how the system will influence | what they are building or doing. The senior member will think | about how the thing they are doing/building will in turn | affect the whole (and weigh the consequences). | moffkalast wrote: | > 33. (Patton's Law of Program Planning) A good plan violently | executed now is better than a perfect plan next week. | | Ah yes, unfortunately it's only halfway through the execution | that you realize it wasn't a good plan, wasn't even an okay plan | but a straight up terrible one. | Razengan wrote: | By the way, since you need to apply thrust from any direction to | maneuver flexibly in 3D space (without wind or gravity), wouldn't | spherical/disc(saucer) shaped spacecraft be the most efficient? | dmbche wrote: | The space between things in space is quite large, so you're | going in a single direction for a while. The thrust from the | spacecraft is also used to exploit gravitational energy | (slingshoting around planets) for the most part, from my | understanding. | | In Sci-fi, it's generally understood that very fast crafts | (0.1c and up) will need to reverse and apply thrust opposite | their direction to slow down for a very large part of the | voyage (up to more than half) - so could be a good idea to be | able to flip around and apply thrust the other way too. | 0cf8612b2e1e wrote: | Plus, without deflector shield voodoo, a skinny tube design | minimize your cross sectional area and how much debris you | will impact. | icegreentea2 wrote: | Only if instantaneous large accelerations in arbitrary | directions is amongst your primary performance requirements. | You'd need to have thrusters ready to fire in arbitrary | directions as well. A spherical (specifically) spacecraft would | also have more heat dissipation challenges. | carabiner wrote: | There are 1,000 other requirements that do not demand maximum | 3D rotation efficiency. | pdonis wrote: | No. Such a craft would either need to have full thrust engines | pointing in every possible direction (way too costly and | overbuilt) or would have to have some way of rotating its full | thrust engines to be at any arbitrary angle relative to the | ship (which then means you have to transfer all the thrust | through gimbal mounts or whatever you're using to be able to | rotate the engines, and those things won't be able to withstand | that kind of stress). It's much easier and simpler to point | your full thrust engines in one direction (out the back of the | ship), so the thrust gets transferred through the entire ship's | fixed structure, and then have smaller thrusters to rotate the | _ship_ to point in the direction you want to go. | JoeAltmaier wrote: | Number 13. Design is based on requirements. There's no | justification for designing something one bit "better" than the | requirements dictate. | | Isn't that the margin for error? I want to go up in a ship that's | a little better than the absolute minimum. | rahimnathwani wrote: | Then specify that in the requirements. | dylan604 wrote: | >There's no justification for designing something one bit | "better" than the requirements dictate. | | Are the Martian rovers outliers to this rule? | | >I want to go up in a ship that's a little better than the | absolute minimum. | | This makes me think of the "this was built by the lowest | bidding contractor" quote | whats_a_quasar wrote: | This is the only one I have reservations about. It is also part | of the engineer's job to understand the customer, understand | what they need, and negotiate the requirements (within reason). | It's hard (impossible?) for the customer to fully design | exactly what they need, and it works much better to the | engineers to build something with continuous customer input | than to build rigidly to a spec sheet | firewolf34 wrote: | You're describing the (albeit quite common) situation where | requirements were not conclusive enough and need to be | revised throughout lifetime of development, which can be | natural as you begin to understand the problem space as you | work within it. But the key is that the requirements should | be as conclusive and accurate to resolving your problem as | they possibly can be, at any given point in time. | | In the "frictionless environment, ideal world" scenario - | requirements should always be completed as close to the | letter as possible and no further. | | In the practical scenario, requirements should be _written_ | as close to perfect as can be achieved where perfect is | defined as what is necessary to resolve your problem space, | limited by your understanding of the problem space. | firewolf34 wrote: | Requirements set constraints which guide the development | process. Without them set early on, you risk not understanding | completely what you're setting out to do, you risk differing | expectations/assumptions between members of your team, and you | risk creep as the project goes on which means you will diverge | from your intended outcome. | | In any project, resources (time, money, etc) are limited so the | most successful project will be one that uses resources most | efficiently. So good explicit requirements _allow you_ to | determine the most efficient manner to achieve them as they | codeify the problem and give you goalposts to optimize within. | | This all _relies_ on you being able to set good requirements | from the outset, which can be done by _understanding_ what you | 're setting out to achieve (the problem you're trying to | solve). | | I have a comment in this thread which discusses the | consequences of this rule specifically. | https://news.ycombinator.com/item?id=37069168 | imoreno wrote: | Margin of error should be calculated at the design stage, not | as an afterthought during implementation. ___________________________________________________________________ (page generated 2023-08-09 23:00 UTC)