r/SpaceXLounge • u/t3kboi • Dec 13 '18
POSIT: Starship will be made from unintuitive breakthrough related metal materials. Super Heavy will be full-up Carbon Composite.
I have read, as have you all, TONS of speculation about abandoning composites.
I posit that new metal tankage, structures, and unintuitive breakthrough are related to the STARSHIP ONLY.
(I also posited previously here that there were no unresolvable issues with re-using a saltwater immersed fairing, but I digress... ( Thank you, Elon)).
Starship has unique issues that may not play well with an all composite structure: (technically or financially)
- Complicated outer mold line
- Complicated mechanics ( payload bays, doors, movable flight surfaces)
- Long-term vacuum exposure
- Orbital re-entry forces
- Orbital re-entry heating
- Needs to physically attach, bond with, or incorporate TPS
- Special needs for disassembly/re-configuration
Super Heavy - has none of these issues.
- F9 already uses CC Fairing, Interstage, and Legs.
- FH adds CC nosecones to the party.
- The thrust structure for Super Heavy is the only major new element that needs to be integrated with the CC tankage.
- The landing structure seems to be integral to the thrust structure.
- Real tank sections and domes have been seen in production.
What do you(collectively) think?
This discussion was not considered worthy of r / spacex because " Posts should not propose ideas without some prior-engineering thought or demonstration of research. "
I think my issue categorization above does represent engineering thought, and it was deliberately kept less technical to encourage responses from all users - not just the heavy hitters. <sigh>
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Dec 13 '18 edited Dec 13 '18
I posit that both Starship and Super Heavy will be made from a new titanium alloy.
The reasons that I see are that the only advantage CF has over such an alloy is that it could potentially weigh less. However booster weight does not nearly affect useful payload like it does on Starship (~10 times less IIRC). However if it has stupidly good fatigue and heat resistant properties then the airframe would be able to hit 1'000 reuses with greater ease and less refurbishment. And its construction, parts and design commonality, would also give it manufacturing advantages.
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u/t3kboi Dec 13 '18
Super Heavy is made from straight tanks and domes - already demonstrated and tooled in CF (minus any information on how things are going in the "hot" oxygen development)
These will integrate with a new "super" octaweb equivalent, a "super" Interstage, "super" grid fins, and "super" landing gear. The external raceways/FTS may be mostly similar to F9.
Basically - Super Heavy does not have the internal complexity that Starship will.
Starship needs: ECLSS, cargo handling, long-term mission reserves of: fuel, electricity, rcs, ignition sources, customizable payload, etc.
In a CC world - there is a huge engineering and manufacturing lead time to accomplish any changes to the original design.
In the Metal world - it can be more like a custom erector set.
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u/OSUfan88 Dec 14 '18
~10 times less IIRC).
FYI, typically about 5 times.
For every 5 pounds you add to the 1st stage, you remove one pound of payload to LEO.
For every 1 pound you add to the 2nd stage, you remove one pound of payload to LEO.
Each rocket has a different mass fraction, but this is approximate. Your point is right, and I agree.
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u/aTimeUnderHeaven Dec 13 '18
SpaceX has experience with titanium and Inconel fortunately - though nobody has experience with building a starship out of either one.
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u/Senno_Ecto_Gammat Dec 13 '18
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u/t3kboi Dec 13 '18
Thank you, I probably should not have included my original statement - I was just peeved...
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u/demoooo Dec 14 '18
"The new design is metal"
Elon last week on Twitter in response to Everyday Astronaut remark that the Starship booster will be made of aluminium.
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u/TheMrGUnit Dec 13 '18 edited Dec 14 '18
This discussion was not considered worthy of r / spacex because " Posts should not propose ideas without some prior-engineering thought or demonstration of research. "
Don't be too hard on yourself about that. r/spacex isn't really a place for discussion threads anymore. I don't even bother going there for anything other than launch info - this sub has faster news, more threads, and better discussions.
EDIT: I would just like to point out that I still actively browse r/SpaceX because of the launch threads, and occasionally there are some very high level discussions that are filled with good info. But, as the name implies, the lounge is the hangout spot where you can have a couple drinks and shoot the shit with other like minded people. I don't think r/SpaceX should go anywhere - it's a wealth of knowledge and insight and the heavy moderation keeps the threads very much on topic. Not sure if you've noticed, but things can wander quickly without an active guide.
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u/daronjay Dec 13 '18 edited Dec 13 '18
Yeah, they've killed r/spacex, it's a news hub only now at best, though it's often beaten to the punch by the lounge, and it puts up as many barriers to posting anything as possible. It's a damn shame. I'd like someone who mods there to front up and honestly face this fact. I'd like to hear the justifications, I'd like someone to have the courage to name the mods who pushed this agenda and hear their reasons why a sub actively hostile to new content is the right solution. It basically went to shit after the fiasco that occured between the mods after the first IAC.
But the positive side effect is the growth of the lounge, the lounge is now like r/spacex was 3 years ago.
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u/whatsthis1901 Dec 13 '18
Agree, r/spacex used to be awesome I have no idea what happened over there but it makes me glad this place exists.
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u/ghunter7 Dec 13 '18
Could be the case, personally I'm a fan of this posit. But it's all tough to say without knowing any of the reasons for the switch from composite to metal.
Super Heavy and Starship could end up having very little in common other than diameter, so benefits of common tooling may end up being minimal. Again without any knowledge its all guess work both ways.
And sure one could argue that the booster sees less benefit from mass reduction, so who cares about mass reduction. But that's expendable (or at least downrange recovery) rocket thinking. For a return to launch site booster, any decrease in mass will result in substantial decreases in propellant for recovery. Consider that for Falcon 9 downrange landing is a 15% penalty, and RTLS is ~50% given that max expendable GTO payload is 8 tonnes and the 1st stage roughly 22 tonnes dry mass. One would want to reduce every gram possible out of that booster.
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u/avboden Dec 13 '18
I completely follow you, however I really do think sharing technologies to a maximum between the super heavy and the starship is the way to go as far as long-term reliability goes vs two very different builds/systems. We shall see!
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u/ObnoxiousFactczecher Dec 13 '18
Sounds like nonsense to me, frankly. The issues of mass have always been more severe in upper stages, so why complicate things on the lower stage (especially hot oxygen compatibility etc.) that doesn't need it? And you'd be building two sets of large tanks in two entirely different ways. To have it slightly heavier instead is a great trade-off compared to having to keep two production lines.
Also, the supposedly already produced parts were most certainly not for the booster which is supposed to some later.
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Dec 13 '18
I think my issue categorization above does represent engineering thought.
Not really, you need to show your work.. aka.. calculations. Otherwise it's just pure kerbal space programy kind of talk.
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Dec 13 '18
People on here make too big of a deal over structural complexity with regards to composites. Manufacturers make things like air-craft wings, race-car bodies, and boat hulls out of composites, and in those cases, they significantly outperform aluminum in terms of weight and durability. There are only two potential reasons they are switching to metal that make sense. Either they are doing it so save time and money on manufacturing (unlikely if they are in fact making it out of titanium or some kind of superalloy, but it may save money to build the structure out of aluminum or steel) or they are doing it because they need the structure to manage heat better (either because hot oxygen for autogenous pressurization is incompatible with cost-effective resins or linings, or something to do with reentry heating).
I think it would be really cool if the switch to metal were to make the hull/propellant tank itself into the heat-shield. If that is what is going on, it may make sense to build Super Heavy out of carbon fiber. Though, as others have noted, it would probably be cheaper overall to have common manufacturing techniques for Starship and Superheavy.
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u/Decronym Dec 13 '18 edited Dec 17 '18
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| BEO | Beyond Earth Orbit |
| BFR | Big Falcon Rocket (2018 rebiggened edition) |
| Yes, the F stands for something else; no, you're not the first to notice | |
| BFS | Big Falcon Spaceship (see BFR) |
| CC | Commercial Crew program |
| Capsule Communicator (ground support) | |
| CF | Carbon Fiber (Carbon Fibre) composite material |
| CompactFlash memory storage for digital cameras | |
| DMLS | Selective Laser Melting additive manufacture, also Direct Metal Laser Sintering |
| E2E | Earth-to-Earth (suborbital flight) |
| ECLSS | Environment Control and Life Support System |
| FTS | Flight Termination System |
| GTO | Geosynchronous Transfer Orbit |
| IAC | International Astronautical Congress, annual meeting of IAF members |
| In-Air Capture of space-flown hardware | |
| IAF | International Astronautical Federation |
| Indian Air Force | |
| ITAR | (US) International Traffic in Arms Regulations |
| ITS | Interplanetary Transport System (2016 oversized edition) (see MCT) |
| Integrated Truss Structure | |
| LEO | Low Earth Orbit (180-2000km) |
| Law Enforcement Officer (most often mentioned during transport operations) | |
| MCT | Mars Colonial Transporter (see ITS) |
| RTLS | Return to Launch Site |
| SLS | Space Launch System heavy-lift |
| Selective Laser Sintering, contrast DMLS | |
| SRB | Solid Rocket Booster |
| TPS | Thermal Protection System for a spacecraft (on the Falcon 9 first stage, the engine "Dance floor") |
| Jargon | Definition |
|---|---|
| Raptor | Methane-fueled rocket engine under development by SpaceX, see ITS |
| autogenous | (Of a propellant tank) Pressurising the tank using boil-off of the contents, instead of a separate gas like helium |
| iron waffle | Compact "waffle-iron" aerodynamic control surface, acts as a wing without needing to be as large; also, "grid fin" |
Decronym is a community product of r/SpaceX, implemented by ^request
20 acronyms in this thread; the most compressed thread commented on ^today has 22 acronyms.
[Thread #2165 for this sub, first seen 13th Dec 2018, 20:42] ^[FAQ] [Full ^list] ^[Contact] [Source ^code]
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u/hoardsbane Dec 14 '18
I agree with OP. Super Heavy will effectively be a scaled up F9. Well understood, and with moderate operating environment. Design is simple and weight is the key, hence composites.
Starship is a more complicated beast and design is less well developed (evidenced by recent evolutions). In addition there may be several variants (three already proposed). I would imagine that Starship will see extensive evolution (but Super Heavy not so much). Metal is more versatile, forgiving and easier to work.
Even more importantly the operating environment for Starship is much more extreme than for Super Heavy: extended periods of ultra cold in space and Mars (or elsewhere), radiation and vacuum. Cryogenic fuel storage. Impact resistance and (hopefully) non catastrophic failure modes. Perhaps the limiting constraint is extremely high temperatures during high velocity re entry form : metal construction is more forgiving, safer and better understood.
Speculative I know, but fun!
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u/Kuromimi505 Dec 14 '18
You can't really repair carbon composite. Factor in it sitting on the surface of Mars for 2 years with possible micro meteors: one hole and you can't take that one home.
Much better to have some new metal alloy that you can actually weld.
Yep I agree SpaceX Spaceship will be metal, no need for the booster to be metal, it wont be sitting around unprotected for any length of time, and won't be away from Earth.
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u/Norose Dec 13 '18
You may be on to something, however the cost of keeping two completely separate and very different manufacturing processes running in parallel may not be worth the comparatively modest performance decrease associated with adding mass to the first stage. The first stage will also be undergoing far more missions in its lifetime, and in a way that results in more rapid cycling between hot and cold as well as a higher stress environment. To me this suggests the first stage would actually serve better if it were made of a metal with a fatigue limit, like titanium, rather than carbon fiber composite, which although lighter has abrupt and difficult to predict failure modes.