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Starship Prototype Unveiled (space.com)
543 points by childintime 19 days ago | hide | past | web | favorite | 330 comments

380s for ISP for the Raptor vacuum engine seems durn good, considering the tradeoffs between hydrogen and methane.

The most efficient engines we've flown, the RL-10 [0] (used on the Delta IV and Atlas rockets as part of the Centaur Upper Stage) and the RS-25 [1], (the Space Shuttle Main Engine) get around 450-460s for their specific impulse. These engines use liquid hydrogen and liquid oxygen. The issue with liquid hydrogen is twofold: it is not very dense, and to keep it from boiling away in liquid form, it needs to be really cold. So you need huge, insulated tanks to store it. Hydrogen is everywhere, but it's kind of a pain to use as rocket fuel.

Merlin Vacuum [2], which is currently used on the Falcon vehicles gets 311s. The RD-0110 [3], used on the Soyuz gets 326s. These use RP-1, which is highly refined kerosene. It's super easy to work with. On earth. Where we have 200 years of infrastructure in place to support using hydrocarbons. It takes that infrastructure to refine it into a form that rocket engines can use without gunking up the works with unburnt carbon and other particulate crap.

Raptor uses methane, which is kind of like a jack of all trades between density, efficiency, ease of processing, storage, and ease of use in engines. This is basically how SpaceX seems to operate: rather than optimizing a single part of the system (like trying to get the most efficient engine), they try to optimize from a systems level. I don't really know much more than that, because there hasn't really been a lot of stuff for civilians to read on methane engines. This is kind of the cutting edge of the second golden age of space exploration. This freaking rules, what a time to be alive.

[0] https://en.wikipedia.org/wiki/RL10

[1] https://en.wikipedia.org/wiki/RS-25

[2] https://en.wikipedia.org/wiki/Merlin_(rocket_engine_family)

[3] https://en.wikipedia.org/wiki/RD-0110

> This is basically how SpaceX seems to operate: rather than optimizing a single part of the system (like trying to get the most efficient engine), they try to optimize from a systems level.

They're optimizing for "real" reusability, as in eventually aiming for airline-like turnarounds. None of the earlier engines you noted were reusable except the RS-25, and given how long it took to turn the Shuttle around one could argue it doesn't really count as "reusable" in sense SpaceX is aiming for.

Aiming for reusability and ease of maintenance leads to different optimization paths, in particular we should expect that any one component is going to be less powerful, it'll need to account for wear & tear, not use once and crash it into the ocean.

But raw performance on a single trip doesn't matter much if you can just deliver the same payload in two trips to orbit instead.

> and given how long it took to turn the Shuttle around one could argue it doesn't really count as "reusable" in sense SpaceX is aiming for.

Not just the time but the cost, if you take the figure of how much the space shuttle program cost, and divide it by total number of flights (including the two lethal ones), it cost somewhere between $900 million to $1.1bn every time the thing launched. It was very far from the early 1970s dream of an economically reusable spacecraft.

Indeed, the space shuttle was so expensive it burned up much of the rest of NASAs budget-- keeping that disastrous, failed program running is why NASA doesn't have manned spaceflight capability at the moment.

Well, from an outsider perspective, the SLS/Orion program is pure pork. Nobody holding the purse strings cares whether the thing ever flies. Heck, probably they even prefer if it never flies (always just a few years and tens of billions in the future); a failed launch is potentially politically catastrophic.

> But raw performance on a single trip doesn't matter much if you can just deliver the same payload in two trips to orbit instead.

Except that you're doubling the cost if you have to do two trips.

If you throw away the rocket, sure, you're doubling the cost if you have to do trips.

If the rocket is reusable, then the vehicle cost gets amortized over the total number of trips, and the per-trip cost gets closer to just the cost of fuel (hopefully at least an order of magnitude less than a new vehicle+fuel on each flight).

Fuel and oxidizer is 2-3 orders of magnitude less than the cost of an expendable rocket.

Entirely valid point, but doubling 1% of the cost of a single use system is still pretty good, comparatively speaking.

You just need twice as much methane. So just have PF Chang’s catered and you’re back in orbit in a couple hours.

> The issue with liquid hydrogen is twofold: it is not very dense, and to keep it from boiling away in liquid form, it needs to be really cold

It’s also a bitch to work with. When it’s not trying to immolate or suffocate you it’s busy turning every metal part it touches to garbage [1].

[1] https://en.m.wikipedia.org/wiki/Hydrogen_embrittlement

You missed one of the most important parts about methane as well: The Sabatier Reaction [1]

Hydrogen + CO2 => Methane + Water

This is an extremely important reaction. Mars, for instance, has effectively unlimited Hydrogen and CO2 which also means effectively unlimited Methane and Water. How just absurdly convenient is that?

But it also plays a major role in things like life support. We breathe out CO2. On Earth where we have an enormous atmosphere this doesn't matter. But in closed systems, such as the ISS or what will be the habitation regions on Mars, this is a major issue that needs to be dealt with or we'd kill ourselves with our own exhaust.

NASA, on the ISS, used to deal with life support by producing oxygen from imported water, and discarding the produced hydrogen. They'd then collect exhaled CO2 from the air using CO2 scrubbers and also discard that. That was a pretty inefficient system that required large amounts of imported water to sustain. Now they use the Sabatier Reaction to convert the exhaled CO2 into water and methane. Only the methane is discarded. And as a result of this, instead of needing to import large amounts of water, now all they need to import is a small amount of hydrogen to keep the reaction running.

On Mars this will result in a really cool system. What will be an increasingly large scale life support system will be literally creating rocket fuel as a byproduct. Of course methane is also a controlled and efficient gas, so it can also be safely used for things like cooking dinner.

[1] - https://en.wikipedia.org/wiki/Sabatier_reaction

If you invest more energy you can also turn Methane into longer chain hydrocarbons and produce things like plastics or lubricants.

Here's a Wired article about the raptor engine - it's "a full-flow staged combustion engine, only the third engine in history to employ this technique ... The previous two attempts at such an engine, one in the Soviet Union in the 1960s and another in the US in the early 2000s, never made it beyond testing."


And if you want to get a lot more detail on what makes a "full flow staged combustion engine" so special, this article from Everyday Astronaut goes into some amazing detail on this and many other engines.


This was AMaZING. Exactly the kind of content I want to consume on HN

This guy is amazing. Look out for his interview with Elon Musk that should be released in the next 24 hours on his YT channel [1].

[1] https://www.youtube.com/channel/UC6uKrU_WqJ1R2HMTY3LIx5Q/vid...

I'm sorry but did anyone do a rudimentary spelling and grammar check on that?

"Raptor is designed to power the new reusable vehicles SpaceX’s is building, the Starship spacecraft and the Super Heavy rocket."

Also they call Tim Dodd an "industry expert"...

https://youtu.be/Sdwy9fzQzl4 Scott Manley does a great job explaining such things!

I'm surprised the guy being a youtuber. He is the codecs guy at Apple Computers

Eh, it's just another form of blog at this point. Not the greatest for searching, but a valid medium for expression.

I think they might be suggesting that Scott may have specific exemption from Apple's PR policy (summary: "say nothing to anyone") to be allowed an independent public voice - particularly on a technical/engineering topic. Apple is not, so far as we know, currently developing orbital-class rocketry, but there's genuine potential for product topic overlap in Project Titan vs Tesla and perhaps more besides.

I would not be at all surprised if there's a List Of Things Apple PR Hereby Politely Requests That Scott Doesn't Mention.

When I was at AWS I was similarly forbidden from mentioning anything to do with video games to just about anybody, despite not having anything to do with video games myself, and many other topics besides the obvious (e.g. "don't disclose EC2/S3 capacity numbers"[1], "don't reveal how Glacier works"[2]), and in fact there was a whole programme of PR training and tiered permission to speak at conferences or to the press/analysts that boiled down, mostly, to knowing what you could and couldn't say, and how diplomatically you parried questions on the latter.

Either that or Terry Pratchett's law of rewritten rules applies.

[1] no-one would believe me anyway

[2] it's a massively redundant array of vinyl records

It's also great self-marketing.

He started out (or at least found fame) doing Kerbal Space Program tutorials and play throughs, that's how I first came across him. He's also a pro DJ with an awe inspiring music collection and knowledge of music, though I'm not sure how much of that he still does. Oh, and he's also a fully qualified Astrophysicist and has worked in the field.

I'm shocked that I'm the last person to know this. I didn't know I could be more impressed with him.

Isn't he an astronomer / astrophysicist? You must be talking about another Scott Manley.

Nope, same guy. Scott Manley has a degree in astrophysics (I think) and worked as an astronomer for a while, then got a job coding at Apple. He's a smart guy

Technically he got a job at a startup, which was then bought by Apple.

Yeah, I looked him up on Wikipedia, looks like I got the wrong impression from his videos. Smart guy indeed!

I'm no rocket scientist, so bear that in mind, but something has been bugging me about the flight paths for this vehicle [0]. It has to make some very large, specific orientation changes several times during descent, using the heat shield on one side of the vehicle, and then only rotating to upright orientation in the lower atmosphere, after quite a lot of falling sideways. The orientation maneuvers seem much more complicated than their current booster re-entry flight paths [1]. and even more complex than the space shuttle [2].

[0] https://www.youtube.com/watch?v=LQTnWEHl5qU

[1] https://www.youtube.com/watch?v=6YyV-otP3pI

[2] https://www.youtube.com/watch?&v=TOieURpnbm0

This appears to me to make each flight much more complicated to pull off, introducing more points for it to fail without contingencies, and it makes me nervous. But, again, I am an just an unenlightened observer from an unrelated field. I don't even play Kerbal Space Program! I'm sure they've weighed a million different options and their risks, and have arrived at this one after a lot of thinking, but it has been bugging me. The stainless steel construction certainly looks beautiful out there in Texas.

It’s actually similar to the shuttle, In a couple of ways simpler, and a couple of ways more complex. The shuttles body was also designed to both generate lift and be a blunt body - with a transition of mode between them. The blunt body allowed it to survive reentry while the lifting body allowed it to glide. However that glide was way more complex then NASA generally talked about. The shuttle pulled some aggressive s-turns to bleed off energy during the re-entry.

This approach is more or less the same as what the starship is doing here, except instead of using a glider trajectory for the controlled landing they instead use retropropulsive landing. This is needed because what SpaceX is landing here is a second stage, not a first stage. Way more heat, way more power.

Also they plan to land where there isn't any atmosphere, or an atmosphere too thin to brake significantly.

So they need propulsive landing.

A lot of the complexity is hidden in the second video. It's the exact same deal, it just doesn't look like it. In particular those innocuous 'waffle irons' on the side play an incredibly important role. You miss the scale in the video thanks to how big everything is. Those fins are each 4' x 5' large. And each of them can independently yaw/pitch/roll. And of course the exact angle that the rocket is at when it fires its boostback (as well as when it's coming down), exactly how long the boostback is fired, and a large number of other variables all need to be lined up exactly perfectly. Otherwise you end up literally thousands of miles from your destination, run out of fuel, or otherwise condemn your mission in a surprisingly large number of innovative ways.

The big difference you're seeing compensated for is that Mars atmosphere is less than 1% dense as Earth. So to slow yourself down you need a much larger exposed surface area. Do that exact maneuver on Earth and you'd get an 'unplanned rapid disassembly' during reentry thanks to the thicker atmosphere. That danger and complexity is also something that's hidden.

I cannot recommend Kerbal enough for anybody even vaguely interested in space. Just absurdly fun and does really help you get a feel for all of these issues.

> Do that exact maneuver on Earth and you'd get an 'unplanned rapid disassembly' during reentry thanks to the thicker atmosphere

That is the planned Earth re-entry maneuver. Belly first almost all the way down, using the heat shield on one side, then flipping and completely re-orienting near the ground so that the vehicle is pointed upwards, and then the final burn to land upright.

But it does make sense that this path has arisen from a secondary capability: to land on planets or moons with less atmosphere. It still doesn't make me less nervous about their ability to pulli it off reliably. Here's hoping.

Learning how to reliably control the damn thing on descent is certainly their greatest hurdle. Refueling in orbit being the second biggest. I expect things to go boom at least a few times before they learn to land properly. Saying people Wil go to orbit within a year is most likely not to happen.

Elon said they learned a lot of what they need for orbital refueling just from docking with the ISS.

Methane was chosen to a large extent because you could make it fairly easily on Mars which is necessary if you want to fly people there and then get them back again.

Musk talks about making it on Mars here https://www.youtube.com/watch?v=sOpMrVnjYeY&feature=youtu.be...

Musk thinks like a software engineer. Create simple, reusable, components that can scale efficiently. I’m taking some liberties in saying this, but the gist remains the same. Musk keeps it simple and focused.

Agreed! Only a software engineer would risk a product launch delay because of an uber-bikeshedded pet feature (Model X doors) or wait until the last minute to ship and then construct a makeshift “factory” in a parking lot and make staff go through a death march, QA be damned.

The Model X doors are terrible. It's an SUV that you can't put a roof rack on. Does seem like a case of geek myopia over usability.

Or… optimized for a different case (ease of access for small kids).

I haven't used or wanted a roof rack in 30 years (extra mass and drag at the highest location? No thanks), but the Model X has a lot of storage space, including the frunk so it's a non-issue.

The falcon doors also provide a surprising benefit: cover in the rain. And they are very practical with small children.

Sliding minivan doors get you both.

Optimized for showy and unique features, when a young Tesla really needed its products to stand out.

He actually thinks like a systems engineer and a highly skilled and mature one at that.


Musk does not design the rockets.

Musk was chief designer for Falcon 1, their first rocket. Musk is very much involved in detailed technical decisions.

Musk is very much responsible for why the team works the way it does. He specifically focused on hiring people who experiment and try out things a lot. He did not want just pure theoretical guys.

He doesn't do most of the work but he's very involved. Here's an interview Mueller gave that describes some things Elon did with the Merlin engine, search for "face-shutoff."


> And, uh, I’ve seen that hurt us before, I’ve seen that fail, but I’ve also seen— where nobody thought it would work— it was the right decision. It was the harder way to do it, but in the end, it was the right thing. One of the things that we did with the Merlin 1D was; he kept complaining— I talked earlier about how expensive the engine was. [inaudible] [I said,] “[the] only way is to get rid of all these valves. Because that’s what’s really driving the complexity and cost.” And how can you do that? And I said, “Well, on smaller engines, we’d go face-shutoff, but nobody’s done it on a really large engine. It’ll be really difficult.” And he said, “We need to do face-shutoff. Explain how that works?” So I drew it up, did some, you know, sketches, and said “here’s what we’d do,” and he said “That’s what we need to do.” And I advised him against it; I said it’s going to be too hard to do, and it’s not going to save that much. But he made the decision that we were going to do face-shutoff.

So, he knew about a problem, he heard someone mention a possible solution, and he insisted they use that solution.

That is not what designing is.

Mueller begs to differ "And now we have the lowest-cost, most reliable engines in the world. And it was basically because of that decision, to go to do that. So that’s one of the examples of Elon just really pushing— he always says we need to push to the limits of physics."

His title is literally CEO and Chief Designer.

> This is basically how SpaceX seems to operate: rather than optimizing a single part of the system (like trying to get the most efficient engine), they try to optimize from a systems level.

A system of local optimums is an inefficient system. Sort of the self-identified takeaway of the book _The Goal_, and I haven't stopped thinking about this statement since I read it.

ISRU on Mars makes Methane fuel and excellent choice. Zubrin’s favorite in ‘A case for Mars’.

There won't be much literature because Raptor is essentially the first production methane engine. Everyone in the past seems to have decided to optimize strongly for either Isp, bulk density, or storability, and methane is the best at nothing.

Right, because in the past we were building first stages which had to be optimised for operations in the lower atmosphere, and upper stages which had to be optimised for vacuum. Hence the Saturn V had an RP-1 powered first stage and Hydrolox second stage.

But the raptors on the second stage have to operate efficiently in a vacuuum, but also work well and sea level for the landing. So even taking Mars out of the equation (which we really shouldn't, but just for sake of argument), it's requirements are quite different to anything we've built before.

SpaceX has a good design philosophy. They use cheap, reliable, and sturdy components, take the hit on payload fraction, and just make really big rockets to make sure _total_ payload is adequate. I'm reminded of the old quip apocryphally attributed to Stalin: "quantity has a quality all its own"

RD-58MF - https://en.wikipedia.org/wiki/RD-58 - uses kerosene (or syntin?) and has Isp of 372 s.

Methane, which is cryogenic and less dense, ought to deliver more? Otherwise bigger tanks and operational issues will eat out the benefits.

You can raise the Isp of any vacuum engine by using a bigger nozzle. The RD-58MF is a small engine and there's room for a relatively huge nozzle. That's not true for big engines.

For example, Merlin vacuum has a 1:165 expansion ratio. The RD-58MF has a 1:500 ratio. The Wikipedia article for the RD-58 family shows the increase in Isp from various expansion ratios.


Right. There is however an argument that the smaller total impulse a stage does (RD-58 is used for upper stages, where the stage mass is closer to the stage payload), the smaller the relative mass of fuel+engine of that stage is, and so the fixed mass of the bigger nozzle added to the stage costs more, in Tsiolkovsky equation, that the mass for the bigger stage. Going further, we can argue that for larger stages it's beneficial to spend some mass on nozzle, because that mass is used for larger impulse provided by the stage.

Interesting that using http://rocketworkbench.sourceforge.net/equil.phtml I couldn't get declared Isp (380) for methane-LOX for reasonable nozzle expansion ratios. Maybe the model is too approximate...

I am so amazed by the genius of making it out of steel. It's just so completely counter intuitive but has accelerated their progress so much.

If they told you the stats of the material, better strength at cryo tempertures meaning mass reduction, higher melting point meaning minimal heat shielding and great thermal conductivity it would be easy to imagine it was some new super composite. Then your head explodes when they tell you it's 2% the cost of what they were using before and it's so easy to work with they don't even need a factory they can just weld it in a field.

Imo Elon is starting to get into contention for greatest engineer of all time.

Didn't the Russians use a lot of steel in their Space Age era rockets? It always seemed to me like we went too high tech too quickly and the Soviets were practical to a fault, and the truth should be something in between.

I couldn’t agree more.

Soyouz is simple.

Soyouz is reliable.

Soyouz is cheap.

Soyouz is in use for 50+

Soyouz is still there while NASA has no launcher available nowadays, despite decades of « on the edge innovation ».

Soyouz is great. Its an engineering marvel.

And Starship is likely to become even greater.

> Soyouz is cheap.

Only in relation to other single-use rockets.

SpaceX has been eating russian's (and other countries') space business for years now, simply because they are cheaper.

I find it odd that Russia hasn't fought back and tried to do a reusable program of it's own. Putin talks big talk about wanting to develop high tech industries so why just give up on space?

His nuclear cruise missile program is so lame by comparison.

Russia needs an oil price of at least $74/barrel to balance the budget, which means they've been in a lot of economic pain for the last 5 years. Roscosmos was seen as a cash cow, requiring minimal investment to make reliable $ income off their mature launch business. As a result they were starved of investment and are a pale shadow of their former selves.

Building a dynamic, innovative organisation capable of developing a re-usable architecture would be very expensive, and unless they can not just equal but handily beat SpaceX, there's just no money in it. Their current launch systems already meet their military needs, so there's no political support from that quarter either.

it's $42/barrel, the difference from the market price goes into their war chest

I'm out of date. The Moscow Time says $49, but you're quite right in that Russia has done a lot in the last few years to bring their budget under control.

Their war chest is not looking too healthy though, the hit to oil prices in the last 5 years depleted a lot of their reserves. Thanks for the correction.

The Sputnik rocket was made from AMg-6, aluminum-magnesium alloy. Later space rockets also weren't steel-based...

From memory the MiG-25 interceptor had quite a lot of steel in it for thermal reasons. Titanium was too difficult to work with for them at that time (or something).

too expensive (resource wise). they did build a sub out of titanium though - and they called it the golden fish or something.

> Imo Elon is starting to get into contention for greatest engineer of all time.

I don't know man, did he design it himself?

Depends how you define "design". Most engineers I know are not involved in the bog-standard design, but rather when the decisions get outside the comfort zone of the designers (either engineers or engineering techs themselves). From all accounts ("Switching to stainless steel is one of the best design decisions I've ever made"[1], comments from Tom Mueller about Elon leading the design team on Raptor[2]), Musk is performing the role of a head engineer.

Many jurisdictions would still have an issue with him using the title engineer. (edit: it's recently been determined to infringe on first amendment rights [3]. Still applies in Canada)

[1] https://www.reddit.com/r/spacex/comments/davt2l/cnn_intervie... timestamp around 2:30

[2] https://twitter.com/lrocket/status/1099411086711746560

[3] https://www.vice.com/en_us/article/yw798m/oregon-unconstitut...

Dan Rasky's description[1] of the make-or-buy decision on the PICA heat shield perhaps illustrates a bit of it.

[1] https://www.youtube.com/watch?v=P06X2TZUKZU&list=PLpEqMkxe7X... (From the "Dan Rasky: SpaceX's Collaborative Design Approach" video of the "COTS: Dan Rasky" playlist of "Knowledge @ NASA".)

Meta-engineer? Engineering executive? At least he's trying to advance humanity instead of squandering it all on yachts like almost all the rest of the world's billionaires.

Lets be honest, he's kinda transcended all definitions, and that is necessary to be the kind of full picture problem solver that he is... Gain all the information about the problem areas in all contexts from your experts, while having executive authority to execute radical solutions.

I think visionary is the best descriptor and there aren't too many of those folks alive at a given time that are properly placed to execute, and even fewer who actually DO execute.

I was as entranced with the possibility of a permanent extraterrestrial base while watching the presentation last night as I was when I saw the boosters land tandem style in 2018.

What an amazing thing to see happen, the people Elon has brought together have done amazing things on the shoulders of already incredible work.

Is there a Woz behind Musk?

If he didn't design it himself, the people he hired and gave overall direction to did. And they are doing way better than anyone else, which means he must have done a better job of hiring and directing than anyone else.

Is there any reason to believe it would be happening now if he didn't exist?

Maybe not. That still doesn't qualify him as an Engineer, though.

I doubt SpaceX would be a thing if Elon didn't have engineering capabilities.

I have read that when he gets interested in a technical area, he reads a ton of books at a remarkably fast pace, remembers everything he reads, next analyses everything at a fundamental level, and finally comes up with a radically better plan than anyone else has before. I guess you could call that engineering capabilities.

I had three peers in my entire engineering classes like that. Two became PhDs, one has changed fields and applied himself rapidly.

I wasn't like them, but that ability to understand on a fundamental level, not forget, and then very quickly tackle more and more complex problems so fast was like a superpower. It took me much much longer, without the detailed understanding.

If that's not engineering I don't know what is.

he's intimately involved in every aspect of the design of the vehicles. For example, he's personally responsible for the change to steel construction and had to convince the rest of the team to switch from composites.

He is has been the Chief Designer for SpaceX since Falcon 1.

I know there are 1000 of them 100x smarter than me at all of this, but I have my doubts that the specs for "cold rolled" stainless will hold up after tens of re-entries, as it is effectively being tempered over and over.

From the sounds of it steel structure can basically handle much greater temperatures routinely and also even more in rare situations that might mean retiring the ship afterward but not losing everything. In his presentation Elon says that aluminum alloy or carbon fiber structure is basically done for at 300 to 400 Celsius, well that's the temperature at which stainless steel can just begin to get conditioned by heat, it doesn't structurally 'melt' until over 1000 Celsius.

Although its a curious topic, I would have no doubt that whatever temperature cycling they design parts of the structure to go through in their "rapidly reusable" regime, the effects of "heat fatigue" or whatever to call it will have been rigorously assessed .

What do you mean by Handle?

Steel won't melt at 300-400 Celsius but "handling" those temperatures for 10 minutes will change the properties of the material, possibly by a lot, so you don't need "melting" for structural collapse (Twin Towers style).

As the GP says, if you put cold rolled steel, which has an elastic yield strength of >1500 MPa, at 300-400 Celsius, then it is only a matter of time (30-120 min) till the elastic yield strength sinks to 500 MPa or less.

So either this is a single use device, or the steel isn't reaching temperatures over 250 Celsius, or the steel isn't cold rolled but is a low strength steel instead (although that would have other problems).

Re-entry will take something on the order of 10m or less. Even the space shuttle only took 30 minutes while flying like a plane. There will be no circumstances where the ship is going to be subjected to that amount of heat for 30-120 minutes.

> or the steel isn't reaching temperatures over 250 Celsius

That might be the case. The space shuttle had an aluminum structure that would fail at 175C, and now we have 40 years of technology advancements for the heat shield.

Also I notice Cr-Steel's elastic yield strength at 400C is about 87% of its strength at room temp and I don't think it does alter significantly over these timescales at that temperature. It will be interesting to see how high it can be routinely cycled without losing its temper, but it seems to certainly provide much more overhead for safety margins as well as routine operation.

[1] https://www.engineeringtoolbox.com/young-modulus-d_773.html

it doesn't structurally 'melt' until over 1000 Celsius

Is this why jet fuel can't mel..... ah never mind.

I thought I felt deja vu :)

As of the last time I heard, SpaceX was planning to use an extremely aggressive active cooling system: cold fuel would be bled through many holes in the hull, in a process similar to sweating. The hull may never get above room temperature.

No, the "sweating methane" cooling is no longer happening (per the presentation/q&a last night). Instead they're using ceramic insulating heat shield tiles - similar to the shuttle, but different materials, very different attachment mechanism, and a regular shape (tiles will all be hexagonal)

As I understand it, 300-series stainless is not heat treatable, so this should not be a problem. (304 stainless is routinely used in exhaust systems where they are heated up to glowing red temperatures every time. If the starship tank gets anywhere near that hot on entry I think there are worse problems given that on the other side of the tank is cryogenic propellants.

Not a metallurgist but doesn't tempering make steel stronger? (As long as it is quenched properly?)

Stronger is not a specific enough term with metal, but tempering is the opposite of what you described, which is hardening.

Steel becomes harder and more brittle if quenched (hardening), and softer and less brittle if cooled slowly (tempering).

Cold Rolling steel is done to avoid the heat cycle which would otherwise result in tempering, which is why its specific stats don't strike me as particularly relevant past the first launch.

Heat cycles also have the effect of warping steel.

Uh what? This is exactly the inverse of what happens. Quenching leads to stronger, more flexible steel. Slow cooling leads to harder, but more brittle steel. The reason is grain structure - slow cooling allows larger grains, which don't allow the movement of dislocations as freely, but the loss of flexibility costs in ultimate tensile strength.

Please cite your correction or delete it if you find you are in error. I have provided my 2 sources which are in addition to my peer and personal experience in blacksmithing.

I don't know about his general claim, but a detail within his comment is right.

Smaller grain size leading to stronger material -- this is a result of more grain boundaries as the scale of the grain goes down. Hall-Petch strengthening.[0] A secondary effect is that with smaller grains oriented in random directions the metal is more resistant in general from stresses in all directions; whereas with larger grains you tend to get weakness in a particular direction (along the slip planes.)

This is common knowledge, at least it's basic material physics that I learned in college.

[0] https://en.wikipedia.org/wiki/Grain_boundary_strengthening

The GP comment is claiming the opposite--that larger grain size results in a stronger material.

Actually I said strong is too ambiguous of a term to use. For instance, do you want it "strong" enough to not bend under x force at y temperature, or do you want it "strong" enough to bend rather than shear at z force?

It is more practical to discuss the hardness and ductility at specific temperatures, as well as its ability to keep its carbon content under those temperature conditions.

What I get for combining some rusty mat-sci with layman's understanding of terms. You're right regarding the specific processes

Tempering is used to reduce brittleness in metal.

But I think the word GP was looking for was annealing. Annealed metal bends quite easily (that's the analogy in 'simulated annealing' in optimization theory). For instance the wire bonsai practitioners use is traditionally made of annealed copper. Copper is already pretty ductile but once annealed it's positively floppy. Bending it work-hardens it, causing it to stiffen back up. Eventually one learns that if you bend it just so, it will stay where you wanted it to stay.

You do not want your space craft reconfiguring itself.

Tempering is the correct terminology. Annealing is a slow and controlled heating, gradually reducing the heat over time.

from Wikipedia:

"Tempering [...] is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air."

Here's a good description https://www.metalsupermarkets.com/difference-annealing-tempe...

Surely that is something that could be easily tested in a lab.

working on it outside definitely gives the pictures a "bunch of guys with some metal and a lot of free time" feel haha.

“Field Of Dreams”

How come no one thought of using steel before?

The benefits of standing up to high temperatures are important for reusable rockets that need to land (the heating happens on the way down, not on the way up). If you're not going to land, aluminum-lithium like Falcon 9 is better.

You're only heating your structure that much when you're landing an entire spacecraft. If you just have a capsule going down its usually easier to have an ablative heat shield.

Also, it's a lot easier to foresee the weight of a design than its cost so most space programs use it as a proxy for cost. So generally the space industry would optimize for minimizing weight and not even try to think about how the materials used would affect cost.

Steel was used before for the early Atlas rocket models. But the skin was too thin and collapsed on its own weight. You can see YouTube videos of this.

Those were balloon construction, which is a bit different. They were designed to be kept rigid by the internal pressure of the propellant. Actually the Centaur[0] is still built this way, using stainless steel.

[0] https://en.wikipedia.org/wiki/Centaur_(rocket_stage)

Did any new process/invention make it viable to use steel today that wasn't available before?

Not your parent commenter, but SpaceXs innovations start with pulling most design and fabrication in-house, rather than NASA relying on (multiple levels of) defense contractors redesigning ICBMs. ICBMs are single-use only and cost is no object when you're fighting WW3. Similarly, cost was no object for launching military spy satellites, so there was no reason to reduce the launch cost of a $1B recon satellite.

Here, specifically, with regard to steel rockets? SpaceX stopped optimizing for weight and used thick steel. SpaceX optimized for cost and practicality. Brute force rocket engineering, rather than "the best performance numbers on paper" which is where a lot of rocket designs seemed to get lost in the weeds of some component that ends up being a massive maintenance mess but gives you "the best performance".

The steel tanks that collapsed in the sixtys? They were so thin they needed pressurization at all times or they would collapse. SpaceX realized that was a design and maintenance risk, and just built thick tanks.

Steel has been used before.

I totally understand why they've gone for that design but the welded together steel plates really make me think of the sort of thing Wallace and Gromit would build.

I am totally with you on this - I just can't get over how utterly rudimentary and basic this thing looks! I can't wait to see it fly!

I am so used to seeing space stuff done in clean rooms, and things taking years and years to come to fruition (e.g. hearing about and seeing NASA or ESA probes etc getting made) that to see what is essentially a bunch of guys in a field just welding something together blows my mind.

I mean, is it just the outside that looks like that and inside it is ultra-exotic materials and tanks? Of course the engines are sophisticated machinery, but what about the insides? Are we just seeing the outer shell and it's all unobtanium nano-tube composite on the inside?

I suspect most of the structure that gets really hot or cold is steel. To save weight, they are probably also letting more of the rocket get colder/hotter than normal, thanks to the wider temperature range of steel.

Once the temperatures get reasonable, it might be aluminum or or carbon fiber. The passenger/cargo/avionics section are probably the only areas where this would be true, so a bulk of the rocket will be steel.

Steel can tolerate a lot more deflection before it bends, and much more stress before it cracks. And while I would never expect a space craft mechanic to employ this technique, any bike mechanic will happily offer to bend steel back into shape for you, but bent aluminum or carbon fiber is scrap. Bending it back will fracture it, if it hasn't already.

When Canondale hit the big time, they had one model year where they made the dropouts out of solid aluminum and in the next model year the derailleur hanger was bolted on. It's the easiest part to bend and there's no repairing it. Bad enough for road bikes, spectacularly dumb for mountain bikes.

> Are we just seeing the outer shell and it's all unobtanium nano-tube composite on the inside?

Nope, it's just steel. Outside shell is the tank.

I recall quite a while back, when titanium started first showing up outside of aerospace, that someone had created a titanium-titanium composite by layering plate titanium with titanium cloth and welding it together somehow. Was supposed to be stronger. Wonder if there's a steel equivalent possible.

I think the military was looking at a similar material to replace depleted uranium with something non-radioactive (depleted uranium still experiences alpha particle decay, which is fine if you don't aspirate or ingest it, but a shell can pulverize on impact with a target. Also it's still a heavy metal even if you don't take rads from it).

> I think the military was looking at a similar material to replace depleted uranium with something non-radioactive

I thought the point of depleted uranium projectiles was simply the density of uranium, giving them large impact energy for a given volume. If that's the case, titanium (4.5 g/cm^3) will not even be as good as steel (8 g/cm^3), let alone uranium (19 g/cm^3).

I hope I am never in a position to hear that sound in person.

Yea it's pretty wild. Although I am certain this is just for a prototype. I think the actual ones that will be sent to the Moon & Mars will be done in a clean room.

Is the surface of these less smooth than surface of normal rockets/planes, or is it simply the effect of mirror like surface making bumpiness easier to see?

The latter - a matte surface would be lit from essentially the same angle, but even a tiny discrepancy causes big shifts in a reflection.

We work with multiple tens of ton of SS steel per month, and I would have never thought this heavy thing could fly with all the stress of the sky. I hope it fly good.

> the welded together steel plates really make me think of the sort of thing Wallace and Gromit would build

The most beautiful thing in the world is success.

Scrapped together plates make you wonder how it won't fall apart on ascent or descent...

he addressed in presentation, from what i remember it had a lot to do with cost. Like $130k/ton with carbon vs $3k/ton with steel. He mentioned a few other factors. Also it allowed them to build outside, not sure if t that is true in production.

As he said in the presentation, it was because at cryogenic temperatures (which is the important part when you're building a liquid oxygen / methane tank) 301 stainless is actually _stronger_ than Al / carbon fiber. It also handles heat much better, which allows you to have a much thinner heatshield.

Both characteristics combine to give a lighter rocket than one built out of Al / carbon fiber.

The price is just the cherry on top.

the material isn't the question, it's why they had to weld it together in a patchwork quilt. Elon talked about the next version would simply have rolled coils with a single seam weld (although the cylinders would have to be welded together too), which would be better structurally and cosmetically, and likely lower cost of production. Sounds like they just didn't have the rolling machines to do the job, or perhaps there was an availability issue with the specific alloy.

It will reduce the length of the welds (for the hull) quite a bit.

The number of rings is roughly 35 for Starship, with about ten vertical seams each.

For easier thinking, line the vertical seams up and you see that this gives 50m length per vertical seam from bottom to top of Starship. So there are a total of 500m for that.

35 rings with ~28m circumference add up to about 1km of seams between them.

Now if they can use rolls twice as wide and only a single vertical weld each, then that's 500m between the rings and 50m for a single vertical seam. 550m of welds there instead of 1.5m before. This should speed things up quite a lot and reduce the cost of labour.

Raptor production is the real bottleneck, though.

The way I understood the presenation, they plan to use a single piece of steal, bent at an angle and rolled around (think one of those Pillsbury roll cans) with a single weld seem, in a giant helix.

>Raptor production is the real bottleneck, though.

They are shooting for one per day, no? Based on the differences identified in the three hanging under the Boca Chica vehicle now, it’s still in development.

They just shipped he 12th one. Definitely still in the development/ramp up process.

He said that it's about one per week. One per day will be in several months.

> although the cylinders would have to be welded together too

No, they'll do a helical weld, exactly like large pipes (like this: http://www.xysteelpipe.com/upload/201512118145340710.jpg)

You basically need to do that as the steel rolls off the press, though, which is why they didn't do that for Mk I. They'll need to cold roll the steel onsite.

They will not do a helical weld because the steel's thickness varies from the top to the bottom of the cylinder, according to Elon Musk. https://twitter.com/HarryStoltz1/status/1162595874561617920 https://twitter.com/elonmusk/status/1162601447235604480?lang...

And then you can make it a spiral of steel to eliminate the vertical welds.

He also talked about how stainless steel has a high melting point (which means their re-entry heat shield doesn't need to be as thick) and gets stronger rather than weaker at very low temperatures.

Imagine the autoclave the size of a rocket.

Composite tanks on few rockets being flown with them are made in one of a kind, purpose built autoclaves

Out-of-autoclave methods are mature and common these days.

Do they get you the same strength, fill ratio, and allow for usage with aerospace specialty epoxies?

What I loved the most was the optimistic outlook, the forward looking focus and the implicit belief that any problem will be solved and we'll advance.

This is exceedingly rare in a pessimistic world drowning in the voice of Luddites and backwards-looking preservationists.

Like always, technology solving real world problems versus politicians (professional or amateurs) creating (and never really solving) self-serving perpetual issues.

I suspect that having a sense of urgency and limited resources contributed to this phenomenal pace of development, it's in stark contrast to the glacial pace of the SLS project (Boeing/Nasa) which is much better funded.

One could argue that this also effects Blue Origin, who still haven't reached orbit 19 years after being founded.

As someone else aptly remarked - NASA is no longer a space exploration agency. It's now an employment agency. Hence the glacial pace.

NASA was never a space exploration agency; in its heyday, it was a combination thinly veiled demonstration of military capacity and thinly veiled military projects agency, but most of both of those functions were superfluous by the last decade or so of the Cold War.

I suspect that Starship will fly to space before SLS ever will. I also think Starship has a significantly higher chance of flying at all than SLS.

It is certainly a little bold of Bridenstine to comment on other space companies being behind schedule given NASA’s own delays.

Elon Musk said 5% of SpaceX was working on Starship and that the hardware for crew would be ready this year (in interview to CNN after the QA he said October for in flight abort and November for DM-2).

I think that 5% claim is dubious.

Almost certainly the top minds at spacex are focussed on starship, and the 5% number might only be kinda-true because starship is being built with a lot of contractors.

Well when you tell a customer you will have all hands on deck and then are out back playing with your go-kart then expect your billion dollar customer will say something.

I imagine all the necessary hands are already on deck for Crew Dragon.

Starship wasn’t built by the Falcon or Crew Dragon manufacturing teams, and the vast majority of the design and engineering currently happening for Starship has long been completed for Crew Dragon.

Let’s also remember that NASA is hardly the only company that pays SpaceX, they have other income sources and what they do with that income is ultimately their choice. Unless they are using NASA money to build Starship there should be no problem.

From this[1] article:

"Musk said in 2018 that SpaceX was “all hands on deck for Crew Dragon,” and it would be making trips to the ISS by December 2018.

After that, he said, “most of our engineering resources will be dedicated to BFR, and I think that will make things go quite quickly,” he said. BFR was the earlier name for Starship."

"All hands on deck" is not some subjective term, it is naval and means get everyone on deck now to repel boarders.


Except there is nothing they can do now. There are a ton of safety reviews which depend on NASA, and only a small amount of people at SpaceX are required to keep the NASA team more than filled with work.

Elon responded saying he would do whatever it took to go faster, but there was nothing he could do.

He said, today, that 5% of SpaceX was working on Starship.

Both statements can be true, depending on which portion of space x is engineers and how Elon uses the word resources here

Starship could have Falcon Heavy level of delays (which I think it will) and still beat SLS.

I think people are missing an important point when talking about Falcon Heavy. Yes it was delayed, but the Falcon Heavy that was eventually launched, was WAY, WAY better then the one announced in 2011.

The payload of the 2011 version was almost reached by the Falcon 9 itself. That was one of the major reasons for the delay, not design and production issues. The Falcon Heavy profited from all the advancments on Falcon 9 and it made no sense to actually build a Falcon Heavy before Block 4.

In fact the first costumers for Falcon Heavy flew on Falcon 9 instead.

FH was 5 years+ behind schedule before it was built and launched. Starship already has multiple constructions going on, with multiple prototypes to test and multiple full-size vehicles planned quickly.

In 2011, FH was supposed to have "arrival at launch site" by 2H 2012. It first launched in 2018 (after arriving at launch site in 2018 not 2012). The same level of delay would mean the first Starship does not reach orbit until ~2025. That seems crazy pessimistic and would be a dramatic departure from the otherwise normal delays faced by SpaceX.

I think it's extremely unlikely that Starship would face FH-level delays. That would cancel the Starlink constellation, cede the space-internet game to others, hand the torch to BO or others working on large projects, and absolutely destroy morale at SpaceX.

I just don't see it happening.

FH got delayed because they kept improving the F9, so they didn't need the FH for many of the original target payloads. Some of the delay was due to technical issues, but changes to the F9 were significant over that time period. Starship has no dependencies on the Falcon stack.

Another company would have rushed it out "on schedule" and have been stuck with the results forever. Delaying something until you need-need it can be a very good strategy ensuring the best possible final results at go-time if that avenue is available to you.

The thing with the F9H is, that there was no real need for it for years, it almost got cancelled entirely. The F9 was improved to a point where it could do most missions which initially were thought to require a F9H. So the development of the F9H was done at a lower speed than if the business had depended on it. But as there seem to be some contracts requiring the F9H, they made it eventually. How often it will fly though, entirely depends on how quickly the Starship progresses.

The center core of the Falcon Heavy has been described by Musk as effectively an entirely new rocket, due to the million pound lateral forces holding the three rockets together. It's not just three Falcon 9 strapped together.

Yes but there is still a HUGE amount of communality between the systems.

FH is "just" 3 F9 strapped together. Doing that took them more than 5 years than planned.

Keeping that in mind, having 5 year delay on brand new design, using totally different materials, new engine, etc isn't far fetched.

There is a quote somewhere (by Elon?) saying that FH is not "just" 3 F9s strapped together. A significant source of the slowdown for FH was the desire to not launch it without full reusability of all 3 stages and not to launch it without significant improvements (block 5 etc).

Starship has none of those potential delays and has already solved most of the hard problems (as evidenced by the Hopper hopping already). Starship has all of the learnings and experience that FH and F9 didn't have.

There will be delays, sure. But we won't be waiting 5+ years again for a single launch. Those days are over, and SpaceX is proving it.

Some context, I haven't read this yet: https://www.quora.com/What-makes-SpaceXs-Falcon-Heavy-more-t...


> Keeping that in mind, having 5 year delay on brand new design, using totally different materials, new engine, etc isn't far fetched.

The first full size Starship prototype is already built though (within ~2 years of initial announcement? Not behind schedule basically at all, so far?). IIRC for FH it was a ~5 year delay before SpaceX even starting construction on the first parts. The difference with Starship is staggering. The pace is dramatically faster, the risks are reduced up-front, and the tests are planned on a much shorter timeframe.

We would frequently go 6 months to a year and hear no news at all about FH. There is news, updates and progress available to the public on an hourly or daily basis about the Starship progress. Night and day.

Hopper shows that engine works outside of test lab. That's great, but it's far far away from showing that they solved most of the hard problems.

Experience from FH and F9 is useful, but it's a totally different type of spacecraft, with different use-cases, different materials, engines, cooling, etc. There's TONS of new stuff that they have to research, experiment, fail, try again, etc, until it's doing even 50% of what Elon promised.

Perhaps I'm misunderstanding something. I thought Hopper was not about Raptor tests but about VTOL as well. The FH had to wait while F9 got down the vertical landing science and engineering (though a lot of tests, explosions, delays).

StarHopper seems like it can use those learnings, and that was tested recently. The engine was already functioning on a test stand and mated to Hopper for static fires; the Hopper hop itself is testing the engine, sure, but also the complex math of doing a vertical landing with a gimballing engine, etc.

The general space industry considered reusabable spacecraft that land vertically to be pretty much impossible until F9 and FH did it. But Hopper just does that casually, you don't bat an eye, you don't even comment that Hopper was testing a new rocket dynamics/physics for the math that (almost) only SpaceX has figured out.

I just don't see the pessimism here. I've been watching SpaceX for 12+ years and I don't see any of the same issues plaguing them today as did in the past.

New issues, but not the same ones. The new issues have dramatically smaller turnaround time to resolve.

The days of 5-year SpaceX delays are over.

> The general space industry considered reusabable spacecraft that land vertically to be pretty much impossible until F9 and FH did it. But Hopper just does that casually, you don't bat an eye, you don't even comment that Hopper was testing a new rocket dynamics/physics for the math that (almost) only SpaceX has figured out.

VTVL isn't new. To do it you need ability to throttle engine and do trust vectoring - once you have that, it's "fairly" simple math and physics.

SpaceX is first company that commercialized it, and huge props for that. No one cracked economy of it before (and it's not 100% sure that spacex did - no one saw their financials).

> New issues, but not the same ones. The new issues have dramatically smaller turnaround time to resolve.

We'll see, but I'm extremely sceptic about it. With F9/FH SpaceX did amazing but incremental improvements to current rocket technology. Starship has tons of uncharted territories.

So that quote by the CNES director of launchers praising SpaceX for pioneering supersonic retropropulsion... he's confused and SpaceX didn't do anything new?

I'm not sure I would call starship VTOL maybe vertical takeoff acrobatic landing? I'm sure falcon helped a lot, especially with control surface actuation resilliency, but I think they still have a lot to learn about this amazing new maneuver.

They are building 4 partially functional prototypes to mess up and learn stuff fast.

The FH released did not have the payload capacity they originally intended. The mid-launch fuel bussing was critical to that, and abandoned. Instead they managed to squeeze out more thrust from the engines and make up some of the difference.

Minor: Boeing is BA, if that was the reference

BO = Blue Origin

That makes more sense!

Starship looks stupid simple compared to the FH.

Not entirely sure about that. Have no skin in the game but from what I can tell Starship is just a bigger version of the Falcon 9 second stage. FH on the other hand required a lot of engineering investment to figure out how to bolt three F9s together and how to make the software work between all three.

I'm certain it will be a long time until it can get to Mars, but LEO within the next 2-3 years is probably realistic.

> Starship is just a bigger version of the Falcon 9 second stage

Starship is designed to land from interplanetary speeds (not just LEO orbital speeds), can re-fuel in orbit, and has the world'd most advanced rocket engines. The jump from F9 -> Starship is substantially larger than the jump from F9 -> FH.

edit: spelling

> Starship is just a bigger version of the Falcon 9 second stage

No way, that's where most of the differences are. The Falcon 9 second stage is a classic expendable stage but Starship is a brand new design which aims to be fully reusable.

> from what I can tell Starship is just a bigger version of the Falcon 9 second stage

I know I'm piling on here with this quote but I just don't understand why you'd say this if you'd done the least amount of research. They are about as different as two rockets can be—do you think Starship is "just a bigger version" because it's an upper stage? Because it's built by the same company? Its design and (theoretical, until it flies) capabilities are radically different and expanded relative to F9 stage 2.

> I can tell Starship is just a bigger version of the Falcon 9 second stage

What similarities are you referring to? They're designed to be launched atop another, bigger rocket. Other than that...?

For reference, SLS refers to https://en.m.wikipedia.org/wiki/Space_Launch_System

FWIW SpaceX is exactly the kind of phenomenon that might spur state investment.

To me the SLS is like Brexit: obscenely wasteful and short-sighted, seemingly inevitable, but somehow I still don't believe it will ever leave the ground.

The Artemis thing is like a joke for real, though. After the last 30 years of bullshit we've seen from the US government's manned space exploration efforts I think I'll be living in a SpaceX-manufactured igloo on Titan before Richard Shelby and his obstructionist, pork-slinging ilk manage to put footprints on the moon.

Just as a comment: I really hate seeing Brexit dragged into every conversation.

We're talking about rockets here, which should be a million miles away from any discussion of Brexit.

The SLS is pure politics. You're welcome to ignore that, if you like, but that decision means you won't have a good understanding of why the rocket "exists", or why it's designed the way it is, or what the prospects are for its future.

Yes. Thank you. Brexit is the ultimate 'this proves my world view' and gets dragged into every conversation.

Please enlighten me: what's the world view I'm trying to prove by invoking Brexit?

Eventually the shell will be a single large roll of steel that is unrolled, bent into a tube with a seam going hotdog that is welded. It will be very strong, lighter than the current patchwork, and extremely beautiful. More similar to the renderings. Can’t wait.

Definitely not hotdog (assuming that's from stem to stern). Musk wasn't totally clear when describing it, but he said mk3 would be in three months. The circumference of starship is 28.26 meters. For a single weld the entire length of the ship, the roll itself would need to be that wide.

The largest rolling mills in the world are ~4 meters wide[1]. They require backup rollers[2], ie rollers that push down the rollers that push down the rollers that push down the metal. Bending deflection increases with width^2. A 28 meter wide rolling mill does not exist AFAIK and cannot be built in three months.

[1]: https://www.aleris.com/company/rolled-products/

[2]: http://www.yourarticlelibrary.com/metallurgy/types-of-rollin...

Wow what an incredibly substantive comment. I remember pretty clearly he said that there would be a single seam weld. Maybe I’m remembering wrong. Or maybe they’ll seam weld multiple rolls into a really wide roll and the only weld required to turn the final roll into the shell is that final hotdog weld.

I think when Elon said "there will be a single seam weld" (which I also remember), he meant this in comparison to the current welds.

It's been 12 hours and I only skimmed the video, so I might be misremembering what he said. My understanding was this: Mk1 is welded from plates so at each layer of the stack you have n-1 welds holding the n plates together. My understanding of his comment was that the steel coils will wrap around the major axis of the rocket but instead of each layer containing n-1 welds to join n plates, there will just be one weld in each layer to join the beginning and end of that coil. That would still leave you with welds joining the different layers of coils but only one "seam" weld along the rocket's major axis.

I think the idea's to go like a Pringles can, with a spiraling single seam.

maybe, but that's also pretty unlikely. For reference here's where musk talks about it: https://youtu.be/sOpMrVnjYeY?t=3156

No real indication he means a spiral.

There are a lot of problems with a spiral. Thin sheets of steel, even hot rolled, are very affected by the rolling process. There's also the weld line going up in a spiral. That will cause uneven heat diffusion and expansion, which is a recipe for disaster given that the skin will be cold enough to liquify helium on one side and boiling hot on the other. Then red hot during reentry. Straight lines don't have the same problems.

If getting out of your yoga pants is like opening a can of biscuits, then making a starship is like putting your yoga pants back on...

They can't do that because they need to thickness to taper off up the sides of the vehicle.

this is the correct answer. They can simply use the 4 meter wide steel no problem.

I feel like he was talking about a single weld on each ring section.

The "single piece" method he is talking about is that the individual _rings_ will be made of a single piece with a single weld, and the rings are then stacked. You can see it already in the Starship under construction in Florida. (Look at the unstacked rings.)



How do you picture them rolling a piece of steel 50 meters wide? As far as I know, the widest rolling mills in existence are 5 meters wide.

Think of it like a paper towel tube. It's a spiral.

Single helical weld.

Spiral tube are a bad choice for a rocket. Because rolled steel has the grains largely aligned with the direction of rolling, it is stiffer and has less thermal expansion in one axis than the other. Large forces and temperature changes therefore cause a twisting motion, which can put weird strains on the internal components.

Pillsbury rolls come to mind. The tube is under pressure from the leavening agent, and you apply torsion on the tub until the can ruptures along the spiral seam.

That would not go over well with the occupants.

I recall the rolls scaring the shit out of a fair number of people and those were with the promise of warm, flaky goodness, not hot, fiery death.

This of course matters if the seam is weaker than the rest of the metal.

I've been assured time and again that you can make welds that are stronger than the rest of the metal, but my lizard brain thinks they're all liars.

They said they would do butt welds, not spiral.

Just curious - what industry are you in that you know off of the top of your head the max size of rolled steel?

Nearly anyone who buys sheets of rolled steel eventually finds they can't buy a sheet bigger than a certain size...

Same exists for most goods - try to buy a dustsheet to cover your room, and you can't buy one wider than 5 meters without a seam

NASA is still waiting for SpaceX to complete the Crew Dragon spacecraft that will fly astronauts to and from the International Space Station. The space agency has picked SpaceX (and another company, Boeing) to provide commercial crew flights to the station.

While SpaceX did launch an unpiloted Crew Dragon test flight to the space station this year, a subsequent abort system test failed, leading to the destruction of the vehicle. SpaceX aims to resume abort system tests later this year ahead of the first crewed test flight.

NASA Administrator Jim Bridenstine, it seems, is not happy with the years-long delays of Crew Dragon, as well as Boeing's Starliner spacecraft, especially after seeing SpaceX build Starship Mk1 this year ahead of its own test flight.

"I am looking forward to the SpaceX announcement tomorrow," Bridenstine wrote on Twitter Friday. "In the meantime, Commercial Crew is years behind schedule. NASA expects to see the same level of enthusiasm focused on the investments of the taxpayer. It's time to deliver."


Here's Elons response given in a CNN interview yesterday: https://edition.cnn.com/2019/09/29/business/elon-musk-spacex...

I would love to know what the "Day-in-the-life" of a welder working on those ships would be. Did they train specifically for aerospace welding? How did they land that specific gig. Must be so inspiring to wake up and work on that.

I think the prototype was built by a company that normally builds water towers, so probably not that different from normal industrial welding.

And as I saw someone else say, the welds on a water tower also have to be good under pressure, otherwise the water tower bursts and dumps all its water.

I'd love to know the hiring process. There must be many people applying for these positions and I doubt that whiteboard welding is a thing. Or is it? :)

There is definitely tests for welding jobs. And then their welds are regularly tested to maintain certifications.

The tales I heard from my father were X-ray scans of their finished, grinded, polished welds and they had to be perfect. Not a hair-sized infraction would be permitted.

I can't imagine anything but xray for the entire ship, every mm of weld. Given the forces involved, it seems like a completely new level of perfect is required.

AFAIK it's uncommon skill, you need the steady hands of a surgeon to have a chance. Definitely not work I could do, I know that.

My dad did this kind of work in the oil industry for 30+ years as a pipe fitter. His specialty was stainless and they had to be x-ray perfect welds. He recently retired but was always very proud of his work. It took me a long time to understand why.

I wish he could have gotten into the space industry vs oil refineries. The latter is much harder on a person.

> was always very proud of his work. It took me a long time to understand why.

I'm a mediocre amateur welder and I totally understand why.

Was he prudent in maintaining good work habits? I hear the industry can be quite hard on people if they are not careful in how they work[1]

[1] https://www.thefabricator.com/article/safety/the-invisible-r...

Ahaha absolutely. He's as square and as prudent as it gets. I mean to an extreme. My siblings have always laughed at him for it [outside of the workplace and in everyday matters where he carries those habits on].

It's hard on people regardless. And the oil industry is not known for being prudent in looking after their workers' health.

They got real pissed when he filed a workers compensation claim for a hearing aid before he retired. Thankfully he had support from his union.

And the number of stories he's told me where he was nearly killed...

I've no sympathy for the industry.

I've no sympathy for the industry.

puts sunglasses on


Yeah, having learnt the (very) basics of welding recently it has become very clear to me how much of a skill/art it actually is. Even at the basic level it is a combination of a lot of senses; sight, hearing, touch. And there are multiple movements which need to happen both simultaneously and smoothly, and be adjusted based on the aforementioned senses.

I used to wander around the reactor auxiliary building at the nuclear plant I worked at and take pictures of the piping welds. They were works of art. The skill was obvious.

There's always https://www.reddit.com/r/Weldingporn/top/?t=all for nice pictures of welds.

And the NSFW equivalent https://www.reddit.com/r/goneweld , with naughty captions of welding seams.

> I used to wander around ... the nuclear plant I worked at and take pictures

DHS would like your location...

Sooo...it's rocket surgery for real?

That's the best description. "Joe over there? Oh, he's a rocket surgeon." Now I can't help remembering a sketch from Mitchell and Webb.[1]

1: https://m.youtube.com/watch?v=THNPmhBl-8I

My Dad tried to teach me to weld. It definitely takes a lot of practices to be average at it.

Somehow my Dad managed to swipe that thing around like he was painting or something. It was impressive.

Best internet resource that goes into the detail of this?

A good weld on 301 steel isn't very different regardless the purpose.

and welds are very testable via x-ray (perhaps some other techniques), and I believe repairable unless someone really screws up.

I imagine for the Mk1/2 they are using in house teams but for the hopper they contracted out the construction to a company that builds water towers (Caldwell Tanks). I mean - it makes sense, it's really just a water tank with an extra bulkhead that SpaceX just so happens to want to attach a rocket engine to...

> How did they land that specific gig

The https://www.spacex.com/careers/list ? There are currently several entries for Welder (Starship) and Tank Fabricator/Welder.

I'd watch a Bob Ross of welding if that channel existed.

1950s Science Fiction illustrators are feeling so vindicated right now.

That was my very first thought, seeing that image: Ray Bradbury would be absolutely beaming to see it.

For real. I wonder how much innovation really exists because the engineers have read golden age sci-fi 25-40 years ago as kids. Could be also that human aspirations are predictable, but I do believe this link should not be ignored. Musk himself acknowledges it some by naming Space X barges after sentient spaceships from Iain M Banks "Culture" series. Or maybe not Musk himself, but whoever named the barges.

The SpaceX/Musk presentation video: https://www.youtube.com/watch?v=sOpMrVnjYeY

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