[drchewbacca]

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.

[hinkley]

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.

[0wis]

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.

[bufferoverflow]

> 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.

[drchewbacca]

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.

[simonh]

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.

[bushin]

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

[avmich]

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

[antod]

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).

[choonway]

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

[afterburner]

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

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

[SECProto]

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...

[mncharity]

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".)

[Paperweight]

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.

[tomxor]

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.

[kfrzcode]

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.

[travisporter]

Is there a Woz behind Musk?

[woodandsteel]

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.

[AimForTheBushes]

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

[aflag]

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

[AimForTheBushes]

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

[woodandsteel]

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.

[uncleberg]

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.

[fastball]

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

[simonh]

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.

[nickik]

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

[elif]

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.

[strainer]

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 .

[fluffything]

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).

[ricardobeat]

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.

[strainer]

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

[ryanmarsh]

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

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

[strainer]

I thought I felt deja vu :)

[whatshisface]

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.

[SECProto]

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)

[lutorm]

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.

[Blakestr]

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

[elif]

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.

[XorNot]

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.

[elif]

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.

[CriticalCathed]

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

[XorNot]

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

[hinkley]

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.

[elif]

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...

[7952]

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

[chasd00]

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

[toomuchtodo]

“Field Of Dreams”

[davidivadavid]

How come no one thought of using steel before?

[wolf550e]

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.

[Symmetry]

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.

[vermontdevil]

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.

[simonh]

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)

[davidivadavid]

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

[NortySpock]

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.

[SomeOldThrow]

Steel has been used before.