How SpaceX streamlined the Raptor engine

WalterBright 2 hours ago | parent | next [-]

According to Isaacson's biography of Musk, Musk relentlessly challenges the existence of every part in Tesla and SpaceX machines. He's willing to go too far, having to sometimes put a part back in.

Everything in the manufacturing process is also challenged to justify its existence.

This is how he managed to reduce the costs by 90%.

	▲	nickff 32 minutes ago \| parent \| next [-]
		>"According to Isaacson's biography of Musk, Musk relentlessly challenges the existence of every part in Tesla and SpaceX machines." This removal of surplus-age is common in the automotive industry, and one of the reasons that cars are such an amazing value. It seems like Musk's remarkable ability to achieve cost reductions (at least in the aerospace context) is his pursuit of vertical integration. Airframers (aeronautical vehicle designers & manufacturer) are bound by the costs dictated by their component suppliers, especially after a configuration has achieved regulatory approval. SpaceX has managed to avoid being 'held hostage' by pseudo-monopoly suppliers.
	▲	nortlov an hour ago \| parent \| prev [-]
		Slight aside, he also has driven capability that was challenging to justify existence for, and was later removed re: Dragon 2 propulsive landing via SuperDracos, landing legs, and the ballast sled. I'm sure the Dragonfly programs matured their abort programs, but surely, that was a ton of time and effort wasted. You win some, you lose some.

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thinkcontext 3 hours ago | parent | prev | next [-]

> And the problems haven’t been completely ironed out: the first launch attempt of Starship’s flight test 13 was aborted automatically by the vehicle’s flight software at T-0 (right before liftoff) this past July when several Raptor 3 engines failed to start

And several engines failed to relight on the booster for flight 13. I believe ice in feed lines is viewed as the most likely cause.

	▲	Tuna-Fish 11 minutes ago \| parent [-]
		I'm pretty sure that the heat exchanger is going to end up being one part they have to put back in. Pushing CO2 and H2O (both ices at prop temp) into the tanks just seems so ill-advised to me. The amounts of contamination are small, but there are just so many different ways that can go wrong.

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ecshafer 5 hours ago | parent | prev | next [-]

I find it mind boggling that you can 3d print rocket engines. I thought that the standard line is that 3d printing metal wasn't developed enough for anything serious. Not a mechanical/materials engineer, but if you can 3d print rockets what's off the table? Jet Engines and that's about it I think?

From the article links, I am amused that SpaceX uses cybertrucks to tow their rocket engines around the grounds and not a normal cheaper truck. They also do it in a totally uncovered trailer, which must be good for the guys taking pictures for forums. But isn't that also good for guys taking pictures for competitors / Russians/ China?

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doctoboggan 4 hours ago | parent | next [-]

> I thought that the standard line is that 3d printing metal wasn't developed enough for anything serious.

This hasn't been true for over a decade. High value relative to weight, highly complicated internal geometry, or repeated need for one off parts are all reasons to choose 3d printing today for production parts.

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MSKJ 3 hours ago | parent | prev | next [-]

3D printed metal components are also in Hyper cars, Bugatti and Koenigsegg have implemented them for different components

https://newsroom.bugatti.com/en/press-releases/bugatti-refin...

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reportingsjr 2 hours ago | parent | prev | next [-]

Apple uses some 3d printed components at volume, i.e. the ultra 3 and 4 watch cases.

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jackmott42 5 hours ago | parent | prev [-]

3d printing metal has some strength downsides, I'm not sure what it is for the raptor engines, but I've heard other space companies claim ~5% less strength that traditional methods for aluminum structures, but that can be worth it in cases where you are able to make shapes that wouldn't be possible with traditional methods, or if you save enough money by printing it. Rocket engines often can benefit from intricate internal channels and shapes that you can 3d print as once piece with no way to do it via subtractive manufacturing.

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fbd_0100 5 hours ago | parent [-]

It has mild strength downsides, but very severe fatigue and damage tolerance downsides. Knowing this, it makes sense that 3d printing tech would make headway in space industry but not (yet) in aviation

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naasking 5 hours ago | parent [-]

What's the current theory for why this is?

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fbd_0100 5 hours ago | parent | next [-]

crack growth in metals is driven by microscopic flaws that cause high-intensity but very localized stress concentrations. Over time even low stress levels cause these flaws to grow to the point where they start causing strength problems. Even in traditional aluminum machined parts, increased surface roughness can have a large impact on fatigue life.

3D printed parts are chock-full of these microscopic flaws, porosity, and have horrible surface roughness (most parts you see in production are post-machined to improve the finish). Additionally, the repeated heating-cooling of the layers as they are deposited builds up residual stress in the part. All just due to the nature of how they are manufactured.

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naasking 4 hours ago | parent [-]

Is there a known source of internal flaws/porosity in an otherwise solid part? Presumably laser melting produces a puddle which shouldn't allow for internal pores, as long as it isn't printed too fast (or solidifies too fast, which is why I think most chambers are internally heated to near melting temp).

Re: surface roughness, I can understand that the powder grain size creates a sort of minimal structure size, and can in principle be the start of a crack if a surface grain gets knocked loose. Is that the sort of thing you mean? I can see that for any internal or external surfaces, and a rocket engine combustion is certainly applying a lot of heat and pressure on surface grains. Can this be alleviated by smaller grain sizes, or is there some limit there?

Re: repeated heating/cooling and internal stresses, this strikes me as just requiring standard post-printing stages like tempering to alleviate internal stresses.

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fbd_0100 4 hours ago | parent | next [-]

I can't speak to the proximal cause of the roughness and porosity, but if you've ever held a raw printed aluminum part in your hand it is immediately apparent. That said there are processes to deal with porosity like Hot Isostatic Pressure (HIP) treatment that basically crushes all the voids with immense pressure. This does come at the cost of dimensional accuracy though (HIP will compress the part somewhat).

Similarly, annealing a 3D-print to relieve residual stress does work, but it also will cause warping as those stresses are relieved. Again, sacrificing dimensional accuracy. Frontier AM companies have ways to compensate for all of these effects but it's a trial and error process for each part essentially.

At this point you're now stacking multiple processes on each other just to try to get to near-billet properties. Calibration Trials > Print > HIP > Anneal > Machine. The cost adds up quickly. It can be justified especially in non-fatigue-critical applications but it's no free lunch

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gus_massa 3 hours ago | parent [-]

I'm not sure if it make sense but... is it possible to put the printer inside a vacuum chamber so there is no air to fill the internal bubbles?

	▲	pixl97 an hour ago \| parent [-]
		Cooling would be an interesting problem. Atmosphere takes away the heat pretty readily. You could have a cooling plate the work is on. But the higher temperature difference is apt to cause warping.

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numpad0 2 hours ago | parent | prev [-]

SLS printers lay a layer height worth of powdered metal and fuse it with a laser engraver. Thee bed lowers one layer and the process is repeated. They don't bring materials used like inconel to full melting temperature, only do what it takes for the metal sand to clump together. That's one source of pores.

I assume you can just anneal or print then recast in sand or whatever, maybe even lostwax with Al as wax, but the point is that porosity in a print itself is inevitable with current powder based tech.

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tredre3 5 hours ago | parent | prev | next [-]

3D printed metal is now as strong as machined metal, assuming an identical alloy. The process has been pretty well perfected.

The strength loss comes from the fact that not all alloys are 3d-printing friendly, so you often have to compromise and you end up with a less than ideal alloy for your application.

	▲	Tuna-Fish 9 minutes ago \| parent \| next [-]
		Eh. A lot of materials get their strength from being worked, which 3d printing doesn't do at all.
	▲	naasking 5 hours ago \| parent \| prev [-]
		Sure, but I mean what's the technical reason a material isn't it 3D printing friendly? Are we talking grain structure here? Is it something that can be at least partly mitigated by some post-printing heat treatments, like tempering?

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carabiner 3 hours ago | parent | prev [-]

Don't get good crystal/grain structure from 3d printing.

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avmich a day ago | parent | prev | next [-]

The thrust vector control (TVC) subsystem is usually considered a part of the engine. The major change the Soviet NK-33 underwent for a USA model was the addition of TVC, and the engine was named differently, so there are two engines, named differently, which mostly differ by the presence of TVC.

Raptors can be used without TVC. Be that by using differential thrust, or just not needing that - because rocket is controlled using other means, or other engines - it's possible. Tory Bruno specifically explained that he meant - among other things - that absence.

A picture of the engine working on the test stand can be that for the engine - or for the chamber, a significant component of the engine, with or without turbopumps involved.

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w8vY7ER 12 hours ago | parent | next [-]

Oh yeah, Tory Bruno made that gaffe of a comment publicly, and completely unprompted, before he abruptly quit. I had forgotten, but you’re right of course.

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brandonagr2 3 hours ago | parent | prev [-]

https://www.spacex.com/content/starship/holy-grail-of-rocket... at 13:35 has a good view of a raptor 3 with TVC, do you think that adds substantially to what is pictured at the top of the article?

	▲	numpad0 2 hours ago \| parent [-]
		TLDW but TVC for rocket engines is usually achieved by like one hydraulic suspension rod each for X and Y axes(Y and Z in rocketry? idk) serving as parts of the engine mounting frame. It shouldn't add a lot to the system.

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advisedwang 2 hours ago | parent | prev | next [-]

> A full-flow staged combustion engine is very complex, and prior to the Raptor only two had been built, neither of which successfully flew on a rocket.

Isn't the Space shuttle main engine / SLS engine a full-flow staged combustion engine?

	▲	Tuna-Fish 4 minutes ago \| parent \| next [-]
		In SSME, most of the LOX never goes through a preburner. The SSME uses the same kind of fuel-rich combustion chambers for both preburners. This presents a problem for the oxidizer side because any leaking along the shaft between ox pump and turbine in either direction would be catastrophic. This is resolved by an extremely expensive and complex multi-stage helium-purged rotating seal. One of the cool parts about most FFSC designs, and the raptor in particular, is that they can afford slight leaking from high pressure to low pressure through any seal in the system and it's broadly safe, and only marginally reduces performance. This allows them to be made much more cheaply.
	▲	nbadg 2 hours ago \| parent \| prev \| next [-]
		No, it's a fuel rich staged combustion cycle: https://en.wikipedia.org/wiki/RS-25
	▲	pixl97 an hour ago \| parent \| prev [-]
		As it said raptor was the first and the SLS engines are way older. I think China has made a full flow engine too.

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fragmede 20 hours ago | parent | prev | next [-]

3d printing metal has come a long way!

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philipwhiuk 4 hours ago | parent | prev [-]

> There turned out to be less detail available here than I hoped.

I'm surprised the author was surprised that a component of a multi-billion dollar company which is vital to it's future success in the industry and is covered by US regulations governing information export wasn't available as a cut-away diagram.