How did they do that? The SpaceX Raptor Engine Evolution

You have probably seen this photo a number of times now. The three-stage evolution of the SpaceX rocket engine. A visual exemplar of engineering excellence.
It is indeed an impressive feat; many have wondered at how the plumbing was simplified so much. Some have even felt some pride; being part of the same professional family. It has also been motivation for other engineers; seeing what can be done when enough engineering effort and skill are applied to a task. And, finally, some simply thought the photos were not genuine; maybe the best evidence that the engineers had done well.
But the real value would come from asking how it was done.
By understanding the engineering thought that was behind such achievement, you can then better reflect upon your own skills and how to improve them.
And that’s what I will do here.
By using the above image, insights I have read about the engine’s evolution, and the knowledge I have shared with you in my book on engineering expertise, I will share with you some concrete examples of this expertise in practice.
First, two things we should note:

• Given how he has become such a controversial figure of late, it should be noted that this not about deifying (or demonising) Elon Musk. That fact is, even though he would have influenced the approach, the engineering was carried out by a team. And it is their work we are considering.
• What I write here, while being thoroughly informed by the most recent understanding of engineering expertise, is an inference. There will not be specifics – only higher-level insights into the engineering strategies used.

Now let’s talk about that plumbing. It is obviously the first thing most of us notice. And clearly the best way to get the part count down in such an engine – where most of the engineering effort is focused on ensuring the flow of fuel, oxidant and coolant.
The major reduction is from the first to the second.
It has been reported that the second version was a complete redesign. This is very much aligned with coevolution: where your understanding of the problem evolves with the implementation of the solution. There would have most likely been many lessons learned when designing and implementing the first design.
The lesson here for you is twofold:

1. If you are working on something very new, then expect that the first effort will be more about learning than about achieving. Even if that first effort is to go into service.
2. There will likely be little in the first design/effort that is worth keeping. This can be hard to accept. We can become attached to our designs. But work on being more appreciative of the knowledge gained.

The reduction in plumbing as the design evolved from the second to the third version is still significant. Ratio wise, it is probably the same as the respective reduction for the evolution from the first to the second.
The difference here though, is how it was achieved.
In this instance there was the goal put forward to reduce the number of protective engine shrouds. This is an example of framing – identifying the engineering challenge that will be the focus.
The number of shrouds was reduced by integrating many sensors and plumbing into the housing wall. This is an example of systemic thinking. By understanding how each part and subsystem interacts with others, opportunities can be found to harmonise all elements of the design. In this case, they could all use the same heat shield.
In addition, parts were combined into one (via welding as opposed to bolted joints). Having fewer parts means a more compact and lighter design. But, in this case, and often in others, it means more difficult servicing. The judgment would have been made that the increased cost in servicing was less than the money made carrying more cargo. These competing needs can both be quantified – so, it would be expected that, first principles would have been used to establish the most profitable compromise.

In summary:

• When doing something very new, the engineers leant into coevolution.
• Much of the reduction in complexity came from developing the right frame and then using systemic thinking.
• First principles were used to find the right compromise between revenue generation and servicing cost.

If you can’t recall the details of things like framing, systemic thing, and first principles, then take a listen here – it will take you 10 minutes.

If you have any questions or thoughts about how engineering expertise was applied in these engines or about developing your own abilities, so you too could do that, then leave a comment or send me a message.

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