​After the interest in the last post I wrote on SpaceX and the general interest in SpaceX, I decided that at some time I would come back to the topic - once I thought of an ideal way for readers like you to get as much out of this as possible.

And now is that time now.
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In the video below, you will see an interview with Elon Musk by the host of Everyday Astronaut: Tim Dodd. If you are not familiar with Everyday Astronaut, then you should put it on one of your subscription lists - it is an excellent ongoing series that provides you with examples of engineering practice that you can use to hone your own engineering understanding and skills.

In the above video, a number of key concepts are discussed. By contemplating these, you can dig into the underlying principles of engineering practice. From doing this, you become better at understanding these principles, and you can then better apply them.

Below are some things I noted - I am sure that they will help you. But I am also keen to know what you noticed. After reading what I have, please share, in the comments, some of your observations on engineering practice examples - good or bad - from the interview. I always enjoy talking about such things, and would enjoy talking with you about them too.

Use of first principles to inform the goals
At 14:20 they note from theory that they can’t get more efficiency so now effort can be directed elsewhere. Why do I find this interesting? Because it shows how, as technology and engineering projects evolve, engineers need to and can change mode. Without this use of theory, there could have been an ongoing fixation with combustion efficiency - even though that’s not what’s really needed by the end user.

Framing the mixing challenge
There is a detailed explanation of the mixing process at the 16:00 minute mark. The conversation revealed that the approach was to premix prior, so that the combustion chamber does not need to do as much mixing - only the last 10%. I like this because it shows how as you progress from the bigger picture to the details you can still be framing.

Strategic design thinking informed by engineering attributes
It is noted at the 18:00 point that they are still using hydraulics as opposed to full electrics for the actuators. The reason is that they have had to focus on other things at that time and the actuators can be separated enough from other systems - so it is something they can look into later. This is a good use of systemic thinking to help optimsie the design strategy which is a great example of modal shifting. There is also a good use of systemic thinking and first principles when they explain how a hydraulic system is still a good idea in other contexts - so they are not designing by heuristics! 

Framing the design strategy
“If you’re not adding back at least 10% of things you’re deleting, you’re not deleting enough."
This is clearly a design strategy suited for the case where weight and complexity need to be reduced. This would not make sense in other cases - say a civilian nuclear reactor - but it is well aligned in this case. And it is an ideal tool to help all engineers keep the mindset suited the challenge - especially if they have tendencies toward different mindsets because of their background (very Global Engineer). There is also at this time the reference to focusing on production and then automation - this shows it is very much a commercial venture. Finally, there is the acknowledgement of the need to iterate - because the limits of first principles use are being reached. I like that last notion because itis informed iteration, and not random trial and error.

Systemic thinking and opportunism
It is noted, around the 23:00 mark, how adjusting the system to protect items from heat and aero load can eliminate the need for the shields. I like this because it shows the synergistic value from combining the attributes of an expert engineer - and not just treating them separately.

Trouble with theory
I was surprised by what appeared to be difficulty with explaining cavitation at the 28:00 mark. The two seem to think they are just bubbles and maybe affected by the chemical environment. It did not seem to be understood that they are supersonic shocks that literally break up solids. It shows that we all keep on learning first principles.

More trouble with theory
Correct me I am wrong, but it seems to me that at the 37:00 mark they provide the exact definition of Isp as an alternative to the Isp. Another example that we can all keep learning.

Now it's your turn
What did you notice in the video? What principles or mistakes stood out to you? Were there other moments that highlighted good systemic thinking, clever framing, or design trade-offs? Drop a comment below—I’d genuinely love to hear your perspective, so I will respond.

​If you're not sure where to start, just share one moment that made you stop and think. These conversations are how we all get better. You can also recap some engineering basics here to better spot examples in the video.

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.