> Musk has shown that the key to making space flight affordable isn’t breakthroughs in engine performance, and its not reusability, at least not yet. Before Spa

> Musk has shown that the key to making space flight affordable isn’t breakthroughs in engine performance, and its not reusability, at least not yet. Before SpaceX ever landed a booster they were 30x cheaper than the Shuttle, and 20x cheaper than the SLS. How did they do it when the Falcon 9 engine has very average performance, and when they didn’t reuse any of them? > The reason is same as Henry Fords, assembly line manufacturing. They mastered making Merlins cheaply by building them in high volumes and constantly improving at it. Nine engines per rocket made that possible, just as it’s a key to their making reuse work. This is one ingredient, and may be the largest, but there are several others as well. To start with, engine R&D costs were significantly reduced because Elon was able to build atop a well-established foundation by Tom Mueller whom he hired from TRW. That's not a dig - it has proven to be a very smart move. Vertical integration, and not having to pay Aerojet Rocketdyne their margin on each engine also helps. Another is that a lot of his initial R&D was done via the Falcon 1, sponsored in significant part by DARPA. Yet another is that the legacy rocket companies do business with the traditional "Mission Assurance" mindset that accompanies national security space missions as well as high-value commercial missions (e.g., GEO sats). Starting in the late 2000s free of that legacy enabled a completely different culture that was far less plodding, risk-averse, and legacy-driven. Additional mission assurance was then driven in after failures (like the early Falcon 1 flights) and more when SpaceX put themselves through the USAF launch certification process. Don't underestimate the impact of the legacy mission assurance mindset. The US has a major Federally-Funded Research and Development Center, The Aerospace Corporation where likely the largest component of its income is being involved in DoD mission assurance.