Hitting the Books: Elon Musk and the Quest to Build a Better Rocket Engine
Getting people into orbit safely is no small feat, especially without the seemingly limitless R&D budgets for national space programs. However, that hasn’t done much to deter a new generation of private spaceflight companies from looking up at the skies above and thinking, “Yeah, I can get up there, no sweat.” In Take off: Elon Musk and the desperate early days that launched SpaceX, Senior Ars Technica Space Editor-in-Chief Eric Berger recounts the company’s tumultuous 20-year efforts to deploy reliable and reusable rocket technologies, culminating in a decade-long exhilarating race at the forefront of private spaceflight.
From the book LIFTOFF: ELON MUSK AND THE DESPERATE FIRST DAYS THAT LAUNCHED SPACEX by Eric Berger. Copyright © 2021 by Eric Berger. Posted on 03/02/2021 by William Morrow, an imprint of HarperCollins Publishers. Reprinted with permission.
In the spring of 2016, Amazon founder Jeff Bezos invited a handful of reporters to his rocket factory in Kent, Washington. No media had been allowed in before, but Bezos’ 15-year-old secret space company named Blue Origin was finally starting to reveal the full scope of his plans. Like Musk, Bezos had identified low-cost space access as the main obstacle between humans and passage through the solar system. He too had started to build reusable rockets.
For three hours, Bezos led a tour of his glossy factory, showing Blue Origin’s tourist spaceship, big rocket engines, and large 3D printers in turns. He also shared his basic Gradatim ferociter, Latin philosophy for “Step by step, ferociously”. Development of the rocket begins with the engine, explained Bezos, who was then working on his fourth-generation engine, known as the BE-4. “It’s the longest product,” he said, walking through the factory, wearing a blue and white plaid shirt and designer jeans. “When you look at the construction of a vehicle, the development of the engine is the most dynamic part. It takes six or seven years. If you’re optimistic, you think you can do it in four years, but you still need at least six more. “
In the fall of 2019, as we spoke aboard his Gulfstream private jet, I shared this story with Musk. It was a Saturday afternoon, and we were flying from Los Angeles to Brownsville, Texas. This interview was originally scheduled for the evening before, at the SpaceX plant in Hawthorne, California. On Friday, an hour after the scheduled time, his apology assistant texted that a seizure had occurred. Musk was feeling bad, she said, but we’ll have to do the interview at a later date. I returned to my hotel, preparing to return to Houston, when the assistant called back that evening. Musk had decided to visit the company’s South Texas Starship construction site this weekend and wanted to know if I wanted to follow him. We could do the interview during the flight.
Three of Musk’s sons joined their father on the trip, along with their dog Marvin (as in Marvin the Martian). A well-groomed and bred Havanese, he adored his master. Marvin at Musk’s feet, we gathered around a table in the back of the plane for the interview. Dressed in a black “Nuke Mars” T-shirt and black jeans, Musk wanted the boys to hear daddy’s stories about the old days.
Musk laughed when told about Jeff Bezos’ timeline for engine development. “To be blunt, Bezos isn’t good at engineering,” he said. “The thing is, my ability to tell if someone is a good engineer or not is very good. And then I’m very good at optimizing the engineering efficiency of a team. I am generally very good at engineering, personally. Most of the design decisions are mine, good or bad. “Bragging? Maybe.
But SpaceX built and tested its first rocket engine in less than three years with Musk in the lead. Musk and Bezos, at least, would agree on this point: The process of building a rocket begins with the engine. After all, the engine is the engineer’s root word. In principle, the propulsion system of a rocket is simple: oxidizer and fuel flow from their respective tanks into an injector, which mixes them as they enter the combustion chamber. Inside this chamber, fuels ignite and burn, producing super hot exhaust gas.
The engine nozzle channels the flow of this exhaust in the opposite direction a rocket is supposed to go. Newton’s third law of motion – for every action there is an equal and opposite reaction – does the rest.
Sadly, the reality of building a machine to handle the flow of these fuels, control their combustion, and channel an explosion to lift something skyward is staggeringly complex. And that’s not to mention the fuel consumption. The thrust of a rocket engine depends on the amount of fuel burned, its output speed and pressure. The larger each of these variables, the more thrust an engine produces and the greater the payload it can supply in orbit. Conversely, if it takes too much fuel to produce enough thrust, or if the engine is too heavy, a rocket will never leave the ground.
Musk recognized early on that when it comes to propulsion, [founding member of SpaceX and American aerospace engineer Tom] Mueller was not a good engineer – he was a great engineer. For the Falcon 1 rocket, Musk wanted a light, efficient engine that produced around seventy thousand pounds of thrust. That, he thought, should be enough to put a small satellite into orbit. Mueller had helped design and build several engines at TRW, some more powerful than this one, others less. The Merlin Engine would take inspiration from some of these concepts and ideas, but Mueller said he and Musk started out with a “clean sheet” design.
Few of Mueller’s friends in the industry believed that building an entirely new liquid-fueled rocket engine without government support was possible. “All of these guys told me that a private company can’t build a booster engine, which takes the government,” Mueller said. SpaceX did not invent the entire fabric Merlin engine. As with almost all rocket engines, the Merlin took inspiration from earlier work. For example, although Mueller developed many different engines, he lacked experience with turbopumps. Rockets use a staggering amount of fuel, and a turbopump is the machine that powers a propellant in a rocket engine as quickly as possible. Inside the Falcon 1 rocket, liquid oxygen and kerosene fuels would flow from their tanks into a rapidly rotating pump, which would spit out this high pressure propellant, delivering fuel into the primed combustion chamber for produce maximum thrust. One of the first problems Mueller had to solve was how to build a turbopump.
By the late 1990s, NASA had developed a rocket engine almost as powerful as the proposed Merlin engine called the Fastrac. There were other similarities. Fastrac used the same mixture of fuels, liquid oxygen and kerosene, a similar injector, and had potential for reuse. Despite a series of successful test fires, NASA canceled the program in 2001. Given these commonalities, Mueller figured SpaceX might be able to use NASA’s turbopumps built for the Fastrac engine. He and Musk visited NASA’s Marshall Space Flight Center in Alabama shortly after Fastrac disappeared in 2002, and asked if they could have them. Yes, they were told, but SpaceX would have to go through NASA’s procurement program, which could take a year or two. It was too slow for SpaceX, so Musk and Mueller switched to Barber-Nichols, the contractor who built the turbopumps.
As it turned out, Barber-Nichols had had a blast building the Fastrac turbopump. To work with the larger Merlin engine, Barber-Nichols would need a lot of overhaul. They went back and forth with SpaceX engineers. During a visit to the Colorado-based company, a designer suggested a name for the engine to Mueller. Musk had chosen the name Falcon for the rocket, but said Mueller could name the engine, only stating that it shouldn’t be anything like FR-15. He should have a real name. A Barber-Nichols employee, who was also a falconer, said Mueller should name the engine after a hawk. Then she began to list various species of the bird. Mueller chose the Merlin, a mid-size Falcon, for the first stage engine. He named the second-stage engine after the smallest of the falcons, the Kestrel.
When Barber-Nichols finally delivered the redesigned turbopump to SpaceX in 2003, he still had major issues. This forced Mueller and his small team to start a crash course in turbopump technology. “The bad news is we had to change everything,” Mueller said. “The good news is that I’ve learned everything that can go wrong with turbopumps and how to fix them.” Because pressurizing rocket fuel allows an engine to squeeze maximum thrust, good turbopumps are essential. This would become one of the secrets of SpaceX’s eventual dominance in the global launch market. Mueller said the original Barber-Nichols pump weighed 150 pounds, with an output of around 3,000 horsepower. Over the next fifteen years, SpaceX engineers continued to iterate, modify the design, and upgrade its parts.
The modern Falcon 9 rocket’s Merlin turbopump still weighs 150 pounds, but produces 12,000 horsepower.