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Elon Musk Explains Why SpaceX Prefers Clusters of Small Engines (arstechnica.com)
An anonymous reader quotes a report from Ars Technica: The company's development of the Falcon 9 rocket, with nine engines, had given Musk confidence that SpaceX could scale up to 27 engines in flight, and he believed this was a better overall solution for the thrust needed to escape Earth's gravity. To explain why, the former computer scientist used a computer metaphor. "It's sort of like the way modern computer systems are set up," Musk said. "With Google or Amazon they have large numbers of small computers, such that if one of the computers goes down it doesn't really affect your use of Google or Amazon. That's different from the old model of the mainframe approach, when you have one big mainframe and if it goes down, the whole system goes down."
For computers, Musk said, using large numbers of small computers ends up being a more efficient, smarter, and faster approach than using a few larger, more powerful computers. So it was with rocket engines. "It's better to use a large number of small engines," Musk said. With the Falcon Heavy rocket, he added, up to half a dozen engines could fail and the rocket would still make it to orbit. The flight of the Falcon Heavy likely bodes well for SpaceX's next rocket, the much larger Big Falcon Rocket (or BFR), now being designed at the company's Hawthorne, California-based headquarters. This booster will use 31 engines, four more than the Falcon Heavy. But it will also use larger, more powerful engines. The proposed Raptor engine has 380,000 pounds of thrust at sea level, compared to 190,000 pounds of thrust for the Merlin 1-D engine.
For computers, Musk said, using large numbers of small computers ends up being a more efficient, smarter, and faster approach than using a few larger, more powerful computers. So it was with rocket engines. "It's better to use a large number of small engines," Musk said. With the Falcon Heavy rocket, he added, up to half a dozen engines could fail and the rocket would still make it to orbit. The flight of the Falcon Heavy likely bodes well for SpaceX's next rocket, the much larger Big Falcon Rocket (or BFR), now being designed at the company's Hawthorne, California-based headquarters. This booster will use 31 engines, four more than the Falcon Heavy. But it will also use larger, more powerful engines. The proposed Raptor engine has 380,000 pounds of thrust at sea level, compared to 190,000 pounds of thrust for the Merlin 1-D engine.
Of course, it has to be actual redundancy. The Soviet N1 moon rocket had a problem that when its engines failed, they tended to take out adjacent engines. You have to be absolutely sure that failures aren't going to spread (pieces of shattering turbopumps, fires, backpressure, etc), or you're actually making the problem worse.
Of course, everyone working on rockets today knows the lessons of the N1 and it'd be incompetence not to exhaustively test for resilience against cascading failures.
Beyond redundancy, one neat thing about engine clusters is that you can create a virtual aerospike effect to some degree.
It's time for Operation Crazy Plan.
Friendly reminder, millenials aren't kids anymore.
Yes they are. Get off my lawn!
The rocket is built to contain engine explosions. We don't know if that'll be effective for all engine failures, but they've already had at least one engine failure on a F9 flight without consequences for the mission.
They said that failure was because of lack of fuel, so more engines wouldn't help that.