Obviously it must be easier to do this with a bunch of little rockets than one big one. Or cheaper. Or more fixable. Or, simply more controllable (although, while they can gimbal, they can’t vary the thrust once it’s started, right? It’s still basically a controlled explosion.).
I’m sure there have been any number of papers about why this approach, but can someone ELI5 it for me?
I’m reminded of the old programming languages-as-racecars metaphor, where Erlang is that you don’t build one big racecar, you build hundreds, and while many will crash, many will also make it to the finish line and some might win. However, if even one of the fails during ascent, is it manageable? Is this also redundancy?
although, while they can gimbal, they can’t vary the thrust once it’s started, right?
While solid rocket boosters can’t vary their thrust, most liquid-fueled rocket engines can throttle down to reduce thrust when required.
can someone ELI5 it for me?
I can try :)
If you want to land a booster propulsively (like Falcon 9) you need several small engines rather than a few big engines. When a booster returns to earth, its mass is only a fraction of what it was at launch, as most of the propellant has been used up. It would be difficult for a big engine to accurately perform the landing maneuver, and the forces and acceleration could damage the rocket.
However, if even one of the fails during ascent, is it manageable? Is this also redundancy?
Yes, having a large number of engines can provide redundancy. Falcon 9 can lose an engine and still complete most missions, and a Starship booster (33 engines) could likely lose a few engines. That said, I think designing a rocket with 100+ engines is a bit excessive :)
Obviously it must be easier to do this with a bunch of little rockets than one big one. Or cheaper. Or more fixable. Or, simply more controllable (although, while they can gimbal, they can’t vary the thrust once it’s started, right? It’s still basically a controlled explosion.).
I’m sure there have been any number of papers about why this approach, but can someone ELI5 it for me?
I’m reminded of the old programming languages-as-racecars metaphor, where Erlang is that you don’t build one big racecar, you build hundreds, and while many will crash, many will also make it to the finish line and some might win. However, if even one of the fails during ascent, is it manageable? Is this also redundancy?
While solid rocket boosters can’t vary their thrust, most liquid-fueled rocket engines can throttle down to reduce thrust when required.
I can try :)
If you want to land a booster propulsively (like Falcon 9) you need several small engines rather than a few big engines. When a booster returns to earth, its mass is only a fraction of what it was at launch, as most of the propellant has been used up. It would be difficult for a big engine to accurately perform the landing maneuver, and the forces and acceleration could damage the rocket.
Yes, having a large number of engines can provide redundancy. Falcon 9 can lose an engine and still complete most missions, and a Starship booster (33 engines) could likely lose a few engines. That said, I think designing a rocket with 100+ engines is a bit excessive :)
That was a good ELI5, thanks. Answered my questions!
You’re welcome! Glad I could help!