The thing that's impressive to me, in addition to the sheer size of these machines, is the engines . The Raptor 2 is groundbreaking. And there's 30+ of them between both stages. It's just incredible, and there's nothing like it that's been done.
> The thing that's impressive to me, in addition to the sheer size of these machines, is the engines. The Raptor 2 is groundbreaking. And there's 30+ of them between both stages. It's just incredible, and there's nothing like it that's been done. I may be wrong, but isn't the reason there are so many engines on their rockets is because SpaceX isn't good at building big rocket engines?
No, that's completely wrong. There are challenges in running a bunch of engines, but it's critical to pull off for reusability. All rocket engines have a strict floor on how low it's possible to throttle them. Even 40-50% is quite hard, and I believe the Raptor is 40% though with the goal of getting somewhat lower. And for old space expendable rockets that was plenty.
But to land a rocket, you necessarily need to be dealing with bringing it down when it's nearly empty. Rockets are mostly fuel by mass, and when that's expended are very light. The thrust necessary to lift a fully fueled rocket up is massively ginormously more then would be needed for its empty weight. So if you light up at full power even for a moment it's going to fly right back up again. You want a low enough minimum thrust/weight ratio (TWR), ideally below 1 (so you can gradually descend/hover), though a rocket can get by with a bit above with a "hover slam approach" approach like the F9 uses. But it can't be that far above. But you can't just throttle a rocket engine down to 1% either. What to do?
The answer is multiple engines. Throttle is limited, but you can always turn an engine off. So if you have 10 engines which each can throttle to 50%, your effective ability to throttle from max thrust is .5/10 or 5%. With 30 engines at 40% would be .4/30 = 1.3%. Very helpful. Also means more potential redundancy for landing.
There are challenges with plumbing, harmonics, control etc which are real, so as always with rockets complex tradeoffs, and big engines have their own issues. Small engines are also easier gimble, another valuable thing for landing, and to mass manufacturer which is a whole extra aspect for SpaceX, Starship is about economics remember. But there are many solid technical reasons for the choice.