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.
https://mobile.twitter.com/elonmusk/status/14139104042465239...
The most comparable scale they’re targeting for manufacturing Starships is jet airplanes. They’re supposed to be space busses, essentially. The way Musk sees them is, as “cattle, not pets”.
Source for 1M Ton Target: https://www.space.com/elon-musk-spacex-starship-update-orbit...
I'm not saying it's impossible, but it does mean SpaceX will really have to scale up. Where is that capital going to come from? I'm not even sure even with all of Musk's personal assets and selling out on launches they'll get there for decades.
How did Musk solve this problem?
SpaceX haven't, yet.
> As I recall, the Soviet moon rocket failed because it had a cluster of engines that they could never get to work together. The Saturn V had a cluster of only 5, and barely were able to get that to work.
N-1 rocket had many troubles with the engines, but it wasn't specifically due to the number of engines: the NK-15 engine couldn't be test fired, vs the Raptor definitely can. You can read more about the four failures here[1].
Similarly, the biggest issues with the F1 engine (powered the first stage of the rocket) was with the injector plates: there was a lot of combustion instability due to uneven mixing in the giant combustion chamber. The Raptor, by virtue of injecting both fuel and oxidizer in gaseous form, will mix better (and it has much smaller combustion chamber anyway)
Having two launch pads (they're starting work on a second tower at the Cape) is also a big help, as they would have backup launch site in case there's an explosion.
[1] https://en.wikipedia.org/wiki/N1_%28rocket%29#Launch_history
Soviets were desperate by then, no money, no time, and political pressure.
> How did Musk solve this problem?
Raptor 2 apparently has melting issues, you can only imagine what will happen when you have whole array of them firing.
What they are doing is trying to figure out how much cooling they need to make many reuses possible but still have the highest possible performance.
The N-1 failed partly because the engine were untested and had high failure rates. The could not be tested on the ground and had a lot of manufacturing issues.
The N-1 failed because the on board computers couldn't handle engine shut downs very well. They basically just shut down the opposite engine.
In some flights that problem lead to complex piping being broken as well, but its by far not the reason the rocket failed.
And SpaceX has already done the Falcon Heavy with 27 engine and its perfectly fine.
What matters is that your engine work well and that if something happens to one engine the computer can figure that out and perfectly adjust all other engines to that new reality.
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?
I thought combustion chamber instability was the biggest issue with the big engines. Are solid rockets much more stable?
Solids rocket are like a candle with a hole threw it. They burn inside out, not from the button to the top. So there is not really a thrust chamber in the same way. A channel goes from buttom to the top inside the booster. So the 'thrust chamber' is essentially the hole length of the booster. And all that material gets pushed down in the direction of the nozzle.
I have never heard any rocket engineer explicitly explain this, but my assumption is that on the way down when everything is pushed threw the neck the gas has time to mix enough so that the instabilities are not that large anymore. I also think the pressure is lower in a solid.
Solids have higher thrust but lower efficiency. The thrust comes from the fact that in the solid fuel mix there is lots of other stuff that need to form the solid. Heavier elements that don't participate in burning (thus less efficient) but add thrust.
Solids also have the draw back of being incredibly loud and having massive vibrations.
Solids also can have 'stability' problems as in that if they are not correctly manufactured, they might not burn uniformly and that can lead to a whole lot of problems and additional vibrations too.
Almost no new rocket company uses solids. Its far to expensive and operationally dangerous. At best you can reuse some outer shell, but not the expensive part.
They always have the option of designing another larger engine later.
also less bad to lose ~3.3% of your total thrust than 100% of it.
It also gives you engine out capability and also the ability to effectively throttle the rocket in a much more fine grained way by shutting off 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.
The only downside is that if any of the engines explodes catastrophically, it will take the entire rocket down. This used to be a big problem in the Soviet N-1 lunar rocket, but contemporary technology can mitigate it quite a bit: with enough telemetry and computer power, you can determine that the engine is acting funny before it explodes, and you can switch it off. Losing one engine out of 30 isn't fatal.
Also, with computer modeling, a lot of the engine design and testing process takes place on screen, so many failure modes are debugged early.