Why rockets dozens of smaller thrusters instead of one giant one?
In: 6
Safety. If you have a bunch of small ones, having one or two fail isn’t catastrophic. If you only have one or two large ones, a failure is disastrous.
1:ease of manufacture: its simply easier ot produce more of a smaller item and compensate for manufacturing errors. on a large single assembly an error means that whole part may have to be remade from scratch.
2:efficiency(fuel and thrust): you can make very powerful and fuel efficient rockets that are relatively small but this efficiency drops as size increases.
3:Safety: redudancy is a hell of a thing ot have on such complex projects, last thing you need in a launch is your main and only source of thrust ot fail(whihc evne in the strict standard of space agencies its not a 0% chance). in this event you rather have multiple redudtant sources of thrust you can adjust on the fly(especially as the rocket gets lighter as it goes due ot burning the weight of its own fuel away.)
In general, the cost of a device goes down as more of them are made. If you make one big engine, you maximize the cost to develop it. If you make many smaller engines, some of them will be less expensive as efficiencies of scale emerge.
From a technical perspective, machines operate most efficiently over a range of conditions. Making a big engine that is continuously efficient from 0.001% output to 100% output is very, very difficult. Making a small engine that’s pretty efficient from 20% to 100% efficiency is much more achievable. If you have many engines, then using only one is a way to scale down the output.
You also have more control while launching the rocket. Being able to control which boosters go off at different parts of the staging process gives them better control over the flight.
You need to get the fuel into the combustion chamber, mix it really well, combust it and push the gas out the nozzle. As a rocket gets bigger, the mixing gets harder and combustion instability gets worse. The biggest single rocket engine is still the F-1 engine from the Saturn V. It’s probably about as big as you can get and have efficient stable combustion. And it is pretty big, the turbo pump alone was making 55,000 horse power just to pump the fuel and oxidizer.
There are a few reasons…
One reason is that bigger combustion chambers are a little less efficient as the mixing of propellants isn’t quite as good. They can also lead to combustion instability; this was a *huge* development problem with the F-1 engine used on the Saturn V first stage. They ultimately resorted to detonating explosives inside the engine bell to cause instability so they could verify that the engine could deal with it.
This was a big enough problem for the Soviets that they resorted to building single engines with multiple combustion chambers – like the RD-180 used on the Atlas V.
For a launcher like the Falcon 9, a high engine count is required to be able to land the booster after a launch. If it had fewer engines the thrust of a single engine would be too high to be able to land safely.
Latest Answers