Rutherford is really reliable. Why not use like 27 of them? Is there some reason that this is inherently bad?
It would probably be less efficient to use lots of small engines, but perhaps the reduced cost of using an already existing engine that you can mass produce would make up for it.
Its not the number of engines that is the problem.
The problem is how efficient is your engine, how is the Trust-to-Weight ratio.
To do a reusable launcher you need to be really damn efficient on every part of the rocket. Elon explains this pretty well in the talks he gave around 2014.
Tangent: a lot of the rocky planets we have found in the universe are larger than Earth.
With Earth's gravity is seems like we are just barely able to make a reusable launch system by pushing the physics of chemical propulsion to its limits. Better technology can only help so much. We are already close to the limits of physics for things like rocket efficiency, material masses, etc.
Make Earth even say 10% bigger than we'd never be able to build reusable chemical rockets. Make it even bigger still and disposable chemical rockets might be infeasible, making nuclear propulsion the only viable way to get out of your gravity well. A nuclear first stage launching from inside your biosphere is not a great idea, and making nuclear rockets reusable is harder than making chemical rockets reusable. Keep increasing gravity and it only gets exponentially harder still. At some point any kind of space flight become impractical even if you're willing to irradiate yourself.
But... make a planet smaller than Earth and pretty soon you start to have trouble holding onto an atmosphere! Look at what happened to Mars.
This could be yet another Fermi paradox answer. Earth may be right on a knife edge between too small to have a long term stable biosphere and too big to get off the thing!
Of course maybe an intelligence would eventually develop a propulsion system that could crawl out of a super-Earth gravity well using something like nuclear fusion or microwave beamed power, so who knows... it's just another possibility.
> A nuclear first stage launching from inside your biosphere is not a great idea
I disagree. There are nuclear rocket designs that don't have radioactive exhaust.
Sure, its a little bit of a problem if it explodes, but not to bad.
And actually if you do that, then you are much better set up for deep space exploration.
> and making nuclear rockets reusable is harder than making chemical rockets reusable
Not sure that is actually true. I don't see a reason why something like a NERVA engine should be just as reusable as any chemical engine.
We have way to much fear of radiation. We should be already living in the nuclear age.
Given that NERVA was a 1960 engine I don't think that answer works for Fermi, specially given how many more smaller planets there are (we just have not found them).
Read the launch history most of it the engines weren't the problem. *edit control was the problem, it just happens to be connected to parts of the engines.
It would probably be less efficient to use lots of small engines, but perhaps the reduced cost of using an already existing engine that you can mass produce would make up for it.