[1]: https://en.wikipedia.org/wiki/Rutherford_(rocket_engine)
Atmospheric drag effects rocket performance less and less the larger a rocket gets (square-cube law), so that a rocket like the Space Shuttle can effectively ignore the atmosphere. Conversely, the smaller a rocket gets, the harder and harder launch gets. This is the problem Rocket Lab has decided to attack.
A decade ago, SpaceX launched the very similar Falcon 1. Falcon 1 was designed a decade ago, and you can see a large amount of the tech advancements in the last decade in Rocket Lab's design:
1. Cheap, lightweight Lithium Polymer (LiPo) batteries.
2. Cheap and performant brushless motor controllers.
3. Additive manufacturing for cheaply making complex parts without significant labor costs.
4. Advances in composites to enable the first orbital-class composite-bodied rocket.
Without any one of these advances, Rocket Lab would not be viable. It still may end up not being viable. Rocket Lab can never compete on bulk orbital cargo pricing. However, Rocket Lab's vision of applying recent tech advancements to bring down the smallest possible launcher size is extremely commendable.
Rocketlab business model is to compete with SpaceX on scheduling and orbits for small satellites. Not on price per Kg to orbit. That fits in with the trend to make satellites smaller.
Without a number of advances, the iPad and iPhone wouldn't have been viable. (As evidenced by the appearance of tablets and smartphones many years before.) Tablets can't compete with larger form factors on bulk pricing of computation. However, there is a technology inflection point where smaller and more flexible becomes usable enough. I guess that's what RocketLab is aiming for.
Electric has two issues. First of all, the energy density (after controlling for efficiency of electric motors / turbo pumps) is lower than that of rocket fuel. Second of all, an empty battery weighs as much as a full one, whereas used fuel no longer weighs down the rocket.
I'm suspicious that electrics are viable for first stages where performance advantage is less important. For first stages the cost is linear with ISP. Where it's exponential for second and third stages. (X^2 and X^3!!) For instance the Protons's first stage specific impulse is 285, Electron rockets specific impulse is 303. That's totally comparable.
Does metal 3D printing mitigate any of these challenges? Or is the problem a packaging problem where there is a minimum size required for the mechanical parts?
https://www.aacademica.org/hernan.emilio.tacca/9.pdf
I did some more looking, the linked study says that turbopumps scale better then electric as the burn time increases. Because burning fuel and oxidizer is more weight efficient than batteries. At short burn times that's offset by the increased weight of the turbopump.
Along with my earlier comment, the Proton first stage only burns for 130 seconds. Which puts first stages in the short burn category where eletrics do well. *but never as good as turbo pumps. Which supports the idea that electric systems can compete for large first stages by being simple, cheap, and reliable.
More whack is relanding first stage electric fed rockets. Ala SpaceX.
Any good websites or books you recommend to learn more about them?
I remember reading an interview with some NaSA engineers who were reverse engineering the F1 engines used for the Saturn V. He said notable was the amount of welded assemblies vs ones machined using 5 axis mills, and parts created via Powder Metallurgy on modern designs.
http://atlaspressedmetals.com/index.php/pm-advantages/histor...