Can rocketry become more efficient?

Question

I was watching a video of a Saturn 5 Rocket launch and I was amazed at how much fuel was used and how massive the explosion at the beginning was (and how massive the continuous fuel burn was).

But it got me thinking can we, in the future, develop rockets which can lift more payload per gallon of fuel or are all of our rockets equally efficient in terms of the rocketry version of “Miles per Gallon” because of some law of physics which we already mastered?

And I know there are alternatives like Space Elevators, but I’m specifically curious about rockets.

In: 6

Answer 1

We measure the efficiency of rockets in Specific Impulse which is how much momentum change(impulse) you get from a kilogram of fuel, rocket efficiency is all about mass not volume

Why do we care about momentum change instead of energy in the fuel? Because rockets are momentum based engines, not energy based like your car

We have a variety of different fuels that have various efficiencies. Hydrogen and oxygen are generally the most efficient(up to 450) but since hydrogen isn’t very dense you end up with massive fuel tanks like on the Saturn V. Other fuels like RP-1(basically kerosene) and methane are denser and easier to work with but aren’t quite as efficient

There are some cheats that can get you wildly more efficient rockets.

Nuclear thermal rockets run a propellant (generally hydrogen) through a hot nuclear core which heats it up and shoots it out the back. Now the rocket is only carrying the propellant instead of a propellant and oxidizer so the efficiency can be a lot higher but the thrust-weight ratio is generally worse.

Ion thrusters use electricity to accelerate gas up to stupid high speeds and shoot it off into space. Since the gas particles are moving super fast they have a fair amount of momentum so you get really good efficiency. Unfortunately we’ve yet to make one big enough to even lift more than about 10kg off the surface of the Earth so its only good once you’re up there and just making tiny adjustments, they also need a stupid amount of power (3.75MW for 88 Newtons of thrust)

Basically you can make more efficient spacecraft propulsion, but most things that provide the stupid amount of thrust required to get out of this gravity well end up being only moderately efficient but we are equipping satellites with ion thrusters that are 10x as efficient to extend their life with their limited fuel supply