Kevin Carey, in the middle of an article about how Silicon Valley is upending higher education, has a supergreat metaphor:
So he walks over to the whiteboard that makes up the entire wall of the conference room and deftly sketches out the inner workings of a rocket engine, showing what happens when thousands of gallons of rocket fuel are sprayed into a chamber of fire, thus igniting and creating fantastic amount of force, the eddies and whorls of which need to be predicted and calculated in minute, down-to-the-millisecond detail, so that the force can be directed down through the closed chamber in which the initial combustion occurs and out the bottom of the rocket in the form of enough thrust to take something the size and weight of, say, a telecommunications satellite, up and away from the gravitational bonds of our planet.[…]
The real holy grail is a more efficient use of fuel to create thrust. The amount of thrust needed to liberate X amount of weight from the Earth’s gravity well is a brute math problem. It’s inescapable. And, crucially, as Scott explains it, when the rocket is sitting on the launching pad, most of the weight is fuel.
Most of the weight is fuel. […]
Because when most of the weight is fuel, Scott explains, a reduction in the amount of fuel you need to create thrust increases the payload weight you can move from Earth into orbit along a logarithmic scale. It’s not a linear, one-to-one thing. The less fuel you need, the less fuel you need. It’s exponential.
I’ve been thinking about this since I read it three days ago, which probably means it’s true in some way. It’s a good article!