How Rockets Work

From Newton's third law to a full-flow engine and a booster that lands. Learn it by taking the hardware apart.

By the end you can

Explain why a rocket accelerates, in space as well as in air
Use the rocket equation to say why most of a rocket is propellant
Trace oxygen and methane through a full-flow staged-combustion engine, part by part
Explain why rockets drop stages, and how a booster flies back and lands
Read a rocket's spec sheet and check its numbers with back-of-envelope arithmetic

Before you start

School-level ideas of force, mass and pressure; no maths beyond multiplying and dividing

Syllabus

01
Why rockets fly
30 min · planned
A rocket throws mass backwards fast and is pushed forwards in return. It needs nothing to push against, so it works best in a vacuum.
Fig · a small engine on a thrust stand with a load cell and a propellant tank on a scaleNewton's third lawmomentumthrustthrust-to-weight
02
The rocket equation
35 min · planned
Every bit of speed costs propellant, and the propellant has to lift itself. That is why more than nine tenths of a rocket on the pad is propellant.
Fig · a stack of propellant tanks on a scale beside a small payload, draining one by onedelta-vexhaust speedmass ratioTsiolkovsky
03
Inside the engine
30 min
A rocket engine is a pump problem. SpaceX's Raptor burns a little of each propellant just to drive its pumps, and nothing is thrown away.
Fig · Raptor 2 on a vertical test stand, taken apart part by part and firedturbopumppreburnerfull-flow staged combustionchamber pressurenozzleRaptor 2
04
Staging and reuse
35 min · planned
Dropping empty tanks is the cheapest way to go faster. Bringing the booster back is how you stop paying for it every flight.
Fig · a two-stage stack on a launch mount that separates in flightstagingboostbacklanding burnreuse
05
Steering
30 min · planned
Rockets steer by pointing their engines. Grid fins take over when the booster falls back through the air.
Fig · an engine on a gimbal with two actuators under a pivoting stagegimbalthrust vector controlgrid finsguidance
06
Getting to orbit
30 min · planned
Orbit is falling and missing the ground. It takes about 7.8 km/s sideways at low altitude, which is why going up is the easy part.
Fig · Newton's cannon on a mountain on a small globeorbitorbital speedgravity turn

Syllabus

Why rockets fly

The rocket equation

Inside the engine

Staging and reuse

Steering

Getting to orbit