A rocket that splits into pieces is called a multi-stage rocket. Why split? Because once a tank is empty, it is dead weight. Throwing away the big, empty booster means the top part no longer has to haul it to space, so it can go much faster on the fuel it has left.

Super Heavy is 9 m wide, about as wide as a three-lane road. When it is full, it holds about 3,400 tonnes of propellant, the mix of fuel and oxygen that rockets burn.

The ship has a big cargo bay in its nose. It can carry satellites, supplies, or, in NASA's plan for the Artemis missions, astronauts down to the surface of the Moon.

Most rockets throw every stage away after one flight, like a paper cup. Starship's big idea is that both stages fly back and are used again, like a plane. That could make getting to space far cheaper.

Everything about the tower is huge. It stacks the ship onto the booster with its two big arms, called chopsticks, which slide up and down the tower on rails.

Under the rocket sits the launch mount, a steel ring on legs. Below it, a steel plate sprays water up into the flame at launch to soak up heat and noise, so the concrete pad isn't blasted away.

This trick is called hot staging. Older rockets usually separate first and then light the next stage, which wastes a few seconds in free fall. Lighting while still attached means the ship never stops pushing.

The ship's fire hits the top of the booster, so a steel shield and the vented ring were added to let the hot gas escape sideways instead of cooking the tank below.

Space starts at about 100 km up, but just getting that high isn't enough. Anything up there still falls. To stay up, you must go sideways so fast that as you fall, the curved Earth drops away beneath you just as fast. At about 7.8 km per second, that happens, and you circle the planet.

Three of the ship's engines are 'sea-level' Raptors with small bells, and three are 'vacuum' Raptors with much bigger bells, which work better in the empty space above the air.

The first catch happened on 13 October 2024, on Starship's fifth test flight. The booster came back about 7 minutes after launch, lit 13 engines to slow down, and the arms closed on two small pins just under the grid fins.

Why not just land on legs like smaller rockets? Legs strong enough for a 200-tonne booster are heavy. Leaving them off means more cargo, and a booster caught by the tower is already sitting right where it needs to be to fly again.

Steel is heavier than aluminium, so why use it? It is cheap (about 50 times cheaper than carbon fibre), easy to weld outdoors, and much stronger at the extreme temperatures a rocket goes through.

Each ring is rolled from a big flat sheet and welded closed. Stacked rings are then welded to each other. You can see those weld lines as faint stripes around the rocket.

The frost line shows exactly how full the tanks are: below it the metal touches super-cold liquid, above it there's only gas. Watch a launch video and you'll see the frost band climb as the tanks are filled.

Stainless steel's special trick is that its atoms are packed in a pattern that doesn't crack in the cold. Some normal steels shatter at low temperatures, which is thought to be part of why the Titanic's hull cracked in icy water.

Aluminium rockets must be kept cool with thick insulation, which adds weight. Steel's high melting point means only the side facing the heat needs a shield; the other side can stay bare.

Heat is really the speed of jiggling atoms. The hotter something gets, the harder its atoms shake, until they break free of each other and the solid melts. Steel's atoms hold on much tighter than aluminium's.

Most of the heat isn't from rubbing (friction). It comes from squeezing. The ship pushes air out of the way faster than the air can move, so it piles up in front, gets compressed, and compressed gas gets hot, just like a bike pump gets warm when you pump hard.

The tiles are mostly empty space: a foam of glass fibres full of air. Heat travels through them very slowly, so the steel behind stays cool enough. Each tile is held on by small metal pins, so a broken one can be swapped like a LEGO brick.

A falling object speeds up until the air pushing back on it equals its weight. That top speed is called terminal velocity. A long ship falling sideways shows far more area to the air than one falling nose-first, so its terminal velocity is much lower, a few hundred km/h near the ground.

The flaps are moved by electric motors. Tilting the front flaps more than the back ones pitches the nose up or down, and moving left and right flaps differently rolls the ship, just like a skydiver tilting a hand.

To flip, the engines tilt their thrust to swing the tail down, and the flaps fold to get out of the way. The last metres are flown on engine power alone, so the ship can touch down gently, or one day be caught by the tower, like the booster.

Every gram of propellant used for landing is a gram that can't carry cargo, so the landing burn is kept as short as possible. That's why the flip happens so late, and why it looks so dramatic.

A gas is atoms or molecules flying around far apart. Cool them down and they slow, until the tiny pulls between them win and they huddle together as a liquid. For methane, that happens at −161.5 °C.

As a liquid, methane takes up about 600 times less room than as a gas. Without turning it into a liquid, no tank could ever hold enough.

The oxygen tank is bigger because the engines burn about 3.6 kg of oxygen for every 1 kg of methane. Oxygen is also heavier, so it sits lower, which keeps the rocket's weight low down and stable.

Liquid oxygen is about 1.14 times as dense as water. It's slightly magnetic too: pour it between the poles of a strong magnet and it sticks there.

Because the liquids boil away, the rocket is filled only in the last ~40 minutes before launch, and topped up until the end. The gas that boils off is vented, which is why you see white clouds puffing from a waiting rocket.

SpaceX goes one step further: it cools the propellant a few degrees below its boiling point using heat exchangers full of liquid nitrogen. Colder liquid is denser, so more of it fits in the same tank. This is called subcooling.

Engineers call this autogenous pressurisation, which just means self-made pressure: each tank is pressed by its own gas. Hot methane gas goes back into the methane tank, hot oxygen gas into the oxygen tank. Many other rockets use helium for this, which is expensive and needs extra tanks.

Pressure also makes the thin steel tanks stiff, like a blown-up balloon. A safety vent at the top lets gas out if the pressure gets too high.

The dome curves downward because the methane is pressing down on it. A curved shape spreads the pressure out evenly, like an egg shell or a dam.

A common dome only works because methane and oxygen boil at similar temperatures. If one tank held something much colder (like liquid hydrogen at −253 °C), the shared wall would need thick insulation, or it would freeze the oxygen solid.

The downcomer is about as wide as a person and many metres long. It's a cold pipe inside a cold tank, so neither liquid gets warmed by passing the other.

At the bottom, the methane and oxygen both flow into a manifold, a branching set of pipes, that splits them out to all 33 engines.

An atom is the smallest piece of an element: carbon, hydrogen, oxygen. Atoms bond by sharing tiny particles called electrons. Different bonds hold different amounts of energy.

Methane is the simplest hydrocarbon, a molecule made of just hydrogen and carbon. Petrol and jet fuel are longer chains of the same two atoms.

Burning is just this grabbing. Oxygen breaks methane apart and holds on to its carbon and hydrogen instead. The new bonds are much stronger and tighter than the old ones, and the difference comes out as heat.

That's also why a fire goes out when it runs out of oxygen, and why a rocket must carry oxygen to burn where there is no air.

No atoms are created or destroyed: the 1 carbon, 4 hydrogens and 4 oxygens on the left are all still there on the right, just rearranged. Only the energy changes.

Each kilogram of methane burned with oxygen releases about 50 million joules: enough to boil about 150 litres of water from room temperature.

Why many small engines instead of a few huge ones? Smaller engines are easier to build and test, made on a production line, and if one fails, the others can make up for it.

Each Raptor engine is only about 1.3 m wide at the bottom of its bell and about 3 m tall, small enough to fit through a garage door.

A gimbal is a pivot that lets something swing in two directions. Hydraulic or electric actuators, like strong robot arms, push each engine to the angle the computer asks for.

A rocket is very top-heavy and unstable, like a pencil on a fingertip. Without constant steering it would tip over within seconds.

The outer engines only fire for launch. They don't need to restart in flight, so they skip some of the equipment the inner engines carry.

Engine-out tolerance: Starship can lose a few engines and still reach the right speed by burning the others longer. Early flights did exactly that.

A pump raises pressure. Its curved blades spin tens of thousands of times a minute, flinging liquid outward and squeezing it into the pipes. Raptor's pumps push the propellants up to several hundred times the air pressure around you.

Each pump needs tens of thousands of horsepower, more than a whole grid of Formula 1 cars. It gets that power from a turbine, a spinning wheel blown by the hot gas from a small fire called a preburner.

Higher pressure means more molecules hitting the walls every second, so more push from a smaller engine. Raptor 2 runs at about 300 bar, and Raptor 3 at about 350 bar. A car tyre is about 2 bar.

The injector mixes the liquids so they burn evenly. If one spot gets too much oxygen, the hot oxygen can start burning the engine's own metal. Uneven mixing is one of the classic ways rocket engines fail.

At the narrow neck (called the throat) the gas reaches the speed of sound. Strangely, for gas going faster than sound, a widening pipe makes it speed up even more, so the bell flares out to keep accelerating the exhaust.

The faster the exhaust leaves, the more push you get from each kilogram of propellant. Engineers call this 'specific impulse': how long one kilogram of propellant can keep pushing. Vacuum Raptors have much bigger bells to squeeze out extra speed where there's no air pushing back.

Hot oxygen-rich gas is fierce: it tries to burn the metal it touches. SpaceX had to invent a special metal mix, an alloy called SX500, that can survive it.

Because the turbine's gas goes into the main chamber afterwards, none of the propellant is wasted. In simpler engines, the turbine's gas is just dumped overboard.

Before reaching its preburner, the methane takes a detour down the engine to cool the nozzle and chamber walls (next step!). It arrives warmed up, which helps it burn smoothly.

Fuel-rich gas is much gentler on metal, but can leave soot. Methane makes very little soot, which is one reason SpaceX picked it.

Gas mixes faster than liquid, so two gases meeting burn quickly and evenly, which lets the chamber be shorter. And the turbines can run cooler, because each has a huge flow of gas to use, which makes the engine last longer.

Before Raptor, only two full-flow engines had ever been test-fired (a Soviet one in the 1960s and an American one in the 2000s), and neither flew. Raptor is the first to fly.

Heat always flows from hot to cold. The hotter the gas and the faster it moves, the faster heat flows into the wall. In a rocket chamber, every square centimetre takes in heat thousands of times faster than a stove top.

Engineers also leave a thin layer of slightly cooler, fuel-rich gas right next to the wall, called a film. It acts like a thin blanket between the flame and the copper.

This is called regenerative cooling. 'Regenerative' because the heat isn't wasted: it warms the methane that's about to be burned anyway, so the energy goes back into the engine.

The coolant must keep moving fast. If a channel gets blocked, its stretch of wall can melt in less than a second, which is why engines are full of filters.

Copper alone is soft and would burst under hundreds of bar. Steel alone would hold the pressure but couldn't pass the heat on fast enough, so its hot face would melt. Together they work.

The liner's hot face is only about a millimetre from the cold methane. Across that tiny gap, the temperature drops by hundreds of degrees.