Why Do Rockets Have Multiple Stages?

“Byeoli, what are those lines on the rocket? It looks like it’s split into pieces.”

“That’s right, those mark the rocket’s separate stages. Most rockets are built from several sections, usually a first, second, and third stage.”

“Why not just build it as one solid piece instead of splitting it up?”

“Once a rocket burns through its fuel, that empty tank becomes nothing but dead weight. Dragging an empty fuel tank along takes extra effort to keep flying. So once a stage runs dry, it gets dropped without hesitation. That makes the remaining rocket much lighter, so it needs less power to keep speeding up.”

Hyeongseop imagined the rocket soaring upward, dropping its huge lower tank behind it.

“So what happens after the first stage drops away?”

“The second stage ignites and pushes upward with fresh power. This process repeats, getting lighter stage by stage while a new engine takes over the push each time, until the rocket reaches faster and faster speeds all the way up to space.”

“Do the dropped tanks just get thrown away?”

“They used to just fall into the ocean and get abandoned. But reuse technology has improved a lot recently. Some rockets have a first stage that reignites its engine after finishing its job and lands upright, either on the ground or on a ship floating at sea. Then that stage can be repaired and flown again on a future launch.”

“Whoa, so rockets get recycled too?”

“Exactly. Building a single rocket costs an enormous amount of money. So if a used stage can fly again, it cuts the cost of reaching space dramatically. Thanks to that, rockets can launch much more often these days than they used to.”

“Do landings ever fail?”

“Definitely, they used to. Early on, while developing this technology, rockets toppled over or exploded more than once. But every failure got analyzed and fixed a little more each time, and now nearly every landing succeeds. It’s the result of not fearing failure and just kept trying.”

“What’s left once all three stages are used up?”

“In the end, only the real payload remains, the spacecraft or satellite that was actually meant to reach space. Only after shedding every heavy shell does the most important part finally arrive at its destination.”

Hyeongseop pictured the rocket rising into the sky, setting down one heavy piece after another, growing lighter with each step. Somehow, the idea that shedding heavy things was what let it climb higher and farther didn’t feel like it was only true for rockets.