Three-stage-to-orbit

The "three-stage-to-orbit" is like when you play with your toy rocket ship and make it go up into space. Except, it's a real rocket ship and it has three parts that help it get into space instead of just one.

The first part is called the "booster" and it's like the engine that helps the rocket get off the ground. It's super powerful and helps push the rocket up into the sky really fast.

The second part is the "orbiter" and it's like the middle of the rocket. It helps the rocket stay in space and move around once it gets up there.

The third and final part is the "lander" and it's like the bottom of the rocket. This part helps the rocket land back on Earth safely once it's done exploring space.

So, the "three-stage-to-orbit" means that the rocket ship has three parts that work together to get it up into space and safely back down to Earth again.