Two Stage Rockets (Rocket Motor)

A two stage rocket is a vehicle made of mo rockets stacked on top of one another. The lower rocket, called the first stage, or booster, fires first, lifting and accelerating the entire assembly until it burns out and falls away. Then the upper rocket, called the second stage, fires, and continues on to the intended altitude. Two stage rockets are a challenge to build, and interesting to fly. To an inexperienced observer the rocket goes through a normal lift-off-accelerate-coast sequence. Then to the observer’s surprise, the booster drops off and parachutes back to the ground, while the second stage fires, repeats the accelerate-coast sequence, and releases its own parachute at a higher altitude.
The advantage of a two stage rocket is that, by the time the second stage fires, it is already high in the air and moving rapidly upward. The result is that the combination reaches a greater altitude than either rocket would have reached on its own. Figure 2-13 is a cutaway drawing of a two stage rocket as it appears before ignition. If you look closely, you’ll see a small pipe extending from the hole in the booster’s forward bulkhead into the core of the second stage motor. It’s made out of paper, but a soda straw will work. I call it a flame tube, and it transfers the fire from the front of the booster into the core of the second stage motor. I’ll discuss it later in detail.
In Figure 2-14 the rocket is lifting off the ground. In Figure 2-15 the rocket is in full flight, and most of the booster’s propellant has been consumed. In Figures 2-16 and 2-17 the booster and the second stage have separated. The flame tube has transferred the fire from the booster’s motor into the second stage motor. The second stage motor has ignited, and the second stage is on its way.