Space pioneers were challenged by Earth’s gravity field, and the unknown space environment. In order to get into space, scientists had to create launch vehicles, electronics, guidance, and control systems.

Launch vehicles are rockets in three or four parts, or stages. They provide the power needed to launch spacecraft and satellites. Each stage is designed to fall away once the craft has reached a certain height or speed.

Although early rockets had only one stage, no single-stage rocket could reach the orbital velocity needed to escape Earth’s gravitational pull. Multistage rockets were necessary for space exploration. In these systems, two or more rockets are assembled in tandem and ignited in turn; once the lower stage’s fuel is exhausted, it detaches and falls back to earth.

The first stage rocket is the biggest, because it has to lift the weight of the entire rocket and its fuel off the ground. Once the rocket is several miles in the air, the fuel of the first stage is used up, and the stage I rocket falls away.

Then smaller second stage engines take over to propel the rest of the rocket out of the atmosphere. The third stage gives the rocket its final push to free it from Earth’s gravity. Depending on the weight and where it needs to go, some rockets even have a fourth stage that helps position the satellite into orbit.