How Do We Launch Things Into Space?

Satellites and spacecraft are sent into space using rockets powered by large amounts of propellant. This fuel provides the energy needed for the rocket to escape Earth’s surface. Due to Earth’s gravitational pull, heavier and larger spacecraft require more powerful rockets and greater quantities of fuel.

How does a rocket take off?

Over 300 years ago, Isaac Newton introduced three fundamental laws of motion. One of these states that every action has an equal and opposite reaction—this principle is key to understanding how rockets operate.

During a launch, you can observe flames, gases, and smoke shooting out from the bottom of the rocket. This is known as exhaust, produced by burning the rocket’s fuel.

As the exhaust is expelled downward (the action), it creates a force that pushes the rocket upward in the opposite direction (the reaction), allowing it to lift off the ground.

Does a rocket keep moving after launch?

The process is not that straightforward. Earth’s gravity continues to pull the rocket downward. When the rocket burns fuel and expels exhaust, it generates an upward force called thrust. For a successful launch, this thrust must be stronger than the downward pull of gravity.

To remain in space, a rocket must accelerate to at least about 17,800 miles per hour and travel above most of Earth’s atmosphere along a curved path. This prevents it from falling back to the surface. What happens next depends on the mission’s destination.

How do satellites stay in orbit?

If the goal is to place a satellite into orbit, the rocket carries it to a certain altitude before releasing it.

The satellite continues moving because of momentum—the energy gained during launch—while Earth’s gravity pulls it inward. The balance between these two forces keeps the satellite circling the planet.

Satellites closer to Earth experience stronger gravitational pull and therefore must travel faster to stay in orbit compared to those farther away.

For example, the International Space Station orbits about 250 miles above Earth and moves at roughly 17,150 miles per hour. In contrast, Tracking and Data Relay Satellites orbit much higher—over 22,000 miles—and travel more slowly, at around 6,700 miles per hour, to maintain their position.

How do rockets reach other planets?

Traveling to another planet requires even greater speed to escape Earth’s gravity—around 25,000 miles per hour. Timing is also critical.

Take Mars as an example: Earth and Mars come closest to each other roughly every two years. This period is ideal for launching missions because it requires less fuel and time. Even then, the launch must be precisely timed so the spacecraft and the planet arrive at the same point in space simultaneously.

Planning becomes even more complex for missions to the outer solar system. For instance, a spacecraft heading toward Saturn might be routed past other planets like Mars or Jupiter to take advantage of gravitational assists along the way.