You might picture a clear line where Earth ends and space begins. There is no sharp edge to Earth's atmosphere. The Karman line, set at 100 km (62 miles), is a convention, and scientists often say space begins there. A satellite is placed a few hundred or thousands of kilometres up, above the thick air that would slow it. There the rocket's engines give it a push, as if from the top of a very tall tower, to start its orbit. A satellite about 300 km (190 miles) above Earth goes around the planet once in about 90 minutes. A spacecraft in low Earth orbit travels about 17,500 miles per hour. To leave Earth for good, it must reach escape velocity, about 11.2 km per second.
Around 400 B.C., a Greek named Archytas is said to have flown a wooden pigeon, held on wires and pushed along by escaping steam. It was an early use of the action-reaction principle that rockets rely on. In 1232, at the battle of Kai-Keng, Chinese defenders drove back Mongol invaders with "arrows of flying fire", simple rockets. NASA gives that date for the first use of true rockets. In the 1500s a German fireworks maker, Johann Schmidlap, invented the step rocket: a big rocket carried a smaller one that kept climbing after the big one burned out.
The science of rocketry began with a book Isaac Newton published in 1687, usually called the Principia. It stated three principles of motion that govern objects on Earth and in space. Rockets work by Newton's third law. The rocket pushes its exhaust backward, and the exhaust pushes the rocket forward. A rocket burns fuel to make hot gas. A rocket engine works in space, where there is no air, because the rocket carries its own oxygen.
At liftoff, a rocket's push, called thrust, is stronger than its weight, so it rises off the launch pad. A rocket starts off slowly and goes faster and faster as it climbs. Most of a rocket's mass before launch is fuel and oxidizer, which together are called propellant. The more a rocket carries, the more fuel it needs, and the fuel itself is heavy. Rockets burn two kinds of fuel, liquid or solid. A solid rocket cannot be shut off once it is lit, but a liquid rocket's thrust can be controlled with valves.
A rocket that flew straight up would fall back to Earth when it ran out of fuel, so rockets tilt to the side as they climb. A rocket launched toward the east gets a boost from the speed of Earth's spin. Most rockets drop the parts of themselves that are used up, in pieces called stages. The Saturn V's first stage engines burned for about 2.5 minutes, taking the rocket and its payload to an altitude of about 38 miles. The Space Shuttle had three major parts: the Orbiter that carried the crew, a large External Tank holding fuel for the main engines, and two Solid Rocket Boosters that gave most of the lift in the first two minutes of flight.
In 1914, Robert Goddard received two patents, one for a liquid-fuel rocket and one for a multistage rocket. In 1915 he proved by experiment that a rocket can make thrust in a vacuum. On March 16, 1926, he launched the world's first liquid-fueled rocket in Auburn, Massachusetts. It rose only 41 feet. As his rockets got bigger, Goddard moved his tests to Roswell, New Mexico.
On October 4, 1957, the Soviet Union launched Sputnik, the first human-made satellite. Sputnik sent out a radio "beep-beep" signal that people around the world could hear. It fell back into Earth's atmosphere and burned up on January 4, 1958. In April 1961, Yuri Gagarin of the Soviet Union was the first person in space. On July 16, 1969, a Saturn V rocket launched the Apollo 11 astronauts on their way to the Moon. The Saturn V stood 363 feet tall, taller than the Statue of Liberty.
The Space Shuttle was reusable. Its orbiter landed on a runway, and its solid rocket boosters were recovered from the sea. The second stage of a Falcon 9 went on to launch communications satellites into low Earth orbit. As of November 2026, the first stage of a Falcon 9 rocket can land upright after launch, so it can be flown again. SpaceX landed one on a landing pad near its Florida launch site.
Words to know
- thrust: a rocket's push
- propellant: fuel and oxidizer
- stages: used-up rocket parts
- satellite: goes around Earth
