A rocket burns fuel to make hot gas. Rockets work by Newton's third law. The rocket pushes the gas backward, and the gas pushes the rocket forward. 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.
Scientists often say space begins at the Karman line, 100 km (62 miles) above sea level. Rockets launch satellites into orbit around Earth. 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, or about 7.8 km per second. To leave Earth for good, a spacecraft must reach escape velocity, about 11.2 km per second (7 miles per second). A rocket launched toward the east gets a boost from the speed of Earth's spin.
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.
The first known rockets were used in China in the 1200s. 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.
Most rockets drop the parts of themselves that are used up, in pieces called stages. The Space Shuttle was reusable. Its orbiter landed on a runway. Its solid rocket boosters were recovered from the sea. 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 pad near its Florida launch site while the second stage went on to launch communications satellites into low Earth orbit.
Words to know
- thrust: a rocket's push
- propellant: fuel and oxidizer
- stages: used-up rocket parts
- satellite: goes around Earth
