Reaching space and reaching orbit are different. Orbital flight is a combination of altitude and horizontal velocity. The SpaceShipOne flight reached the altitude to "go into space" but lacked the horizontal velocity to "go into orbit". Scientists often say space begins at the Karman line, 100 km (62 miles) above sea level. You might picture a clear line you could see, but there is no sharp edge to Earth's atmosphere. The role of a launcher is first to pass through the atmosphere with its cargo, and then to provide the horizontal velocity push necessary to get into orbit. Aerodynamic forces matter little for satellite launchers: the rocket gets out of the atmosphere as quickly as possible, then gains the sideways velocity it needs to stay in orbit.

In flight a rocket is acted on by four forces: weight, thrust, lift and drag. On an airplane lift overcomes weight, but on a rocket thrust works against weight and lift is often used only to stabilize and control the direction of flight. Rockets work by Newton's third law. The rocket pushes its exhaust backward, and the exhaust pushes the rocket forward. A rocket in airless space must carry its own oxidizer, which weighs far more than the fuel. So the rocket first has to lift not just its payload but also the much greater weight of its propellant. The propellant needed to launch a payload into Earth orbit is usually at least 20 times more massive than the payload itself.

A rocket's mass shrinks as its engines burn off propellant, so its acceleration has to increase. That is why a rocket starts off moving slowly and goes faster and faster as it climbs into space. At liftoff, a rocket's push, called thrust, is stronger than its weight, so it rises off the launch pad. The thrust of a rocket engine depends on the mass flow rate through the engine, the exit velocity of the exhaust, and the pressure at the nozzle exit. All three depend on the design of the nozzle. In space there is no air and so no air friction, so once a satellite is in orbit gravity lets it circle Earth with almost no further help from engines.

Staging: several minutes into the ascent most launchers discard weight, and often light a second engine on an upper stage. The first stage can be retrieved, as with the Space Shuttle's boosters, or thrown away, as on the Apollo moon rockets. On an Ariane 5 flight, the boosters separated about 2 minutes up at around 60 km. The main stage burned for about 12 minutes. During a roughly 13-minute upper-stage burn the launcher reached its highest velocity, around 8 km per second. Most rockets drop the parts of themselves that are used up, in pieces called stages.

Sitting on a launch pad near the equator, a rocket is already moving at over 1,650 km per hour with Earth's spin. Compared to a far-from-the-equator launch, the same vehicle needs less propellant or can lift a more massive spacecraft. A rocket launched toward the east gets a boost from the speed of Earth's spin. 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. To reach Earth orbit, a rocket must go about 8 km (5 miles) per second. To leave Earth for good, a spacecraft must reach escape velocity, about 11.2 km per second (7 miles per second).

The Saturn V's first stage used five F-1 engines with a total thrust of 7.5 million pounds, arranged with a fixed center engine and four outer engines that could swivel (gimbal) to steer. The first stage engines burned for about 2.5 minutes, taking the rocket and its payload to an altitude of about 38 miles. After the second stage, the third stage burned about 2.75 minutes to reach an orbital speed of about 17,500 mph. It was shut down with fuel left and stayed attached in Earth orbit, ready for its J-2 engine to reignite. At launch the Saturn V was the largest and most powerful launch vehicle the United States had ever built.

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. The Shuttle's three main engines made a combined thrust of more than 1.2 million pounds, and its two solid rocket boosters made some 5.8 million pounds. The external tank fed the engines liquid hydrogen fuel and liquid oxygen. The Space Shuttle was reusable. Its orbiter landed on a runway, and its solid rocket boosters were recovered from the sea.

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. The German V-2 was the world's first large-scale liquid-propellant rocket vehicle and the first long-range ballistic missile, and it is the ancestor of today's large rockets. In 1949 the "Bumper-WAC", a small WAC Corporal missile riding on a German-made V-2, became the first human-made object to enter space, climbing to 393 kilometers (244 miles).

Sputnik was launched on an R-7 rocket that Soviet designer Sergei Korolev's team had built as an intercontinental ballistic missile, to put a scientific satellite into orbit before the end of 1957. 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. Reactions in the United States to Sputnik included shock and amazement and led to Congressional hearings that ultimately created NASA in 1958.

In April 1961, Yuri Gagarin of the Soviet Union was the first person in space. From the start, the plan was that Gagarin would not land inside his Vostok spacecraft after his April 12, 1961 orbit. Apollo 11 lifted off on a Saturn V rocket on July 16, 1969. Two hours, 44 minutes after Apollo 11 launched, the Saturn V's third stage fired a second time for five minutes, 48 seconds. That sent the spacecraft toward the Moon.

As of November 2026, the first stage of a Falcon 9 rocket can land upright after launch, so it can be flown again. The Falcon 9 medium-lift rocket can carry payloads of up to 22,800 kg (about 50,000 pounds) into low Earth orbit. Ariane 6, Europe's rocket, comes in two versions: Ariane 62 with two boosters, which can launch about 10.3 tonnes into low Earth orbit, and Ariane 64 with four boosters. NASA's Space Launch System first flew on November 16, 2022, on the uncrewed Artemis I test flight. At launch its Block 1 makes 8.8 million pounds of thrust, 15% more than the Saturn V.

Words to know

• thrust: a rocket's push
• propellant: fuel and oxidizer
• gimbal: swivel to steer
• payload: the cargo