Full-scale launchers rely on a sophisticated guidance system to balance and steer during flight, and the rocket's thrust is gimbaled, or rotated, to produce maneuvers. Some full-scale rockets can move (gimbal) their nozzles, making a force that is not lined up with the center of gravity. The resulting torque about the center of gravity is used to steer the rocket. 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 to steer. The narrowest part of a rocket nozzle is called the throat. There the hot exhaust is choked: its Mach number equals 1.0. 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.
As the height of an orbit increases, the speed needed to stay in orbit decreases. A spacecraft in a lower orbit must travel faster than one in a higher orbit. 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). Heavier payloads and higher or interplanetary orbits need more power to fight Earth's gravity than lighter payloads and lower orbits. 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.
The rocket equation, also called the Tsiolkovsky rocket equation after Konstantin Tsiolkovsky (1857-1935), describes the motion of a vehicle that accelerates itself by expelling part of its mass. 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. Most of a rocket's mass before launch is fuel and oxidizer, which together are called propellant.
In 1955 the U.S. Air Force hired Rocketdyne to build an engine of 1 million pounds of thrust to launch future satellites. After Sputnik and the creation of NASA the F-1 was pushed on to 1.5 million pounds, and it first fired as a prototype in 1961. The F-1 engine had combustion instability: pressure swings in the burning propellants made hot spots and vibrations strong enough to destroy it, and in 1961 it caused a test engine meltdown. Engineers solved it by adding copper baffles to the injector plate. Von Braun, who helped develop the German V-2 and later came to the United States, played a significant role in the development of the Saturn rockets that took people to the Moon between 1968 and 1972.
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. 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, stayed attached in Earth orbit, then its J-2 engine reignited to send Apollo toward the Moon. 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. At launch the Saturn V was the largest and most powerful launch vehicle the United States had ever built.
Launches from the US east coast (Kennedy Space Center) are suitable only for low-inclination orbits, because major population centers lie under the path needed for high-inclination launches. High-inclination launches go from Vandenberg in California, where the path avoids population centers. 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. 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.
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 Space 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. 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.
As of November 2026, NASA's Space Launch System (SLS) first flew on November 16, 2022, on the uncrewed Artemis I test flight, making it the most powerful rocket NASA had launched. SLS uses its four RS-25 engines and twin boosters together: in about eight minutes the core stage burned 735,000 gallons of liquid propellant for two million pounds of thrust, while the boosters made more than seven million pounds. At launch its Block 1 makes 8.8 million pounds of thrust, 15% more than the Saturn V. NASA's launch pad sound suppression system dampens the sound and vibration of liftoff to keep the rocket and pad safe, with 450,000 gallons of water released onto the mobile launcher and flame deflector.
As of November 2026, 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. Its core stage is 32 m tall and powered by one Vulcain 2.1 engine burning liquid oxygen and hydrogen for 138 tonnes of thrust. It propels the rocket for the first 10 minutes of flight, up to about 200 km. The upper stage uses the restartable Vinci engine and can fire up to four times, dropping passengers into different orbits on one flight, then deorbit itself to avoid becoming space debris. The Falcon 9 medium-lift rocket can carry payloads of up to 22,800 kg into low Earth orbit.
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. 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 the first stage of a Falcon 9 upright on a landing pad near its Florida launch site while the second stage went on to launch communications satellites into low Earth orbit.
Words to know
- gimbal: swivel to steer
- baffles: copper injector fix
- propellant: fuel and oxidizer
- throat: narrowest nozzle part
