By 1908 Robert Goddard had concluded that magnetic, atomic, cannon, flywheel and solid-fuel launch methods were impractical, and that only liquid fuels, and then only the easier-to-handle ones, offered a feasible path to orbit. He found that gunpowder rockets, which had existed for almost 1,000 years, did not generate enough thrust to reach space. He calculated that liquid oxygen with liquid hydrogen gives the best specific impulse (Isp), a measure of a rocket engine's efficiency: the thrust produced per weight of propellant used each second. But he chose liquid oxygen with gasoline because it was less volatile and so more practical. In 1919 the Smithsonian published his study "A Method of Reaching Extreme Altitudes", in which he argued from a firm theoretical base that only liquid-fueled rockets could reach the upper atmosphere and Earth orbit.
In 1914, 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, and it rose only 41 feet. He also worked out how to steer a rocket: in April 1932 he ran a brief test in which a rocket's flight path was primitively but successfully controlled with gyroscopic technology. His designs, including gyroscopic control, steering by vanes in the exhaust jet, gimbal steering and power-driven fuel pumps, shared many similarities with those developed by German rocket engineers in the 1930s and during World War II.
Historians do not agree about how much Goddard mattered. Some credit Goddard as an inspiration but say he contributed little to modern rocketry, while the National Park Service says the significance of his research was fully recognized only after the German V-2 appeared in 1943. 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).
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, 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 solid-propellant rockets, the date NASA gives 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, which stated three principles of motion that govern objects on Earth and in space.
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. The faster a rocket throws mass out, the faster it can move forward, and the equation's delta-v is the greatest change of speed a rocket can get by expelling some of its mass, if no outside forces act. As of November 2026, the highest exhaust speed is around 4.5 km per second for liquid-propellant engines and about 2.5 km per second for solid-propellant rockets, while non-chemical systems such as ion engines can reach about ten times more. Ion engines, powered by photovoltaics or nuclear reactors, are not for the launch phase; they are useful for gently but steadily accelerating a spacecraft that is already in Earth orbit or beyond.
The convergent-divergent (CD) nozzle at the heart of a modern rocket engine was developed in the 19th century by Swedish inventor Gustaf de Laval, who was working on a more efficient steam engine. The narrowest part of a rocket nozzle is called the throat, and there the hot exhaust is choked: its Mach number equals 1.0. The area ratio from a nozzle's throat to its exit sets the exhaust's exit velocity and exit pressure. A rocket's thrust must also account for the exit pressure of its exhaust: it equals free-stream pressure only at some design conditions, so engineers use the longer generalized thrust equation, which includes a pressure term. A Space Shuttle main engine made 375,000 pounds of thrust at sea level but 470,000 pounds in a vacuum, burning liquid oxygen and liquid hydrogen at a mixture ratio of 6 to 1.
Liquid propellants are fairly dense, so their tanks can be relatively small and light, and that gives a high mass ratio, which is part of why large launchers use liquid-fuel stages. Most of a rocket's mass before launch is fuel and oxidizer, which together are called propellant. 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.
At a 100-mile-high orbit around Earth the orbital velocity is 17,478 mph, and launched from the Moon or Mars, a rocket would need a different orbital speed because those worlds have different radius and gravity. As the height of an orbit increases, the speed needed to stay in orbit decreases, so a spacecraft in a lower orbit must travel faster than one in a higher orbit. Escape velocity for a planet does not depend on the mass of the rocket: it is about 11.2 km per second for Earth, and it depends on the planet, so leaving the Moon takes less speed than leaving Earth, and Jupiter's is many times Earth's. Sitting on a launch pad near the equator, a rocket is already moving at over 1,650 km per hour with Earth's spin. A launch vehicle that accelerates generally in the direction of Earth's orbital motion adds that motion, an average of about 100,000 km per hour along Earth's path around the Sun, to the speed it gets from Earth's rotation.
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. In 2011 a Soyuz rocket launched from Europe's Spaceport in French Guiana for the first time, lofting the first two Galileo navigation satellites into orbit. The Soyuz-2 launcher could place up to 3 tonnes into geostationary transfer orbit, compared to the 1.7 tonnes that could be launched from Baikonur in Kazakhstan.
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. 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, and its first stage engines burned for about 2.5 minutes, taking the rocket and its payload to an altitude of about 38 miles.
After the Saturn V's 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, and two hours, 44 minutes after launch, 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. 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.
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, and it sent out a radio "beep-beep" signal that people around the world could hear. Sputnik 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, and from the start, the plan was that Gagarin would not land inside his Vostok spacecraft after his April 12, 1961 orbit.
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, and 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 Ariane 6 booster motor, the P120C, holds about 142 tonnes of solid propellant and gives about 4500 kN of maximum thrust, and it also serves as the first-stage motor of Vega-C, burning for 130 seconds up to about 70 km.
As of November 2026, the Falcon 9 medium-lift rocket can carry payloads of up to 22,800 kg (about 50,000 pounds) 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.
Words to know
- gimbal: swivel to steer
- propellant: fuel and oxidizer
- nozzle: engine's exhaust outlet
- baffles: copper injector fix
