Today, rockets routinely take astronauts into space, launch satellites and do tests in the upper atmosphere. But it's really only been in the past 70 years or so that these machines have been used for applications leading to space exploration.
The principles of rocketry were tested out more than 2,000 years ago, and it was a long road through military and other applications before people were launched on these machines. A bit about the history of rocketry is below.
There are tales of rocket technology being used thousands of years ago. For example, around 400 B.C., Archytas, a Greek philosopher and mathematician, showed off a wooden pigeon that was suspended on wires. The pigeon was pushed around by escaping steam, according to NASA.
Roughly 300 years after the pigeon experiment, Hero of Alexandria is said to have used an aeolipile, NASA added. The sphere-shaped device sat on top of a boiling pool of water. Gas from the steaming water went inside of the sphere, and escaped through two L-shaped tubes on opposite sides. The thrust created made the sphere rotate.
The Chinese are recorded as using the first real rockets around the first century A.D.. They were used for colorful displays during religious festivals, sort of like today's fireworks. It appears that the first rocket propulsion systems were used between the years 1200 and 1300 in Asia, using a propellant that included a mix of saltpeter, sulfur and charcoal, according to Encyclopedia Britannica.
For the next few hundred years, rockets were mainly used for military purposes, including a version called the Congreve rocket in the early 1800s. As guns became more effective, the use of rockets was reduced until World War II, when the Germans used their V-2 rockets routinely to bombard Britain from the safety of their own country.
Fathers of rocketry
In the modern era, those who work in spaceflight today often acknowledge three “fathers of rocketry” who helped push the first rockets into space. Of those three people, however, only one of them survived long enough to see rockets being used for space exploration.
Russian Konstantin E. Tsiolkovsky (1857-1935) published what is now known as the “rocket equation” in 1903, in a Russian aviation magazine, according to NASA. The equation concerns relationships between rocket speed and mass, as well as how fast the gas is leaving when it exits and how much propellant there is. He also published a theory of multistage rockets in 1929.
Robert Goddard (1882-1945) is an American who sent the first liquid-fueled rocket aloft in Auburn, Mass., on March 16, 1926. He had two U.S. patents for using a liquid-fueled rocket, and also for a two- or three-stage rocket using solid fuel, according to NASA. However, his research received scathing attention from the media (including the New York Times) and Goddard died before seeing his work vindicated. The New York Times published a correction to its work in 1969, one day after Apollo 11 embarked on the first moon-landing mission.
Hermann Oberth (1894-1989) was born in Romania and later moved to Germany. He became interested in rocketry at an early age, NASA wrote, and at age 14 thought about a "recoil rocket" that could move through space using nothing but its own exhaust. As an adult, his studies included multistage rockets and how to use a rocket to escape Earth's gravity. (His legacy is mixed as he also helped to develop the V-2 rocket for Nazi Germany during World War II.)
Rockets in spaceflight
Following World War II, several German rocket scientists emigrated to both the Soviet Union and the United States, assisting those countries in the Space Race of the 1960s. The contest was one to demonstrate military superiority, in part becoming a battle of capitalism vs. communism using space as the frontier.
Rockets were also used to take measurements of radiation in the upper atmosphere after nuclear tests. The nuclear explosions mostly ceased after 1963's Limited Test Ban Treaty.
While rockets looked great on paper, figuring out how to send things into space on them was difficult. Engineering was in its infancy and computer simulations were not available, meaning that numerous flight tests ended with the rockets dramatically exploding seconds or minutes after leading the pad.
With time and experience, however, progress was made. The first time a rocket was used to send something into space was the Sputnik mission, which sent a Soviet satellite aloft on Oct. 4, 1957. After some failed attempts, the United States used a Jupiter-C rocket to heft its Explorer 1 satellite into space on Feb. 1, 1958.
It took several more years before the countries felt confident enough to use rockets to send people into space, with animal tests taking place on both sides (using monkeys and dogs, for example). Yuri Gagarin was the first human in space, leaving Earth on April 12, 1961, aboard a Vostok-K rocket for a multi-orbit flight. About three weeks later, Alan Shepard followed for a suborbital flight on a Redstone rocket. Later in NASA's Mercury astronaut program, it switched to Atlas rockets to achieve orbit.
When both countries were ready for the moon, NASA used the Saturn V rocket, which at 363 feet tall included three stages — the last one designed to break Earth's gravity. The rocket was successfully used to launch six moon-landing missions between 1969 and 1972. The Soviet Union was also developed a moon rocket called N-1, but a prototype exploded and destroyed much of the surrounding area, effectively halting the program.
Rockets were gradually used to send spacecraft through the solar system, with early, hesitant attempts to go past the moon, Venus and Mars in the early 1960s expanding into exploration of dozens of moons and planets. Today, thanks to rocketry, we've been able to breach the solar system's barrier with the Voyager 1 spacecraft. And we have spacecraft imagery of every planet, dozens of moons, and many comets, asteroids and smaller objects.
Rockets in the past few decades
NASA's space shuttle program (1981-2011) used solid rockets for the first time to boost humans into space, which is notable because unlike liquid rockets, they cannot be turned off. The shuttle itself had three liquid-fuelled engines, with two solid rocket boosters strapped on the sides. In 1986, a solid rocket booster's O-ring failed and caused a catastrophic explosion, killing seven astronauts aboard the space shuttle Challenger. The solid rocket boosters were redesigned after the incident.
The space shuttle was once envisioned as the way to make space missions less expensive, and the Department of Defense used shuttle missions for several years to heft its satellites. After the Challenger explosion, however, DOD switched back to uncrewed rockets. There are now several providers around the world — in the United States, India, Europe and Russia, to name a few — that routinely send military and civilian payloads into space.
With the invention of smaller satellites such as CubeSats, it's now common for rockets to carry one big, main payload and several smaller ones at cheaper cost. And there are other advances for rockets on the horizon. DARPA, for example, is considering using rockets to launch satellites from a flying military craft. And SpaceX is testing a reusable first-stage rocket for its Falcon 9 booster, which could make the cost of space exploration cheaper in the long run.