The principles of rocketry were first tested more than 2,000 years ago, but it's really only been in the past 70 years or so that these machines have been used for applications in space exploration. Today, rockets routinely take spacecraft to other planets in our solar system. Closer to Earth, rockets carrying supplies up to the International Space Station can return to Earth, land on their own and be used again.
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.
Around 300 years after the pigeon experiment, Hero of Alexandria is said to have invented the aeolipile (also called Hero's engine), 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 by the escaping steam made the sphere rotate.
Historians believe the Chinese developed the first real rockets around the first century A.D. They were used for colorful displays during religious festivals, similar to modern fireworks.
For the next few hundred years, rockets were mainly used as military weapons, including a version called the Congreve rocket, developed by the British military in the early 1800s.
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. Only one of the three 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 the propellant system's exhaust and how much propellant there is. Tsiolkovsky also published a theory of multistage rockets in 1929.
Robert Goddard (1882-1945) was an American physicist who sent the first liquid-fueled rocket aloft in Auburn, Massachusetts, 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.
Hermann Oberth (1894-1989) was born in Romania and later moved to Germany. According to NASA, he became interested in rocketry at an early age, and at age 14 he imagined 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 tainted by the fact that he helped develop the V-2 rocket for Nazi Germany during World War II; the rocket was used for devastating bombings on London. Oberth lived for decades after space exploration began and saw rockets bring people all the way to the moon and watched the reusable space shuttle heft crews into space again and again.
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. In that contest, both countries vied to demonstrate technological and military superiority, 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 Nuclear Test Ban Treaty.
While rockets worked well within Earth's atmosphere, figuring out how to send them into space was difficult. Rocket engineering was in its infancy and computers weren't powerful enough to perform simulations. This meant that numerous flight tests ended with the rockets dramatically exploding seconds or minutes after leaving the launchpad.
With time and experience, however, progress was made. A rocket was used for the first time to send something into space on the Sputnik mission, which launched a Soviet satellite on Oct. 4, 1957. After a few 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 either country felt confident enough to use rockets to send people into space; both countries started with animals (monkeys and dogs, for example). Russian cosmonaut Yuri Gagarin was the first human in space, leaving Earth on April 12, 1961, aboard a Vostok-K rocket for a multiorbit flight. About three weeks later, Alan Shepard made the first American suborbital flight on a Redstone rocket. A few years later in NASA's Mercury program, the agency switched to Atlas rockets to achieve orbit, and in 1963, John Glenn became the first American to orbit Earth.
When aiming for the moon, NASA used the Saturn V rocket, which, at 363 feet tall, included three stages — the last one designed to be powerful enough to break away from Earth's gravity. The rocket successfully launched six moon-landing missions between 1969 and 1972. The Soviet Union developed a moon rocket called N-1, but its program was permanently suspended after multiple delays and problems, including a deadly explosion.
NASA's space-shuttle program (1981 to 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-fueled 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.
Rockets have since been used to send spacecraft farther into our solar system: past the moon, Venus and Mars in the early 1960s, which later expanded into the exploration of dozens of moons and planets. Rockets have carried spacecraft throughout the solar system so that astronomers now have imagery of every planet (as well as the dwarf planet Pluto), many moons, comets, asteroids and smaller objects. And, because of powerful and advanced rockets, the Voyager 1 spacecraft was able to leave our solar system and reach interstellar space.
Rockets of the future
Several companies in many countries now manufacture uncrewed rockets — the United States, India, Europe and Russia, to name a few — and routinely send military and civilian payloads into space.
And scientists and engineers are continually working toward developing even more sophisticated rockets. Stratolaunch, the aerospace design company backed by Paul Allen and Burt Rutan, aims to launch satellites using civilian aircraft. SpaceX and Blue Origin have also developed reusable first-stage rockets; SpaceX now has reusable Falcon 9 rockets that routinely make cargo runs to the International Space Station. [In Photos: SpaceX's 1st Falcon Heavy Rocket Launch Success!]
Experts predict that rockets of the future will be able to carry bigger satellites into space and may be able to carry multiple satellites at the same time, the Los Angeles Times reported. These rockets could use new composite materials, advances in electronics or even artificial intelligence to perform their work. Future rockets may also use different fuels — such as methane — that are healthier for the environment than the more traditional kerosene that is used in rockets today.