Prelude to spaceflight

Precursors in fiction and fact

Since ancient times, people around the world have studied the heavens and used their observations and explanations of astronomical phenomena for both religious and practical purposes. Some dreamed of leaving Earth to explore other worlds. For example, the French satirist Cyrano de Bergerac in the 17th century wrote Histoire comique des états et empires de la lune (1656) and Histoire comique des états et empires du soleil (1662; together in English as A Voyage to the Moon: With Some Account of the Solar World, 1754), describing fictional journeys to the Moon and the Sun. Two centuries later the French author Jules Verne and the English novelist and historian H.G. Wells infused their stories with descriptions of outer space and of spaceflight that were consistent with the best understanding of the time. Verne’s De la Terre à la Lune (1865; From the Earth to the Moon) and Wells’s The War of the Worlds (1898) and The First Men in the Moon (1901) used sound scientific principles to describe space travel and encounters with alien beings.

In order to translate these fictional images of space travel into reality, it was necessary to devise some practical means of countering the influence of Earth’s gravity. By the beginning of the 20th century, the centuries-old technology of rockets had advanced to the point at which it was reasonable to consider their use to accelerate objects to a velocity sufficient to enter orbit around Earth and even to escape Earth’s gravity and travel away from the planet.

Tsiolkovsky

The first person to study in detail the use of rockets for spaceflight was the Russian schoolteacher and mathematician Konstantin Tsiolkovsky. In 1903 his article “Exploration of Cosmic Space by Means of Reaction Devices” laid out many of the principles of spaceflight. Up to his death in 1935, Tsiolkovsky continued to publish sophisticated studies on the theoretical aspects of spaceflight. He never complemented his writings with practical experiments in rocketry, but his work greatly influenced later space and rocket research in the Soviet Union and Europe.

Goddard

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In the United States, Robert Hutchings Goddard became interested in space exploration after reading works such as The War of the Worlds. Even as a young man, he dedicated himself to working on spaceflight. In his 1904 high-school graduation speech, he stated that “it is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow.” Goddard received his first two patents for rocket technology in 1914, and, with funding from the Smithsonian Institution, he published a theoretical treatise, A Method of Reaching Extreme Altitudes, in 1919. Goddard’s claim that rockets could be used to send objects as far as the Moon was widely ridiculed in the public press, including The New York Times (which published a retraction on July 17, 1969, the day after the launch of the first crewed mission to the Moon). Thereafter, the already shy Goddard conducted much of his work in secret, preferring to patent rather than publish his results. This approach limited his influence on the development of American rocketry, although early rocket developers in Germany took notice of his work.

In the 1920s, as a professor of physics at Clark University in Worcester, Massachusetts, Goddard began to experiment with liquid-fueled rockets. His first rocket, launched in Auburn, Massachusetts, on March 16, 1926, rose 12.5 metres (41 feet) and traveled 56 metres (184 feet) from its launching place. The noisy character of his experiments made it difficult for Goddard to continue work in Massachusetts. With support from aviator Charles A. Lindbergh and financial assistance from the philanthropic Daniel Guggenheim Fund for the Promotion of Aeronautics, he moved to Roswell, New Mexico, where from 1930 to 1941 he built engines and launched rockets of increasing complexity.

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Famous Astronauts and Cosmonauts

Oberth

The third widely recognized pioneer of rocketry, Hermann Oberth, was by birth a Romanian but by nationality a German. Reading Verne’s From the Earth to the Moon as a youth inspired him to study the requirements for interplanetary travel. Oberth’s 1922 doctoral dissertation on rocket-powered flight was rejected by the University of Heidelberg for being too speculative, but it became the basis for his classic 1923 book Die Rakete zu den Planetenräumen (“The Rocket into Interplanetary Space”). The work explained the mathematical theory of rocketry, applied the theory to rocket design, and discussed the possibility of constructing space stations and of traveling to other planets.

In 1929 Oberth published a second influential book, Wege zur Raumschiffahrt (Ways to Spaceflight). His works led to the creation of a number of rocket clubs in Germany as enthusiasts tried to turn Oberth’s ideas into practical devices. The most important of these groups historically was the Verein für Raumschiffahrt (VfR; “Society for Spaceship Travel”), which had as a member the young Wernher von Braun. Although Oberth’s work was crucial in stimulating the development of rocketry in Germany, he himself had only a limited role in that development. Alone among the rocket pioneers, Oberth lived to see his ideas become reality: he was Braun’s guest at the July 16, 1969, launch of Apollo 11.

Other space pioneers

Although Tsiolkovsky, Goddard, and Oberth are recognized as the most influential of the first-generation space pioneers, others made contributions in the early decades of the 20th century. For example, the Frenchman Robert Esnault-Pelterie began work on the theoretical aspects of spaceflight as early as 1907 and subsequently published several major books on the topic. He, like Tsiolkovsky in the Soviet Union and Oberth in Germany, was an effective publicist regarding the potential of space exploration. In Austria, Eugen Sänger worked on rocket engines and in the late 1920s proposed developing a “rocket plane” that could reach a speed exceeding 10,000 km (more than 6,000 miles) per hour and an altitude of more than 65 km (40 miles). Interested in Sänger’s work, Nazi Germany in 1936 invited him to continue his investigations in that country.

Germany

It was space exploration that motivated the members of the German VfR to build their rockets, but in the early 1930s their work came to the attention of the German military. In 1932 Wernher von Braun, at age 20, became chief engineer of a rocket-development team for the German army. After Adolf Hitler came to power in 1933, Braun was named the civilian head of that team, under the military command of Walter Robert Dornberger. To give Braun’s engineers the needed space and secrecy for their work, the German government erected a development and test centre at Peenemünde on the coast of the Baltic Sea. There they developed, among other devices, the V-2 (originally designated the A-4) ballistic missile. First launched successfully in 1942, the V-2 was used on targets in Europe beginning in September 1944. Although built as a weapon of war, the V-2 later served as the predecessor of many of the rockets used in the early space programs of the United States and the Soviet Union. As World War II neared its end in early 1945, Braun and many of his associates chose to surrender to the United States, where they believed they would likely receive support for their rocket research and space exploration plans. Later in the year they were taken to the United States, as were their engineering plans and the parts needed to construct a number of V-2s. The German rocket team played a central role in the early development of space launchers for the United States.

United States

In 1936, as Braun was developing rockets for the German military, several young American engineers led by graduate student Frank Malina began working on rocketry at the Guggenheim Aeronautical Laboratory of the California Institute of Technology (GALCIT). Malina’s group was supported by the eminent aerodynamicist Theodore von Kármán, GALCIT’s director, and it included Chinese engineer Qian Xuesen (Ch’ien Hsüeh-sen), who in the 1950s returned home to become one of the pioneers of rocketry in China. In 1943 Malina and his associates began calling their group the Jet Propulsion Laboratory (JPL), a name that was formally adopted the following year. JPL soon became a centre for missile research and development for the U.S. Army. Following World War II, those weapons were adapted for use in early U.S. space experiments. After 1958, when it became part of the newly established National Aeronautics and Space Administration (NASA), JPL adapted itself to being the leading U.S. centre for solar system exploration.

Soviet Union

In the U.S.S.R. the government took an interest in rockets as early as 1921 with the founding of a military facility devoted to rocket research. Over the next decade that centre was expanded and renamed the Gas Dynamics Laboratory. There in the early 1930s, Valentin Glushko carried out pioneering work on rocket engines. Meanwhile, other rocket enthusiasts in the Soviet Union organized into societies that by 1931 had consolidated into an organization known as GIRD (the abbreviation in Russian for “Group for the Study of Reactive Motion”), with branches in Moscow and Leningrad. Emerging as leaders of the Moscow branch were the aeronautical engineer Sergei Korolev, who had become interested in spaceflight at a young age, and the early space visionary Fridrikh Tsander. Korolyov and a colleague, Mikhail Tikhonravov, on August 17, 1933, launched the first Soviet liquid-fueled rocket. Later that year the Moscow and Leningrad branches of GIRD were combined with the Gas Dynamics Laboratory to form the military-controlled Rocket Propulsion Research Institute (RNII), which five years later became Scientific-Research Institute 3 (NII-3). In its early years the organization did not work directly on space technology, but ultimately it played a central role in Soviet rocket development.

Korolyov was arrested in 1937 as part of the Soviet leader Joseph Stalin’s great purges of intellectuals and was sent to a Siberian prison. After Stalin recognized the imprudence of removing the best technical people from the Soviet war effort, Korolyov was transferred to a prison-based design bureau, where he spent most of World War II working on weapons, although not on large rockets. By the end of the war, Stalin had become interested in ballistic missiles, and he sent a team, which included Korolyov, on visits to Germany to investigate the V-2 program. A number of German engineers were relocated to the Soviet Union in the aftermath of the war, but they did not play a central role in postwar Soviet rocket development; most returned to Germany in the early 1950s.

Preparing for spaceflight

Between 1946 and 1951, the U.S. Army conducted test firings of captured German V-2 rockets at White Sands, New Mexico. These sounding-rocket flights reached high altitudes (120–200 km [75–125 miles]) before falling back to Earth. Although the primary purpose of the tests was to advance rocket technology, the army invited American scientists interested in high-altitude research to put experiments aboard the V-2s. An Upper Atmosphere Research Panel, chaired by the physicist James Van Allen, was formed to coordinate the scientific use of these rocket launchings. The panel had a central role in the early years of American space science, which focused on experiments on solar and stellar ultraviolet radiation, the aurora, and the nature of the upper atmosphere. As the supply of V-2s dwindled, other U.S.-built sounding rockets such as the WAC Corporal, Aerobee, and Viking were put into use. In other countries, particularly the Soviet Union, rocket-based upper-atmosphere research also took place after World War II.

In the early 1950s scientists began planning a coordinated international investigation of Earth, to be called the International Geophysical Year (IGY), that would be held in 1957–58 under the auspices of the International Council of Scientific Unions. By this time, progress in rocket development had advanced such that orbiting of an artificial Earth satellite by 1957 seemed feasible. At the urging of American scientists, IGY planners in 1954 called for scientifically instrumented satellites to be launched as part of IGY activities. Soon thereafter, the governments of the Soviet Union and the United States each announced plans to do so.

In the years following World War II, the United States and the U.S.S.R. became political and military competitors in what soon was being called the Cold War. Because the Soviet Union was a closed society, U.S. leaders gave high priority to developing technology that could help gather intelligence on military preparations within the Soviet borders. As orbiting satellites neared realization, the idea of equipping such satellites with cameras and flying them over Soviet territory became more attractive to U.S. planners, and the U.S. Air Force began work on a reconnaissance satellite project. Still unresolved, however, was the question of whether it would violate national sovereignty to fly over a country’s territory in orbit, above most of the atmosphere. One reason the U.S. government had committed itself to the IGY satellite program was that it wanted to establish the principle that outer space was not subject to claims of territorial sovereignty and thus that an orbiting satellite could pass freely over any point on Earth. Such overflights were essential if reconnaissance satellites were to have intelligence value.

As scientific and military planners contemplated initial space projects and engineers worked on developing the needed launch vehicles, the idea that humans would soon begin the exploration of space entered popular imagination. In Europe since the 1930s, the British Interplanetary Society had been actively promoting the idea that human space travel was soon to happen. American movies such as The Day the Earth Stood Still (1951), Destination Moon (1950), and When Worlds Collide (1951) contained vivid images of such journeys. Reports were widespread of sightings of unidentified flying objects (UFOs), which were thought by some to be spacecraft from alien worlds.

Authors such as Isaac Asimov, Robert A. Heinlein, and Arthur C. Clarke both discussed the reality of space technology in popular writings and constructed believable science-fiction stories based on its use. A central figure in popularization efforts within the United States was Wernher von Braun. A charismatic spokesman for the idea of space travel, Braun, in a series of talks, books, magazine articles, and television appearances during the 1950s, reached millions of people with his ideas for establishing orbiting space stations and human travel to the Moon and Mars. The efforts of Braun and other popularizers helped create a receptive climate for initial government proposals to undertake space activities and, particularly, to put humans in space.

The first satellites

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Although Soviet plans to orbit a satellite during the IGY had been discussed extensively in technical circles, the October 4, 1957, launch of Sputnik 1 came as a surprise, and even a shock, to most people. Prior to the launch, skepticism had been widespread about the U.S.S.R.’s technical capabilities to develop both a sophisticated scientific satellite and a rocket powerful enough to put it into orbit. Under Korolyov’s direction, however, the Soviet Union had been building an intercontinental ballistic missile (ICBM), with engines designed by Glushko, that was capable of delivering a heavy nuclear warhead to American targets. That ICBM, called the R-7 or Semyorka (“Number 7”), was first successfully tested on August 21, 1957, which cleared the way for its use to launch a satellite. Fearing that development of the elaborate scientific satellite intended as the Soviet IGY contribution would keep the U.S.S.R. from being the first into space, Korolyov and his associates, particularly Tikhonravov, designed a much simpler 83.6-kg (184.3-pound) sphere carrying only two radio transmitters and four antennas. After the success of the R-7 in August, that satellite was rushed into production and became Sputnik 1. A second, larger satellite carrying scientific instruments and the dog Laika, the first living creature in orbit, was launched November 3. The even larger, instrumented spacecraft originally intended to be the first Soviet satellite went into orbit in May 1958 as Sputnik 3. (For additional information on Korolyov’s contribution to the Soviet space program, see Energia.)

After President Eisenhower, in May 1955, had committed the United States to an IGY satellite, the army, navy, and air force competed for the assignment. (No civilian organization existed that was capable of developing the launch vehicle needed.) The mission was assigned to the Naval Research Laboratory rather than to the army’s Redstone Arsenal, where Braun worked, so that the work would not interfere with Redstone’s higher-priority development of ballistic missiles. The navy project, called Vanguard, would use a new launch vehicle based on modified Viking and Aerobee sounding rockets to orbit a small scientific satellite. Vanguard made slow progress over the subsequent two years, but, after Sputnik’s success, the White House pressed to have the satellite launched as quickly as possible. On December 6, 1957, the Vanguard rocket rose only slightly off its launch pad before exploding and sending the satellite not into orbit but onto a Florida beach.

Braun and his army superiors had not agreed with the decision to assign the satellite mission to the navy. After the launches of the first two Sputniks, they secured permission to attempt their own satellite launch. In anticipation of such a situation, they had kept in touch with JPL and Van Allen and so were able to prepare a satellite quickly. On January 31, 1958, Braun’s Jupiter-C launch vehicle, a modified Redstone ballistic missile, carried into orbit Explorer 1, the first U.S. satellite. Designed at JPL, Explorer 1 carried Van Allen’s experiment to measure cosmic rays. The results from this experiment and similar ones aboard other U.S. and Soviet satellites launched that same year revealed that Earth is surrounded by two zones of radiation, now known as the Van Allen radiation belts, comprising energetic particles trapped by Earth’s magnetic field.

Initial satellite launches were scientific in character, but U.S. government interest in reconnaissance satellites persisted. In February 1958, President Eisenhower authorized the development, under conditions of great secrecy, of such a spacecraft. The project, which came to be called Corona, would take pictures over the Soviet Union and return them to Earth by dropping the exposed film in a capsule that would be snatched out of the air as it parachuted back from space. After 12 failures, the first successful Corona mission took place on August 18, 1960; the returned film contained images of many previously unknown Soviet airfields and missile sites.

Development of space organizations

International participation

A number of international organizations are involved in space activities. The United Nations General Assembly established a Committee on the Peaceful Uses of Outer Space in 1959 to discuss scientific, technical, and legal issues related to international space activities; 95 countries were members of the committee in 2020. The committee has provided the forum for the development of five treaties and a number of declarations of principles related to space activities. The most important of them is the 1967 Outer Space Treaty, which sets forth the general legal principles governing the uses of space. Other parts of the UN system, most notably the International Telecommunications Union (ITU), are engaged in space-related concerns. The ITU is responsible for allocation of radio frequencies and orbital locations for various satellites providing public and commercial services.

At the initiative of the United States, an International Telecommunications Satellite Consortium (Intelsat) was founded in 1964 to develop and operate a global system of communications satellites. By 1969 the organization had established a system of satellites with global coverage; in the late 1980s it provided services to more than 200 countries and territories. Intelsat membership grew to 144 countries before a decision was made in 1999 to change the ownership of the organization from national governments to the private sector. A similar consortium, the International Maritime Satellite Organization (Inmarsat), was established as an intergovernmental organization in 1979 to supply maritime and other mobile communications services via satellite; it also was later transformed into a privately owned entity. In addition, a number of regional organizations have been created to operate communication and meteorologic satellites.

Involvement of industry

Building the systems and components needed to carry out both government and commercial space programs has required the participation of private industry, and a number of firms have grown to have substantial space involvement. Often these firms have also been major suppliers of aviation and defense products, a reflection of the common technological foundation for what has become known as the aerospace industry. Other private firms have specialized in providing space-based services in such areas as telecommunications and Earth observation.

Vostok

Soon after the success of the first Sputniks, Korolyov and his associate Tikhonravov began work on the design of an orbital spacecraft that could be used for two purposes. One was to conduct photoreconnaissance missions and then return the exposed film to Earth. The other was to serve as a vehicle for the first human spaceflight missions, in which a human being would replace the reconnaissance camera. The spacecraft was called Vostok when it was used to carry a human into space. Vostok had two sections—a spherical capsule in which the person would ride and a conical module that contained the instruments needed for its flight. The spacecraft was large for the time, weighing 4.73 metric tons. The crew capsule was completely covered by a thermal coating to protect it during reentry. Vostok was designed so that the human aboard need not touch any control from launch to touchdown; he would be essentially just a passenger. Nor would he land with the spacecraft. Rather, he would be ejected from it at an altitude of 7 km (4.3 miles) and parachute to dry land while the spacecraft landed nearby with its own parachutes.

After a series of five test flights carrying dogs and human dummies, the first person, by that time designated as a cosmonaut, lifted into space in Vostok 1 atop a modified R-7 rocket on April 12, 1961, from the Soviet launch site at the Baikonur Cosmodrome in Kazakhstan. The passenger, Yuri Gagarin, was a 27-year-old Russian test pilot. After firing of the retro-rocket 78 minutes into the mission, the crew capsule separated from the instrument module—although not without problems—and Gagarin parachuted to a soft landing 108 minutes after his launch. He had reported during the mission “I feel fine” and showed no ill effects from his one-orbit trip around the globe.

There were five additional one-person Vostok missions. In August 1961, Gherman Titov at age 25 (still the youngest person ever to fly in space) completed 17 orbits of Earth in Vostok 2. He became ill with space sickness (the equivalent of motion sickness on Earth) during the flight, an incident that caused a one-year delay in Vostok flights while Soviet physicians investigated the possibility that humans could not survive for extended times in the space environment. In August 1962, two Vostoks, 3 and 4, were orbited at the same time and came within 6.5 km (4 miles) of one another. This dual mission was repeated in June 1963; aboard the Vostok 6 spacecraft was Valentina Tereshkova, the first woman to fly in space.

Mercury

The initial U.S. effort to launch a human into space was known as Project Mercury. It was carried out by NASA, which had been given that responsibility over air force objections. NASA engineers, led by Robert Gilruth and Maxime Faget, designed a small cone-shaped capsule for the mission. Compared with the nearly 5-metric-ton Vostok, it weighed only 1.94 metric tons. Unlike the Soviet approach, in which a cosmonaut was orbited on the first human spaceflight, NASA planned several suborbital test flights in which an astronaut would be in space for only a few minutes of his 15-minute up-and-down ride. Only after the Mercury equipment was checked out and the effects of suborbital flight on the human body were measured would the United States commit to an orbital flight attempt. The Mercury capsule would parachute with its passenger all the way back to Earth’s surface, to land in the ocean and be recovered by navy ships. Also in contrast to Vostok, the Mercury capsule was designed to allow the astronaut to control some aspects of its flight while in space.

The United States used chimpanzees, rather than dogs, as test subjects prior to human flights. In what was intended to be the final test flight before a human launch, the chimpanzee Ham rode a suborbital trajectory on January 31, 1961, using a Redstone rocket developed by Braun’s team. Because the flight had experienced minor problems, Braun insisted on one more test flight with an unoccupied dummy spacecraft. If instead, as originally scheduled, that March 1961 flight had carried an astronaut, the United States would have been first with a human in space, although not in orbit. Alan B. Shepard, Jr., made the first crewed Mercury flight atop a Redstone rocket on May 5, 1961. A second suborbital Mercury mission, carrying Virgil I. Grissom, followed in July.

John H. Glenn, Jr., became the first American astronaut to orbit Earth in his three-orbit mission on February 20, 1962. His Mercury spacecraft was launched by a modified air force Atlas ICBM. Three more one-man Mercury orbital flights, carrying astronauts M. Scott Carpenter, Walter M. Schirra, Jr., and L. Gordon Cooper, Jr., were conducted, the last being a 22-orbit mission in May 1963.

Gemini and Voskhod

In 1961 Pres. John F. Kennedy announced that the United States would send people to the Moon “before this decade is out.” In order to test many of the techniques that would be needed to carry out a lunar mission, particularly rendezvousing and docking two objects in space, the United States in late 1961 decided to develop a two-person spacecraft called Gemini. The Gemini spacecraft was much more complex than the rudimentary Mercury capsule and, at 3.81 metric tons, was twice as heavy. Another converted air force ICBM, a Titan II, was used to launch the Gemini spacecraft.

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The first crewed Gemini mission lifted into space in March 1965; nine more missions followed, the last in November 1966. On the second mission, in June 1965, Edward H. White II became the first American astronaut to operate outside a spacecraft. His 20-minute space walk—also known as extravehicular activity (EVA)—was without incident. Although problems developed on many of the Gemini flights, the program demonstrated that people could live and work in space for as long as 14 days, more than the time needed for a round trip to the Moon. It also showed that astronauts could carry out a rendezvous in space and could make useful observations of Earth, both visually and photographically.

As plans in the United States for multiple-astronaut missions became known, the Soviet Union worked to maintain its lead in the space race by modifying the Vostok spacecraft so that it could carry as many as three persons. Korolyov could accomplish this only by having the crew fly without wearing spacesuits. The redesigned spacecraft was known as Voskhod. There were two Voskhod missions, one with three people aboard in October 1964 and another with a two-man crew in March 1965. On the second mission, cosmonaut Aleksey Leonov became the first human to leave an orbiting spacecraft, less than three months before White. His 12-minute EVA was full of problems, and his reentry of the Voskhod spacecraft was particularly difficult.

Soyuz

Korolyov and his associates began work in 1962 on a second-generation spacecraft, to be called Soyuz. It was to be a much more complex vehicle than Vostok, holding as many as three people in an orbital crew compartment, with a separate module for crew reentry and a third section containing spacecraft equipment and rocket engines for in-orbit and reentry maneuvers. Soyuz was to be capable not only of flights in Earth orbit but also, in modified versions, of flights around the Moon and even as part of a lunar landing mission.

The first launch of Soyuz, with a single cosmonaut, Vladimir Komarov, aboard, took place on April 23, 1967. Once the spacecraft reached orbit, it suffered a number of problems, which prompted ground controllers to bring Komarov back to Earth as soon as possible. After reentry, however, the spacecraft’s main parachute did not fully deploy, and the Soyuz hit the ground at high speed. Komarov became the first person to perish during a spaceflight, and the accident dealt a major blow to Soviet hopes of orbiting or landing on the Moon before the United States.

After the problems with the Soyuz design were diagnosed and remedied, various models of the spacecraft served as the means of access to space for the Soviet, and then Russian, program of human spaceflight for more than 50 years. Versions of Soyuz have been used both to transport crews to and from the International Space Station and to serve as the crew rescue vehicle—the lifeboat—for the ISS.

The American commitment

In the immediate aftermath of Gagarin’s orbital flight, President Kennedy was advised by NASA and by his vice president, Lyndon B. Johnson, of Braun’s belief that the Soviet Union, using Korolyov’s existing R-7 launcher, could well succeed in sending a multiperson spacecraft into Earth orbit and perhaps even around the Moon before the United States. The first competition that the United States had a good chance of winning would be that of a crewed lunar landing, because it would require each country to develop a new, more-powerful rocket. On those technical grounds and because a lunar landing would be a very visible demonstration of American strength, Kennedy announced on May 25, 1961, that the United States would commit itself to a lunar landing before 1970. At that time, only one American human spaceflight, Shepard’s 15-minute suborbital journey, had been made.

In response to Kennedy’s decision, the United States carried out a warlike, but peaceful, mobilization of financial and human resources. NASA’s budget was increased almost 500 percent in three years, and at its peak the lunar landing program involved more than 34,000 NASA employees and 375,000 employees of industrial and university contractors.

By the end of 1962, the basic elements of what was called Project Apollo were in place. The launch vehicle would be a powerful Saturn V rocket, 110.6 metres (362.9 feet) tall and power-driven by five huge engines generating a total of 33,000 kilonewtons (7.4 million pounds) of lifting power at takeoff—100 times the takeoff thrust of the Redstone rocket that had launched Shepard. After an intense debate, NASA chose a spacecraft configuration for Apollo that could be sent up in one launch, rather than a larger spacecraft that would need to be assembled in a series of rendezvous in Earth orbit. The Apollo spacecraft would have three sections. A Command Module would house the three-person crew on liftoff and landing and during the trip to and from the Moon. A Service Module would carry various equipment and the rocket engine needed to guide the spacecraft into lunar orbit and then send it back to Earth. A Lunar Module, comprising a descent stage and an ascent stage, would carry two people from lunar orbit to the Moon’s surface and back to the Command Module. The ability of the Lunar Module’s ascent stage to rendezvous and dock in lunar orbit with the Command Module after takeoff from the Moon was critical to the success of the mission. NASA also created a large new launch facility on Merritt Island, near Cape Canaveral, Florida, as the Apollo spaceport.

The Soviet response

While committing the United States to winning the Moon race, President Kennedy also made several attempts in the early 1960s to convince the Soviet leadership that a cooperative lunar landing program between their two countries would be a better alternative. No positive reply from the Soviet Union was forthcoming, however. In fact, between 1961 and 1963, there was still vigorous debate within the Soviet Union over the wisdom of undertaking a lunar program, and no final decision had been made on the question.

Meanwhile, the separate design bureaus headed by Korolyov and his rival Vladimir Chelomey competed fiercely for a lunar mission assignment, either a flight around the Moon or an actual landing. Finally, in August 1964, Korolyov received the lunar landing assignment, and soon afterward Chelomey was given responsibility for planning a circumlunar flight to be carried out before the 50th anniversary of the Bolshevik Revolution, which would take place in October 1967. In 1965 Soviet leaders decided to combine the efforts of the two rivals for the circumlunar mission, using a version of Korolyov’s Soyuz spacecraft and a new rocket, the UR-500 (also called the Proton), designed by Chelomey.

The rocket that Korolyov designed for the lunar landing effort was called the N1. Like the Saturn V, it was huge, standing 112.8 metres (370.1 feet) tall and having a planned takeoff thrust of 44,500 kilonewtons (10 million pounds). Instead of a few large rocket engines in its first stage, however, the N1 had 30 smaller engines. These were developed by Nikolay Kuznetsov, an aircraft-engine chief designer who had little experience with rocket engines, rather than the more capable Glushko. Korolyov and Valentin Glushko, already personal adversaries for many years, had disagreed on the proper fuel for the N1, and they finally decided that they could no longer work together. Consequently, Korolyov turned to Kuznetsov, who chose the small-engine approach.

Indecision, inefficiencies, inadequate budgets, and personal and organizational rivalries in the Soviet system thus posed major obstacles to success in the race to the Moon. To these was added the unexpected death of Korolyov, age 59, during surgery on January 14, 1966. This was a serious setback to the Soviet space program. Korolyov had been a charismatic leader and organizer. His successor, Vasily Mishin, attempted to maintain the program’s momentum, but he was not the effective manager or politically sophisticated operator that Korolyov had been.

Interim developments

In the United States, Apollo moved forward as a high-priority program; after the assassination of President Kennedy in November 1963, it became seen as a memorial to the fallen young president. A major setback occurred on January 27, 1967, when astronauts Grissom, White, and Roger Chaffee were killed after their Apollo 1 Command Module caught fire during a ground test. The first crewed Apollo mission, designated Apollo 7 and intended to test the redesigned Command Module, was launched into Earth orbit on October 11, 1968. The launcher used was a Saturn IB, a less-powerful rocket than the Saturn V needed to reach the Moon. The mission’s success cleared the way for a bold step—the first launch of a crew atop a Saturn V to the lunar vicinity. On December 21, 1968, the Apollo 8 Command and Service Modules were put on a trajectory that sent them into orbit around the Moon on Christmas Eve, December 24. The three astronauts—Frank Borman, James A. Lovell, Jr., and William A. Anders—sent back close-up images of the lunar surface, read from the biblical book of Genesis, and brought back vivid colour photographs of a blue planet Earth rising over the desolate lunar landscape. By the end of the mission, it was clear that the first lunar landing was only months away.

One reason for conducting the Apollo 8 mission was to allow NASA to test most of the systems needed for a lunar landing attempt while waiting to carry out a crewed trial in Earth orbit of the Lunar Module, whose development was behind schedule. Another was the concern that the Soviet Union would beat the United States in sending people to the lunar vicinity. A circumlunar mission indeed had been part of Soviet plans, but the Soyuz 1 accident had made the October 1967 deadline infeasible. During 1968 a number of test flights of a circumlunar mission were made, using the Proton launcher and a version of the Soyuz spacecraft designated Zond. In September Zond 5 carried a biological payload, including two tortoises, around the Moon and safely back to Earth, but two months later the Zond 6 spacecraft depressurized and then crashed on landing, ending any hope for a quick follow-on launch with a human crew. Plans to send cosmonauts around the Moon in a Zond spacecraft were postponed indefinitely in March 1969, but two more scientifically successful uncrewed circumlunar missions, Zond 7 and Zond 8, were carried out in 1969 and 1970, respectively.

The Soviet lunar landing program went forward rather fitfully after 1964. The missions were intended to employ the N1 launch vehicle and another variation of the Soyuz spacecraft, designated L3, that included a lunar landing module designed for one cosmonaut. Although an L3 spacecraft was constructed and three cosmonauts trained for its use, the N1 rocket was never successfully launched. After four failed attempts between 1969 and 1972—including a spectacular launch pad explosion in July 1969—the N1 program was finally canceled in May 1974, and Soviet hopes for human missions to the Moon thus ended.

Risks and benefits

Human spaceflight is both risky and expensive. From the crash landing of the first crewed Soyuz spacecraft in 1967 to the breakup of the shuttle orbiter Columbia in 2003, 18 people died during spaceflights. Providing the systems to support people while in orbit adds significant additional costs to a space mission, and ensuring that the launch, flight, and reentry are carried out as safely as possible also requires highly reliable and thus costly equipment, including both spacecraft and launchers.

From the start of human spaceflight efforts, some have argued that the benefits of sending humans into space do not justify either the risks or the costs. They contend that robotic missions can produce equal or even greater scientific results with lower expenditures and that human presence in space has no other valid justification. Those who support human spaceflight cite the still unmatched ability of human intelligence, flexibility, and reliability in carrying out certain experiments in orbit, in repairing and maintaining robotic spacecraft and automated instruments in space, and in acting as explorers in initial journeys to other places in the solar system. They also argue that astronauts serve as excellent role models for younger people and act as vicarious representatives of the many who would like to fly in space themselves. In addition is the long-held view that eventually some humans will leave Earth to establish permanent outposts and larger settlements on the Moon, Mars, or other locations.

Selecting people for spaceflights

Most of the individuals who have gone into space are highly trained astronauts and cosmonauts, the two designations having originated in the United States and the Soviet Union, respectively. (Both taikonaut and yuhangyuan have sometimes been used to describe the astronauts in China’s crewed space program.) Those governments interested in sending some of their citizens into space select candidates from many applicants on the basis of their backgrounds and physical and psychological characteristics. The candidates undergo rigorous training before being chosen for an initial spaceflight and then prepare in detail for each mission assigned. Training centres with specialized facilities exist in the United States, at NASA’s Johnson Space Center in Houston, Texas; in Russia, at the Yuri Gagarin Cosmonaut Training Centre (commonly called Star City), outside Moscow; in Germany, at ESA’s European Astronaut Centre in Cologne; in Japan, at JAXA’s Tsukuba Space Center, near Tokyo; and in China, at Space City, near Beijing.

Astronauts and cosmonauts who undertook multiple spaceflights traditionally fell into one of two categories. The first consisted of pilots, often with military backgrounds, who had extensive experience in flying high-performance aircraft. They were responsible for piloting space vehicles such as the space shuttle and Soyuz. The other category included scientists and engineers who are not necessarily pilots. They had primary responsibility for carrying out the scientific and engineering activities scheduled for a particular mission. They were known in the U.S. space program as mission specialists and in the Russian space program as flight engineers. With the development of long-duration space stations such as Mir and the ISS, the distinction between pilot and nonpilot astronauts and cosmonauts has become less clear, because all members of a space station crew carry out station operations and experiments.

A third category of individuals who have gone into space was called variously payload specialists or guest cosmonauts. These individuals include scientists and engineers who accompany their experiments into orbit; individuals selected to go into space for political reasons, such as members of the U.S. Congress or persons from countries allied with the Soviet Union or the United States; and a few nontechnical people—for example, the rare journalist or teacher or the private individual willing to pay substantial amounts of money for a spaceflight. These people are intensively trained for their particular flight but usually go into space only once. The first orbital spaceflight with a crew of private individuals, one of whom had chartered the spacecraft, Inspiration4, launched in 2021. At some future time, the costs and risks of human spaceflight may become low enough to accommodate a booming business of space tourism, in which many people would be able to experience spaceflight. Until then, access to orbit will be restricted to a comparatively small number of people. However, several firms have planned for paying customers brief suborbital flights that would provide a few minutes of weightlessness and dramatic views of Earth as they are launched on a trajectory carrying them just below 100 km (62 miles) in altitude, the generally recognized border between airspace and outer space.

Biomedical, psychological, and sociological aspects

Human beings have evolved to live in the environment of Earth’s surface. The space environment—with its very low level of gravity, lack of atmosphere, wide temperature variations, and often high levels of ionizing radiation from the Sun, from particles trapped in the Van Allen radiation belts, and from cosmic rays—is an unnatural place for humans. An understanding of the effects on the human body of spaceflight, particularly long-duration flights away from Earth to destinations such as Mars, is incomplete.

Many of those going into space experience space sickness (see motion sickness), which may cause vomiting, nausea, and stomach discomfort, among other symptoms. The condition is thought to arise from a contradiction experienced in the brain between external information coming from the eyes and internal information coming from the balance organs in the inner ear, which are normally stimulated continually by gravity. Space sickness usually disappears within two or three days as the brain adapts to the space environment, although symptoms may reappear temporarily when the space traveler returns to Earth’s gravity.

The virtual absence of gravity causes loss of tissue mass in the calf and thigh muscles, which are used on Earth’s surface to counter the effect of gravity. Muscles that are less involved with gravity, such as those used to bend the legs or arms, are less affected. Some loss of muscle mass in the heart has been observed in astronauts on long-duration missions. In the absence of gravity, blood that normally pools in the body’s lower extremities initially shifts to the upper regions. As a result, the face appears puffy, the person experiences sinus congestion and headaches, and blood production decreases as the body attempts to compensate. In addition, in the space environment, some weight-bearing bones in the body atrophy.

Although the changes in muscle, bone, and blood production do not pose problems for astronauts in space, they do so on their return to Earth. For example, in normal gravity, a person with decreased bone mass runs a greater risk of breaking a bone during normal strenuous activity. Countermeasures, particularly various forms of exercise while in space, have been developed to prevent these effects from causing health problems later on Earth. Even so, people recovering from long-duration flights require varying amounts of time to readjust to Earth conditions. Light-headedness usually disappears within one or two days; lack of balance and symptoms of motion sickness, in three to five days; anemia, in one to two weeks; muscle atrophy, in three to five weeks; and bone atrophy, in one to three years or more.

Except for the Apollo trips to the Moon, all human spaceflights have taken place in near-Earth orbit. In this location, Earth’s magnetic field shields humans from potentially dangerous exposure to ionizing radiation from recurrent major disturbances on the Sun and interplanetary cosmic rays. The Apollo missions, which were all less than two weeks long, were timed to avoid exposure to anticipated high levels of solar radiation. If, however, humans were sent on journeys to Mars or other destinations that would take months or even years, such measures would be inadequate. Exposure to high levels of solar radiation or cosmic rays could cause potentially fatal tumours and other health problems (see radiation injury). Space engineers will need to devise adequate radiation shielding for interplanetary crewed spacecraft and will require accurate predictions of radiation damage to the body to ensure that risks remain within acceptable limits. Biomedical advances are also necessary to develop methods for the early detection and mitigation of radiation damage. Nevertheless, the effects of radiation may remain a major obstacle to long human voyages in space.

In addition to the biomedical issues associated with human spaceflight are a number of psychological and sociological issues, particularly for long-duration missions aboard a space station or to distant destinations. To be in space is to be in an extreme and isolated environment. Mission planners will have to consider issues relating to crew size and composition—particularly if the crews are mixtures of men and women and come from several nations with different cultures—if interpersonal conflicts are to be avoided and effective teamwork achieved.

Solar and space physics

The first scientific discovery made with instruments orbiting in space was the existence of the Van Allen radiation belts, discovered by Explorer 1 in 1958. Subsequent space missions investigated Earth’s magnetosphere, the surrounding region of space in which the planet’s magnetic field exerts a controlling effect (see Earth: The magnetic field and magnetosphere). Of particular and ongoing interest has been the interaction of the flux of charged particles emitted by the Sun, called the solar wind, with the magnetosphere. Early space science investigations showed, for example, that luminous atmospheric displays known as auroras are the result of this interaction, and scientists came to understand that the magnetosphere is an extremely complex phenomenon.

The focus of inquiry in space physics was later extended to understanding the characteristics of the Sun, both as an average star and as the primary source of energy for the rest of the solar system, and to exploring space between the Sun and Earth and other planets (see interplanetary medium). The magnetospheres of other planets, particularly Jupiter with its strong magnetic field, also came under study. Scientists sought a better understanding of the internal dynamics and overall behaviour of the Sun, the underlying causes of variations in solar activity, and the way in which those variations propagate through space and ultimately affect Earth’s magnetosphere and upper atmosphere. The concept of space weather was advanced to describe the changing conditions in the Sun-Earth region of the solar system. Variations in space weather can cause geomagnetic storms that interfere with the operation of satellites and even systems on the ground such as power grids.

To carry out the investigations required for addressing these scientific questions, the United States, Europe, the Soviet Union, and Japan developed a variety of space missions, often in a coordinated fashion. In the United States, early studies of the Sun were undertaken by a series of Orbiting Solar Observatory satellites (launched 1962–75) and the astronaut crews of the Skylab space station in 1973–74, using that facility’s Apollo Telescope Mount. These were followed by the Solar Maximum Mission satellite (launched 1980). ESA developed the Ulysses mission (1990) to explore the Sun’s polar regions. Solar-terrestrial interactions were the focus of many of the Explorer series of spacecraft (1958–75) and the Orbiting Geophysical Observatory satellites (1964–69).

In the 1980s NASA, ESA, and Japan’s Institute of Space and Astronautical Science undertook a cooperative venture to develop a comprehensive series of space missions, named the International Solar-Terrestrial Physics Program, that would be aimed at full investigation of the Sun-Earth connection. This program was responsible for the U.S. Wind (1994) and Polar (1996) spacecraft, the European Solar and Heliospheric Observatory (SOHO; 1995) and Cluster (2000) missions, and the Japanese Geotail satellite (1992).

Among many other missions, NASA has launched a number of satellites, including Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED, 2001); the Japanese-U.S.-U.K. collaboration Hinode (2006); and Solar Terrestrial Relations Observatory (STEREO, 2006), part of its Solar Terrestrial Probes program. The Solar Dynamics Observatory (2010); the twin Van Allen Probes (2012); and the Parker Solar Probe (2018), which made the closest flybys of the Sun, were part of another NASA program called Living with a Star. A two-satellite European/Chinese mission called Double Star (2003–04) studied the impact of the Sun on Earth’s environment.

Exploring the universe

Until the dawn of spaceflight, astronomers were limited in their ability to observe objects beyond the solar system to those portions of the electromagnetic spectrum that can penetrate Earth’s atmosphere. These portions include the visible region, parts of the ultraviolet region, and most of the radio-frequency region. The ability to place instruments on a spacecraft operating above the atmosphere (see satellite observatory) opened the possibility of observing the universe in all regions of the spectrum. Even operating in the visible region, a space-based observatory could avoid the problems caused by atmospheric turbulence and airglow.

Beginning in the 1960s, a number of countries launched satellites to explore cosmic phenomena in the gamma-ray, X-ray, ultraviolet, visible, and infrared regions. More recently, space-based radio astronomy has been pursued. In the last decades of the 20th century, the United States embarked on the development of a series of long-duration orbital facilities collectively called the Great Observatories. They include the Hubble Space Telescope, launched in 1990 for observations in the visible and ultraviolet regions; the Compton Gamma Ray Observatory, launched in 1991; the Chandra X-Ray Observatory, launched in 1999; and the Spitzer Space Telescope, launched in 2003. Europe and Japan have also been active in space-based astronomy and astrophysics. Europe’s Herschel infrared observatory, launched in 2009, studied the origin and evolution of stars and galaxies. A telescope aboard Japan’s Akari spacecraft, launched in 2006, also observed the universe in the infrared spectrum.

The results of these space investigations have made major contributions to an understanding of the origin, evolution, and likely future of the universe, galaxies, stars, and planetary systems. For example, the U.S. Cosmic Background Explorer (COBE) satellite, launched in 1989, mapped the microwave background radiation left over from the early universe, providing strong support for the theory that the universe was created in a primordial explosion, known as the big bang. Precision measurements of this cosmic microwave background by the American Wilkinson Microwave Anisotropy Probe (WMAP, 2001) and the European Planck spacecraft (2009) enabled astronomers to determine the age, size, and shape of the universe. The U.S. satellite Kepler (2009) discovered thousands of planetary candidates of startling diversity orbiting distant suns. The European satellites Hipparcos (1989) and Gaia (2013) precisely mapped the position of more than a billion stars. The striking images of cosmic objects obtained by the Hubble Space Telescope not only added significantly to scientific knowledge but also shaped the public’s perception of the cosmos, perhaps as significantly as did the astronomer Galileo’s observations of the Moon and Jupiter nearly four centuries earlier. Working as complements to ground-based observatories of increasing sensitivity, space-based observatories helped create a revolution in modern astronomy.

Microgravity research

A spacecraft orbiting Earth is essentially in a continuous state of free fall. All objects associated with the spacecraft, including any crew and other contents, are accelerating—i.e., falling freely—at the same rate in Earth’s gravitational field (see Earth: Basic planetary data). As a result, these objects do not “feel” the presence of Earth’s gravity but instead experience a state of weightlessness, or zero gravity. True zero gravity, however, is experienced only at the centre of mass of a freely falling object. With increasing distance from the centre of mass, the influence of gravity increases in both directions perpendicular to the object’s flight path. These constant but tiny accelerations make necessary the use of the term microgravity to describe the space environment. (It is possible to create a similar absence of gravity’s effects only briefly on Earth or in an aircraft.) Human activity or the operation of equipment in a spacecraft causes vibrations that impart additional accelerations and so raise gravity levels, which can make it difficult to carry out highly sensitive experiments under sufficiently low microgravity conditions. Although spacecraft designers cannot totally eliminate gravitational effects, they hope to reduce them in some parts of the International Space Station to one microgravity—one-millionth of Earth’s gravity—by isolating those areas from vibrations and other disturbances as much as possible.

The opportunity to carry out experiments in the absence of gravity has interested scientists from the beginning of activities in orbit. In addition to concern about the effects of the weightlessness on humans sent into space (see above Biomedical, psychological, and sociological aspects), scientists are interested in its effects on the reproductive and developmental cycles of plants and animals other than humans. The overall goal is to use space-based research to add to the general understanding of a wide range of biological processes.

Life-sciences experiments were carried out on the Skylab, Salyut, and Mir space stations and constitute a significant portion of work aboard the ISS. Such research also was conducted on space shuttle missions, particularly within the Spacelab facility. In addition, the Soviet Union and the United States launched a number of robotic satellites dedicated to life-sciences research. Together these experiments have involved a wide range of nonhuman organisms, from bacteria, plants, and invertebrate animals to fish, birds, frogs, turtles, and mammals such as rats and monkeys. Human crew members also have served as experimental subjects for research on such topics as the functioning of the neurological system and the process of aging. In October 1998, the U.S. senator and former Mercury astronaut John H. Glenn, Jr., at age 77 returned to space on a shuttle mission dedicated to life-sciences research, which included studies of similarities between the aging process and the body’s response to weightlessness. The hope is that the results of biomedical experiments conducted in microgravity can be used to improve human health and well-being on Earth.

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The microgravity environment also offers unique conditions for experiments designed to explore the behaviour of materials. Among the areas of inquiry are biotechnology, combustion science, fluid physics, fundamental physics, and materials science. Experiments in the microgravity environment on various materials, including metals, alloys, electronic and photonic materials, composites, colloids, glasses and ceramics, and polymers, have resulted in a greater understanding of the role of gravity in similar laboratory and manufacturing processes on Earth. The microgravity environment offers the potential for producing biological materials, including highly ordered protein crystals for crystallographic analysis and even materials resembling human tissues, that are difficult or impossible to make on Earth. Although microgravity research is still largely at the basic level, scientists and engineers hope that additional work—another major focus for the ISS—will lead to practical knowledge of great usefulness to manufacturing processes on Earth.

Observing Earth

Satellites, space stations, and space shuttle missions have provided a new perspective for scientists to collect data about Earth itself. In addition to practical applications (see below Space applications), Earth observation from space has made significant contributions to fundamental knowledge. An early and continuing example is the use of satellites to make various geodetic measurements, which has allowed precise determinations of Earth’s shape, internal structure, and rotational motion and the tidal and other periodic motions of the oceans. Fields as diverse as archaeology, seismology, and oceanography likewise have benefited from observations and measurements made from orbit.

Scientists have begun to use observations from space as part of comprehensive efforts in fields such as oceanography and ecology to understand and model the causes, processes, and effects of global climate change, including the influence of human activities. The goal is to obtain comprehensive sets of data over meaningful time spans about key physical, chemical, and biological processes that are shaping the planet’s future. This is a coordinated international effort, in which the United States, Europe, Japan, and other countries are providing satellites to obtain the needed observations.

Meteorology

Meteorologists initially thought that satellites would be used primarily to observe cloud patterns and thus provide warnings of impending storms. They did not expect space observations to be central to improved weather forecasting overall. Nevertheless, as the technology of space-based instrumentation became more sophisticated, satellites were called upon to provide three-dimensional profiles of additional variables in the atmosphere, including temperature, moisture content, and wind speed. These data have become critical to modern weather forecasting.

Meteorological satellites are placed in one of two different kinds of orbit. Satellites in geostationary orbit provide continuous images of cloud patterns over large areas of Earth’s surface. From changes in those patterns, meteorologists can deduce wind speeds and locate developing storms. Satellites in lower orbits aligned in a north-south direction, called polar orbits, can obtain more detailed data about changing atmospheric conditions. They also provide repetitive global coverage as Earth rotates beneath their orbit. In the United States, military and civilian agencies each have developed independent polar-orbiting meteorological satellite systems; China, Europe, and Russia also have deployed their own polar-orbiting satellites. The United States, Europe, Russia, China, India, and Japan have orbited geostationary meteorological satellites.

Although the research and development activity needed to produce meteorological satellites has been carried out by various space agencies, control over satellite operation usually has been handed over to organizations with general responsibility for weather forecasting. In the United States the National Oceanographic and Atmospheric Administration (NOAA) operates geostationary and polar-orbiting satellites for short- and long-term forecasting; the Department of Defense (DOD) also has developed similar satellites for military use. In Europe an intergovernmental organization called Eumetsat was created in 1986 to operate Europe’s meteorological satellites and provide their observations to national weather services. Agencies around the world cooperate in the exchange of data from their satellites. Meteorological satellites are an excellent example of both the ability of space systems to provide extremely valuable benefits to humanity and the need for international cooperation to maximize those benefits.

Positioning, navigation, and timing

In 1957 scientists tracking the first satellite, Sputnik 1, found that they could plot the satellite’s orbit very precisely by analyzing the Doppler shift (see Doppler effect) in the frequency of its transmitted signal with respect to a fixed location on Earth. They understood that if this process could be reversed—i.e., if the orbits of several satellites were precisely known—it would be possible to identify one’s location on Earth by using information from those satellites.

This realization, coupled with the need to establish the position of submarines carrying ballistic missiles, led the United States and the Soviet Union each to develop satellite-based navigation systems in the 1960s and early ’70s. Those systems, however, did not provide highly accurate information and were unwieldy to use. The two countries then developed second-generation products—the U.S. Navstar Global Positioning System (GPS) and the Soviet Global Navigation Satellite System (GLONASS)—that did much to solve the problems of their predecessors. The original purpose of the systems was the support of military activities, and they have continued to operate under military control while serving a wide variety of civilian uses.

GPS requires a minimum of 24 satellites, with four satellites distributed in each of six orbits. Deployment of the full complement of satellites was completed in 1994 and included provision for continual replenishment and updating and the maintenance of several spare satellites in orbit. Each satellite carries four atomic clocks accurate to one nanosecond. Because the satellites’ orbits are maintained very precisely by ground controllers and the time signals from each satellite are highly accurate, users with a GPS receiver can determine their distance from each of a minimum of four satellites and, from this information, pinpoint their exact location in three dimensions with an accuracy of approximately 3 metres (10 feet) horizontally and 5 metres (16 feet) vertically.

GLONASS, which became operational in 1995, functions on the same general principles as GPS. The fully deployed system consists of 24 satellites distributed in three orbits. Because of Russia’s economic difficulties, however, GLONASS for some years was not well maintained, and replacement satellite deployment was slow. However, with improved economic conditions, the Russian government gave high priority to achieving and maintaining a fully operational GLONASS system.

Notwithstanding the military origin of GPS and GLONASS, civilian users have proliferated. They range from wilderness campers, farmers, golfers, and recreational sailors to surveyors, car-rental firms, bus and truck fleets, and the world’s airlines. The timing information from GPS satellites is also used by the Internet and other computer networks to manage the flow of information. Users have found ways to increase the accuracy of position location to a few centimetres by combining GPS signals with ground-based enhancements or with GLONASS signals, and affordable GPS receivers make the system widely accessible.

The United States regards GPS as a global utility to be offered free of charge to all users and has stated its intent to maintain and upgrade the system into the indefinite future. Concern has been expressed, however, that important worldwide civilian activities such as air traffic control should not depend on a system controlled by one country’s military forces. In response, Europe began in the late 1990s to develop its own navigation satellite system, called Galileo, to be operated under civilian control. Galileo became operational in 2016. In the early 21st century China began to develop its own global navigation system, called Beidou (“Compass”). Initially consisting of three satellites in geostationary orbit over China, Beidou began operation in 2000. A full global version of Beidou was completed in 2020. Japan and India developed systems for regional use, the Quasi-Zenith Satellite System (QZSS) and Navigation with Indian Constellation (NavIC), respectively, which both became operational in 2018.

Military and national security uses of space

Those countries and organizations with armed forces deployed abroad were quick to recognize the great usefulness of space-based systems in military operations. The United States, Russia, the United Kingdom, France, China, the North Atlantic Treaty Organization (NATO), and, to a lesser degree, other European countries have deployed increasingly sophisticated space systems—including satellites for communications, meteorology, and positioning and navigation—that are dedicated to military uses. In addition, the United States and Russia have developed satellites to provide early warning of hostile missile launches. Many of these satellites have been designed to meet unique military requirements, such as the ability to operate in a wartime environment, when an opponent may try to interfere with their functioning.

To date, military space systems have served primarily to enhance the effectiveness of ground-, air-, and sea-based military forces. Commanders rely on satellites to communicate with troops on the front lines, and, in extreme circumstances, national authorities could use them to issue the commands to launch nuclear weapons. Meteorological satellites assist in planning air strikes, and positioning satellites are used to guide weapons to their targets with high accuracy.

Despite the substantial military use of space, no country has deployed a space system capable of attacking a satellite in orbit or of delivering a weapon to a target on Earth. Nevertheless, as more countries acquire military space capabilities and as regional and local conflicts persist around the world, it is not clear whether space will continue to be treated as a weapons-free sanctuary.

In addition to recognizing the value of space systems in warfare, national leaders in the United States and the Soviet Union realized early on that the ability to gather information about surface-based activities such as weapons development and deployment and troop movements would assist them in planning their own national security activities. As a result, both countries deployed a variety of space systems for collecting intelligence. They include reconnaissance satellites that provide high-resolution images of Earth’s surface in close to real time for use in identifying threatening activities, planning military operations, and monitoring arms-control agreements. Other satellites collect electronic signals such as telephone, radio, and Internet messages and other emissions, which can be used to determine the type of activities that are taking place in a particular location. Most national-security space activity is carried out in a highly secret manner. As the value to national security of such satellite systems has become evident, other countries, such as France, Germany, Italy, China, India, Japan, and Israel, have developed similar capabilities, and still others have begun planning their own systems.

Commercial space transportation

The prosperity of the communications satellite business was accompanied by a willingness of the private sector to pay substantial sums for the launch of its satellites. Initially, most commercial communications satellites went into space on U.S.-government-operated vehicles. When the space shuttle was declared operational in 1982, it became the sole American launch vehicle providing such services. After the 1986 Challenger accident, however, the shuttle was prohibited from launching commercial payloads. This created an opportunity for the U.S. private sector to employ existing expendable launch vehicles such as the Delta, Atlas, and Titan as commercial launchers. In the 1990s, an American commercial space transportation industry emerged. Whereas the Titan was not a commercial success, the other two vehicles found a few commercial customers. However, the business was not profitable, and American firms no longer compete for commercial launch contracts, with the exception of Space Exploration Technologies (SpaceX), which has marketed launch services using its Falcon 9 booster to customers around the world.

Europe followed a different path to commercial space transport. After deciding in the early 1970s to develop the Ariane launcher, it created under French leadership a marketing organization called Arianespace to seek commercial launch contracts for the vehicle. In the mid-1980s both the U.S.S.R. and China initiated efforts to attract commercial customers for their launch vehicles. As the industry developed in the 1990s, American companies initiated joint ventures with Russia and Ukraine to market those countries’ launchers; in the 2000s these companies ended their involvement in marketing Russian launchers. China continued to market its Long March series of launch vehicles for commercial use, and other countries, such as India and Japan, hoped to market their indigenous launchers on a commercial basis. The main competition for launching large communications satellites to geosynchronous orbit, the most lucrative commercial opportunity, was between companies in Russia, China, and Europe.

However, in the 2010s, SpaceX’s partially reusable Falcon 9 rocket came to dominate the commercial launch industry with its low prices. The Russian space agency Roscosmos discontinued flights of its Proton launch vehicle because of price competition, and the American company United Launch Alliance, a joint venture between Lockheed Martin and Boeing, which used the Delta IV and Atlas V rockets, lost its monopoly on U.S. military launches when the air force awarded a contract to SpaceX. In 2018, out of 41 commercial launches, the Falcon 9 did 16.

In 2008 in the United States, NASA contracted on a commercial basis for the transportation of cargo to the International Space Station (ISS) rather than manage such launches itself. In 2010 this approach was extended to transporting astronauts to the space station. The first demonstration of commercial cargo delivery to the ISS took place in May 2012, with the flight of a SpaceX Dragon capsule; operational cargo flights began later that year. Commercial missions carrying crew to orbit began in 2020.

In 2017 the revenues of the commercial space transportation industry were estimated to be $5.5 billion. Analysts forecast an average of 42 commercial launches per year in the ensuing decade.

New commercial applications

Space advocates have identified a number of possible opportunities for the future commercial use of space. For their economic feasibility, many depend on lowering the cost of transportation to space, an objective that to date has eluded both governments and private entrepreneurs. Access to low Earth orbit has typically cost tens of thousands of dollars per kilogram of payload—a significant barrier to further space development. However, one company, SpaceX, lowered this cost by a factor of 10 with its Falcon 9 rocket and promises to reduce it still further with its planned Falcon Heavy.

The ISS originally was expected to be the scene of significant commercially funded research and other activity as its laboratories began to operate. This was projected to include both industry-funded microgravity research in ISS laboratories and less-conventional undertakings such as hosting fare-paying passengers, filming movies on the facility, and allowing commercial endorsements of goods used aboard the station. Commercial success for the ISS was predicted to lead to the development of new, privately financed facilities in low Earth orbit, including research, manufacturing, and residential outposts, and perhaps to privately financed transportation systems for access to those facilities. Because of delays in completing the station—particularly after the grounding of the shuttle fleet following the Columbia accident in 2003—such commercial demand for access to the station did not emerge. However, with the ISS planned to operate until at least 2024, it is possible that the private sector may use the ISS more if early research results demonstrate the facility’s benefits.

Another potential commercial application is the transport of fare-paying passengers into space, known as space tourism. Various surveys have suggested a willingness among many in the general public to spend considerable sums for the opportunity to experience space travel. Although a very limited number of wealthy individuals have purchased trips into Earth orbit to visit the ISS at a very high price, large-scale development of the space tourism market will not be possible until less-expensive, highly reliable transportation systems to orbit have been developed.

One variant of space tourism is to take fare-paying passengers to the edge of space—generally set at 100 km (62 miles) altitude—for brief suborbital flights that offer a few minutes of weightlessness and a broad view of Earth. In 2004, in response to a prize competition initiated in the late 1990s, a privately funded spacecraft, named SpaceShipOne, became the first of its kind to carry human beings (in this case, test pilots) on such flights. This achievement could herald the beginning of a commercial suborbital travel business. Even so, the speed reached by SpaceShipOne was just over three times the speed of sound, roughly one-seventh of the speed required for entering a practical low-Earth orbit. Frequent commercial flights into orbit appear to be some years in the future.

However, several companies, such as Virgin Galactic with its SpaceShipTwo, hope to begin commercial suborbital flights. In addition to carrying space tourists, such flights could provide opportunities for research and technology development. One 2012 estimate suggested that there could be daily suborbital flights within 10 years of the first commercial suborbital flight.

As an alternative to existing sources of energy, suggestions have been made for space-based systems that capture large amounts of solar energy and transmit it in the form of microwaves or laser beams to Earth. Achieving this objective would require the deployment of a number of large structures in space and the development of an environmentally acceptable form of energy transmission to create a cost-effective competitor to Earth-based energy-supply systems.

Resources available on the Moon and other bodies of the solar system, particularly asteroids, represent additional potential objectives for commercial development. For example, over billions of years the solar wind has deposited large amounts of the isotope helium-3 in the soil of the lunar surface. Scientists and engineers have suggested that helium-3 could be extracted and transported to Earth, where it is rare, for use in nuclear fusion reactors. In addition, there is evidence to suggest that the Moon’s polar regions contain ice, which could supply a crewed lunar outpost with drinking water, breathable oxygen, and hydrogen for spacecraft fuel. Significant quantities of potentially valuable resources such as water, carbon, nitrogen, and rare metals may also exist on some asteroids, and space mining of those resources has been proposed.