Uncrewed spaceflight

Since 1950, humankind has used robotic spacecraft such as satellites, probes, and telescopes both to gather strategic intelligence and to explore the outer reaches of the solar system.

The Cold War

It became quite obvious by late 1945 that a significant political and strategic rift was forming between the Soviet Union and its wartime allies. During the course of the German retreat from Russia, Soviet troops had occupied most of the nations of Eastern Europe. In time, the United States and Great Britain accepted the fact that the Soviet Union was intent upon creating a strategic buffer zone out of these nations by making them satellites of the Soviet Union. The Soviet Union gave military and economic support to the Marxist groups in these countries, and by 1948 the entire Eastern bloc was under Soviet control. Concurrently, World War II had unleashed the atomic age and introduced the use of long-range weapons of destruction. Both the United States and the Soviet Union recognized the potential strategic power of placing atomic bombs on intercontinental ballistic missiles (ICBMs). The economic and political pressures of the Cold War necessitated that each side have a clear understanding of the strategic capabilities of its opponent. The Soviet Union and the United States created a system of spy satellites that was used as an important tool in curtailing the spread of nuclear weapons. Soviet premier Nikita Khrushchev and U.S. president Dwight D. Eisenhower expanded the use of robotic spacecraft because they were less expensive to build and maintain than conventional weapons. Spy satellites had the added advantage of taking the human factor out of the military equation. If a robotic spacecraft crashed in enemy territory there was no danger of the embarrassment of a pilot standing trial before the international community.

Early Space Exploration

During the first years of the space race, human knowledge of the solar system came from a series of robotic explorers. On January 31, 1958, the United States successfully launched the Explorer 1 satellite that discovered the existence of belts of radiation around Earth. This phenomenon would eventually be designated the Van Allen Belt, named for the chief scientist of the Explorer Program. This discovery took the American scientific establishment by surprise; initially it was believed that the radiation was the result of a Soviet nuclear test. The National Aeronautics and Space Administration (NASA) continued to expand its understanding of this radiation when Explorer 4 mapped the region of the belts between July and September, 1958. The Moon was the next target of uncrewed spaceflight. By the late 1950’s, scientists in both the United States and the Soviet Union were seriously considering the possibility of landing humans on the Moon, but extensive environmental information about the Moon was necessary before such a landing could be made. Beginning in August, 1958, the United States sent a series of probes designated Pioneer 1 through 4 toward the Moon, but all four failed to reach their destination. The Russian Luna probes were more successful. On September 15, 1959, Luna 2 reached the Moon, but the force of its impact destroyed the spacecraft. The Soviets were finally successful with Luna 3. This probe made a successful landing and sent back the first pictures of what astronomers refer to as the “dark side” of the Moon. By the early 1960’s, the Soviet Union and the United States were actively involved in the exploration of the inner planets. The United States’ Mariner Program was developed to collect data from Venus. The first attempt at a flyby of the 4planet was made in July, 1962. Unfortunately, the spacecraft experienced a major malfunction and crashed soon after takeoff. NASA was more successful in December, 1962, when Mariner 2 successfully landed on the surface of Venus. Astronomers discovered that the cloud cover that made Venus the object of planetary beauty was actually a toxic collection of poisonous greenhouse gases that had created a hot, deadly environment. The Soviets were also successful in their attempts to explore Venus, and their spacecraft sent back some of the first accurate topographical details of the planet’s surface. Throughout the mid-1960’s, both the Soviet Union and the United States were successful at using robotic spacecraft to expand human knowledge of the inner planets.

The Planetary Grand Tour

In 1965, two American space scientists, Michael Minovitch and Gary Flandro, published scientific reports that described a technique for the exploration of the solar system’s outer planets described as gravity propulsion. The centerpiece of this new theory was the giant of the solar system, Jupiter. Minovitch and Flandro described how the gravitational force of Jupiter could be used to act as a slingshot to propel a probe to the far reaches of the solar system. The two scientists continued to work on this theory, and in 1966 they issued a second paper that stated that the best planetary alignment for such an endeavor in the next 179 years would be in 1977 and 1978. The vast majority of the United States’ space community was interested in this new theory, and despite its focus on the Apollo Program, NASA made plans to explore the outer reaches of the solar system and beyond. In 1972, the program was momentarily sidetracked when President Richard M. Nixon, focusing upon the importance of crewed spaceflight in the struggle against the Soviet Union, approved the beginning of the space shuttle program. In 1972, the United States was suffering an economic slowdown as a result of the large expenditures of the Vietnam War. The federal budget was already under considerable strain; therefore, the space program was pushed to make choices that would have both a scientific and political impact. Fortunately, the cost of the trip to the outer planets was modest and funding was restored.

The Politics of Space Exploration

The first series of probes to attempt the Grand Tour were designated Pioneers 10 and 11. Most of the scientists involved with the project believed that if the spacecraft made it out of the solar system without any significant damage, there was an excellent chance that the probes could explore the universe for centuries. A small but significant sector of this scientific community also believed that there was other intelligent life in the universe. The Cornell University astronomer Carl Sagan and his wife Linda designed a plaque that was to be attached to each probe. These plaques were intended to be a message of peace and discovery to any other intelligent life. Each plaque contained a model of our solar system, which communicated that the craft originated on the third planet from the Sun. There was also a prelaunch blueprint of the entire spacecraft designed to show the rocket that had launched the probe into space. This, along with a diagram representing the location of fourteen pulsars, was included to show the extent of human scientific knowledge and capabilities. Finally, the plaque contained a representation of a naked man and woman depicting the physical characteristics of the species that had constructed the probe. The male figure held his right hand up in a gesture of peace, and the woman was situated next and slightly behind her male counterpart. The plaque turned out to be the most controversial aspect of the program, and it united various groups from both sides of the political spectrum. The cultural and religious conservatives were upset with the fact that the man and woman were naked. A number of prominent newspapers, including the Chicago Sun-Times, removed the genitalia from both figures when it published a picture of the plaque in their newspapers. The decision to place the woman slightly behind the man outraged American feminists. These women perceived the diagram as another example of America’s unequal, male-dominated society. Because the silhouettes were represented with racial features of European Americans, minority communities also took objection to the plaque. In time, the controversy calmed down and this symbolic message of peace and hope accompanied the spacecraft on its journey.

The Journey to Jupiter and Saturn

Two robotic probes were launched toward Jupiter and Saturn by the United States in the early 1970’s. Pioneer 10 began its journey in mid-July, 1972, and successfully navigated the potentially dangerous asteroid belt located between the orbits of Mars and Jupiter. It then sent back the first photographs of the solar system’s largest planet. Astronomers learned that Jupiter had at least twelve moons and that its atmosphere contained deadly levels of radiation. In its travels around the giant planet, Pioneer 10 also confirmed that the famous Giant Red Spot was actually a massive storm six times the size of Earth. Astronomers were also able to acquire important pictures of three of the four Galilean moons. Finally, the space probe confirmed a long-held belief that, like its neighbor Saturn, Jupiter possessed a system of rings. With its mission accomplished, Pioneer 10 traveled to the planet Pluto and then into interstellar space.

Pioneer 11 flew by Jupiter long enough to take a second look at the Giant Red Spot and then proceeded to its primary destination, Saturn. The spacecraft spent a total of ten days mapping Saturn’s great system of rings. Astronomers discovered that the planet also emanated large amounts of radiation and possessed a very strong magnetic field, as well. Finally, Pioneer 11 gave scientists a close-up look at the largest moon in the solar system, Titan. Many astronomers believe that Titan might one day be the location of a space colony.

The Space Telescope

Most scientists believe that the most important robotic instrument launched into space in the last decade of the twentieth century is the Hubble Space Telescope. This sophisticated instrument was sent into space on April 25, 1990, and it has the potential to initiate the most significant scientific and philosophical discussions in the first decade of the third millennium. The telescope has the ability to look deep into the farthest reaches of outer space. This has allowed astronomers to study the conditions that existed moments after the beginning of the universe, described by cosmologists as the Big Bang. The Hubble telescope has allowed scientists to observe the process by which both stars and planets originate. Many cosmologists believe that humankind is on the verge of discovering how the universe was created. The great debate over a “grand design” could be settled with the information discovered by the Hubble telescope.

The Future of Uncrewed Spaceflight

One of the great debates in the U.S. scientific community revolves around the question of whether or not the United States should make the commitment to continue highly sophisticated space travel. Many scientists believe that the United States should concentrate its energies and financial resources on robotic spaceflight. The success of these uncrewed programs, especially the first Mars Lander and the Hubble telescope, confirms their belief that the frontiers of human knowledge can be served best by creating new missions for these highly reliable spacecraft.


  • Burrows, William E. This New Ocean. New York: Modern Library, 1999. A comprehensive one-volume history of spaceflight providing a detailed, chronological account of the age of space exploration.
  • Harford, James. Korolov: How One Man Masterminded the Soviet Drive to Beat Americato the Moon. New York: John Wiley & Sons, 1997. A unique and very interesting look inside the Soviet space establishment as seen through the life of Russia’s most important space scientist.
  • Heppenheimer, T. A. Countdown: A History of Space Flight. New York: John Wiley & Sons, 1997. An excellent one-volume history of spaceflight describing the economic, social, and political impact of the Space Age.
  • McDougal, Walter A. The Heavens and Earth: A Political History of the Space Age. Baltimore: The Johns Hopkins University Press, 1985. An outstanding political history of the space race describing the important linkage between the events of the Cold War and American and Soviet space programs.

Astronauts and cosmonauts

Crewed spaceflight


National Aeronautics and Space Administration


Russian space program

Space shuttle


Vanguard Program

Viking Program

Uncrewed space vehicles can send information back to Earth from locations not yet reachable by humans. This is the first photograph of the surface of Mars, taken by the Viking 1 on July 23, 1976.