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Spaceflight, History of

Spaceflight, History of

On October 4, 1957, the Union of Soviet Socialist Republics (USSR) launched a rocket that inserted a small satellite into orbit around Earth. Three months later, on January 31, 1958, the United States launched a satellite into a higher Earth orbit. Most historians consider these two events as denoting the beginning of the space age. This new age historically marked the first time that humans had been able to send objectsand, later, themselvesinto outer space, that is, the region beyond the detectable atmosphere. The flight of machines into and through space, while a product of mid-twentieth-century technology, was a dream held by scientists, engineers, political leaders, and visionaries for many centuries before the means existed to convert these ideas into reality. And while the USSR and United States first created the enabling space technologies, the ideas that shaped these machines spanned other continents and the peoples of many other nations. The idea of spaceflight, like the capabilities that today's spaceships and rockets make possible, belongs to humanity without the limitations of any single nation or people.

The Origins of Spaceflight

The ideas that gave birth to spaceflight are ancient in origin and international in scope. Like many such revolutionary concepts, spaceflight was first expressed in myth and later in the writings of fiction authors and academicians. The Chinese developed rudimentary forms of rockets, adapted from solid gunpowder, as devices for celebrations of religious anniversaries. In 1232 China used rockets for the first time as weapons against invading Mongols. A decade later, Roger Bacon, an English monk, developed a formula for mixing gunpowder into controlled explosive devices. In the eighteenth century, British Captain Thomas Desaguliers conducted studies of rockets obtained from India in an attempt to determine their range and capabilities. In the nineteenth century William Congrieve, a British colonel, developed a series of rockets that extended the range of the rockets developed by India and that were adapted for use by armies. Congrieve's rockets were used in the Napoleonic wars of 1806. The nineteenth century would see the growth of the technology of solid-fueled rockets as weapons and the wider application of their use.

In 1857 a self-taught Russian mathematics teacher, Konstantin Eduardovich Tsiolkovsky, was born. Over the next eight decades, his writings and teachings would form the basis of modern spaceflight goals and systems, including multistage rockets, winged shuttlecraft, space stations, and interplanetary missions. Upon his death in Kaluga, Russia, on September 19, 1935, Tsiolkovsky would be considered one of the major influences upon space technology and later became known as the "Father" of the Soviet Union's space exploration program.

During the same period, the idea of space travel received attention in the form of fiction writings. The French science fiction author Jules Verne penned several novels with spaceflight themes. In his 1865 novel From the Earth to the Moon, Verne constructed a scenario for a piloted flight to the Moon that contained elements of the future space missions a century later, including a launching site on the Florida coast and a spaceship named Columbia, the same name chosen for the Apollo 11 spaceship that made the first lunar landing mission in July 1969. In his 1869 novel The Brick Moon and an 1870 sequel Life in the Brick Moon, American writer Edward Everett Hale predicted the first uses for an orbiting space station, including military and navigation functions. These novels, first published in the Atlantic Monthly magazine, address issues related to permanent spaceflight and satellite observations of Earth.

Twentieth Century Development of the Liquid-Fueled Rocket

In the early years of the twentieth century, American academician Robert Goddard developed the first controlled liquid-fueled rocket. Launching from a rudimentary test laboratory in Auburn, Massachusetts, on March 16, 1926, his rocket flights and test stand firings advanced the technology of rocketry. In Europe, rocket enthusiasts formed the Society for Space Travel to better promote rocket development and space exploration themes. Members of the group included Hermann Oberth, whose writings and space advocacy would include engineering and mathematical models for interplanetary rocket flights, and Wernher von Braun, who designed the Saturn V booster that carried Apollo spacecraft to the Moon. Germany also paidfor rocketry research conducted by Austrian engineer Eugen Sänger. Sänger and his research assistant (and later his wife) Irene Brendt contributed studies on advanced winged cargo rockets that were the forerunners of today's space shuttles. In the Soviet Union, academician Valentin P. Glushko developed the USSR's first liquid propellant rockets.

Although there were many others as well whose works detailed different types of space vehicles, space missions, and space utilization, the basis of many of the space launch vehicles of the twentieth century arose from the work of von Braun, who was subsidized by the German government during World War II (1939-1945). Working at a laboratory and launching complex called Peenemünde on the Baltic coast, von Braun and his associates developed the first ballistic missiles capable of exiting Earth's atmosphere during their brief flights. The most advanced of these designs was called the V-2. On October 3, 1942, the first of the V-2 rockets were successfully launched to an altitude of 93 kilometers (58 miles) and a range of 190 kilometers (118 miles). The successful test was referred to by German Captain Walter Dornberger, von Braun's superior at the Peenemünde complex, as the "birth of the Space Age," for it marked the first flight of a missile out of the atmosphere, in essence the world's first spaceship. While von Braun's task was to develop military weapons, he and his staff stole away as much time as possible to work on rocket-powered spaceship designs, a fact that was discovered by the German military. This discovery led von Braun to be briefly imprisoned until he was able to assure the Nazi military that the energy of his workers was directed toward weapons and not planetary rocket flights.

After the war ended in 1945, von Braun, his engineers and technicians, his unfired inventory of V-2 rockets, and his research data formed a treasure trove of space and rocketry concepts for both the United States and the Soviet Union. Von Braun himself and much of his team came to the United States, bringing along a good portion of the German rocketry archive and many V-2 rockets and rocket parts. Others of the von Braun group and some of the V-2 missiles and data were captured by the Soviet government. These two elements of the former German rocketeers led to major advances for the space enthusiasts of the United States and USSR. Beginning in January 1947, at a site located at White Sands, New Mexico, von Braun modified his V-2 rockets for scientific flights to the upper atmosphere. In the Soviet Union, Sergei Korolev undertook similar testing, using the captured V-2s. Over the next decade, data gained from firings of the V-2s led eachnation to develop its own rocket and space vehicle designs.

Space Program Development

In the Soviet Union, a ballistic missile called the R-7 was the first design to emerge from the early Soviet rocket programs that was powerful enough to strike targets in the United States or to insert satellites into Earth orbits. In the United States, a series of intermediate, medium, and intercontinental missiles emerged from the drawing boards. These had names such as Thor, Redstone, Atlas, and Titan. Along with the R-7, these missiles became the foundation of space-launching vehicles used by both nations to send the first satellites, probes, and human beings into space. Once begun on October 4, 1957, this so-called space race for dominance of the space environment was a defining element of the Cold War between the two superpowers. Rocketry gave each nation both a means to carry destructive nuclear weapons to the soil of the other country and a means of gaining scientific exploration of space. This race eventually formed up around four major elements: humans in space, advanced space exploration, reusable spaceflight, and permanent spaceflight.

The early humans in space efforts saw leadership by the Soviet Union. On April 12, 1961, using a version of the R-7 missile, the Soviet Union launched the first human, Air Force Major Yuri Gagarin, into orbital flight around Earth. Sealed inside a single seat in the space capsule Vostok 1, Gagarin completed a single orbit before descending under parachute for a landing in the Soviet Union (Gagarin himself actually ejected from the capsule's cabin before it landed in a field about ninety minutes after liftoff). The United States followed with more limited suborbital flights of astronauts Alan B. Shepard Jr. and Virgil I. "Gus" Grissom aboard single-seat Mercury spacecraft named Freedom 7 and Liberty Bell 7 on May 5 and July 19, 1961. Throughout 1961, 1962, and 1963 the United States and the USSR launched astronauts and cosmonauts into Earth orbit aboard these limited craft.

Beginning in 1965, the United States launched a two-seat space capsule called Gemini using larger Titan II missiles. The Soviet Union continued to launch Vostok capsules, modified to carry two and three persons. But the American Gemini craft were more capable, performing rendezvous and docking and long-duration space missions. This era of advanced human spaceflight now centered on a race between the superpowers to send a human expedition to the Moon's surface.

The Americans announced a program to land astronauts on the Moon called Project Apollo. The United States initiated a series of advanced space vehicles, including a new three-seat capsule capable of maneuvering between Earth and the Moon, a lunar landing craft that could carry two astronauts to the Moon's surface, and a family of advanced space rockets not based on earlier missile designs. The Soviets began a series of advanced rocket designs and a series of advanced Earth-orbiting space capsules called Soyuz. A lunar landing program was also underway in secret in the Soviet Union. But from 1965 to 1969 the Americans maintained a lead in human space missions that included the first space rendezvous and docking of two craft in orbit and long-duration spaceflights of one and two weeks in duration. Following the first walk in space performed during the Soviet Voshkod 2 mission in March 1965, American spacewalkers achieved extensive data on working outside space vehicles, considered key learning steps before astronauts could walk on the Moon's surface. But both nations suffered casualties during this peaceful scientific race. In January 1967, the first crew of an Apollo flight, Apollo 1, was killed in a launch pad fire. In April 1967 the first cosmonaut testing the Soyuz capsule was killed during a reentry mishap. Gradually, however, the United States was pulling ahead in the lunar race.

Using the lifting power of the Saturn rockets, the United States sent the first astronauts beyond Earth to lunar orbit in December 1968. The following summer, Apollo 11 and its crew of astronauts Neil A. Armstrong, Edwin E. "Buzz" Aldrin Jr., and Michael Collins were launched toward the Moon and on July 20, 1969, accomplished the first of six piloted landings. The Soviets were forced to abandon their lunar landing program because of continued malfunctions of the large N-1 lunar booster. No Russian cosmonauts ever made the attempt.

Instead, the Soviet space program redefined itself by the development of semipermanent space stations. The first in this series, called Salyut, was launched in 1971. Eventually the experience gained in the Salyut space station series led the Soviets to develop a larger and more expandable station complex called Mir. The Mir space station, resupplied by both Soyuz rockets and U.S. space shuttles, provided valuable long-duration space experience from 1986 to the spring of 2001 when the Mir complex was successfully and safely deorbited.

Both the U.S. and Soviet programs explored space with robotic probes. The Soviets were successful in accomplishing landings on Venus with an unmanned probe called Venera. Soviet robots also landed on the Moon and returned lunar soils to Earth for analysis by Russian scientists. The United States successfully accomplished robotic landings on Mars in 1976 and 1997 in the Viking and Mars Pathfinder programs.

An era of reusable space vehicles began in April 1981 with the first launch of the partially reusable space shuttle. From 1981 through 2001 more than 100 flights of the shuttles were accomplished. Only one, the launch of space shuttle Challenger on January 28, 1986, was unsuccessful and resulted in the loss of the spacecraft and the entire crew of seven astronauts. Following the accident, the shuttles were redesigned and returned to safe spaceflight. A Soviet shuttle project called Buran was abandoned in 1993 because of the collapse of the Russian economy. Construction of a permanent space station began in 1998. The project brought together sixteen international partners, including Russia and the United States.

As the twenty-first century began, space activities assumed more of an international and commercial flavor, begetting a process of evolution and change as old as the idea of spaceflight itself.

see also Apollo (volume 3); Government Space Programs (volume 2); International Cooperation (volume 3); International Space Station (volume 3); Mir (volume 3); NASA(volume 3).

Frank Sietzen, Jr.


Emme, Eugene M. A History of Space Flight. New York: Holt, Rinehart and Winston,1965.

Gatland, Kenneth. The Illustrated Encyclopedia of Space Technology. New York: Harmony Books, 1981.

Ley, Willy. Events in Space. New York: David McKay Co., 1969.

Neal, Valerie, Cathleen S. Lewis, and Frank H. Winter. Spaceflight: A Smithsonian Guide. New York: Macmillan, 1995.

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Spaceflight, History of

Spaceflight, History of

In the early-thirteenth century, the Chinese invented the rocket by packing gunpowder into a tube and setting fire to the powder. Half a millenium later, the British Army colonel, William Congreve, developed a rocket that could carry a 20-pound warhead nearly three miles. In 1926, the American physicist Robert Goddard built and flew the first liquid-fueled rocket, becoming the father of rocket science in the United States. In Russia, a mathematics teacher named Konstantin Tsiolkovsky derived and published the mathematical theory and equations governing rocket propulsion.

Tsiolkovsky's work was largely ignored until the Germans began to employ it to build rocket-based weapons in the 1920s under the leadership of mathematician and physicist Hermann Oberth. In October of 1942, the Germans launched the first rocket to penetrate the lower reaches of space. It reached a speed of 3,500 miles per hour, giving it a range of about 190 miles. The technology and design of the German rocket were essentially the same as those pioneered by Goddard. The successors of this first rocket would be the infamous V-2 ballistic missiles, which the Nazis launched against England in 1944 and 1945. This assault came too late to turn the course of the war in Germany's favor, but devastating enough to get the full attention of the U.S. government.

Many of the German V-2 rocket scientists, led by Werhner von Braun, surrendered to the Americans and were brought to the United States, where they became the core of the American rocket science program in the late-1940s, 1950s, and 1960s. Von Braun and his team took the basic technology of the V-2 missiles and scaled it up to build larger and larger rockets fueled by liquid hydrogen and liquid oxygen.

The Weapons Race Leads to a Space Race

In the beginning, the focus of the American rocket program was on national defense. After World War II, the United States and the Soviet Union emerged as the world's two most formidable powers. Each country was determined to keep its arsenal of weapons at least one step ahead of the other's. Chief among those arsenals would be intercontinental ballistic missiles, huge rockets that could carry nuclear warheads to the cities and defense installations of the enemy. To reach a target on the other side of the world, these rockets had to make suborbital flights, soaring briefly into space and back down again. In the 1950s, as rocket engines became more and more powerful, both nations realized that it would soon be possible to send objects into orbit around Earth and eventually to the Moon and other planets. Thus, the Cold War missile race gave birth to the space race and the possibility of eventual space flight by humans.

Werhner von Braun and his team of rocket scientists were sent to the Redstone Army Arsenal near Huntsville, Alabama and given the task of designing a super V-2 type rocket, which would be called the Redstone, named for its home base. The first Redstone rocket was launched from Cape Canaveral, Florida on August 20, 1953. Three years later, on September 20, 1956, the Jupiter C Missile RS-27, a modified Redstone, became the first missile to achieve deep space penetration, soaring to an altitude of 680 miles above Earth's surface and traveling more than 3,300 miles.

Meanwhile, in the Soviet Union, rocket scientists and engineers, led by Sergei Korolyev, were working to develop and build their own intercontinental ballistic missile system. In August of 1957, the Soviets launched the first successful Intercontinental Ballistic Missile (ICBM), called the R-7. However, the shot heard round the world would be fired two months later, on October 4, 1957, when the Soviets launched a modified R-7 rocket carrying the world's first man-made satellite, called Sputnik. Sputnik was a small, 23-inch aluminum sphere carrying two radio transmitters, but its impact on the world, and especially on the United States, was enormous. The "space race" had begun in earnestthere would be no turning back.

One month later, the Soviets launched Sputnik 2, which carried Earth's first space traveler, a dog named Laika. The United States government and its people were stunned by the Soviet successes and the first attempt by the United States to launch a satellite was pushed ahead of schedule to December 6, 1957, just a month after Laika's journey into space. The Vanguard launch rocket, which was supposed to propel the satellite into orbit, exploded shortly after lift-off. It was one of a series of U.S. failures, and dealt a serious blow to Americans' confidence in the country's science and engineering programs, which were previously thought to be the best in the world. Success finally occurred on January 31, 1958 with the launch of the first U.S. satellite, Explorer 1, which rode into space atop another Jupiter C rocket.

The Race to the Moon

Both the Soviet Union and the United States wanted to be the first to send a satellite to the Moon. In 1958, both countries attempted several launches targeting the Moon, but none of the spacecraft managed to reach the 25,000 miles per hour speed necessary to break free of Earth's gravity.

On January 2, 1959, the Soviet spacecraft Luna 1 became the first artificial object to escape Earth's orbit, although it did not reach the Moon as planned. However, eight months later, on September 14, 1959, Luna 2 became the first man-made object to strike the lunar surface, giving the Soviets yet another first in the space race. A month later, Luna 3 flew around the Moon and radioed back the first pictures of the far side of the Moon, which is not visible from Earth.

The United States did not resume its attempts to send an object to the Moon until 1962, but by then, the space race had taken on a decidedly human face. On April 12, 1961, an R-7 rocket boosted a spacecraft named Vostok that carried 27-year-old Soviet cosmonaut Yuri Gagarin into Earth orbit and into history as the first human in space. Gagarin's 108-minute flight and safe return to Earth placed the Soviet Union clearly in the lead in the space race. Less than a month later, on May 5, 1961, a Redstone booster rocket sent the U.S. Mercury space capsule, Freedom 7, which carried American astronaut Alan Shepard, on a 15-minute suborbital flight. The United States was in space, but just barely. An American would not orbit Earth until February of 1962, when astronaut John Glenn's Mercury capsule, Friendship 7, would be lifted into orbit by the first of a new generation of American rockets known as Atlas.

Just weeks after Shepard's suborbital flight in 1961, U.S. President John F. Kennedy announced that a major goal for the United States was to send a man to the Moon and return him safely to Earth before the end of the decade. The fulfillment of that goal was to be the result of one of the greatest scientific and engineering efforts in the history of humanity. The project cost a staggering $25 billion, but Congress and the American people had become alarmed by the Soviets' early lead in the space race and were more than ready to fund Kennedy's bold vision.

The Mercury and Vostok programs became the first steps in the race to the Moon, showing that humans could survive in space and be safely brought back to Earth, but the Mercury and Vostok spacecraft were not designed to take humans to the Moon. By 1964, the Soviet Union was ready to take the next step with a spacecraft named Voskhod. In October of 1964, Voskhod 1 carried three cosmonauts, the first multi-person space crew, into orbit. They stayed in orbit for a day and then returned safely to Earth. In March of 1965, the Soviets launched Voskhod 2 with another three-man crew. One of the three, Alexei Leonov, became the first human to "walk" in space.

Within weeks of Leonov's walk, the United States launched the first manned flight of its second-generation Gemini spacecraft. The Gemini was built to carry two humans in considerably more comfort than the tiny Mercury capsule. Although Gemini was not the craft that would ultimately take men to the Moon, it was the craft that would allow American astronauts to practice many of the maneuvers they would need to use on lunar missions. Ten Gemini missions were flown in 1965 and 1966. On these missions, astronauts would walk in space, steer their spacecraft into a different orbit, rendezvous with another Gemini craft, dock with an unmanned spacecraft, reach a record altitude of 850 miles above Earth's surface, and set a new endurance record of 14 days in space. When the Gemini program came to an end in November of 1966, the United States had taken the lead in the race to the Moon. The Soviets had abandoned their Voskhod program after just two missions to concentrate their efforts on reaching the Moon before the United States. Both countries developed a third-generation spacecraft designed to fly to the Moon and back. The Soviet version was called Soyuz, while the American version was named Apollo. Both could accommodate a three-person crew.

In November of 1967, Werhner von Braun's giant Saturn V rocket was ready for its first test flight. The three-stage behemoth stood 363 feet high, including the Apollo command module perched on top. Its first stage engines delivered 7.5 million pounds of thrust, making it the most powerful rocket ever to fly. On its first test flight, the mighty Saturn launched an unmanned Apollo spacecraft to an altitude of 11,000 miles above Earth's surface. On December 21, 1968, the Saturn V boosted astronauts Frank Borman, Jim Lovell, and Bill Anders inside their Apollo 8 spacecraft into Earth orbit. After two hours in orbit, the Saturn's third stage engines fired one more time, increasing Apollo 8's velocity to 25,000 miles per hour. For the first time in history, humans had escaped the pull of Earth's gravity and were on their way to the Moon.

On December 24, Apollo 8 entered lunar orbit, where it would stay for the next twenty hours mapping the lunar surface and sending back television pictures to Earth. Apollo 8 was not a landing mission, so on December 25, the astronauts fired their booster rockets and headed back to Earth, splashing down in the Pacific Ocean two days later. The last year of the decade was about to begin and the stage was set to fulfill President Kennedy's goal. Two more preparatory missions, Apollo 9 and Apollo 10, would be used to do a full testing of the Apollo command module and the lunar module, which would take the astronauts to the surface of the Moon.

The astronauts chosen to ride Apollo 11 to the Moon were Neil Armstrong, Edwin "Buzz" Aldrin, and Michael Collins. Liftoff occurred on July 16, 1969, with Apollo 11 reaching lunar orbit on July 20. Armstrong and Aldrin squeezed into the small spider-like lunar module named Eagle, closed the hatch, separated from the command module, and began their descent to the lunar surface. Back on Earth, the world watched in anticipation as Neil Armstrong guided his fragile craft toward the gray dust of the Moon's Sea of Tranquility. Armstrong's words came back across 239,000 miles of space: "Houston. Tranquility Base here. The Eagle has landed." At 10:56 p.m., eastern standard time, July 20, 1969, Armstrong became the first human to step on the surface of another world. "That's one small step for a man," he proclaimed, "and one giant leap for mankind." Aldrin followed Armstrong onto the lunar surface, where they planted an American flag and then began collecting soil and rock samples to bring back to Earth. The Apollo 11 astronauts returned safely to Earth on July 24, fulfilling President Kennedy's goal with five months to spare.

Five more teams of astronauts would walk and carry out experiments on the Moon through 1972. A sixth team, the crew of Apollo 13, was forced to abort their mission when an oxygen tank exploded inside the service module of the spacecraft. On December 14, 1972, after a stunning three-day exploration of the lunar region known as Taurus-Littrow, astronauts Eugene Cernan and Harrison Schmitt fired the ascent rockets of the Lunar module Challenger to rejoin crewmate Ron Evans in the Apollo 17 command module for the journey back to Earth.

Apollo 17 was the final manned mission to the Moon of the twentieth century. The American people and their representatives in Congress had exhausted their patience with paying the huge sums necessary to send humans into space. The Soviets never did send humans to the Moon. After the initial Soyuz flights, their Moon program was plagued by repeated failures in technology, and once the United States had landed men on the Moon, the Soviet government called off any additional efforts to achieve a lunar landing.

Although the Apollo program did not lead to an immediate establishment of scientific bases on the Moon or human missions to Mars as was once envisioned, human spaceflight did not end. The three decades following the final journey of Apollo 17 have seen the development of the space shuttle program in the United States, as well as active space programs in Russia, Europe, and Japan. Scientific work is currently under way aboard the International Space Station, with space shuttle flights ferrying astronauts, scientists, and materials to and from the station. Deep spaceflights by humans to the outer planets and the stars await significant breakthroughs in rocket propulsion.

see also Astronaut; Space, Commercialization of; Space Exploration; Space, Growing Old in; Spaceflight, Mathematics of.

Stephen Robinson


Hale, Francis J. Introduction to Space Flight. Upper Saddle River, NJ: Prentice Hall, 1998.

Heppenheimer, T. A. Countdown: A History of Spaceflight. New York: John Wiley and Sons, 1999.

Watson, Russell and John Barry. "Rockets." In Newsweek Special Issue: The Power of Invention. Winter (19971998): 6466.

lnternet Resources

NASA Goddard Space Flight Center Homepage. <>.

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space travel

space travel Manned space flight commenced with the orbital flight by Gagarin in April 1961. By 1996 over six hundred human beings had flown in space for periods of time varying between a few hours and 438 days. Space travel is set to become more frequent in the twenty-first century, although the financial cost of the vehicles and their propulsion systems will limit the number of individuals who will experience the excitements and wonders of space flight. Flight in space is characterized by the absence of gravity, the absence of the Earth's atmosphere with the associated absence of protection against solar and cosmic radiation, and the vast distances which have to be traversed to reach other planets.

A spacecraft must be accelerated to a velocity of 8 km per second (17 900 mph) to enter into orbital flight around the Earth and to a velocity of 11.6 km per second (25 900 mph) to escape Earth's gravitational field and travel into outer space. Similar changes in velocity are required to return safely to the surface of the Earth. The velocity required to enter orbital flight can be attained by suitable combinations of acceleration (G) and time (828 G seconds are required to reach orbital velocity). In practice, the pattern of acceleration is determined by the design of the rocket motors. Development of the latter has resulted in a progressive reduction in the maximum acceleration from 5–7 G in early flights to 3 G in the Space Shuttle. The effects of the G on the circulation are minimized by placing the long axis of the body of the astronaut at right angles to the direction of travel of the space vehicle. The accelerative forces associated with returning to the Earth from orbital flight are about half those of launch into orbit, and the physiological effects are minimized by appropriate orientation of the spacecraft.

An artificial gaseous environment must be produced with the spacecraft, and its cabin must be sealed to a very high standard to avoid the loss of gases to the vacuum of space. Although 100% oxygen at a pressure of 1/3 atmosphere was employed in early American space vehicles, air at 1 atmosphere is the environment of choice in order to avoid the deleterious physiological effects of prolonged exposure to 100% oxygen and the high risk of fire associated with an oxygen atmosphere. Air at a pressure of 1 atmosphere does, however, have the disadvantage that, with present designs of space suits, 100% oxygen must be breathed for several hours before undertaking extra-vehicular activity in order to avoid decompression sickness. The atmosphere of the sealed cabin must be conditioned continuously by the removal of carbon dioxide and the addition of oxygen. The heat generated by occupants and some of the equipment within the cabin is removed by cooling the air and removing water vapour. The environmental control required in the cabin of a spacecraft has also to be provided in individual space suits. Inflation of a space suit to a pressure of 1 atmosphere is associated with an unacceptable loss of mobility due to the ‘stiffness’ of the suit. Suit pressures of the order of 0.3 to 0.5 atmosphere are generally employed, with an internal suit atmosphere of 100% oxygen. Heat produced by the body and by incident solar radiation is removed by means of a liquid conditioning garment worn beneath the suit. The heat gained by the fluid circulating through the garment is rejected to space by evaporation of a suitable refrigerant.


The principal effects of the microgravity (also termed weightlessness) of space travel arise in the vestibular, cardiovascular, and musculo-skeletal systems. Space sickness, which comprises nausea, a general feeling of malaise, and often actual vomiting, occurs early in a flight and is greatly aggravated by rapid movements of the head. Adaptation occurs over the first few days of flight and the condition seldom persists for longer than 5–6 days. Like other forms of motion sickness, space sickness is due to a conflict of sensory information from the vestibular system and eyes to the central nervous system. The abnormal sensory input in space sickness is the absence of signals from the otolith organs. The incidence and severity of the condition is reduced by avoiding head movements, especially rapid ones. The use of anti motion-sickness drugs during the first few days of flight is of considerable value.

In contrast to the effects of +Gz (see G and G-suits), microgravity abolishes all the hydrostatic pressure gradients within the circulation so that blood and tissue fluids move from the lower parts of the body to the head and chest. It is estimated that the volume of blood and tissue fluid in the lower limbs is reduced by 1.0–1.5 litres within the first 24 hours of exposure to microgravity. The veins of the head and neck are distended, and there is puffiness of the face and congestion of the nasal passages. The distension of the heart caused by the central movement of blood stimulates an increase in the excretion of urine, which in turn produces a reduction in the total volume of blood in the body. The circulation is well maintained whilst in microgravity. The most important effect of the circulatory changes induced by microgravity, is, however, a reduced tolerance to the shift of blood to the feet which occurs on return to the 1 G environment on the surface of the earth. The astronaut may feel faint and indeed a few have fainted on standing upright after landing.

The muscular effort required to maintain posture and to carry out physical tasks is reduced in microgravity. This reduction in muscle activity gives rise to a progressive loss of muscular strength and wasting (atrophy) of muscles over days and weeks in much the same manner as a long period of rest in bed. These effects of microgravity can be reduced by special regimes which exercise the muscles, especially those of the trunk and lower limbs. Cycling on an ergometer has been widely used during prolonged space flights.

Of even greater concern in long duration spaceflight is the loss of minerals from bone produced by microgravity. The maintenance of normal bone structure and calcification of bone depend upon the physical stresses which living and working in a 1 G environment impose upon the bones. The greatly reduced forces in microgravity lead to demineralization of the bones. There is an increase in the loss of calcium from the body and a decrease in the absorption of calcium from food. Studies conducted to date suggest that the loss of calcium, bone structure, and bone strength continue for as long as the individual is exposed to microgravity. The concern is the risk of fracture of bones on return to normal gravity, or even in spaceflight when the duration of the flight extends into many months. Although exercises which place high stresses on bones may retard the demineralization process, the effect of microgravity upon bone is probably an important determinant of the time which an individual may spend in space.

Cosmic radiation

Very little of the ionizing radiation present in space reaches the surface of the Earth, owing to the shield provided by the atmosphere and the magnetic field of the Earth. Once outside this protection a space vehicle is exposed to galactic radiation and to radiation from the sun. Furthermore, the Van Allen belts of high energy particles which lie between 250 and 44 000 km above the surface of the Earth form a potential hazard on missions deep into space. Most manned space flights to date have occurred at altitudes well below the inner Van Allan belt. The damaging effect which ionizing radiation has upon living matter varies with the nature and dose of the radiation, from damage to blood-forming organs to prolonged vomiting and nausea, to incapacitation and death within a few hours. At present the cumulative dose of radiation to which astronauts can be exposed over their total career in space is limited by considerations of damage to the most sensitive tissues such as the bone marrow, the lens of the eye, and the skin. The dose of radiation received by individual astronauts is monitored routinely in space flights. The effect of cosmic radiation is probably the principal hazard for prolonged interplanetary space flight. There is a limit to the protection which can be afforded by either passive or active shielding against the ionizing radiation of space.

John Ernsting


Ernsting, J. and and King, P. (1988). Aviation medicine, (2nd edn). Butterworth-Heinemann, Oxford.
Nicogossian, A. E.,, Leach Huntoon, C.,, and and Pool, S. L. (1993). Space physiology and medicine, (3rd edn). Lea and Febiger, Malvern, Pennsylvania.

See also G and G suits; radiation, ionizing.

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Space vehicles encompass different categories of spacecraft, including satellites ,rockets , space capsules ,space stations , and colonies. In general, satellites are considered any object launched by a rocket for the purpose of orbiting Earth or another celestial body. A rocket, on the other hand, is a vehicle or device, especially designed to travel through space, propelled by one or more engines.

A Brief History of Space Vehicles

The Soviet Union launched the first successful satellite, Sputnik 1 in October 1957. America's first satellite, Explorer 1, followed Sputnik by three months, in January 1958. Soon after satellites orbited the Earth, space capsules were launched containing closed compartments designed to hold and protect humans and/or equipment. Less than three years after Sputnik 1, both the United States and Soviet Union put capsules into space with humans aboard. In 1961 cosmonaut Yuri Gagarin became the first person in space aboard a Vostok space capsule. A month later, American astronaut Alan Shepard in the Mercury capsule Freedom 7 made a 14.8-minute sub-orbital flight, becoming the first U.S. astronaut in space.

While the American space program focused first on the Apollo missions to the Moon and then turned to development of the space shuttle (the first reusable launch vehicle) and low Earth orbit operations, the Soviet Union established a series of space stations in Earth orbit. Space stations are large spacecraft equipped to support a crew and remain in orbit for an extended period of time to serve as a base for launching exploratory expeditions, conducting scientific research, repairing satellites, and performing other space-related activities. The Soviets' first space station, Salyut 1, was launched in 1971. Later, the Soviet Union and Russia orbited the Mir space station. America's first space station, and the only one that it deployed during the first four decades of human spaceflight, was the 100-ton Skylab launched in 1973. Today, the United States, Russia and other international partners are constructing the International Space Station, Alpha.

The Future of Space Vehicles

A major imperative for the future is to reduce the cost of getting to orbit. To this end significant funds have already been invested in technology development towards a single-stage-to-orbit reusable space vehicle to replace the shuttle. Problems with the X-33 scaled prototype led to a recognition that development of such a vehicle is still years away. The U.S. government has committed to a series of shuttle upgrades to keep the fleet flying and to improve safety and capability. A likely intermediate stage is development of a two-stage-to-orbit reusable vehicle, possibly building on shuttle components with fly-back boosters. (The shuttle discards its solid rocket boosters minutes after launch. The casings are reclaimed from the sea and towed back to land to be reused. A booster that could fly back to the space center runway on automatic pilot after fulfilling its role in boosting the spacecraft launch would be a significant advance.)

Looking to the far horizon, space elevators, launch systems driven by a massive catapult system (the so-called slingatron), or sophisticated magnets, could revolutionize the way payloads are launched to space. New forms of nuclear propulsion, plasma propulsion,antimatter systems, vastly improved solar sail techniques, faster-than-light travel, or the exploitation of zero point energy for transportation through space could move humankind into a new space age that leaves traditional chemical propulsion behind.

The establishment of permanent space colonies has fascinated people for decades. Permanent settlements have been proposed for the Moon and Mars, as well as stable positions in space equidistant from both Earth and Moon called the Lagrangian libration points . Space visionaries advocated a space colony at L5 early in the space age. More recently NASA scientists have considered placing a space station at L2. In the future, space transportation vehicles serving humans and space habitats will become more spacious and more conducive to long journeys or permanent habitation. Eventually, space settlers, like the immigrants who came to America, might consider their settlement "home" and become increasingly self-sufficient by growing their own food and using solar energy to generate electricity and manufacture goods.

see also Capsules (volume 3); Getting to Space Cheaply (volume 1); Launch Vehicles, Expendable (volume 1); Lunar Bases (volume 4); Mars Bases (volume 4); Reusable Launch Vehicles (volume 4); Satellites, Types of (volume 4); Settlements (volume 4); Space Elevators (volume 4); Space Shuttle (volume 3); Space Stations of the Future (volume 4)

Pat Dasch and John F. Kross


Hacker, Barton C., and James M. Grimwood. On the Shoulders of Titans: A History of Project Gemini. Washington, DC: NASA Historical Series (NASA SP-4203), 1977.

Lewis, Richard S. Appointment on the Moon. New York: The Viking Press, 1968.

Millis, Marc G. "Breaking through to the Stars."Ad Astra 9, no. 1 (January-February1997):36-41.

Puthoff, H. E. "Space Propulsion: Can Empty Space Itself Provide a Solution?"Ad Astra 9, no. 1 (January-February 1977):42-46.

Yenne, Bill. The Encyclopedia of US Spacecraft. New York: Exeter Books, 1988.

Internet Resources

Colonization of Space. NASA Ames Research Center.<>.

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Space Travel

Space Travel

Water forms Earth's oceans, lakes, and rivers, and is also present in the atmosphere. All Earth's creatures rely on water to sustain life. It comprises 90 percent of a human's body weight. Water transports nutrients and electrolytes from one part of the body to another, and washes out wastes and toxins from the body.

Spacecraft Ecosystem

Because of water's essential nature, the mini-ecosystem of a spacecraft must provide water to sustain the crew and any live organisms. Based on the average quantities of water, food, and oxygen that people use everyday, water constitutes about 95 percent of the total mass of "consumables" required for human life support within a spacecraft.

Systems within a spacecraft also are required for the disposal of, or storage and return of, waste (urine) or "grey" (dirty) water (flush, laundry, dishes). This wastewater amounts to about 30 kilograms per person each day, or about 97 percent of the total output mass of human by-products. If water were not recycled by the crew, the mass of water required to be "launched" for a 2-year round trip to Mars with six crew members would be a phenomenal 129,473 kilograms, or 134,070 liters (35,375 gallons)!

Cooling Garments.

Water is also needed for use in the spacesuit's liquid cooling garment, which circulates chilled water through about 91 meters (300 feet) of plastic tubing laced in stretchable spandex fabric long underwear. It can absorb up to 2,000,000 joules (about 478 food calories) of body heat per hour, a rate produced by extremely vigorous physical activity (approximately 160 joules, or 38 food calories, are released when burning a piece of newspaper one square centimeter, or 0.16 square inch).


Too much water in the atmosphere of the spacecraft's cabin is a problem. If relative humidity is too high (from 25 to 75 percent is desirable), as it tends to be in space habitats, condensation on surfaces can occur. Such moisture can damage electronics and increase fungal and microorganism growth that is difficult to control. Humidity also inhibits the cooling of the human body (in confined spacecraft habitats) through the evaporation of perspiration. In microgravity environments, water droplets stay on the skin without the presence of convection .


For long duration missions and especially if humans are to venture beyond the orbit of Earth, spacecraft and other space habitats must be self-sufficient by recycling air and water. Water available for recycling comes from three primary sources: humidity condensate, wash-water, and urine. Two different processes can be used to purify these three wastewater sources. The first process involves physicochemical technologies, which use distillation, filtration and phase change processes (for example, vapor compression distillation). The second process involves bioregenerative processes, which use photosynthetic plants grown in aquaculture.

Bioregenerative Processes.

Plants supply essentially pure water through transpiration. Typically, plants transpire 200 to 1,000 liters (50 to 260 gallons) of water for one kilogram of dry biomass . Such plants can take up wastewater (such as contaminated shower and laundry water) and the resulting transpiration water (water given off by the plants) can be condensed and collected from the plant chamber onto a condensing heat exchanger. This water, along with condensate from the crew chamber, is treated by ultraviolet light to remove bacteria and degrade trace organic compounds. Any surplus water is returned to the aquaculture system or the hydroponic nutrient solution.

Bioregenerative systems are slow, can operate with little electrical power, and are multifunctional (plants absorb carbon dioxide, generate oxygen, and can provide food). Physicochemical technologies for air and water regeneration tend to be fast-acting but power-hungry. By carefully combining both technologies, a hybrid design can be developed with distinct advantages over purely individual systems.

see also Mars, Water on; Reclamation and Reuse; Solar System, Water in the.

Joan Vernikos


Schwarzkopf, Steven H. "Design of a Controlled Ecological Life Support System." Bioscience 42 (1994):526535.

Waligora, James M., Michael R. Powell, and Richard L. Sauer. "Spacecraft Life Support Systems." In Space Physiology and Medicine. A. E. Nicogossian, C. Leach Huntoon, and S. L. Pool, eds. Philadelphia, PA: Lea & Febiger (1994):109127.

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space travel

space travel: see space exploration; space science.

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