"The earth is the cradle of mankind - one cannot remain in the cradle forever"
-- Konstantin Tsiolkovsky

Working Out the Theory
To design and build a spacecraft, you need to be able to figure out how big to make it, how heavy it can be, how fast it will have to go, how much fuel it needs and so forth. For that, you need a theory of how objects move in space and how to make the calculations. Three brilliant men worked out almost all theory of space flight over a period of nearly three centuries - from 1600 to 1900.

Johannes Kepler: was the German mathematician who, in 1609, figured out the equations for orbiting planets & satellites. In particular, he determined that the planets move in ellipses (flattened circles) rather than true circles.

Isaac Newton: in 1687 he wrote what is probably the single greatest intellectual achievement of all time. In a single book he established the basic laws of force, motion, and gravitation and invented a new branch of mathematics in the process (calculus). He did all this to show how the force of gravity is the reason that planet's orbits follow Kepler's equations.

Konstantin Tsiolkovsky: a Russian school teacher who, without ever launching a single rocket himself, was the first to figure out all the basic equations for rocketry - in 1903!
Some of his greatest achievements include:

• Determining that liquid fuel rockets would be needed to get to space, and that the rockets would need to be built in stages (he called them "rocket trains").
• Concluded that oxygen and hydrogen would be the most powerful fuels to use

Building the First Rockets - Robert Goddard

• An American who is now called "the father of modern rocketry."
• He was a university professor who also developed the theory of rocketry and although he didn't know about Tsiolkovsky's work, reached the same conclusions as Tsiolkovsky. Goddard proved the theory was true.
• In 1926 he launched the world's first liquid fueled rocket. In the course of his experiments in Massachusetts and Roswell, New Mexico, he virtually developed the entirety of rocket technology.
• He invented everything required for modern rocketry and earned over 200 patents. By himself he developed the same components and designs that took the Germans hundreds of scientists and engineers and millions of dollars to develop independently at Peenemunde during World War II.

Convincing the World - Hermann Oberth

• He independently determined the same rocketry principles as Tsiolkovsky and Goddard.
• The difference with Oberth is that in 1929 he published The Rocket Into Interplanetary Space, a highly influential book which was internationally acclaimed and persuaded the world that the rocket was something to take seriously as a space vehicle.

Taking Man Into Space - Wernher Von Braun

• Together with Oberth and an enormous team of scientists and engineers at Peenemunde, he developed and launched the German V2 rocket, the first rocket capable of reaching space.
• At the end of World War II, Von Braun led the top scientists and engineers out of Germany to the Americans (he didn't want to be captured by the Russians).
• He led the US development of military and space exploration rockets. Von Braun was crucial in the effort to convince the US government to pursue a landing of men on the moon, and guided US efforts to success.
• He led the development of the Saturn rockets, the only series of rockets ever developed to have worked perfectly on every launch.

History of Space Travel
From our small world we have gazed upon the cosmic ocean for untold thousands of years. Ancient astronomers observed points of light that appeared to move among the stars. They called these objects planets, meaning wanderers, and named them after Roman deities -- Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the god of love and beauty, and Saturn, father of Jupiter and god of agriculture. The stargazers also observed comets with sparkling tails, and meteors or shooting stars apparently falling from the sky.

Science flourished during the European Renaissance. Fundamental physical laws governing planetary motion were discovered, and the orbits of the planets around the Sun were calculated. In the 17th century, astronomers pointed a new device called the telescope at the heavens and made startling discoveries.

But the years since 1959 have amounted to a golden age of solar system exploration. Advancements in rocketry after World War II enabled our machines to break the grip of Earth's gravity and travel to the Moon and to other planets.

The United States has sent automated spacecraft, then human-crewed expeditions, to explore the Moon. Our automated machines have orbited and landed on Venus and Mars, explored the Sun's environment, observed comets, and asteroids, and made close-range surveys while flying past Mercury, Jupiter, Saturn, Uranus and Neptune. Future historians will likely view these pioneering flights through the solar system as some of the most remarkable achievements of the 20th century.

The earliest solid rocket fuel was a form of gunpowder, and the earliest recorded mention of gunpowder comes from China late in the third century B.C. Bamboo tubes filled with saltpeter, sulphur and charcoal were tossed into ceremonial fires during religious festivals in hopes the noise of the explosion would frighten evil spirits.

Certainly by the year 1045 A.D.--21 years before William the Conqueror would land on the shores of England--the use of gunpowder and rockets formed an integral aspect of Chinese military tactics.

By the beginning of the 13th Century, the Chinese Sung Dynasty, under pressure from growing Mongolian hordes, found itself forced to rely more and more on technology to counter the threat. Chinese ordnance experts introduced and perfected many types of projectiles, including explosive grenades and cannon. The rocket seems to have arrived in Europe around 1241 A.D. Rockets appear in Arab literature in 1258 A.D., describing Mongol invaders' use of them to capture the city of Baghdad.

Quick to learn, the Arabs adopted the rocket into their own arms inventory and, during the Seventh Crusade, used them against the French Army of King Louis IX in 1268. It is certain that, not later than the year 1300, rockets had found their way into European arsenals, reaching Italy by the year 1500, Germany shortly afterwards, and later, England. A 1647 study of the "Art of Gunnery" published in London contains a 43-page segment on rockets. The Italians are credited, by the way, with adopting military rockets for use as fireworks -- completing the circle, so to speak, of the bursting bamboo used at the Chinese festivals 1,700 years earlier.

Dutch military rockets appear by 1650 and the Germans' first military rocket experiments began in 1668. By 1730, a German field artillery colonel, Christoph Fredrich von Geissler, was manufacturing rockets weighing 25 to 54 kilograms (55 to 120 pounds).

As the 18th Century dawned, European military experts began to take a serious interest in rockets -- if only because they, like the Magyars 500 years earlier, found themselves on the receiving end of rocket warfare.

Both the French and the British, during the Eighteenth Century, began wrestling for control of the riches of India. In addition to fighting one another, they also found themselves frequently engaged against the Mogol forces of Tippoo Sultan of Mysore. One of Tippoo Sultan's rockets is now displayed in the Royal Ordnance Museum at Woolwich Arsenal, near London.

Profiting from their Indian experience, the British, led by Sir William Congrieve, began development of a series of barrage rockets ranging in weight from 8 to 136 kilograms (18 to 300 pounds). Congrieve-design rockets were used against Napoleon. An official rocket brigade was created in the British Army in 1818. Rockets came to the New World during the War of 1812.

On December 4, 1846, a brigade of rocketeers was authorized to accompany Maj. Gen. Winfield Scott's expedition against Mexico. The rocket battery was used March 24, 1847, against Mexican forces at the siege of Veracruz. Later, the rockets were used in the capture of the fortress of Chapultepec, which forced the surrender of Mexico City.

The first recorded use of rockets in the Civil War came on July 3, 1862, when Maj. Gen. J.E.B. Stuart's Confederate cavalry fired rockets at Maj. Gen. George B. McClellan's Union troops at Harrison's Landing, VA. Later in 1862, an attempt was made by the Union Army's New York Rocket Battalion to use rockets against Confederates defending Richmond and Yorktown, Virginia. It wasn't an overwhelming success. When ignited, the rockets skittered wildly across the ground, passing between the legs of a number of mules. One detonated harmlessly under a mule, lifting the animal several feet off the ground and precipitating its immediate desertion to the Confederate Army.

As an interesting sidelight, the author Burke Davis, in his book Our Incredible Civil War, tells a tale of a Confederate attempt to fire a ballistic missile at Washington, D.C., from a point outside Richmond, VA.

According to the author, Confederate President Jefferson Davis witnessed the event at which a 3.7 meter (12 foot) solid-fueled rocket, carrying a 4.5 kilogram (10 pound) gunpowder warhead in a brass case engraved with the letters C.S.A., was ignited and seen to roar rapidly up and out of sight. No one ever saw the rocket land. It's interesting to speculate whether, almost 100 years before Sputnik, a satellite marked with the initials of the Confederate States of America might have been launched into orbit.

If the military was lukewarm to rockets, another profession welcomed them with open arms. The international whaling industry developed rocket-powered, explosive-tipped harpoons that were most effective against the ocean-going leviathans.

During the First World War, rockets were first fired from aircraft attempting to shoot down enemy hydrogen gas-filled observation balloons. The French were the principal users of aerial rockets, using a model developed by a Naval lieutenant, Y.P.G. LePrieur.

The principal drawback to rockets throughout this period of development was the type of fuel. Both here and abroad, experiments were under way to develop a more powerful, liquid-propelled rocket. Two young men stand out in this effort -- one an American, Robert H. Goddard -- the other a German, Wernher von Braun.

Von Braun and his colleagues produced a number of experimental designs, the most famous of which was the A-4 rocket, which has gained distinction in history under another name -- the vengeance weapon number two -- V-2 for short. The V-2 was the first successful, long range ballistic missile, and von Braun is credited as its principal developer.

As World War II drew to a close, von Braun led his contingent of several hundred rocket scientists and engineers -- all marked for death by the Nazis to prevent their capture by the Allies -- into American lines.

In 1946, von Braun and his team arrived at White Sands, N.M., where, for the first time, von Braun learned of work done by the American rocket pioneer Robert Goddard.

As the 20th century began, Wilbur and Orville Wright were preparing to become the first men to fly. Goddard, however, was already designing rockets to probe the upper atmosphere and delve into space. Half a world away -- and unknown to Goddard -- a Russian school teacher, Konstantin Tsiolkovsky, was thinking along much the same lines. Both came to the conclusion independently that, if a rocket was going to do the things they dreamed of, it would have to be powered by liquid fuels. Solid fuels of the time simply didn't have sufficient power. Tsiolkovsky lacked Goddard's practicality. While Tsiolkovsky worked out many principles of astronautics and designed suitable rockets, he never built any. By contrast, Goddard was a technical man. He could and did build rockets.

Goddard began his experiments in rocketry while studying for his doctorate at Clark University in Worcester, Mass. He first attracted attention in 1919 when he published a paper that outlined his ideas on rocketry and suggested, none too seriously, that a demonstration rocket should be flown to the Moon.

The general public ignored the scientific merit of the paper -- latching instead onto Goddard's Moon rocket proposal. At the time, such an endeavor was absurd and most dismissed Goddard as a "crank."

The experience taught Goddard a hard lesson -- one that caused him to shy away from future opportunities to publicize his work. Publicity was far from Goddard's mind on the morning of March 16, 1926. On that day, barely a year after Wernher von Braun's rocket wagon fiasco, Goddard launched a liquid-powered rocket he had designed and built from a snow-covered field at his Aunt Effie Goddard's farm in Auburn, Mass. The rocket flew only 46 meters (152 feet) -- about the same distance as the Wright Brothers' first manned flight -- but it did fly! It was the first flight of a liquid-fueled rocket in history.

By December 1934, von Braun scored his first successes with an A2 rocket powered by ethanol and liquid oxygen. Two years later, as plans for the follow-on A3 rocket were being finalized, initial planning began for the A4 rocket. As noted earlier, most know the A4 by another name -- the V-2.

Between 1937 and 1941, von Braun's group launched some 70 A3 and A5 rockets, each testing components for use in the proposed A4 rocket.

The first A4 rocket flew in March 1942. The rocket barely cleared some low clouds before crashing into the sea a half-mile from the launch site. The second launch in August 1942 saw the A4 rise to an altitude of 11 kilometers (7 miles) before exploding. The third try was the charm. On October 3, 1942, another A4 roared aloft from Peenemuende, followed its programmed trajectory perfectly, and landed on target 193 kilometers (120 miles) away. This launch can fairly be said to mark the beginning of the space age. The A4, the first successful ballistic rocket, is the ancestor of practically every rocket flown in the world today.

Production of the A4 began in 1943 and the first A4s, now renamed V2s, were launched against London in September 1944. The V-2 offensive came too late to affect the course of the war. By April 1945, the German Army was in full retreat everywhere and Hitler had committed suicide in his bunker in Berlin.

At an inn near Oberjoch, the Haus Ingeburg, von Braun and over 100 of his rocket experts waited for the end. The entire team had been ordered executed by Hitler to prevent their capture. On May 2, the same day Berlin fell to the Soviet Army, von Braun and his rocket team entered American lines and safety.

With the fighting over, von Braun and his team were heavily interrogated and jealously protected from Russian agents. V2s and V2 components were assembled. German rocket technicians were rounded up. In June, General Eisenhower sanctioned the final series of V2 launches in Europe. Von Braun and his team soon moved to nearby White Sands Proving Ground where work began assembling and launching V2s. By February 1946, von Braun's entire Peenemuende team was reunited at White Sands and, on April 16, the first V2 was launched in the United States. The U.S. space program was under way!

Up to 1952, 64 V2s were launched at White Sands. Instruments, not explosives, packed the missiles' nosecones. A V2 variant saw the missile become the first stage of a two stage rocket named Bumper. The need for more room to fire the rockets quickly became evident and, in 1949, the Joint Long Range Proving Ground was established at remote, deserted Cape Canaveral, Fla. On July 24, 1950, a two-stage Bumper rocket became the first of hundreds to be launched from "the Cape."

The von Braun team worked to develop what was essentially a super-V2 rocket, named for the U.S. Army arsenal where it was being designed -- the Redstone. A version of the Redstone rocket, known as the Jupiter C, was used on January 31, 1958, to launch America's first satellite, Explorer I. Three years later, Mercury Redstones launched Alan Shepard and Virgil I. "Gus" Grissom on suborbital space flights, paving the way for John Glenn's first orbital flight.

In 1958, NASA was established, and, two years later, von Braun, his team, and the entire Army Ballistic Missile Agency were transferred to NASA to become the nucleus of the agency's space program. In seeking its first space pilots, NASA emphasized jet aircraft flight experience and engineering training, and it tailored physical stature requirements to the small cabin space available in the Mercury capsule then being designed. Basically, those 1959 requirements were: Less than 40 years of age; less than 5ft. 11 inches tall; excellent physical condition; bachelor's degree or equivalent in engineering; qualified jet pilot; graduate of test pilot school, and at least 1500 hours of flying time.

More than 500 hundred men qualified. Military and medical records were examined; psychological and technical tests were given; personal interviews were conducted by psychological and medical specialists. At the end of the first screening, many candidates were eliminated and others decided they did not want to be considered further.

Even more stringent physical and psychological examinations followed, and in April 1959 NASA announced its selection of seven men as the first American astronauts. They were Navy Lieutenant M. Scott Carpenter; Air Force Captains L. Gordon Cooper, Jr., Virgil I. "Gus" Grissom, and Donald K. "Deke" Slayton; Marine Lieutenant Colonel John H. Glenn, Jr., and Navy Lieutenant Commanders Walter M. Schirra, Jr., and Alan B. Shepard, Jr..

In 1961, almost as Alan Shepard was drying off from his landing in the Atlantic following his riding a Marshall-designed Redstone rocket on a sub-orbital flight which made him the first American in space, President Kennedy committed this nation to being first on the Moon. NASA's Marshall Center was charged with developing the family of giant rockets that would take us there.

The Saturn rockets developed at Marshall to support the Apollo program and to honor President Kennedy's pledge were, at the time, the most powerful space launch vehicles yet to have been invented.

Engineers, scientists, contractors, and other support personnel built well. On July 20, 1969, a transmission from the Moon's Sea of Tranquility reported: "The Eagle has landed."

Marshall's Saturn rockets first took us around the Moon, then to its cratered surface. Marshall-developed lunar excursion vehicles -- the ungainly Moon Buggies -- carried astronauts on far-ranging excursions in pursuit of samples of lunar soil and rock.

Closer to home, the team at Marshall developed America's first space station -- Skylab. Built to replace the upper stage of a Saturn V moon rocket, the Skylab module was successfully placed in orbit early on May 14, 1973. Placing Skylab in orbit marked a major transition in the story of rocketry. Up until Skylab, the rocket had been the star -- the featured attraction. The focus had been on the up and down -- launch and recovery. For the first time, space became a place in which to live and work.

After Apollo, the team at Marshall tackled designing a revolutionary national space transportation system, which came to be known simply as "The Space Shuttle." It is anything but simple! The space shuttle main engines are among the most powerful, most sophisticated devices ever invented. They represent a quantum leap in technology advancement over the engines that powered the Saturn V. Each of the three main engines in tail of the shuttle can provide almost a half-million pounds of thrust, a thrust equal to that produced by all eight of the Saturn I's first stage engines. Unlike most previous rocket engines, which were designed to be used only once -- and then for only a few minutes -- the space shuttle's main engines are designed to be used again and again, for up to 7.5 hours. The thrust to weight ratio for these engines is the best in the world -- each engine weighs less than 7,000 pounds but puts out the power equivalent of seven Hoover Dams!

Then came the Challenger disaster....

The disaster-enforced hiatus in shuttle operations gave Marshall -- and other NASA installations -- an opportunity to address other shuttle-related concerns. When America returned to manned spaceflight in 1988, it did so in a space vehicle that was vastly safer and more capable.

NASA also is examining using expendable launch vehicles on missions that do not require the shuttle's unique capabilities, and is looking into development of a new generation of heavy lift launch vehicles under its Space Launch Initiative.

These will become the next chapter in the story of rocketry -- a story whose first chapters were written more than 2,400 years ago.

No one can say where our path will lead or when -- hopefully never -- the last chapter in this history will be written.

Chronology of solar system discoveries
From the dawn of history until the beginning of the 17th century the known universe consisted of only 8 bodies:

• Sun
• Mercury
  Venus
• Earth
  Moon
• Mars
• Jupiter
• Saturn
• plus the "fixed" stars. In Europe, the prevailing view was the Ptolemaic system with the Earth at the center and the other bodies revolving around it.

The 17th Century
In 1610 Galileo Galilei first turned a telescope on the heavens and the universe exploded. By the end of the 17th century, nine new bodies had been discovered and Copernicus's heliocentric theory was widely accepted. The total number of known bodies had more than doubled to 17:

The 18th Century
Only five new bodies (not counting comets) were discovered in the 18th century (all by William Herschel) bringing the total to 22. Herschel's most significant discovery was Uranus in 1781.

The 19th Century
The number of bodies in the solar system increased dramatically in the 19th century with the discovery of the asteroids (464 of which were known at by 1899) but only 9 more "major" bodies were discovered. The number of major bodies rose to 31 (almost doubling the 17th century total):

The 20th Century
So far, in 20th century 40 more major bodies (and thousands of comets and asteroids) have been discovered (27 by the Voyager probes) more than doubling the count again to 71:

In the past decade, we have discovered more than twenty planets around other stars, including one just 5 light years away.

The National Aeronautics and Space Administration's (NASA's) automated spacecraft for solar system exploration come in many shapes and sizes. While they are designed to fulfill separate and specific mission objectives, the craft share much in common. Each spacecraft consists of various scientific instruments selected for a particular mission, supported by basic subsystems for electrical power, trajectory and orientation control, as well as for processing data and communicating with Earth.

Electrical power is required to operate the spacecraft instruments and systems. NASA uses both solar energy from arrays of photovoltaic cells and small nuclear generators to power its solar system missions. Rechargeable batteries are employed for backup and supplemental power.

Imagine that a spacecraft has successfully journeyed millions of miles through space to fly but one time near a planet, only to have its cameras and other sensing instruments pointed the wrong way as it speeds past the target! To help prevent such a mishap, a subsystem of small thrusters is used to control spacecraft.

The thrusters are linked with devices that maintain a constant gaze at selected stars. Just as Earth's early seafarers used the stars to navigate the oceans, spacecraft use stars to maintain their bearings in space. With the subsystem locked onto fixed points of reference, flight controllers can keep a spacecraft's scientific instruments pointed at the target body and the craft's communications antennas pointed toward Earth. The thrusters can also be used to fine-tune the flight path and speed of the spacecraft to ensure that a target body is encountered at the planned distance and on the proper trajectory.

Between 1959 and 1971, NASA spacecraft were dispatched to study the Moon and the solar environment; they also scanned the inner planets other than Earth -- Mercury, Venus and Mars. These three worlds, and our own, are known as the terrestrial planets because they share a solid-rock composition.

For the early planetary reconnaissance missions, NASA employed a highly successful series of spacecraft called the Mariners. Their flights helped shape the planning of later missions. Between 1962 and 1975, seven Mariner missions conducted the first surveys of our planetary neighbors in space.

All of the Mariners used solar panels as their primary power source. The first and the final versions of the spacecraft had two wings covered with photovoltaic cells. Other Mariners were equipped with four solar panels extending from their octagonal bodies. Although the Mariners ranged from the Mariner 2 Venus spacecraft, weighing in at 203 kilograms (447 pounds), to the Mariner 9 Mars Orbiter, weighing in at 974 kilograms (2,147 pounds), their basic design remained quite similar throughout the program. The Mariner 5 Venus spacecraft, for example, had originally been a backup for the Mariner 4 Mars flyby. The Mariner 10 spacecraft sent to Venus and Mercury used components left over from the Mariner 9 Mars Orbiter program. In 1972, NASA launched Pioneer 10, a Jupiter spacecraft. Interest was shifting to four of the outer planets -- Jupiter, Saturn, Uranus and Neptune -- giant balls of dense gas quite different from the terrestrial worlds we had already surveyed.

Four NASA spacecraft in all -- two Pioneers and two Voyagers -- were sent in the 1970s to tour the outer regions of our solar system. Because of the distances involved, these travelers took anywhere from 20 months to 12 years to reach their destinations. Barring faster spacecraft, they will eventually become the first human artifacts to journey to distant stars. Because the Sun's light becomes so faint in the outer solar system, these travelers do not use solar power but instead operate on electricity generated by heat from the decay of radioisotopes.

NASA also developed highly specialized spacecraft to revisit our neighbors Mars and Venus in the middle and late 1970s. Twin Viking Landers were equipped to serve as seismic and weather stations and as biology laboratories. Two advanced orbiters -- descendants of the Mariner craft -- carried the Viking Landers from Earth and then studied Martian features from above.

Two drum-shaped Pioneer spacecraft visited Venus in 1978. The Pioneer Venus Orbiter was equipped with a radar instrument that allowed it to "see" through the planet's dense cloud cover to study surface features. The Pioneer Venus Multiprobe carried four probes that were dropped through the clouds. The probes and the main body -- all of which contained scientific instruments -- radioed information about the planet's atmosphere during their descent toward the surface.

A new generation of automated spacecraft -- including Magellan, Galileo, Ulysses, Mars Observer and Cassini -- is being developed and sent out into the solar system to make detailed examinations that will increase our understanding of our neighborhood and our own planet.

Time Line-- Space Exploration (abridged)
October 4, 1957 - Sputnik 1, the first man-made object to orbit the Earth, is launched by the U.S.S.R., and remains in orbit until January 4, 1958.

November 3, 1957 - Sputnik 2, carrying the dog Laika for 7 days in orbit, is launched by the U.S.S.R., and remains in orbit until April 13, 1958.

January 31, 1958 - Explorer 1, the first U.S. satellite in orbit, lifts off at Cape Canaveral using a modified ABMA-JPL Jupiter-C rocket. It carries a scientific experiment of James A. Van Allen, and discovers the Earth's radiation belt.

October 1, 1958 - National Aeronautics and Space Administration (NASA) is founded, taking over existing National Advisory Committee on Aeronautics.

January 2, 1959 - Luna 1, first man-made satellite to orbit the sun, is launched by the U.S.S.R.

September 12, 1959 - Luna 2 is launched, impacting on the moon on September 13 carrying a copy of the Soviet coat of arms, and becoming the first man-made object to hit the moon.

April 1, 1960 - Tiros 1, the first successful weather satellite, is launched by the U.S.

April 12, 1961 - Vostok 1 is launched, carrying Cosmonaut Yuri A. Gargarin, the first man in space.

May 5, 1961 - Mercury Freedom 7 carries Alan B. Shepard,Jr., the first U.S. Astronaut into space.

February 20, 1962 - Mercury Friendship 7 lifts off with John H. Glenn, Jr., the first American in orbit.

December 14, 1962 - U.S. Mariner 2, the first successful planetary spacecraft.

June 16, 1963 - Vostok 6 carries Soviet Cosmonaut Valentia Tereshkova, the first woman in space.

March 18, 1965 - The first space walk is made from Soviet Voskhod 2 by Cosmonaut Alexei A. Leonov.

July 14, 1965 - U.S. Mariner 4 returns the first close-range images about Mars.

April 23, 1967 - Soviet Soyuz 1, carrying Vladimir M. Komarov. It crashed, the first spaceflight fatality.

December 21, 1968 - Apollo 8 is launched with Frank Borman, James A. Lovell, Jr. and William A. Anders, the first Apollo to use the Saturn V rocket, and the first manned spacecraft to orbit the Moon.

July 20, 1969 - Neil Armstrong and Edwin Aldrin, Jr. make the first manned soft landing on the Moon.

September 12, 1970 - Soviet Luna 16 is launched, conducting the first successful return of lunar soil.

May 25, 1973 - First crew to Skylab.

April 12, 1981 - The first manned mission of the Space Transportation System (STS-1), Columbia.

June 19, 1983 - Sally K. Ride is the first U.S. woman to travel in space, on Challenger mission STS-7.

January 28, 1986 - The space shuttle Challenger explodes shortly after liftoff of mission STS-51L.

February 20, 1986 - The core unit of Soviet space station Mir is launched.

April 24, 1990 - Space Shuttle Discovery launches the Hubble Space Telescope.

July 4, 1997 - Mars Pathfinder becomes the first probe to successfully land on Mars since Viking 2 in 1976. It is also the first planetary probe to include a separate roving robot probe (Sojourner) since the Soviet Union's Luna 21 in 1973.

October 29, 1998 - Space Shuttle Discovery lifts off with John Glenn aboard, first American to orbit Earth and at 77, the oldest man to fly in space.

November 20, 1998 - the first component of the International Space Station, Zarya, is launched.

December 11, 1998 - Mars Climate Orbiter is launched by NASA. The probe is lost due to an error in propulsion software.

January 3, 1999 - Mars Polar Lander lifts off on its ill-fated mission to Mars.

October 31, 2000 - the Expedition One crew is launched on a Soyuz transport to become the first crew of the ISS.

January 9, 2001 - the first launch of the "true" millenium is Chinese, with the second test flight of the manned Shenshou spaceship, reported to be carrying a monkey, a dog, and a rabbit.

March 23, 2001 - fifteen years after its first launch, and after nearly 10 years of continuous occupation by astronauts, the Mir space station is de-orbited, breaking up in the atmosphere and impacting in the Pacific Ocean.

April 7, 2001 - the 2001 Mars Odyssey probe is launched on a trajectory for Mars orbit to be achieved in October, with a mission similar to that of the Mars Climate Orbiter launched December 1998.

April 28, 2001 - Soyuz spacecraft TM-32 lifts off for the ISS with the first space tourist, business executive Dennis Tito, who pays the Russians $20 million for the ride.