Space has always been infinitely wondrous and frustrating. A few centuries ago it was entirely misunderstood. Just five decades ago it remained inaccessible, little more than a dream generator. Now its nearest reaches are partly conquered.

Yet the bulk of space remains unexplored. Nearby planets, faraway stars and untold dark corners invite inspection by the latest technology or the bravest humans.

Leaving Earth: January 31, 1958
NASA's early years involved a game of catch-up, and failure was more a rule than an exception. Beaten into space by the Soviet Union's launch of Sputnik on Oct. 4, 1957, a nervous United States lofts Explorer 1 into orbit during the Cold War.

Lunar Flyby: March 3, 1959
After several dismal attempts to send a probe to the Moon (most did not escape Earth orbit, some blew up before even leaving the atmosphere) Pioneer 4 gets close. It goes the distance, missing the Moon by 37,500 miles (60,500 kilometers). The Russians had already sent a probe past the Moon in January, and in September they would score the first direct lunar hit.

First American in Space: May 5, 1961
Alan Shepard, a former Navy test pilot, becomes the first American in space. His flight is a mere 15 minutes long on a suborbital trajectory. The triumph comes with a huge footnote: On April 12, 1961, the Soviet Union had made fighter pilot Yuri Gagarin the first man in space. Gagarin also orbited the planet, once, in a 108-minute flight.

First American in Orbit: February 20, 1962
The charismatic John Glenn becomes the first American to orbit Earth, aboard Friendship 7. He circles the planet three times and returns the same day, amid concern that a potentially dislodged heat shield might lead to disaster. America is poised to take over the lead in the Space Race, but victory will be years in the making, and there will be a human price to pay.

First Interplanetary Spacecraft: August 27, 1962
Mariner 2 flies by Venus and sends back pictures of the mysterious, cloud-shrouded planet.

Gemini 8 Tumbles: March 16-17, 1966
The race to the Moon requires maneuverable spacecraft. The Gemini missions serve the role of developing this technology. A maneuvering thruster on Gemini 8 malfunctions, however, and the craft tumbles through space. Neil Armstrong and Dave Scott use their re-entry control system to stabilize the craft, barely escaping disaster.

Surveying the Moon: 1966
The Surveyor landers begin exploring the surface of the Moon while a series of Lunar Orbiters photograph it from above. The combined effort yields science and paves the way for the Apollo landings.

Apollo 1 Fire: January 27, 1967
Virgil I. "Gus" Grissom, Edward White and Roger Chaffee die in a blaze inside their Apollo capsule during a countdown test three weeks before a scheduled liftoff at Kennedy Space Center. The fire feeds off the command module's pure oxygen environment, and rescue personnel can't open a cumbersome hatch. An electrical short is later determined to be the likely cause. The Apollo program is delayed for 20 months.

Saturn Rocket Success: November 9, 1967
In a technological turning point for the Apollo program, the first Saturn rocket, tall as a football field is long, powers into the sky in a test launch.

Men near the Moon: December 24, 1968
Apollo 8 carries Frank Borman, Jim Lovell and Bill Anders to an orbital journey around the Moon. For 20 hours, they take pictures and make observations. Their re-entry speed back at Earth of 25,000 mph (40,230 kph) is faster than humans had ever traveled. Among their legacies is to turn the human view of the cosmos upside down with a picture of Earth rising above the Moon.

Men on the Moon: July 20, 1969
"Houston, Tranquillity Base here," says Neil Armstrong. "The Eagle has landed." With these words we learn that the first men are on the Moon. Armstrong plants his foot in the dust of the Sea of Tranquillity about seven hours later and declares: "That's one small step for [a] man, one giant leap for mankind." Buzz Aldrin follows Armstrong to the surface. Mike Collins remains in orbit aboard Columbia, the command ship of Apollo 11. The mission had lifted off on July 16, and the crew would return to Earth July 24.

Apollo 13: April 11, 1970
A near disaster becomes one of NASA's finest moments. Apollo 13 lifts off on this day with no trouble. About 55 hour later, however, an oxygen tank explodes. Jim Lovell, Jack Swigert and Fred Haise abort the mission. They employ the lunar lander as a lifeboat, using its oxygen, radio and engines. Exhausted and nearly frozen, the crew splashes down safely April 17. By 1972, the return of Apollo 17 would mark the end of human trips to the Moon.

Mariner 9: May 9, 1971
With the only obvious and nearby physical target somewhat conquered, NASA turns to robots to explore deeper into space. Mariner 9 goes into orbit around Mars and starts mapping the planet, revealing volcanoes and canyons larger than any seen on Earth.

On to Jupiter: March 3, 1972
Pioneer 10 completes the first flyby of an outer planet, Jupiter.

Early Cooperation: July, 1975
The first international piloted space mission takes place as three U.S. astronauts and two Soviet cosmonauts meet up when an Apollo command module docks with a Soyuz module. The Apollo-Soyuz Test Project (ASTP) is the last flight of a Saturn-series rocket and an Apollo capsule. It would be almost six years before Americans return to space.

Mars up Close: July 20, 1976
Viking 1 lands on Mars, becoming the first spacecraft to safely touch down on another planet. No life is found, but much is learned about the Martian soil and atmosphere that will inform and inspire future missions.

Back to Space: April 12, 1981
Commander John Young, an Apollo and Gemini veteran, and rookie copilot Bob Crippen guide the most complex space vehicle ever built into orbit. The mission is named STS-1, for Space Transportation System. The craft: The Space Shuttle Columbia. By 1984, shuttle astronauts would make the first in-space repair of a satellite. In 1985, a fleet of four shuttles would complete nine missions, and talk of putting regular citizens in space would rumble within NASA.

Sally Ride: June 18, 1983
In an era when spaceflight is becoming routine and astronauts anonymous, Sally Ride captures the hearts and imaginations of kids and adults as the first American woman in space. She first flies aboard Challenger. Ride goes on to devote much of her time to educating children and, in particular, working to inspire girls to study science. An important footnote: The Russians had put a woman in space clear back in 1963. Valentina Tereskhkova, a former cotton mill worker, spent nearly three days aboard Vostok 6.

Challenger Explosion: January 28, 1986
In the worst space accident to date, the Space Shuttle Challenger disintegrates 73 seconds after liftoff, killing all seven astronauts aboard. They were: Francis R. "Dick" Scobee, Michael Smith, Judith Resnick, Ellison Onizuka, Ronald McNair, Gregory Jarvis and schoolteacher Christa McAuliffe. The external fuel tank explodes, destroying the orbiter. O-ring seals in one of the two solid rocket boosters are ultimately blamed, with cold weather a factor. Shuttle flights don't resume until September 1988.

Hubble Space Telescope: April 24, 1990
The shuttle program helps prove its worth by launching the $1.5 billion telescope into orbit. Hubble's eyesight is severely flawed, and in a 1993 shuttle mission astronauts would perform a remarkable space walk and fix Hubble by installing corrective lenses. Thereafter, Hubble would reveal the universe beyond our solar system more spectacularly than any other hunk of metal in history.

Voyager Looks Back: 1991
The twin Voyager spacecraft showed us the solar system, often in ways we could not imagine. In 1991, Voyager takes a picture of Earth from more than 4 billion miles away. In his 1994 book Pale Blue Dot, Carl Sagan employs the photograph as a metaphor for the insignificance of our world compared to the cosmos.

Mars Observer Disappears: August 21, 1993
In one of the most serious setbacks ever to NASA's robotics program, contact is lost with Observer just as it is set to go into orbit around Mars. The $1 billion loss would compel NASA toward a future of smaller, cheaper spacecraft performing more specific duties.

Historic Visit: June 27, 1995
The Space Shuttle Discovery docks with the Mir space station, renewing a space partnership with the Russians and beginning to lay the foundation for working together that would lead to the construction of the International Space Station.

Pathfinder Wows: July 1997
NASA returns to Mars with great flourish, and the timing could not have been better. A fledgling Internet provides a medium for daily release of photographs and data from Pathfinder and its cute companion, the Sojourner rover.

All Aboard: November 2, 2000
The first crew boards the International Space Station after arriving in a Russian Soyuz craft. Expedition 1, as they are known, is led by Commander Bill Shepherd, who dubs the station "Alpha." With him are Russian cosmonauts Yuri Gidzenko and Sergei Krikalev. The orbiting outpost was first proposed in 1984 by President Ronald Reagan.

A New Odyssey: October 23, 2001
After two more Mars failures in 1999 -- Mars Climate Orbiter, Mars Polar Lander -- the Mars program is back on track with the arrival of Odyssey. Shortly after going into orbit, Odyssey returns the most compelling data to date for vast amounts of frozen water very near the surface of the dusty planet. It is water that many scientists think will compel NASA to eventually send humans to Mars.

Columbia Tragedy: February 1, 2003
The Space Shuttle Columbia disintegrates over Texas upon re-entry into Earth's atmosphere. All seven astronauts die. They are: Rick Husband, Laural Clark, Bill McCool, Dave Brown, Kalpana Chawla Mike Anderson and Ilan Ramon, the first Israeli in space.

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