Though human spaceflight could never have been achieved without the initial work of aviation pioneers like the Wright Brothers, the greatest achievements have been made in the past 50 years.
Here is a timeline of the highs and lows of spaceflight since the first orbital flight in 1961:
April 12, 1961: Cosmonaut Yuri Gagarin makes the first human spaceflight when he orbits the Earth in the Soviet Union's Vostok 1 capsule.
May 5, 1961: Astronaut Alan Shepard becomes the first American to fly into space during a suborbital flight aboard NASA's Mercury 3 mission capsule, also known as Freedom 7.
Feb. 20, 1962: John Glenn becomes the first American to orbit the Earth, piloting NASA's Mercury 6 mission capsule, also known as Friendship 7.
June 16, 1963: The first woman in space is Valentina Tereshkova, launched by the Soviet Union on board the Vostok 6 capsule.
March 18, 1965: The Soviet Union's Aleksei Leonov makes the first spacewalk ever when he dons an extra-vehicular activity backpack and steps outside the Voskhod 2.
June 3, 1965: Astronaut Edward White makes the first American spacewalk when he steps outside NASA's Gemini 4 capsule.
Jan. 27, 1967: An electrical fire during a ground-based training session on NASA's Apollo 1 capsule kills all three crew members.
April 24, 1967: Cosmonaut Vladimir Komarov becomes the first person to die during a spaceflight when the parachute on his Soyuz 1 capsule fails to open as he returns to Earth.
Dec. 24, 1968: Astronauts William Anders, Frank Borman and Jim Lovell become the first humans to orbit the moon. They are in NASA's Apollo 8 spacecraft.
July 20, 1969: Astronaut Neil Armstrong of the Apollo 11 mission becomes the first person to set foot on the moon.
June 30, 1971: The Soviet Union's Soyuz 11 capsule returns to Earth as planned, but technicians soon discover that the three crew members inside are dead. It is discovered that an oxygen leak during re-entry caused the crew to suffocate.
Dec. 7-19, 1972: NASA's Apollo 17 mission marks the last time humans visit the moon.
May 25, 1973 - June 22, 1973: Astronauts Pete Conrad, Joseph Kerwin and Paul Weitz spend a record 28 days in space during a visit to NASA's Skylab space station.
July 15, 1975: Despite the Cold War, astronauts from the United States and the Soviet Union meet up in space for the first time during a rendezvous between the Apollo 18 and Soyuz 19 spacecraft.
July 16, 1979: The Skylab space station re-enters Earth's atmosphere as planned and disintegrates over the Indian Ocean and Western Australia.
April 12, 1981: Astronauts Robert Crippen and John Young fly the U.S. space shuttle for the first time. The shuttle, called Columbia, disintegrates during another flight 22 years later, killing seven crew members.
June 18, 1983: Astronaut Sally Ride becomes the first American woman in space -- two decades after the Soviet Union launched a woman in space.
Jan. 28, 1986: Space shuttle Challenger explodes just after launch, killing all seven astronauts on board.
Feb. 19, 1986: The Soviet Union launches the first module for the new Mir space station.
Nov. 20, 1998: The Soviet Union launches the first component of the International Space Station.
Nov. 2, 2000: The International Space Station gets its first crew, which includes one American astronaut and two Russian cosmonauts.
March 23, 2001: The Russian Mir space station re-enters Earth's atmosphere and falls into the Pacific Ocean as planned.
Feb. 1, 2003: The seven crew members of space shuttle Columbia are killed when their shuttle breaks up over the United States upon re-entry.
Oct. 15, 2003: China launches its first manned space mission. Yang Liwei is at the controls.
June 21, 2004: Mike Melvill becomes the first human to make a suborbital space flight without government backing. He is flying on board SpaceShipOne, a privately built spacecraft.
Oct. 4, 2004: Brian Binnie helps the SpaceShipOne team win the Ansari X Prize by piloting the spacecraft to an altitude of 100 kilometers. It is the second time the spacecraft has reached that height within 14 days, as required by the prize rules.
