- December 21 marks the 50th anniversary of NASA's Apollo 8 moon mission, which was the first crewed flight to the moon.
- Humanity has since racked up an impressive list of firsts in human and robotic spaceflight.
- Our spacecraft have visited every planet in the solar system, reached interstellar space, sampled comets and asteroids, enabled astronauts to live in orbit for two decades, and more.
The year 1968 is not exactly remembered as a great time in the US, let alone on Earth.
"There was the Vietnam War going on, it was not a popular war, especially with the younger people," Jim Lovell, a retired NASA astronaut, previously told Business Insider. "There were riots, there were two assassinations of prominent people during that period, and so things were looking kind of bad in this country."
But Lovell and his fellow crew members' unprecedented mission to the moon - Apollo 8 - brought much of America and the world together.
They entered the history books as the first humans ever to leave Earth's clutches, reach the moon, and orbit it. They were also the first to see and personally describe the humbling splendour of our planet from almost 390,000km away.
"When I put my thumb up to the window I could completely hide it," Lovell said. "Then I realised that behind my thumb that I'm hiding this Earth, and there are about 6 billion people that are all striving to live there."
Since that first lunar flight almost exactly 50 years ago, humanity has reached even farther and more ambitiously into space.
Here are some of the most important feats of human and robotic spaceflight since Apollo 8.
Apollo 8 astronauts launched on the first-ever crewed moon mission on December 21, 1968.
Lovell and his crew mates Frank Borman and Bill Anders became the first humans to orbit the moon on December 24, 1968. Their mission was to study the moon and photograph its surface for possible landing sites.
Apollo 8 is famous for the "Earthrise" photo that showed how small the planet looks in the void of space. Lovell previously told Business Insider that this view made him think, "you go to heaven when you're born."
Apollo 11 put people on the lunar surface for the first time on July 20, 1969.
It was "a giant leap for mankind," Neil Armstrong famously said. Buzz Aldrin followed him onto the moon while their crew mate Michael Collins remained in orbit.
The astronauts returned home with a cache of rocks, dust, and stunning photos. After they landed, NASA put the three men in quarantine for 21 days to make sure they had not brought any lunar contagions back to Earth.
Venera 7 became the first robot to land on another planet (Venus) on December 15, 1970.
The Soviet spacecraft was designed to land on Venus, but its parachute ripped during the descent and Venera 7 slammed into the surface. However, the plucky robot still managed to send back data on the planet's temperature, atmospheric pressure, and wind speed before its signal stopped.
The Soviet Union launched Salyut 1, the world's first space station, on April 19, 1971.
Salyut 1 was 14m long and had just one docking port. The first crew aboard Salyut 1 spent 23 days at the station, but the three men tragically died on their way back to Earth when all the air leaked out of their Soyuz spaceship.
Mariner 9 became the first satellite to orbit another planet (Mars) on November 14, 1971.
NASA's Mariner 9 probe transformed what we previously knew about Mars: it discovered that the planet used to have water. The satellite also took the first images of Mars' polar caps and its two moons, Phobos and Deimos.
Mars 3 achieved the first successful soft landing on the Martian surface on December 2, 1971.
The Soviet lander reached the red planet's surface, but failed just 20 seconds after touching down. The first fully fruitful Martian surface mission wouldn't occur until NASA's nuclear-powered Viking 1 and Viking 2 landers got to Mars in 1976.
Apollo 17, NASA's last crewed mission to the moon, left the lunar surface on December 14, 1972. No crewed spacecraft has landed on the moon since.
The Apollo 17 mission collected just over 100kg of samples - more rock and soil than any prior lunar mission.
A study published in April 2018 found that collectively, the astronauts who walked on the moon probably caused its surface to warm up by as much as 6 degrees Fahrenheit (-14 degrees Celsius) because of the dust they kicked up. The research was based on heat-flow experiments that astronauts installed during the Apollo 15 and Apollo 17 missions.
Pioneer 10 became the first spacecraft to fly by Jupiter on December 3, 1973.
NASA launched the spacecraft in March 1972, and it became the first probe ever to pass through the Asteroid Belt. Pioneer 10 revealed to Earthlings that Jupiter is predominantly a liquid planet. The spacecraft also returned data about Jupiter's magnetic field and radiation belts.
Mariner 10 made the first visit to Mercury on March 29, 1974.
NASA's Mariner 10 flew by Mercury three times, photographing half of the planet's surface. Data collected by the spacecraft showed that Mercury has a metallic core that makes up about 80% of the planet's mass. Mariner 10 also found that Mercury's temperatures range from 187 degrees Celsius to -183 degrees.
Viking 1 became the first US lander to reach Mars on July 20, 1976.
The lander spent six years taking thousands of photos for NASA. It gathered data on conditions like weather patterns and radiation - factors we'd need to understand before putting humans on Mars. Viking 1 found that Mars' weather was consistent on a day-to-day basis, though the planet experiences seasonal variations.
NASA's twin Voyager probes launched in 1977, starting a "Grand Tour" of the solar system that was made possible by a rare planetary alignment.
NASA's Voyager twins are the longest-operating, farthest-flying space probes in human history. Voyager 2 launched first, on August 20, 1977, and Voyager 1 launched on September 5.
The numbers aren't based on order of launch; rather, scientists knew Voyager 1 would eventually fly faster and farther than Voyager 2.
Over many years, Voyager 1 took advantage of a rare planetary alignment that occurs only once every 176 years to perform a "Grand Tour" of the outer solar system. The probe visited both Uranus and Neptune for the first time. The spacecraft are also the only two ever to reach interstellar space - the void between stars.
Pioneer 11 made the first flyby of Saturn on September 1, 1979.
Pioneer 11 passed Jupiter in late 1974, and the planet's gravity gave the probe enough of a boost to reach Saturn. Both Pioneer 10 and Pioneer 11 carried plaques that include basic information on the human race.
Space shuttle Columbia, the world's first reusable spacecraft, first launched on April 12, 1981.
NASA's space shuttle programme flew 133 successful missions between 1981 and 2011. The fleet included five main spaceships: Columbia, Challenger, Discovery, Atlantis, and Endeavour.
Two missions failed. Challenger broke apart during a launch in 1986, killing all seven crew, including teacher Christa McAuliffe. In 2003, Columbia was destroyed during re-entry on its 28th mission, killing seven people.
American Bruce McCandless II completed the first spacewalk without a tether on February 7, 1984.
The astronaut's spacewalk near the Challenger space shuttle was the first use of the Manned Maneuvering Unit, a device that was propelled by nitrogen and controlled by hand. The MMU allowed McCandless to move more freely than previous astronauts who needed to be tethered to a spacecraft.
The first spacewalk ever (with a tether) was conducted nine years prior, by cosmonaut Alexey Leonov on March 18, 1965.
Voyager 2 made its closest approach to Uranus in the first-ever flyby of the planet on January 24, 1986.
Voyager 2's closest approach to Uranus was 80,400km away from the planet's cloud tops. Data from this part of the Voyager mission helped NASA scientists discover 11 new moons and two new rings.
Voyager 2 then came within 4,800km of Neptune in the first-ever flyby of that planet on August 25, 1989.
After leaving Uranus, Voyager 2 came within 4,800km of Neptune's north pole.
Both Voyager probes are still going. In November 2018, NASA data indicated that Voyager 2 had exited the heliosphere, which is the main region of the sun's influence.
The Hubble Space Telescope launched on April 24, 1990.
The Hubble Space Telescope is the biggest advancement in astronomy since Galileo's discoveries in the 1600s. Scientists have used Hubble to study planets in our solar system, observe distant stars, and learn more about other galaxies.
Cosmonaut Valeriy Polyakov returned to Earth after the longest human stay in space on June 1, 1995.
On January 8, 1994, Polyakov flew to the Soviet Union's Mir space station and spent nearly 438 consecutive days in space. He orbited the Earth 7,075 times. Polyakov was trained as a doctor so that he could provide medical help in space.
Cassini launched on October 16, 1997 — the first (and so far only) probe dedicated to exploring Saturn and its moons.
Cassini's launch was contentious, since the spacecraft contained about 33kg of red-hot plutonium-238 - a nuclear fuel that can power a probe for decades. But the probe succeeded in making incredible discoveries and capturing stunning images that have changed our view and understanding of Saturn.
Cassini spent about 13 years orbiting the world and studying its icy moons, several of which may have oceans and possibly even alien life. When it was time to end the mission, NASA had the Cassini spacecraft execute a series of risky "dives" between the planet and it enigmatic rings. Cassini eventually plunged into the clouds of Saturn on September 15, 2017, destroying the roughly 2,100kg orbiter.
NASA's Deep Space 1, the first interplanetary robot to use ion thrusters, launched on October 24, 1998.
After launch, Deep Space 1 started up its ion engines to begin a slow, steady, and record-breakingly efficient journey to asteroid 9969 Braille and comet Borrelly. The mission demonstrated that xenon-ion thrusters could be used to explore space while minimising the need for cumbersome fuel. This breakthrough led to the Dawn mission's exploration of the Asteroid Belt.
NASA launched the Stardust mission to collect the first comet samples on February 7, 1999.
In 2004, Stardust flew by the comet Wild-2, capturing comet and interstellar dust in a space-age material called aerogel (which was originally discovered in 1931). The spacecraft allowed scientists to look at extraterrestrial material from beyond the moon for the first time, though it took two years for the samples to make it back to Earth.
The first crew docked at the International Space Station on November 2, 2000.
Astronaut Bill Shepherd as well as cosmonauts Yuri Gidzenko and Sergei Krikanev delivered more than 20 tons of equipment to the earliest iteration of the International Space Station (ISS).
They spent more than four months at the orbiting laboratory, kicking off what would become the longest continuous human habitation of space. People have been living in orbit ever since. The ISS has since seen more than $150 billion of investment and has grown to the size of a football field.
A spacecraft landed on an asteroid for the first time on February 12, 2001.
The NEAR Shoemaker spacecraft launched on February 17, 1996 and began orbiting the asteroid 433 Eros on February 14, 2000. Almost a year after that, NEAR spacecraft landed on the asteroid's surface. At the time, asteroid 433 Eros was 315 million kilometres away from Earth. NEAR survived the landing and returned data about the asteroid's surface.
Dennis Tito became the world's first space tourist on April 28, 2001.
The American businessman paid his way onto the International Space Station, travelling aboard a Russian Soyuz spacecraft to get there.
Tito spent six days in space and reportedly paid $20 million for the flight. The private spaceflight industry has grown dramatically since then, with companies like SpaceX, Blue Origin, and Virgin Galactic working on their own spaceships.
China sent its first taikonaut into space on October 15, 2003.
Yang Liwei's flight as the first taikonaut, or Chinese astronaut, lasted about 21 hours.
A private spaceship flew past the edge of space twice in less than a week on October 4, 2004. This feat led its builder, Scaled Composites, to win a $10 million prize.
The $10 million Ansari X Prize was a competition created to encourage private industry to explore space.
Scaled Composites was one of 26 teams in the contest, and the first to meet the X Prize's goal: to fly a crewed reusable spacecraft beyond the edge of space twice in less than one week. Scaled Composites accomplished this using a rocket-plane called SpaceShipOne (SS1).
The company's designs and know-how were scooped up by Richard Branson to establish Virgin Galactic, a suborbital space tourism company. SS1 was retired shortly after the historic flight and is now located at the National Air and Space Museum in Washington, DC.
The European Space Agency's Huygens probe became the first to land on the moon of another planet (Saturn's moon Titan) on January 14, 2005.
Titan is freezing, giant, and weirdly Earth-like. The Huygens probe, which NASA's Cassini spacecraft deployed, helped scientists study Titan's atmosphere and surface. Scientists learned that the moon of Saturn is rich with liquid hydrocarbons, and they now believe it might even hide a subsurface ocean of water.
Taikonaut Zhai Zhigang completed China's first spacewalk on September 27, 2008.
The taikonaut pulled himself out of the Shenzhou VII spacecraft while it was in orbit, attached himself to a handrail with two safety cords, and waved at a camera during a live broadcast in China.
SpaceX launched its Falcon 1 rocket on December 8, 2010, making it the first company to send a spacecraft into orbit on a privately developed rocket.
Elon Musk had nearly gone bankrupt trying to get his aerospace startup, SpaceX - and specifically its Falcon 1 rocket - off the ground. After three failures, a fourth flight finally succeeded, proving to the world that a company like Musk's could use private funding to successfully develop an orbital-class rocket. SpaceX went from being laughed at to upending the entire launch industry with a growing fleet of reusable, lower-cost rockets. The company is now worth more than $27 billion.
A Japanese spacecraft brought the first samples of an asteroid back to Earth on June 13, 2010.
Hayabusa brought back samples of a near-Earth asteroid called 25143 Itokawa. After launching in May 2003, parts of the spacecraft's solar cells were zapped by a solar flare. Despite this problem and a series of others, the probe managed to land on the Itokawa asteroid, collect dust samples, and bring them back to our planet.
Robonaut 2 became the first humanoid robot in space on February 24, 2011.
NASA scientists designed the 150kg robot to use the same tools as its human coworkers on the International Space Station, where it remains today.
Robonaut 2 initially only had a head and arms, but scientists have since added legs. In the future, NASA plans to have the contraption perform the first-ever humanoid robot excursions to maintain, repair, and perform experiments in the vacuum of space outside of the ISS.
NASA launched the last mission of its space shuttle programme on July 8, 2011.
Space shuttle Atlantis delivered a four-person crew to the International Space Station, along with thousands of kilograms of supplies and some spare parts. Atlantis' 5.2-million-mile journey around Earth was the space shuttle programme's 135th and final mission.
Today, NASA is working with private partners such as SpaceX and Boeing to develop vehicles that can deliver cargo and astronauts to and from space.
Voyager 1 entered interstellar space on August 25, 2012.
The heliosphere is a major border in the solar system - it's the bubble in which charged particles and magnetic fields from the sun have influence.
In mid-2014, NASA scientists said Voyager 1, which launched in 1977, had moved out of the heliosphere and into interstellar space. It's identical yet slower-moving twin, Voyager 2, left the heliosphere in November 2018.
The European Space Agency's Philae lander touched down on a comet for the first time on November 12, 2014.
Philae successfully touched down on the comet 67P/Churyumox-Gerasimenko more than 10 years after leaving Earth. Although the lander bounced into a crevasse, it managed to record photos of the comet's surface as well as valuable data about its composition.
Scientists lost contact with Philae in 2015, but the lander was found by the follow-up mission Rosetta in September 2016.
NASA's Dawn spacecraft made the first visit to a dwarf planet on March 6, 2015.
Dawn touched down on the dwarf planet Ceres roughly eight years after leaving Earth. Before coming to Ceres, Dawn studied the protoplanet Vesta, which is the second-largest body in the Asteroid Belt. The spacecraft revealed to planetary scientists that Ceres may hide an ocean of liquid water.
New Horizons visited Pluto and its moons for the first time in history on July 14, 2015.
It took NASA's nuclear-powered New Horizons probe about nine years to reach Pluto - the first visit ever to the now-dwarf planet. The flyby sent back unprecedented pictures of the world along with loads of scientific data.
From that information, scientists have learned that Pluto has an atmosphere that's about 700 times thinner than Earth's. They also think the dwarf planet might have a toxic ocean of ammonia and water hiding beneath its surface. Some experts argue that these recent findings mean Pluto should be reclassified yet again, as a giant comet.
SpaceX landed its first orbital rocket booster on December 21, 2015.
The first successful launch and landing of a Falcon 9 rocket booster was a sea-change for SpaceX and the launch industry overall. This success proved Musk's aerospace company could recover Falcon 9 rockets and later relaunch them, an ability that greatly reduces the steep cost of sending cargo and spacecraft into orbit.
SpaceX launched a car to Mars with a Falcon Heavy rocket on February 6, 2018.
Falcon Heavy's first flight secured its title as the world's most powerful operational rocket. Since explosions are likely during experimental launches, companies typically send a boring payload into space, like massive blocks of steel or concrete.
However, Musk chose to send up his own red Tesla Roadster with a spacesuit-clad dummy named "Starman" in the driver's seat. The vehicle, which was equipped with three cameras, has since sped beyond the orbit of Mars, SpaceX said in November.
The Juno probe photographed the stormy, swirling poles of Jupiter for the first time on August 27, 2016.
Until NASA's tennis-court-size Juno spacecraft started zipping around Jupiter at 130,000 mph, no one had ever seen the gas giant's north and south poles. These high-speed flybys are called perijoves, and they happen every 53.5 days.
China launched the first mission to touch the far side of the moon on December 7, 2018.
In January 2019, Chang'e-4 aims to set down a rover and lander on the part of the lunar surface that Earth never sees. The robots will study the moon's geology and chemistry in an ancient impact crater, and China will also examine whether the area would be a good fit for a deep-space radio telescope or even a base for humans.
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