25 Unforgettable Moments in Space Exploration to Celebrate the 53th Anniversary of Apollo 11 The moon landing was just the beginning.

On July 20, 1969, 650 million people watched as Neil Armstrong and Buzz Aldrin became the first humans to walk on the moon. NASA's lunar landing was years in the making, a feat of engineering and ingenuity taken on by a team of more than 400,000 people to test and build the spacecraft, rockets, suits and instruments on board and to calculate how to get Armstrong, Aldrin and Michael Collins safely there and back -- although at the time there was no guarantee that would be the case.

The space race kicked into high gear in April 1961 when Russian cosmonaut Yuri Gagarin became the first human to orbit the Earth. While the Soviet Union's accomplishment spurred the United States to put a man on the moon before the 1960s came to a close, space exploration has long since become a more internationally collaborative affair.

In the private sector, Virgin Galactic announced that it was going public in 2019, making it the first space tourism company to be publicly listed, beating out main competitors Jeff Bezos's Blue Origin and Elon Musk's SpaceX.

Related: Buzz Aldrin Wants You to Know -- the Sky Is Not the Limit

The company said that it received customer reservations from more than 600 people in 60 countries, who put down $80 million in collected deposits for the chance to head up to space on one of Virgin Galactic's spacecrafts.

Virgin Galactic's founder Richard Branson said at the time that he was aiming to take his first suborbital flight on the lunar landing anniversary. While there hasn't been any official announcements from Branson that he will be making the trip yet, there definitely will be people traveling to space on that special date.

On July 20, 2019, exactly 50 years to the date of the Apollo 11 launch, cosmonaut Alexander Skvortsov, NASA astronaut Andrew Morgan and European Space Agency astronaut Luca Parmitano, who hails from Italy, traveled to the International Space Station. They joined fellow Expedition 60 crew members, NASA astronauts Christina Koch and Nick Hague and cosmonaut Alexey Ovchinin, the current ISS commander.

Read on to glance back on some historic moments and look ahead to what's on the horizon for space exploration.

Don't stop me now.

On March 22, 1946, a rocket called the JPL-Ordnance Wac was the first American rocket to leave earth's atmosphere.

Here's looking at you.

1946 was a big year for out-of-this-world achievements. On Oct. 24, a V2 rocket launched from the White Sands Missile Range in New Mexico equipped with a 35-millimeter camera and captured the first ever images of earth from space.

The space race begins.

On April 12, 1961, the space race was kicked off in earnest when Soviet cosmonaut Yuri Gagarin became the first human ever in Earth's orbit.

America gets in the game.

On May 5, 1961, astronaut Alan B. Shepard completed the Freedom 7 mission -- the United States' first suborbital flight. In July, Virgil I. "Gus" Grissom, completed the second suborbital mission for NASA.

To put a man on the moon.

On May 25, 1961, President John F. Kennedy addressed Congress about the necessity to invest in space exploration, famously saying, "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space; and none will be so difficult or expensive to accomplish."

Beaten to the punch.

From Jan. 31 to Feb. 3, 1966, an unmanned Soviet spacecraft called Luna 9 made the first successful soft landing on the moon and then sent the first radio television transmission back to earth.

Making an impact.

On March 1, 1966, another Soviet ship, the Venera 3, became the first spacecraft to impact the surface of another planet on its mission to Venus.

First contact.

A few months later, on June 2, 1966, Surveyor 1 becomes the first U.S. spacecraft to land on the moon.

Competition is mounting.

On May 19, 1971, Russian spacecraft Mars 2 became the first to make an impact on Mars, with the first soft landing on the planet following on May 28.

Take a lap.

But on Nov. 13, 1971, Mariner 9, an unmanned NASA probe, completed an orbit around Mars and is the first spacecraft to orbit around another planet.

The Red Planet.

A month later, on Dec. 2, 1971, Russia's Mars 3 completes the first unmanned landing on Mars.

A new frontier.

On July 20, 1976, NASA's Viking 1 was the first successful U.S. mission to land on the surface of Mars. Viking 1 ultimately spent four years and conducted 1,489 orbits of the planet, while Viking 2, which arrived on Sept. 3, 1976, worked until July of 1978. Both transmitted images and studied the terrain of the planet, searching for possible life and sending back valuable information to NASA, laying the groundwork for the Curiosity Mars Rover's memorable arrival in 2012.

A tragic day.

On Jan, 28, 1986, the Challenger Space Shuttle explosion saw the terrible loss of the seven crew members on board.

Step right up.

The first-ever commercial space tourist, an American millionaire and businessman from New York named Dennis Tito, hitched a ride up to the International Space Station on the Russian Soyuz-TM 32 on April 28, 2001.

A new member of the team.

On Feb. 24, 2011, the International Space Station got a cool new helper in the form of Robonaut 2, the first ever humanoid robot in space.

A sweet ride.

In February 2016, Richard Branson unveiled Virgin Galactic's second SpaceShipTwo spacecraft -- the first company spacecraft to be manufactured wholly in-house. It is called the VSS Unity.

Sticking the landing.

On April 8, 2016, Elon Musk's 14-year-old SpaceX's Falcon 9 rocket made its first ever landing at sea after successfully delivering cargo to the ISS.

Third time’s a charm.

In April 2017, Amazon founder Jeff Bezos' spaceflight startup Blue Origin launched and landed its reusable rocket for the third time.

Are we alone in the universe?

On April 13, 2017, scientists at NASA shared findings from the agency's Cassini spacecraft mission to Saturn. It seems that a chemical reaction that is occurring underneath the icy surface of one of the planet's moons, Enceladus, could be a sign that it could also support alien life, in another potentially groundbreaking discovery in the search for life beyond Earth. On September 15, 2017, Cassini ended its 20 year mission.

New worlds to explore.

On Feb. 22, 2017, NASA announced the discovery of a planetary system of seven Earth-sized planets orbiting around a red dwarf star. It was named TRAPPIST-1 and it is the first system that NASA has found like it. Three of the planets in the system are in what's called the habitable zone, which means that there is a possibility that the worlds are home to liquid water and a life-supporting atmosphere.

Breaking records and glass ceilings.

In June 2018, Peggy Whitson, the first female commander of the International Space Station and first woman to be chief of NASA's astronaut corps, retired after 32 years with NASA. Whitson completed three missions on board the ISS -- two of which she led -- and spent 665 total days in space, which is more than any other NASA astronaut.

Whitson also conducted more spacewalks than any other female astronaut, spending 60 hours and 21 minutes outside of the space station. On her last space station mission, Whitson became the oldest female astronaut, at 57, to reach orbit.

In February 2020, Astronaut Christina Koch will return to Earth after an 11-month stay onboard the ISS, nearing Kelly's 340 days in orbit. In December 2019, she will pass Whitson's 288 days in space, setting a new record for female astronauts.

The secrets of Mars.

On Nov. 26, 2018, NASA successfully landed the InSight Mars lander on the red planet in order to better understand the inner workings of Mars. NASA will use the probe to take the planet's "vital signs," closely monitoring weather, temperature, tectonic activity -- meaning Marsquakes -- and what happens when meteorites hit the planet. It took the probe six months to travel more than 300 million miles, and was the first landing on Mars since the Curiosity Rover in 2012.

Farewell Kepler, Hello TESS.

On Oct. 30, 2018, NASA's Kepler space telescope was retired, and the nine-year-long planet hunting mission came to an end. The Kepler team discovered 2,899 exoplanet candidates and confirmed the existence of 2,681 exoplanets in the galaxy outside of our solar system.

But while Kepler said goodbye, in April of 2018, NASA launched TESS -- short for Transiting Exoplanet Survey Satellite -- into orbit for a two-year mission to see which exoplanets could harbor and support life.

Going farther than ever before.

On Jan. 1, 2019, NASA's New Horizon spacecraft completed the furthest flyby ever, capturing images of a 20-mile wide minor planet classified as 2014 MU69. Its nickname is Ultima Thule, which translates to "distant places beyond the known world." New Horizons was also the first spacecraft to fly past Pluto in 2015.

Humans living in space?

On April 12, 2019, the results of NASA's Twin Study was published in the academic journal Science. The paper detailed the findings of the research, which monitored the effect of spaceflight on the human body. The study's test subjects were twin brothers and retired NASA astronauts Scott and Mark Kelly.

Scott Kelly spent 340 days in space on the International Space Station and became the first American astronaut to spend almost a year in space. He returned to earth on March 2, 2016. The research revealed the ways spending that much time in space can affect things such as the expression of genes and immune system responses.

"Our space agencies won't be able to push out farther into space, to a destination like Mars, until we can learn more about how to strengthen the weakest links in the chain that make space flight possible: the human body and mind," wrote Kelly in his memoir, Endurance: A Year in Space, A Lifetime of Discovery.