100 Milestones That Took Us to the Stars

Introduction

The story of space exploration is a testament to human curiosity, ingenuity, and ambition. It is a narrative woven from threads of fierce competition, collaboration, and an unrelenting drive to understand our place in the cosmos. For millennia, humanity looked to the heavens with wonder, but in the 20th century, we began to take our first tentative steps into that vast expanse. This journey has unfolded in distinct eras, each building on the last: from the theoretical dreams of pioneers to the frantic pace of a superpower space race; from the first robotic emissaries touching alien worlds to the construction of permanent outposts in orbit; and now, to a new age where commercial visionaries and a global cohort of nations reach for the Moon, Mars, and beyond. These 100 milestones mark the pivotal moments in that journey, charting our transformation from earthbound observers to active explorers of the solar system.

The Dreamers and the Drawing Boards

Before any rocket could leave the ground, the path to space was paved with theory and early experimentation. A handful of visionary thinkers and engineers laid the mathematical and mechanical groundwork, transforming the dream of spaceflight into a tangible possibility. Their work, often conducted in obscurity, provided the essential principles that would later fuel the launch of satellites, probes, and human explorers.

Milestone 1: The Rocket Equation (1813/1903)

The entire endeavor of space exploration rests on a fundamental principle of physics known as the rocket equation. First described in a rudimentary form by British mathematician William Moore in 1813, it was independently derived and published in its comprehensive form by Russian schoolteacher Konstantin Tsiolkovsky in 1903. Tsiolkovsky’s work, “Exploration of Cosmic Space by Means of Reaction Devices,” mathematically demonstrated how a rocket could achieve the necessary velocity to escape Earth’s gravity. The equation relates the change in a rocket’s velocity to the speed of its exhaust and the ratio of its initial mass (full of fuel) to its final mass (empty). It proved that multi-stage, liquid-fueled rockets were the key to reaching space, a concept that would become the blueprint for every major launch vehicle.

Milestone 2: The First Liquid-Fueled Rocket (1926)

Theory became reality on March 16, 1926, in a snowy field in Auburn, Massachusetts. American professor Robert Goddard launched the world’s first liquid-propellant rocket. The spindly, 10-foot craft, nicknamed “Nell,” used liquid oxygen and gasoline as propellants. Its flight was brief, lasting only 2.5 seconds and reaching an altitude of just 41 feet, but its significance was immense. It proved that liquid fuels, which offered far greater control and efficiency than solid powders, were a practical means of propulsion. Goddard’s pioneering work, though little celebrated at the time, established the core technology that would power the Saturn V, the Space Shuttle, and the rockets of today.

Milestone 3: The First Vehicle to Enter Space (1942/1944)

The development of rocketry took a dramatic and ominous leap forward in Nazi Germany under the direction of Wernher von Braun. His team at Peenemünde developed the Aggregat 4 (A-4) rocket, more famously known as the V-2. While designed as a weapon of war, the V-2 was a technological marvel. On June 20, 1944, during a vertical test flight, a V-2 rocket became the first human-made object to cross the Kármán line, the 100-kilometer altitude mark widely considered the boundary of space. This event marked humanity’s physical entry into the space age, born from a program of military conflict. The V-2’s technology and many of its key engineers, including von Braun, would be captured by the Allies after the war, directly seeding the American and Soviet missile and space programs that followed.

Milestone 4: First Photos of Earth from Space (1946)

Two years after the V-2 first touched space, the captured rocket technology provided humanity with its first true look at its home planet. On October 24, 1946, U.S. scientists launched a V-2 rocket from the White Sands Missile Range in New Mexico. Aboard the rocket was a 35-millimeter motion picture camera programmed to take a frame every 1.5 seconds. The rocket soared to an altitude of 105 km (65 miles), and its camera captured the first-ever photographs of Earth from space. The grainy, black-and-white images revealed the planet’s curvature and cloud patterns against the blackness of space, offering a perspective previously confined to science fiction.

Milestone 5: First Animals in Space (1947)

Before sending humans into the unknown, scientists needed to understand the biological effects of high-altitude flight and the space environment. The first living creatures to make the journey were fruit flies. On February 20, 1947, the U.S. launched a V-2 rocket carrying a capsule of fruit flies to an altitude of 109 km (68 miles). The capsule was ejected and successfully parachuted back to Earth. The flies were recovered alive, providing the first data on the impacts of radiation exposure at high altitudes and giving scientists confidence that life could survive the rigors of a trip to space.

The Dawn of the Space Age

The launch of a simple, beeping satellite in 1957 transformed space exploration from a theoretical and experimental pursuit into a global phenomenon. It triggered a period of intense competition between the United States and the Soviet Union, known as the Space Race. This era was defined by a breathtaking series of “firsts,” as each nation strove to demonstrate its technological and ideological supremacy by conquering the high frontier.

Milestone 6: First Artificial Satellite (1957)

On October 4, 1957, the Soviet Union launched Sputnik 1, the world’s first artificial satellite. The 58-cm (23-inch) polished metal sphere, weighing just 83.6 kg (184 pounds), was lofted into low Earth orbit by a modified R-7 intercontinental ballistic missile. For 21 days, its four long antennas broadcast a simple, rhythmic radio pulse—”beep-beep-beep”—that was heard by amateur and professional radio operators around the globe. The event was a stunning technological achievement that shocked the world, particularly the United States, and officially inaugurated the Space Age, igniting the race to the stars.

Milestone 7: First Animal in Orbit (1957)

Less than a month after Sputnik 1, the Soviets achieved another major first. On November 3, 1957, they launched Sputnik 2, a much larger spacecraft carrying the first living creature into orbit: a stray dog from the streets of Moscow named Laika. The mission was designed to test how a complex organism would react to the launch and the environment of orbital spaceflight. At the time, technology for a safe reentry had not been developed, so Laika’s flight was a one-way mission. Though she died from overheating several hours into the flight, her journey provided crucial data demonstrating that a living being could survive weightlessness, paving the way for human spaceflight.

Milestone 8: First U.S. Satellite and a Scientific Discovery (1958)

Stung by the success of Sputnik, the United States accelerated its own satellite program. On January 31, 1958, the U.S. Army successfully launched Explorer 1 into orbit aboard a Jupiter-C rocket. While a direct response to Sputnik, Explorer 1 was more than just a technological demonstration; it was a scientific mission. It carried a small instrument package, including a cosmic ray detector designed by physicist James Van Allen. The instrument detected far lower levels of cosmic radiation than expected, leading Van Allen to theorize that the satellite was passing through belts of intense radiation trapped by Earth’s magnetic field. This discovery of the Van Allen radiation belts was the first major scientific finding of the Space Age.

Milestone 9: First Solar-Powered Satellite (1958)

On March 17, 1958, the U.S. Navy launched Vanguard 1, a tiny, 1.47 kg (3.25 lb) satellite that was a pioneer in space technology. It was the first satellite to use solar cells to power its transmitter, allowing it to continue broadcasting for over six years. Previous satellites relied on batteries that died within weeks. Communication with Vanguard 1 was lost in 1964, but it remains the oldest human-made object still orbiting the Earth, a silent testament to the dawn of sustainable space technology.

Milestone 10: First Human-Made Object to Reach the Moon (1959)

The Soviet Union continued its string of lunar firsts on September 13, 1959, when its Luna 2 probe became the first human-made object to make contact with another celestial body. After a 33.5-hour journey, the spacecraft intentionally impacted the lunar surface east of the Sea of Serenity. It carried with it Soviet pennants, marking a symbolic arrival on the Moon and further cementing the USSR’s early lead in the Space Race.

Milestone 11: First Images of the Moon’s Far Side (1959)

Just weeks later, on October 4, 1959, the Soviet Union launched Luna 3. The probe executed a flyby of the Moon, and its onboard camera system photographed 70 percent of the lunar far side—a hemisphere perpetually hidden from Earth due to tidal locking. The probe developed and scanned the film onboard, then transmitted the grainy but historic images back to Earth. For the first time, humanity saw the rugged, heavily cratered terrain of the Moon’s hidden face, revealing a landscape starkly different from the familiar near side.

Milestone 12: First Weather Satellite (1960)

The practical applications of space technology became clear with the launch of TIROS-1 (Television Infrared Observation Satellite) by the U.S. on April 1, 1960. As the world’s first successful weather satellite, TIROS-1 operated for 78 days and transmitted thousands of images of Earth’s cloud cover. It demonstrated the immense value of a space-based perspective for weather forecasting and Earth science, paving the way for the global satellite weather monitoring systems we rely on today.

Milestone 13: First Animals Returned Alive from Orbit (1960)

While Laika’s mission proved an animal could survive in orbit, a crucial question remained: could they return safely? The Soviet Union answered this on August 19, 1960, with the flight of Sputnik 5. The spacecraft carried two dogs, Belka and Strelka, along with a collection of other animals and plants. After 18 orbits, the capsule successfully reentered the atmosphere and was recovered. The safe return of its living passengers was a landmark achievement, providing the final biological confidence needed to proceed with human spaceflight.

Milestone 14: First Human in Space (1961)

On April 12, 1961, Soviet cosmonaut Yuri Gagarin strapped into his Vostok 1 capsule and made history. Launched from the Baikonur Cosmodrome, the 27-year-old pilot became the first human being to journey into outer space and the first to orbit the Earth. His single, 108-minute orbit reached an altitude of 327 kilometers (203 miles). Upon his safe return, Gagarin became an instant global icon, a symbol of human courage and a monumental victory for the Soviet Union in the Space Race.

Milestone 15: First American in Space (1961)

The United States responded swiftly to Gagarin’s flight. Just 23 days later, on May 5, 1961, NASA astronaut Alan Shepard became the first American in space. Piloting his Mercury capsule, named Freedom 7, Shepard undertook a 15-minute suborbital flight that reached an altitude of 116 miles. Unlike Gagarin’s fully automated flight, Shepard manually controlled his spacecraft’s attitude. The flight was a critical first step for the U.S. human spaceflight program and a major boost to national confidence.

Milestone 16: First Woman in Space (1963)

The Soviet Union once again achieved a major social and technical milestone on June 16, 1963, when Valentina Tereshkova became the first woman to fly in space. A former textile factory worker and amateur parachutist, she was selected for the cosmonaut corps and piloted the Vostok 6 spacecraft. During her mission, she orbited the Earth 48 times over nearly three days, logging more time in space than all American astronauts combined up to that point. She remains the only woman to have flown a solo space mission.

Milestone 17: First Spacewalk (1965)

On March 18, 1965, Soviet cosmonaut Alexei Leonov pushed open the airlock of his Voskhod 2 spacecraft and floated out into the void, attached only by a 5-meter tether. For 12 minutes, he performed the first-ever extravehicular activity (EVA), or spacewalk. The feat was incredibly perilous; his spacesuit ballooned in the vacuum of space, making it nearly impossible for him to re-enter the airlock. He was forced to dangerously bleed air from his suit to squeeze back inside. Leonov’s spacewalk demonstrated that humans could work outside a spacecraft, a capability essential for future missions involving assembly, repair, and lunar exploration.

First Contact: Robotic Emissaries to the Moon and Planets

While humans were taking their first steps into low Earth orbit, fleets of robotic probes were venturing much farther, acting as humanity’s eyes and ears across the solar system. These early missions were voyages into the unknown, challenging long-held assumptions about our planetary neighbors. They revealed worlds of crushing pressures, barren landscapes, and dynamic atmospheres, painting the first detailed portraits of Venus and Mars and setting the stage for decades of planetary science.

Milestone 18: First Successful Planetary Flyby (1962)

On December 14, 1962, NASA‘s Mariner 2 spacecraft flew within 34,773 km (21,607 miles) of Venus, becoming the first probe to successfully encounter another planet. During its flyby, its instruments pierced the planet’s thick cloud cover, returning data that stunned scientists. It measured surface temperatures of at least 425°C (800°F) and revealed a dense, high-pressure atmosphere composed primarily of carbon dioxide. These findings definitively dispelled the romantic notion of Venus as a lush, tropical world, revealing it instead as a scorching, inhospitable inferno.

Milestone 19: First Close-up Photos of Mars (1965)

Humanity got its first close look at the Red Planet on July 14, 1965, when NASA‘s Mariner 4 spacecraft flew past Mars. It captured and transmitted 22 black-and-white images, the first pictures of another planet taken from deep space. The photos revealed a cratered, ancient, and seemingly dead surface, more akin to the Moon than the Earth. The probe also found that Mars had a very thin atmosphere and no global magnetic field. The mission fundamentally reshaped scientific views of Mars, dampening hopes of finding advanced life but igniting a new era of scientific inquiry.

Milestone 20: First Soft Landing on the Moon (1966)

A critical question for the lunar race was whether the Moon’s surface was solid enough to support a lander or if it was covered in a deep layer of soft dust. The Soviet Union’s Luna 9 probe answered that question on February 3, 1966. The spacecraft executed the first successful propulsive soft landing on another celestial body, touching down in the Ocean of Storms. Shortly after landing, it began transmitting the first-ever panoramic images from the lunar surface, showing a firm, rocky landscape and proving that a landing was feasible.

Milestone 21: First Spacecraft to Orbit the Moon (1966)

Two months after Luna 9’s landing, the Soviet Union achieved another lunar first. On March 31, 1966, the Luna 10 probe fired its retrorockets and successfully entered orbit around the Moon, becoming its first artificial satellite. While it carried no cameras, its instruments studied the Moon’s gravitational field, radiation environment, and composition. The mission was a key step in mapping the lunar environment from orbit, a necessary precursor for selecting future landing sites.

Milestone 22: First Atmospheric Entry on Another Planet (1967)

The Soviet Venera program continued to peel back the layers of Venus. On October 18, 1967, the Venera 4 descent capsule separated from its main spacecraft and plunged into the Venusian atmosphere. As it descended by parachute, it transmitted direct measurements of the atmosphere’s temperature, pressure, and density. It was the first probe to perform in-situ analysis of another planet’s atmosphere. The data confirmed a composition of over 90% carbon dioxide and revealed the extreme surface pressure before the probe was crushed at an altitude of about 25 km.

Milestone 23: First Soft Landing on Another Planet (1970)

Building on the lessons from its predecessors, the Soviet Venera 7 lander was built to withstand the extreme conditions on Venus. On December 15, 1970, it accomplished what no other probe had: a successful soft landing on the surface of another planet. Though its parachute failed partially during descent, causing a hard landing, the robust probe survived. It transmitted a weak signal containing temperature data from the surface for 23 minutes, confirming a blistering 475°C (887°F).

Milestone 24: First Spacecraft to Orbit Another Planet (1971)

On November 14, 1971, NASA‘s Mariner 9 spacecraft arrived at Mars and fired its engine to become the first probe to enter orbit around another planet. Its arrival was anticlimactic at first; a massive, planet-encircling dust storm completely obscured the surface. Mission controllers patiently waited, and as the dust settled over the following months, Mariner 9 began its historic mapping mission. It revealed giant volcanoes, a vast canyon system (Valles Marineris), and clear evidence of ancient riverbeds, transforming our view of Mars from a static, cratered body to a geologically dynamic world with a more complex past.

Milestone 25: First Soft Landing on Mars (1971)

Just weeks after Mariner 9’s arrival, the Soviet Union’s Mars 3 mission achieved another planetary first. On December 2, 1971, its lander module successfully executed the first soft landing on the surface of Mars. The lander began transmitting a panoramic image of its surroundings, but after just 110 seconds, all communication abruptly ceased for unknown reasons. Despite the short duration, it was a historic technological achievement, marking the first time a human-made object had landed softly and begun operations on the Red Planet.

Milestone 26: First Pictures from the Martian Surface (1976)

Five years after the brief transmission from Mars 3, NASA‘s ambitious Viking 1 mission provided humanity’s first sustained view from the Martian surface. On July 20, 1976, the Viking 1 lander touched down in Chryse Planitia. It soon returned the first clear, detailed panoramic images, revealing a landscape of reddish, iron-rich soil littered with rocks under a pale pink sky. The Viking 1 lander, along with its twin Viking 2, would operate for years, conducting sophisticated experiments to search for life and providing a foundational understanding of Martian geology and meteorology.

The Apollo Saga: One Giant Leap

The Apollo program stands as one of the most audacious and monumental undertakings in human history. Driven by President John F. Kennedy’s 1961 challenge to land a man on the Moon and return him safely to Earth within the decade, it was a national effort that pushed the boundaries of technology, management, and human courage. The program was not just a single landing but a series of progressively complex missions that took humanity from Earth orbit to the lunar surface, culminating in a triumph that defined a generation.

Milestone 27: First Crewed Flight Beyond Low Earth Orbit (1968)

In a bold, last-minute change of plans, NASA sent the Apollo 8 mission to orbit the Moon. On December 21, 1968, astronauts Frank Borman, Jim Lovell, and Bill Anders launched aboard the first crewed flight of the mighty Saturn V rocket. They became the first human beings to leave Earth’s gravitational embrace, the first to see the far side of the Moon with their own eyes, and the first to witness an “Earthrise” over the lunar horizon. Their Christmas Eve broadcast from lunar orbit, during which they read from the Book of Genesis, was a moment of unity for a world beset by turmoil.

Milestone 28: First Docking of Two Crewed Spacecraft (1969)

While the U.S. focused on the Moon, the Soviet Union was advancing capabilities for future space stations. On January 16, 1969, the Soyuz 4 and Soyuz 5 spacecraft performed the first-ever docking of two crewed vehicles in orbit. In a daring maneuver, two cosmonauts, Aleksei Yeliseyev and Yevgeny Khrunov, conducted a spacewalk to transfer from Soyuz 5 to Soyuz 4. This demonstrated a key technique for assembling larger structures in space and for performing crew rescues.

Milestone 29: First Humans Walk on the Moon (1969)

On July 20, 1969, the world held its breath as the Apollo 11 lunar module, “Eagle,” descended toward the Moon’s Sea of Tranquility. With astronaut Neil Armstrong manually piloting the craft to avoid a field of boulders, he announced, “Houston, Tranquility Base here. The Eagle has landed”. A few hours later, at 10:56 PM EDT, Armstrong descended the ladder and stepped onto the lunar surface, declaring, “That’s one small step for [a] man, one giant leap for mankind”. He was joined by Buzz Aldrin, and together they spent over two hours collecting samples, deploying experiments, and planting the American flag. The event, watched by an estimated 650 million people, was the crowning achievement of the Space Race and a defining moment of the 20th century.

Milestone 30: First Lunar Sample Return (Robotic) (1970)

While Apollo 11 was a human triumph, the Soviet Union demonstrated a different path to lunar science. On September 24, 1970, the robotic Luna 16 probe successfully returned to Earth carrying 101 grams of lunar soil. The mission landed on the Moon, used a robotic drill to collect a core sample, and launched a small ascent stage back to Earth. It was the first time a sample had been retrieved from another celestial body entirely by a robotic spacecraft, showcasing a more cost-effective approach to planetary science.

Milestone 31: First Lunar Rover (Robotic) (1970)

The Soviets followed up their sample return success with another robotic first. On November 10, 1970, the Luna 17 lander deployed Lunokhod 1, the first remote-controlled roving vehicle to explore another world. The eight-wheeled, 756 kg rover explored the Mare Imbrium (Sea of Rains) for nearly 10 months, traveling over 10 kilometers (6 miles) and transmitting thousands of images and soil analyses. It proved the value of mobile robotic explorers, a concept that would later be central to the exploration of Mars.

Milestone 32: A “Successful Failure” and Human Ingenuity (1970)

The Apollo 13 mission, launched in April 1970, is remembered not for reaching the Moon, but for the incredible feat of returning its crew safely to Earth after a catastrophic failure. Two days into the flight, an oxygen tank exploded, crippling the Service Module and its power and life support systems. The lunar landing was aborted, and the mission became a desperate struggle for survival. The three-man crew, commanded by Jim Lovell, used the Lunar Module, “Aquarius,” as a lifeboat, while engineers at Mission Control in Houston worked around the clock to devise procedures to conserve power, water, and scrub carbon dioxide from the air. Their ingenuity and the crew’s calm execution turned a potential tragedy into what is now called NASA’s “successful failure.”

Milestone 33: First Use of a Crewed Lunar Roving Vehicle (1971)

The later Apollo missions were focused on more extensive scientific exploration, a goal made possible by the Lunar Roving Vehicle (LRV). During the Apollo 15 mission in July 1971, astronauts David Scott and James Irwin became the first humans to drive on the Moon. The electric-powered “moon buggy” allowed them to travel far from their lander, covering 28 km (17.5 miles) over three excursions. The LRV dramatically increased the scientific return of the mission, enabling the collection of a diverse range of geological samples and expanding the area of human exploration.

Milestone 34: First Golf Shot on the Moon (1971)

Amid the serious scientific work of the Apollo program, one moment stood out for its simple humanity. Near the end of the final EVA of the Apollo 14 mission in February 1971, commander Alan Shepard, an avid golfer, produced a makeshift 6-iron head he had smuggled onboard and attached it to a sample collection tool. He dropped two golf balls onto the lunar dust and, encumbered by his stiff spacesuit, swung at them. In the low lunar gravity, the second ball sailed for what he described as “miles and miles and miles.” It was a lighthearted gesture that captured the public’s imagination and symbolized the human presence in an utterly alien environment.

Milestone 35: The Final Apollo Lunar Mission (1972)

The era of human lunar exploration came to a close with the Apollo 17 mission in December 1972. It was the first and only Apollo mission to launch at night and the only one to include a professional scientist, geologist Harrison “Jack” Schmitt, in its crew. Schmitt’s expertise greatly enhanced the mission’s scientific fieldwork. The crew spent over three days on the surface, drove the LRV for 35 km (22 miles), and collected a record 111 kg (245 lbs) of lunar samples. On their journey to the Moon, the crew captured the iconic “Blue Marble” photograph—one of the most widely reproduced images in history, showing a fully illuminated Earth. It became a powerful symbol of environmental awareness.

The Apollo program was a monumental achievement, but its singular focus and immense cost made it unsustainable. After Apollo 17, the political will to fund such ambitious deep-space missions vanished. The powerful Saturn V rockets were retired, and the vast infrastructure built for the Moon race was largely dismantled. For the next half-century, no nation possessed the capability to send humans beyond low Earth orbit. This created a “lost generation” of deep-space human exploration, a capability that is only now being painstakingly rebuilt through the Artemis program, which operates in a new paradigm of international and commercial partnership.

Living in Orbit: The First Space Stations and the Space Shuttle

With the Moon race won, the focus of human spaceflight shifted from deep space exploration to long-term habitation in low Earth orbit. The 1970s and 1980s saw the launch of the first space stations—Salyut, Skylab, and Mir—which served as orbital laboratories for studying the effects of prolonged weightlessness on the human body. This era was dominated by the advent of NASA’s Space Shuttle, the world’s first reusable spacecraft, which became a versatile workhorse for deploying satellites, conducting science, and beginning the monumental task of constructing the International Space Station.

Milestone 36: First Space Station (1971)

On April 19, 1971, the Soviet Union launched Salyut 1, the world’s first space station, into orbit. The 18.6-meter-long module was a pioneering effort in long-duration space habitation. Its first crew successfully docked and spent 23 days aboard, but a pressure equalization valve malfunctioned during their Soyuz 11 capsule’s reentry, tragically killing all three cosmonauts. Despite the tragedy, Salyut 1 established the fundamental concept of an orbital outpost, a model the Soviets would refine with subsequent Salyut stations throughout the decade.

Milestone 37: First U.S. Space Station (1973)

The United States launched its first and only solo space station, Skylab, on May 14, 1973. In an ingenious act of repurposing, Skylab was built from the modified upper stage of a Saturn V rocket. Although it suffered damage during launch, with one solar panel torn off and another jammed, the first crew performed a daring spacewalk to repair it. Over the next nine months, three different crews spent a total of 171 days aboard Skylab, conducting nearly 300 experiments in solar astronomy, Earth observation, and human physiology, gathering a wealth of data on long-term adaptation to microgravity.

Milestone 38: First International Docking in Space (1975)

A symbolic end to the Space Race came on July 17, 1975, with the Apollo-Soyuz Test Project. An American Apollo spacecraft docked with a Soviet Soyuz capsule in orbit, and commanders Thomas Stafford and Alexei Leonov greeted each other with a historic handshake through the open hatch. The mission, a moment of détente during the Cold War, required significant technical collaboration to make the two nations’ different spacecraft compatible. It demonstrated that former rivals could work together in space and laid the political and technical groundwork for future international partnerships, most notably the International Space Station.

Milestone 39: First Reusable Spacecraft Launch (1981)

On April 12, 1981—the 20th anniversary of Yuri Gagarin’s flight—NASA launched the Space Shuttle Columbiaon its maiden voyage, STS-1. It was the first flight of the world’s first reusable orbital spacecraft. Unlike capsules that returned via parachute, the shuttle launched like a rocket and landed like a glider on a runway. This revolutionary design promised to lower the cost of access to space and create a versatile “space truck” for deploying and servicing satellites, conducting science, and building large structures in orbit. The shuttle program would go on to fly 135 missions over the next 30 years.

Milestone 40: First American Woman in Space (1983)

On June 18, 1983, astronaut Sally Ride launched aboard the Space Shuttle Challenger on mission STS-7, becoming the first American woman to fly in space. Her historic flight came 20 years after Soviet cosmonaut Valentina Tereshkova’s. During the six-day mission, Ride operated the shuttle’s robotic arm to deploy and retrieve a satellite. Her achievement broke barriers at NASA and inspired millions, becoming a powerful symbol for women in science and engineering.

Milestone 41: First African-American in Space (1983)

Just a few months later, on August 30, 1983, Guion “Guy” Bluford made history as the first African-American in space. He served as a mission specialist on the STS-8 mission of the Space Shuttle Challenger. The mission featured the program’s first night launch and night landing and deployed a communications satellite for India. Bluford would go on to fly four shuttle missions in total.

Milestone 42: First European Spacelab Mission (1983)

The Space Shuttle’s role as an international science platform was realized on November 28, 1983, with the launch of STS-9 and the first Spacelab module. A joint project between ESA and NASA, Spacelab was a pressurized laboratory that fit inside the shuttle’s payload bay, allowing scientists to conduct hands-on experiments in a shirt-sleeve environment. The mission’s crew included Ulf Merbold of West Germany, the first ESA astronaut and the first non-American to fly on a U.S. spacecraft. Spacelab missions became a cornerstone of shuttle science for the next 15 years.

Milestone 43: First Untethered Spacewalk (1984)

A stunning visual of human freedom in space occurred on February 7, 1984, during mission STS-41B. Astronaut Bruce McCandless II donned the Manned Maneuvering Unit (MMU), a nitrogen-propelled backpack, and flew away from the Space Shuttle Challenger without any tethers. He traveled more than 90 meters (300 feet) from the orbiter, a solitary human figure against the backdrop of Earth. The successful test of the MMU demonstrated a remarkable capability for satellite retrieval and repair missions.

Milestone 44: First On-Orbit Satellite Repair (1984)

The shuttle’s utility as a service vehicle was proven in dramatic fashion in April 1984 on mission STS-41C. The crew of Challenger was tasked with capturing and repairing the malfunctioning Solar Maximum Mission satellite (“Solar Max”), which had failed in orbit four years earlier. After initial difficulties grappling the satellite, the crew successfully brought it into the payload bay using the robotic arm. Astronauts George Nelson and James van Hoften then performed two spacewalks to replace faulty modules, restoring the satellite to full function before redeploying it into orbit. It was the first time a satellite had ever been repaired in space.

Milestone 45: First Consistently Inhabited Space Station (1986)

The Soviet Union took the next major step in long-duration spaceflight with the launch of the core module of the Mir space station on February 20, 1986. Unlike previous stations, Mir (“Peace” or “World” in Russian) was designed to be modular and was expanded over the next decade with several new science modules. It became the first space station to be continuously inhabited, hosting crews for long-duration missions that pushed the boundaries of human endurance in space. Mir operated for 15 years, serving as a vital research platform and a symbol of Russian space prowess.

Milestone 46: First Russian Cosmonaut on a U.S. Shuttle (1994)

As the Cold War thawed, cooperation in space grew. On February 3, 1994, veteran cosmonaut Sergei Krikalev became the first Russian to fly on an American spacecraft, launching aboard the Space Shuttle Discovery on mission STS-60. This flight marked the beginning of the Shuttle-Mir program, in which American shuttles would dock with the Russian space station, allowing U.S. astronauts to complete long-duration stays aboard Mir. This program was a crucial dress rehearsal for the international partnership that would build and operate the ISS.

Milestone 47: Longest Human Spaceflight (1995)

On March 22, 1995, Russian physician-cosmonaut Valeri Polyakov completed a record-shattering mission, landing back on Earth after spending 437 consecutive days aboard the Mir space station. His marathon flight was a deliberate experiment to study the long-term physical and psychological effects of weightlessness in preparation for potential human missions to Mars. The data collected from Polyakov’s mission remains a cornerstone of space medicine, providing invaluable information on bone density loss, muscle atrophy, and psychological adaptation to prolonged spaceflight.

The Grand Tour: Exploring the Outer Solar System

While human activities were confined to Earth orbit, robotic explorers embarked on epic journeys to the giant planets of the outer solar system. These missions, some lasting for decades, were humanity’s first reconnaissance of Jupiter, Saturn, Uranus, and Neptune. Taking advantage of a rare planetary alignment, the Voyager probes conducted a “Grand Tour,” fundamentally rewriting textbooks and revealing the stunning diversity and complexity of these distant worlds and their myriad moons.

Milestone 48: First Flyby of Jupiter (1973)

On December 3, 1973, NASA’s Pioneer 10 spacecraft became the first human-made object to reach the outer solar system. After successfully navigating the perilous asteroid belt, it flew past Jupiter, returning the first close-up images of the gas giant and its Great Red Spot. Pioneer 10’s instruments studied Jupiter’s intense radiation belts, powerful magnetic field, and atmospheric composition, providing the first in-situ data from this colossal world and paving the way for all future missions to the outer planets.

Milestone 49: First Flyby of Saturn (1979)

Six years later, on September 1, 1979, Pioneer 10’s twin, Pioneer 11, became the first spacecraft to fly past Saturn. Passing just 21,000 km (13,000 miles) from the planet’s cloud tops, it discovered two new small moons and a new ring, the “F” ring. Its trajectory took it on a daring path between the planet and its rings, testing the route that the more advanced Voyager probes would follow two years later.

Milestone 50: The Voyager Grand Tour Begins (1977)

In the late summer of 1977, NASA launched the twin Voyager 1 and Voyager 2 spacecraft on an unprecedented mission to explore the outer solar system. They were designed to take advantage of a rare alignment of the giant planets that occurs only once every 176 years, allowing them to use gravity assists to swing from one planet to the next. The Voyagers revolutionized our understanding of Jupiter and Saturn, discovering active volcanoes on Jupiter’s moon Io, hinting at a subsurface ocean on Europa, and revealing the intricate complexity of Saturn’s rings.

Milestone 51: First Flyby of Uranus (1986)

After its encounter with Saturn, Voyager 2 continued its journey alone to the outer ice giants. On January 24, 1986, it performed the first and, to date, only close-up flyby of Uranus. The encounter revealed a surprisingly bland, pale blue world, but its instruments discovered 11 new moons, two new rings, and a bizarre magnetic field tilted at nearly 60 degrees to the planet’s axis of rotation.

Milestone 52: First Flyby of Neptune (1989)

Voyager 2’s Grand Tour culminated on August 25, 1989, with its flyby of Neptune, the most distant planet in our solar system. It discovered the “Great Dark Spot,” a massive storm system similar to Jupiter’s Great Red Spot, and found that the planet had the fastest winds in the solar system, reaching speeds of 2,400 km/h (1,500 mph). Perhaps most surprising was the discovery of active geysers of nitrogen ice erupting from the surface of its largest moon, Triton.

Milestone 53: First Spacecraft to Orbit Jupiter (1995)

While flybys provided tantalizing snapshots, long-term study required an orbiter. On December 7, 1995, NASA’s Galileo spacecraft arrived at Jupiter and entered orbit, beginning an eight-year mission to study the planet and its moons in detail. Upon arrival, it deployed an atmospheric probe that plunged into Jupiter’s clouds, returning the first direct measurements of its composition. Despite a crippling failure of its main antenna, the Galileo orbiter used its smaller backup antenna to transmit a wealth of data, providing strong evidence for subsurface oceans on Europa, Ganymede, and Callisto.

Milestone 54: First Spacecraft to Orbit Saturn (2004)

On July 1, 2004, the international Cassini-Huygens mission, a collaboration between NASA, ESA, and the Italian Space Agency, flawlessly executed its orbital insertion maneuver at Saturn. This began a remarkable 13-year orbital tour that transformed our understanding of the entire Saturnian system. Cassini mapped the planet’s storms, studied its complex ring dynamics, and conducted dozens of close flybys of its diverse moons.

Milestone 55: First Landing on an Outer Solar System Moon (2005)

The Cassini mission’s most dramatic moment came on January 14, 2005, when the European-built Huygens probe detached from the orbiter and descended through the thick, hazy atmosphere of Saturn’s largest moon, Titan. It successfully landed on the frigid surface, transmitting data and images for over an hour. It was the first and only landing ever accomplished in the outer solar system. Huygens revealed a stunningly Earth-like world, with a landscape carved by liquid methane and ethane, including shorelines, river channels, and hills rounded by rainfall.

The discoveries made by these long-duration robotic missions fundamentally shifted the focus of planetary science. The evidence for vast, liquid water oceans hidden beneath the icy shells of moons like Europa and Enceladus was particularly transformative. These “ocean worlds” are now considered among the most promising places to search for extraterrestrial life, directly influencing the objectives and designs of a new generation of deep-space probes aimed at exploring these potentially habitable environments.

The Red Planet in Focus: A Fleet of Martian Rovers

While orbiters provided a global perspective of Mars, understanding its history required “boots on the ground”—or, in this case, wheels. Beginning in the late 1990s, NASA embarked on a systematic campaign of robotic surface exploration, sending a series of increasingly sophisticated rovers to act as remote geologists. Each rover, from the microwave-sized Sojourner to the car-sized Perseverance, has built upon the discoveries of its predecessors, collectively painting a picture of a planet that was once warmer, wetter, and potentially habitable.

Milestone 56: First Rover on Another Planet (1997)

On July 4, 1997, NASA’s Mars Pathfinder mission successfully landed on Mars using an innovative system of airbags. A day later, it deployed a small, six-wheeled rover named Sojourner. While it only traveled about 100 meters during its 83-sol mission, Sojourner was a monumental success. It was the first wheeled vehicle to explore the surface of another planet, analyzing the composition of nearby rocks and soil and proving that the rover concept was a viable and powerful tool for planetary exploration.

Milestone 57: The Mars Exploration Rovers Land (2004)

In January 2004, NASA landed two identical, golf-cart-sized rovers on opposite sides of Mars: Spirit and Opportunity. Their primary mission was to “follow the water” by searching for geological evidence of past aqueous environments. Designed to last for just 90 Martian days (sols), both rovers far exceeded their warranties. Spirit operated for over six years before getting stuck in soft sand, while the durable Opportunity roamed the Martian plains for nearly 15 years, finally succumbing to a planet-encircling dust storm in 2018.

Milestone 58: Discovery of Past Water Environments (2004)

Just weeks after landing in Meridiani Planum, the Opportunity rover made a landmark discovery. Using its microscopic imager, it spotted small, iron-rich spherical concretions that scientists nicknamed “blueberries”. It also found layered rock outcrops containing sulfate salts and minerals like jarosite, which on Earth form in the presence of water. This combination of evidence provided the first definitive proof that Opportunity’s landing site was once the shoreline of an ancient, salty body of water.

Milestone 59: Evidence of Ancient Hot Springs (2007)

On the other side of the planet, in Gusev Crater, the Spirit rover made its own compelling discovery about Mars’s watery past. While dragging a malfunctioning wheel through the soil in 2007, it churned up a patch of ground that was startlingly white. Analysis revealed the soil was over 90% pure silica. On Earth, such deposits are typically formed in hot springs or volcanic fumaroles, where hot water dissolves minerals and deposits silica. This finding suggested that Mars once had hydrothermal environments, which are considered prime locations for the emergence of life.

Milestone 60: The Curiosity Rover Lands (2012)

NASA’s next Mars rover, Curiosity, was a significant leap in size and capability. The car-sized, one-ton mobile science laboratory landed in Gale Crater on August 6, 2012, using a complex and daring “sky crane” maneuver that had never been attempted before. Its mission was not just to find evidence of water, but to determine whether ancient Mars ever had the right environmental conditions to support microbial life—to assess its past habitability.

Milestone 61: Confirmation of a Habitable Environment (2013)

Less than a year into its mission, Curiosity achieved its primary goal. The rover drilled into a mudstone rock target named “John Klein” and delivered the powdered sample to its onboard chemistry labs. The analysis revealed the presence of sulfur, nitrogen, hydrogen, oxygen, phosphorus, and carbon—all the key chemical elements essential for life as we know it. The minerals in the rock indicated a freshwater lake environment with a neutral pH, confirming that ancient Mars once possessed conditions that would have been favorable for microorganisms.

Milestone 62: The Perseverance Rover and First Flight on Mars (2021)

The latest rover to join the fleet, NASA’s Perseverance, landed in Jezero Crater on February 18, 2021. Its mission is to take the next step: to seek direct signs of past microbial life (biosignatures) and to collect and cache rock and soil samples for a future mission to return to Earth. Tucked under its belly was a small, experimental helicopter named Ingenuity. On April 19, 2021, Ingenuity lifted off, achieving the first powered, controlled flight on another planet and opening up a new aerial dimension for planetary exploration.

The Mars Rover Family: Key Statistics and Discoveries

The evolution of Mars rovers showcases a clear progression in technological capability and scientific ambition. Each mission has provided the foundation for the next, leading to a transformation in our understanding of the Red Planet.

A Global Laboratory: The International Space Station

The International Space Station (ISS) represents the most complex and expensive engineering project in human history. A collaboration of five space agencies—NASA (USA), Roscosmos (Russia), JAXA (Japan), ESA (Europe), and CSA (Canada)—it is a permanently inhabited orbital laboratory and a symbol of post-Cold War cooperation. Assembled piece by piece over more than a decade, the football-field-sized station has hosted astronauts continuously since 2000, serving as a unique platform for scientific research, technology development, and preparation for future deep-space missions.

Milestone 63: ISS Construction Begins (1998)

The on-orbit assembly of the International Space Station began on November 20, 1998, with the launch of the Russian-built Zarya control module on a Proton rocket. Zarya provided the initial power and propulsion for the nascent station. Two weeks later, on December 4, the crew of Space Shuttle Endeavour (STS-88) captured Zarya and attached the first American component, the Unity connecting node. This joining of the first Russian and American modules marked the official start of ISS construction.

Milestone 64: First Crew Occupies the ISS (2000)

On November 2, 2000, the first resident crew arrived at the fledgling station, marking the beginning of continuous human presence in space. Expedition 1 consisted of American astronaut William Shepherd and Russian cosmonauts Yuri Gidzenko and Sergei Krikalev. They arrived aboard a Soyuz spacecraft and spent 136 days bringing the station’s systems to life, transforming it from a collection of modules into a functioning orbital home and laboratory.

Milestone 65: U.S. Destiny Lab Arrives (2001)

The station’s scientific capabilities expanded significantly with the arrival of the U.S. Destiny laboratory module on February 7, 2001. Delivered by Space Shuttle Atlantis on mission STS-98, the 8.5-meter (28-foot) module became the centerpiece of U.S. research on the station. It houses numerous racks for experiments in life sciences, materials science, fluid physics, and more, enabling a wide range of research in the unique microgravity environment.

Milestone 66: First Tourist in Space (2001)

The era of commercial space tourism began on April 28, 2001, when American businessman Dennis Tito launched with two cosmonauts on a Russian Soyuz mission to the ISS. Tito paid a reported $20 million for the trip, spending nearly eight days in space and about six days aboard the station. His flight, arranged with the Russian space agency despite initial opposition from NASA, opened the door for private citizens to experience spaceflight and signaled the commercial potential of low Earth orbit.

Milestone 67: European and Japanese Labs Arrive (2008)

The ISS became a truly global research facility in 2008 with the addition of laboratories from Europe and Japan. The European Space Agency‘s Columbus module was installed in February, providing a state-of-the-art facility for European science experiments. In March and June, two shuttle missions delivered and installed the components of the Japanese Experiment Module, “Kibo” (Hope), which is the largest single module on the station and features its own robotic arm and an external “porch” for experiments exposed to the vacuum of space.

Milestone 68: The Alpha Magnetic Spectrometer (2011)

One of the most significant scientific instruments ever sent to space was delivered to the ISS by Space Shuttle Endeavour on its final flight in May 2011. The Alpha Magnetic Spectrometer (AMS-02) is a powerful particle physics detector mounted on the station’s exterior truss. Its purpose is to search for evidence of dark matter and antimatter by measuring high-energy cosmic rays with unprecedented precision. Since its installation, the AMS has collected data on over 100 billion cosmic ray events, providing valuable insights into the fundamental composition of the universe.

Milestone 69: First DNA Sequencing in Space (2016)

A revolutionary leap for in-space biology occurred in August 2016 when NASA astronaut Kate Rubins performed the first-ever DNA sequencing aboard the ISS. Using a commercially available, hand-held device called the MinION, she successfully sequenced the DNA of mouse, virus, and bacteria samples. This capability is a game-changer for future space exploration, allowing for real-time diagnosis of astronaut illnesses, monitoring of microbes inside spacecraft, and potentially identifying DNA-based life on other planets without having to return samples to Earth.

Milestone 70: First 3D-Printed Metal Part in Space (2024)

A critical step toward sustainable, long-duration spaceflight is the ability to manufacture parts and tools on demand. On May 30, 2024, the European Space Agency‘s Metal 3D Printer, installed on the ISS, created its first part—a small, S-shaped stainless steel tool. This successful test proved that metal objects can be printed in microgravity, a technology that could one day allow crews on missions to the Moon or Mars to produce their own spare parts, reducing their reliance on supplies from Earth.

International Space Station: Major Assembly Milestones

The construction of the ISS was a marvel of international coordination and orbital engineering, involving dozens of launches by both the Space Shuttle and Russian rockets. This table highlights the key modules that form the backbone of the station.

The New Space Race: The Commercial Revolution

The 21st century has witnessed a paradigm shift in space exploration, driven not by competing superpowers but by a new generation of private companies. This commercial revolution, led by visionary entrepreneurs, has introduced disruptive technologies—most notably rocket reusability—that have dramatically lowered the cost of access to space. What began with suborbital tourism has rapidly evolved into a thriving commercial market for satellite launches, cargo delivery, and now, human spaceflight, fundamentally altering the landscape of the space industry.

Milestone 71: First Privately Funded Human Spaceflight (2004)

The commercial space age effectively began on June 21, 2004, when SpaceShipOne, a radical air-launched spaceplane, became the first privately developed and funded vehicle to carry a human into space. Piloted by Mike Melvill, the craft was designed by the legendary aerospace engineer Burt Rutan and financed by Microsoft co-founder Paul Allen. By completing a second flight within two weeks, the team captured the $10 million Ansari X PRIZE, proving that non-governmental entities could achieve human spaceflight and sparking a wave of commercial space ventures.

Milestone 72: First Privately Developed Liquid-Fuel Rocket in Orbit (2008)

Elon Musk’s company, SpaceX, was on the brink of failure in 2008. After three consecutive launch failures of its Falcon 1 rocket, the company had enough funds for only one more attempt. On September 28, 2008, the fourth Falcon 1 successfully lifted off and reached orbit, making SpaceX the first private company to develop and launch a liquid-fueled rocket into orbit. This crucial success saved the company and demonstrated its potential to become a serious player in the launch industry.

Milestone 73: First Private Spacecraft to Orbit and Return (2010)

Having proven its rocket, SpaceX next had to prove its spacecraft. On December 8, 2010, the company launched its Dragon capsule for the first time. After completing two orbits of the Earth, the unmanned capsule successfully reentered the atmosphere and splashed down in the Pacific Ocean. This made SpaceX the first private company to launch, orbit, and recover a spacecraft—a complex capability previously mastered only by national governments and a critical requirement for carrying cargo and eventually crew.

Milestone 74: First Private Spacecraft to Dock with the ISS (2012)

The ultimate goal of the Dragon capsule was to service the International Space Station. On May 22, 2012, SpaceX launched a Dragon on its first cargo mission to the ISS. Three days later, the station’s crew used the Canadarm2 robotic arm to grapple the spacecraft and berth it to the Harmony module. The successful mission inaugurated NASA’s Commercial Resupply Services program, marking the first time a private company had delivered cargo to the station and ushering in a new era of public-private partnership in space logistics.

Milestone 75: First Vertical Landing of an Orbital Rocket Booster (2015)

For decades, rockets were expendable, their expensive first stages discarded in the ocean after a single use. SpaceX set out to change that. On December 21, 2015, the company launched a Falcon 9 rocket, and after the first stage separated, it performed a series of complex engine burns to reverse its course and fly back to its launch site at Cape Canaveral. It then executed a perfect propulsive vertical landing, touching down gently on a concrete pad. This was a monumental achievement, proving that orbital-class boosters could be recovered and reused.

Milestone 76: First Vertical Landing on a Droneship (2016)

While returning to the launch site is efficient for some missions, high-velocity launches, like those to geostationary orbit, don’t have enough fuel for the booster to fly all the way back to land. The solution was a floating landing platform. On April 8, 2016, after a cargo launch to the ISS, a Falcon 9 first stage successfully landed on the deck of an autonomous droneship named “Of Course I Still Love You” in the Atlantic Ocean. This much more difficult maneuver unlocked the potential for recovering boosters from nearly every mission profile.

Milestone 77: First Reflight of an Orbital-Class Rocket (2017)

The final step in proving the reusability concept was to fly a recovered booster again. On March 30, 2017, SpaceX launched the SES-10 communications satellite using a Falcon 9 first stage that had previously flown and landed a year earlier. The “flight-proven” booster performed flawlessly and was recovered a second time. This historic reflight validated the economic model of reusability, which promised to drastically reduce launch costs and increase launch frequency, fundamentally disrupting the global launch market.

Milestone 78: First Commercial Crewed Spaceflight (2020)

After the Space Shuttle’s retirement in 2011, NASA was reliant on Russian Soyuz rockets to send its astronauts to the ISS. The agency’s Commercial Crew Program aimed to change that by funding private companies to develop human spaceflight systems. On May 30, 2020, SpaceX achieved that goal with the launch of the Crew Dragon “Endeavour”. With NASA astronauts Bob Behnken and Doug Hurley aboard, the mission successfully docked with the ISS, restoring America’s ability to launch its own astronauts from U.S. soil for the first time in nearly a decade.

Milestone 79: First All-Civilian Orbital Mission (2021)

The potential of commercial human spaceflight expanded beyond government astronauts with the Inspiration4 mission in September 2021. Funded by billionaire entrepreneur Jared Isaacman, the mission sent four private citizens—none of whom were professional astronauts—on a three-day journey into orbit aboard a Crew Dragon spacecraft. The flight, which orbited higher than the ISS, was a milestone for space tourism and demonstrated that orbital spaceflight was no longer the exclusive domain of government agencies.

Milestone 80: First Private Lunar Landing (2024)

The commercial reach extended to the Moon on February 22, 2024, when the Odysseus lander, built by the Houston-based company Intuitive Machines, successfully touched down near the lunar south pole. Launched as part of NASA’s Commercial Lunar Payload Services (CLPS) program, Odysseus became the first privately built and operated spacecraft to achieve a soft landing on the Moon. It also marked the first U.S. lunar landing of any kind since the Apollo 17 mission in 1972, heralding a new era of commercial partnership in lunar exploration.

SpaceX: A Decade of Disruption

The rapid succession of milestones achieved by SpaceX in just over a decade fundamentally reshaped the global space industry. This table tracks the company’s most significant “firsts,” illustrating a relentless pace of innovation that turned rocket reusability from a theoretical concept into a routine operation.

New Windows on the Cosmos: The Great Observatories

While probes and rovers explored our solar system up close, a different class of spacecraft revolutionized our view of the universe itself. The Great Observatories are powerful space-based telescopes, each designed to view the cosmos in a different part of the electromagnetic spectrum. By placing them above the distorting effects of Earth’s atmosphere, astronomers gained an unprecedentedly clear and deep view of the stars, galaxies, and the very fabric of spacetime, leading to discoveries that have reshaped modern astronomy.

Milestone 81: First Large Optical Space Telescope (1990)

On April 25, 1990, the Space Shuttle Discovery deployed the Hubble Space Telescope into low Earth orbit. A joint project between NASA and ESA, it was the most ambitious and complex astronomical observatory ever built. Initial excitement turned to dismay when it was discovered that its primary mirror had a tiny flaw—a spherical aberration—that rendered its images blurry. However, a series of five heroic shuttle servicing missions, starting in 1993, not only corrected the flaw but also continuously upgraded its instruments. The repaired Hubble became arguably the most productive scientific instrument in history, revolutionizing nearly every field of astronomy with its stunning images and groundbreaking data on everything from planets in our solar system to the age and expansion rate of the universe.

Milestone 82: First Exoplanets Discovered (1992)

For centuries, planets beyond our solar system—exoplanets—were purely theoretical. That changed in January 1992, when astronomers Aleksander Wolszczan and Dale Frail announced a stunning discovery. By studying the regular radio pulses from a pulsar (a rapidly spinning dead star) named PSR B1257+12, they detected tiny variations in the timing of the pulses. They concluded that these irregularities were caused by the gravitational pull of two, and later a third, rocky planets orbiting the pulsar. These were the first confirmed exoplanets ever discovered, proving that planetary systems were not unique to our Sun, though these particular worlds were bathed in deadly radiation.

Milestone 83: First Exoplanet Orbiting a Sun-like Star (1995)

The discovery that truly opened the floodgates for exoplanet science came in October 1995. Swiss astronomers Michel Mayor and Didier Queloz, using the radial velocity method to detect the “wobble” of a star caused by an orbiting planet, found the first exoplanet orbiting a main-sequence star similar to our Sun, 51 Pegasi. The planet, named 51 Pegasi b, was a shock: a gas giant half the mass of Jupiter orbiting its star in just four days, placing it far closer than Mercury is to our Sun. This new class of “Hot Jupiters” challenged existing theories of planet formation and launched a new field of astronomy dedicated to finding and characterizing these alien worlds.

Milestone 84: The James Webb Space Telescope Begins Operations (2022)

The long-awaited successor to Hubble, the James Webb Space Telescope (JWST), launched on December 25, 2021. A marvel of engineering, JWST is an infrared observatory with a massive 6.5-meter primary mirror made of 18 gold-coated hexagonal segments. After a complex, month-long deployment sequence in which it unfolded its mirror and sunshield a million miles from Earth, the telescope began its science operations in mid-2022. With its ability to peer through dust clouds and see the redshifted light from the dawn of time, JWST is designed to study the first stars and galaxies that formed after the Big Bang, the atmospheres of distant exoplanets, and the birth of stars and planetary systems in our own galaxy.

An Expanding Frontier: Modern Global Achievements

The 21st century has seen space exploration become a truly global enterprise. No longer dominated by just two superpowers, the field now features a diverse array of national and international players who are achieving remarkable “firsts” of their own. Nations like China, India, Japan, the United Arab Emirates, and the member states of the European Space Agency have developed sophisticated capabilities, pursuing ambitious missions to the Moon, Mars, and beyond. This multipolar landscape has fostered a new dynamic of both competition and collaboration, expanding the frontiers of science and technology.

Milestone 85: First Chinese Human Spaceflight (2003)

On October 15, 2003, China cemented its status as a major space power by independently sending a human into orbit. Astronaut Yang Liwei, a former fighter pilot, circled the Earth 14 times in his Shenzhou 5 spacecraft. With this successful mission, China became only the third nation in the world, after Russia and the United States, to possess its own human spaceflight capability, a culmination of a decades-long effort and a clear statement of its long-term ambitions in space.

Milestone 86: First Asteroid Sample Return (2010)

The Japan Aerospace Exploration Agency (JAXA) achieved a monumental feat of deep-space navigation and engineering with its Hayabusa mission. After a seven-year, 6-billion-kilometer journey, the spacecraft returned to Earth on June 13, 2010, carrying a capsule with the first-ever samples collected directly from the surface of an asteroid. Despite suffering numerous technical failures during its encounter with the asteroid Itokawa, the mission successfully retrieved microscopic dust grains. The analysis of these particles provided unprecedented insights into the composition and history of near-Earth asteroids.

Milestone 87: India Reaches Mars on First Attempt (2014)

On September 24, 2014, the Indian Space Research Organisation (ISRO) made history when its Mars Orbiter Mission (MOM), also known as Mangalyaan, successfully entered orbit around Mars. The achievement was remarkable for two reasons: it made India only the fourth entity to reach Mars, and it was the first nation to do so on its very first attempt. Furthermore, the mission was completed for a reported cost of just $74 million, a fraction of the cost of comparable missions, showcasing India’s prowess in frugal yet effective space engineering.

Milestone 88: First Spacecraft to Orbit a Comet (2014)

After a ten-year, 6.4-billion-kilometer journey across the solar system, the European Space Agency‘s Rosetta spacecraft arrived at Comet 67P/Churyumov-Gerasimenko on August 6, 2014. It became the first spacecraft in history to enter orbit around a comet. For the next two years, Rosetta flew alongside the comet as it journeyed toward the Sun, studying in unprecedented detail how the Sun’s heat transforms the icy nucleus, creating its glowing coma and tail.

Milestone 89: First Landing on a Comet (2014)

The Rosetta mission’s most ambitious moment came on November 12, 2014, when it deployed its lander, Philae, to the surface of Comet 67P. The landing was dramatic; harpoons meant to anchor the lander failed to fire, causing Philae to bounce twice before coming to rest in a shaded, tilted position. Despite the difficult landing, the probe’s instruments transmitted valuable data on the comet’s composition for over 60 hours before its batteries were depleted, providing the first-ever in-situ analysis of a comet’s surface.

Milestone 90: First Flyby of Pluto (2015)

After a journey of nine and a half years and nearly 5 billion kilometers, NASA’s New Horizons spacecraft conducted the first-ever close-up exploration of Pluto on July 14, 2015. The flyby transformed Pluto from a distant, fuzzy point of light into a vibrant and complex world. Images revealed towering mountains made of water ice, vast, flowing glaciers of nitrogen ice in a heart-shaped region named Sputnik Planitia, and a surprisingly hazy blue atmosphere. The encounter fundamentally rewrote our understanding of this distant dwarf planet and the Kuiper Belt.

Milestone 91: First Landing on the Far Side of the Moon (2019)

China’s ambitious lunar exploration program achieved a historic world first on January 3, 2019. The Chang’e 4 spacecraft successfully executed the first-ever soft landing on the far side of the Moon, a region that is permanently hidden from Earth. The lander touched down in the vast South Pole-Aitken basin and deployed the Yutu-2 rover. Because direct communication is impossible, the mission relies on the Queqiao relay satellite, which China had placed in a special orbit beyond the Moon a year earlier. The mission opened up a new, unexplored region of the Moon for scientific study.

Milestone 92: First Image of a Black Hole (2019)

On April 10, 2019, astronomers unveiled a discovery that had long been thought impossible: the first-ever direct image of a black hole. The image was captured not by a single instrument, but by the Event Horizon Telescope (EHT), a planet-spanning network of eight radio telescopes synchronized to work together as one virtual, Earth-sized observatory. The target was the supermassive black hole at the center of the galaxy Messier 87, some 55 million light-years away. The image shows a bright ring of superheated gas swirling around the black hole’s event horizon—the point of no return—which appears as a dark central shadow.

Milestone 93: China Returns Lunar Samples (2020)

China became only the third country to successfully retrieve samples from the Moon and return them to Earth with its Chang’e 5 mission. On December 1, 2020, the lander touched down in the Mons Rümker region of the Moon. It collected 1,731 grams (3.8 lbs) of lunar rock and soil, both from the surface and from a 2-meter-deep drill core. The samples were then transferred to an ascent vehicle, which launched from the Moon, docked with the orbiter, and returned to Earth on December 16. The samples, much younger than those from the Apollo missions, provided new insights into the Moon’s recent geological history.

Milestone 94: First Arab Interplanetary Mission (2021)

The United Arab Emirates joined the exclusive club of nations to reach Mars on February 9, 2021, when its Hope probe successfully entered orbit around the Red Planet. The mission was the first interplanetary endeavor by an Arab nation. Hope’s unique, high-altitude elliptical orbit allows it to create the first complete portrait of the Martian atmosphere, studying daily and seasonal weather cycles, dust storms, and how the lower and upper atmospheres interact. Its success was a major milestone for the UAE’s burgeoning science and technology sector.

The Next Chapter: Return to the Moon and Beyond

As space exploration moves deeper into the 21st century, its focus is shifting toward a new set of ambitious goals. These include establishing a sustainable human presence on the Moon, developing technologies for planetary defense, and pushing the frontiers of science by visiting previously unexplored destinations. This modern era is characterized by a blend of government-led flagship missions and dynamic commercial partnerships, all working to lay the foundation for the next great leap in human exploration.

Milestone 95: First Image of Jupiter’s Poles (2016)

NASA’s Juno spacecraft entered a unique polar orbit around Jupiter on July 4, 2016, providing humanity with its first detailed look at the planet’s poles. The images returned were stunning and unexpected. Instead of the orderly belts and zones seen at lower latitudes, Jupiter’s poles are chaotic regions covered in massive, Earth-sized cyclones clustered together in geometric patterns. Juno’s ongoing mission continues to probe deep into Jupiter’s atmosphere to understand its composition, gravity field, and powerful magnetosphere.

Milestone 96: First Spacecraft to “Touch” the Sun (2021)

On April 28, 2021, NASA’s Parker Solar Probe achieved a milestone that was decades in the making: it became the first spacecraft to fly through the Sun’s upper atmosphere, the corona. To survive the extreme heat and radiation, the probe is protected by a revolutionary carbon-composite heat shield. By flying directly through the region where the solar wind originates, Parker is sampling particles and magnetic fields at their source, aiming to solve fundamental mysteries about how the Sun works and how it generates the solar wind that affects the entire solar system.

Milestone 97: First Asteroid Deflection Test (2022)

In a landmark demonstration of planetary defense, NASA’s Double Asteroid Redirection Test (DART) mission successfully tested a technique for protecting Earth from a potential asteroid impact. On September 26, 2022, the DART spacecraft deliberately slammed into Dimorphos, the small moonlet of the asteroid Didymos. The kinetic impact successfully altered Dimorphos’s orbit around Didymos, proving that this technique could be used to deflect a hazardous asteroid if one were ever discovered on a collision course with Earth.

Milestone 98: Artemis I: The Return to the Moon Begins (2022)

On November 16, 2022, NASA launched the most powerful rocket ever built, the Space Launch System (SLS), on its maiden flight for the Artemis I mission. Perched atop the rocket was the uncrewed Orion spacecraft, designed for future human missions to deep space. The 25-day mission sent Orion on a journey thousands of miles beyond the Moon and back, testing the spacecraft’s systems in the harsh environment of deep space and executing a high-speed reentry to validate its heat shield. The successful flight was a critical first step in NASA’s plan to return astronauts to the lunar surface.

Milestone 99: First Precision Lunar Landing (2024)

The Japan Aerospace Exploration Agency (JAXA) demonstrated a new level of landing accuracy with its SLIM (Smart Lander for Investigating Moon) mission. On January 19, 2024, SLIM successfully touched down on the Moon within 55 meters of its target point, a feat of “pinpoint” landing. Traditional landers have landing zones several kilometers wide. This precision navigation technology, which uses real-time image matching to identify craters, will enable future missions to land safely in challenging but scientifically valuable terrain, such as near crater rims or on steep slopes.

Milestone 100: The Future: A Sustainable Lunar Presence

The overarching goal of NASA’s Artemis program, in collaboration with international and commercial partners, is not just to return to the Moon, but to stay. The program plans to land the first woman and the first person of color on the lunar surface by the mid-2020s. It envisions building a sustainable human presence through the Lunar Gateway, an outpost in orbit around the Moon, and an Artemis Base Camp on the surface. This long-term presence on the Moon will serve as a proving ground for the technologies and operational experience needed for humanity’s next giant leap: sending astronauts to Mars.

Summary

The journey from the first theoretical rocket equations to the ambitious plans for a permanent lunar base is a story of accelerating progress. The initial 100 milestones reveal a clear evolutionary arc. The narrative began with a fierce bipolar competition, where national prestige was the primary driver, leading to a rapid series of monumental “firsts.” This gave way to an era of more deliberate, long-term robotic science, where probes like Voyager and Cassini undertook generational voyages that transformed our understanding of the solar system’s outer reaches.

In the 21st century, the landscape has been reshaped by two powerful forces: the globalization of spaceflight and the commercial revolution. Space is no longer the exclusive domain of two superpowers. A diverse community of nations, including China, India, Japan, the UAE, and the European Space Agency, are now leading their own groundbreaking missions, creating a more complex and dynamic environment of both competition and collaboration. Simultaneously, the disruptive innovation of private companies, particularly in rocket reusability, has shattered old cost paradigms and democratized access to orbit.

These threads are converging. The renewed push to the Moon under the Artemis program is a global, public-private endeavor, a model that stands in stark contrast to the singular national effort of Apollo. These first 100 achievements, from Sputnik’s first beep to the first powered flight on Mars, have built the foundation. The next 100 will likely see humanity establish a permanent, sustainable foothold on another world, using it as a stepping stone to venture even deeper into the cosmos. The human reach continues to expand.

Appendix: 100 Milestones in Chronological Order