Space exploration

• 1. Introduction

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  Space exploration begins not with a triumphant launch but with a German rocket climbing 176 kilometers into the dark on the 20th of June 1944. The MW 18014 test flight from the Peenemünde Army Research Center became the first human-made object to reach outer space. It was a vertical test launch, a V-2 rocket that never reached orbital velocity and fell back to Earth in an impact. That short, violent arc above the Karman line opened a question that has not closed since. If a rocket could touch space, what else could be sent there, and how far could it go? This is the story of how astronomy, a practice older than reliable recorded history, became a physical investigation of outer space by robotic probes and human spaceflight. It is a story of rivalry and cooperation, of the Moon and the Sun, of planets that swallow their visitors whole, and of a single probe that has now left the Solar System entirely. The reasons people give for going are many. Scientific research. National prestige. Uniting nations. Ensuring the future survival of humanity. Military and strategic advantage. Each of those reasons shaped a different chapter of the journey.

• 2. The Space Race

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  On the 4th of October 1957, the Soviet Union launched Sputnik 1, the first human-made object to orbit Earth. The satellite weighed about 83 kilograms and is believed to have circled the planet at a height of about 250 kilometers. It carried two radio transmitters, at 20 and 40 megahertz, whose beeps could be heard by radios around the globe. Those beeps were more than a signal of arrival. Analysis of the radio signals gathered information about the electron density of the ionosphere, while temperature and pressure data were encoded in the duration of the beeps. The results indicated the satellite had not been punctured by a meteoroid. Sputnik 1 was launched by an R-7 rocket and burned up upon re-entry on the 3rd of January 1958. The early era of exploration was driven by a contest in which the Soviet Union and the United States competed to demonstrate technological superiority. The Soviet program claimed many of the firsts. The first living being in orbit came in 1957. The first spacewalk, by Alexei Leonov, came on the 18th of March 1965. The first automatic landing on another celestial body followed in 1966. On the 12th of April 1961, Vostok 1 carried the 27-year-old Russian cosmonaut Yuri Gagarin on a single orbit lasting about 1 hour and 48 minutes. His flight opened an entirely new era, human spaceflight, and the next prize was already in sight: the Moon.

• 3. Reaching The Moon

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  Luna 2 became the first artificial object to reach another celestial body when it struck the Moon in 1959, the same year the Soviets obtained the first images of the far side never previously visible to humans. The Moon holds a unique set of distinctions. It was the first remote celestial object to be flown by, orbited, and landed upon by spacecraft, and the only one ever visited by humans. Luna 9 performed the first soft landing on the Moon on the 3rd of February 1966, and Luna 10 became the first artificial satellite of the Moon on the 3rd of April that year. The U.S. effort began with the Ranger 4 impactor in 1962. Just four months after the Soviet landers began returning surface data, Surveyor 1 marked the debut of a successful series of American landers. The Soviet uncrewed missions reached their peak with the Lunokhod program in the early 1970s, which included the first uncrewed rovers and brought lunar soil samples back to Earth, the first and so far only automated return of extraterrestrial soil. Crewed exploration began in 1968, when Apollo 8 became the first time humans orbited any extraterrestrial object. On the 20th of July 1969, Apollo 11 marked the first time humans set foot upon another world. Six spacecraft carried humans to the lunar surface between 1969 and the Apollo 17 mission in 1972, the most recent human visit. More recently, China's Chang'e 4 in 2019 and Chang'e 6 in 2024 achieved the world's first landing and sample return on the far side, while India's Chandrayaan-3 reached the lunar south pole region in 2023.

• 4. The Hostile Planets

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  Venus has had more landers sent to it, nearly all from the Soviet Union, than any other planet in the Solar System, despite having one of the most hostile surface environments anywhere. The first interplanetary flyby was the 1961 Venera 1 pass of Venus, though the 1962 Mariner 2 was the first to successfully return data, with a closest approach of 34,773 kilometers. In 1967, Venera 4 became the first probe to enter and directly examine another planet's atmosphere. In 1970, Venera 7 became the first successful lander to reach the surface of Venus, returning data for 23 minutes. In 1975, Venera 9 returned the first images from the surface of another planet. Venera 13 transmitted from the Venusian surface for over two hours in 1982, the longest ever Soviet planetary surface mission. Mars proved a far more treacherous target. Roughly two-thirds of all spacecraft destined for Mars have failed before completing their missions, some failing before they even began. The high failure rate led researchers to joke about The Great Galactic Ghoul, a creature said to subsist on a diet of Mars probes, a phenomenon also called the Mars Curse. Against that record, India became the first country to succeed on its maiden attempt. Its Mars Orbiter Mission was one of the least expensive interplanetary missions ever undertaken, with an approximate total cost of 450 Crore. Venus and Mars are the only two planets beyond Earth on which humans have conducted surface missions with robotic spacecraft.

• 5. The Outer Worlds

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  Voyager 2 alone has visited Uranus and Neptune, making it the sole spacecraft to reach either. Its closest approach to Uranus came on the 24th of January 1986. The planet, with an axial tilt of 97.77 degrees, showed a uniform appearance with no dramatic storms or atmospheric banding, and great effort was required to identify even a few clouds. Its magnetosphere, profoundly affected by that unusual tilt, proved unique, and the moon Miranda showed evidence of having been unusually geologically active. Voyager 2 examined all five previously known moons of Uranus and discovered ten more. The contrast at Neptune was striking. The flyby on the 25th of August 1989 found obvious banding, visible clouds, auroras, and an anticyclone storm rivaled in size only by Jupiter's Great Red Spot. Neptune also had the fastest winds of any planet in the Solar System, measured as high as 2,100 kilometers per hour. Voyager 2 discovered 900 complete rings and partial ring arcs, found five new moons including Proteus, and supported the view that the largest moon, Triton, is a captured Kuiper belt object. Jupiter and Saturn drew their own visitors. Galileo and Juno are the only spacecraft to have entered Jupiter's orbit, a planet whose small rocky core and absence of a solid surface preclude any landing. At Saturn, the Cassini spacecraft conducted an orbital mission from 2004 until 2017, and the Huygens probe became the only lander ever deployed in the Outer Solar System, descending to Titan, the only moon with an atmosphere denser and thicker than Earth's.

• 6. Smaller Bodies

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  Galileo flew past two asteroids on its way to Jupiter, 951 Gaspra in 1991 and 243 Ida in 1993, both lying near enough to its planned trajectory to be visited at acceptable cost. Until space travel, objects in the asteroid belt were merely pinpricks of light in even the largest telescopes. The first landing on an asteroid was performed by the NEAR Shoemaker probe in 2000, following an orbital survey of 433 Eros. NASA's Dawn spacecraft, launched in 2007, visited the dwarf planet Ceres and the asteroid 4 Vesta. Hayabusa, developed by the Japan Aerospace Exploration Agency, took a different approach, returning a sample from the small near-Earth asteroid 25143 Itokawa. Launched on the 9th of May 2003, it rendezvoused with Itokawa in mid-September 2005, landed twice in November to collect samples, and returned to Earth on the 13th of June 2010. Comets have rarely been visited closely, though many have been studied from Earth across centuries. In 1985, the International Cometary Explorer conducted the first comet fly-by, of 21P/Giacobini-Zinner, before joining the Halley Armada. The Deep Impact probe smashed into 9P/Tempel to study its structure, the Stardust mission returned samples of a comet's tail, and the Philae lander touched down on Comet Churyumov-Gerasimenko in 2014 as part of the Rosetta mission. New Horizons, after its closest approach to Pluto on the 14th of July 2015, went on to fly past the planetesimal Arrokoth in the Kuiper belt in 2019.

• 7. The Human Body In Space

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  Valeri Polyakov's single spaceflight of almost 438 days aboard the Mir space station has not been surpassed. Such endurance comes at a cost the body begins paying almost immediately. Space motion sickness, which affects the neurovestibular system and produces vertigo, dizziness, fatigue, nausea, and disorientation, plagues almost all space travelers within their first few days in orbit. Long stays reveal deeper problems. Bone and muscle loss in low gravity, immune system suppression, eyesight trouble, and radiation exposure all accumulate. The lack of gravity causes fluid to rise upward, building pressure in the eye and producing vision problems, alongside loss of bone minerals, cardiovascular deconditioning, and decreased muscle mass. Radiation is an insidious hazard because it is invisible and can cause cancer. Above Earth's magnetic field, spacecraft lose their protection from the Sun's radiation, and the danger grows more potent in deep space. Mission Control counters these effects with telemedicine, monitoring astronaut health closely. Aboard the International Space Station, on-board treadmills help prevent muscle loss and reduce the risk of premature osteoporosis. A crew medical officer is appointed for each ISS mission, and a flight surgeon is available around the clock through the Mission Control Center in Houston, Texas. As a spacecraft moves further from Earth, communications can be delayed by as much as 20 minutes, so crews are trained to respond to medical emergencies on their own.

• 8. The Reach Of The Future

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  Voyager 1 became the first human-made object to leave the Solar System into interstellar space on the 25th of August 2012, passing the heliopause at 121 AU, and it remains the most distant human-made object from Earth. The push outward continues on several fronts. Breakthrough Starshot, founded in 2016 by Yuri Milner, Stephen Hawking, and Mark Zuckerberg, aims to develop a proof-of-concept fleet of light sail spacecraft named StarChip, capable of reaching the Alpha Centauri star system 4.37 light-years away. Closer to home, the two primary global programs gaining traction in the 2020s are both focused on the Moon. The Chinese-led International Lunar Research Station and the U.S.-led Artemis Program each carry their own set of international partners. The Artemis program aims to land the first woman and the next man at the lunar south pole region, laying the foundation for a lunar economy and eventually sending humans to Mars. Artemis II completed a crewed flyby of the Moon in 2026, traveling 406,773 kilometers from Earth at its furthest point, surpassing the record set when Apollo 13 passed the far side of the Moon in 1970 at 400,171 kilometers. Artemis IV, planned for 2028, is set to be the first lunar landing since Apollo 17. These ambitions echo a much older plan. The rocket scientist Wernher von Braun laid out a sequence of steps, from multi-stage rockets to reusable winged spacecraft to a permanent space station and on to landings on the Moon and eventually Mars. Known as the Von Braun Paradigm, his vision served as the model for human space exploration well into the twenty-first century, even as the steps were taken out of order.