Spaceflight

• 1. Introduction

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  Spaceflight is the use of astronautics to fly objects, usually spacecraft, into or through outer space, with or without humans on board. In June 1944, a single V-2 rocket climbed to an altitude of 189 km during a test flight. It became the first human-made object ever to reach space. That moment sat at the end of a long chain of ideas, and the beginning of an even longer one. A Scottish astronomer had imagined the journey in print decades before any engine existed to attempt it. A Russian schoolteacher had written down the equation that still governs every launch. Most spaceflight, then and now, carries no people at all. So how does a machine break free of gravity, fall around the Earth without falling back, and sometimes leave the Solar System entirely? And why is it, as one principle holds, far easier to reach space than to stay there?

• 2. Equation And Essay

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  William Leitch, a Scottish astronomer and mathematician, published the first theoretical proposal of space travel using rockets in an 1861 essay titled "A Journey Through Space". His idea arrived long before any practical means to test it. More famous is the work of Konstantin Tsiolkovsky, whose study The Exploration of Cosmic Space by Means of Reaction Devices appeared in 1903. Tsiolkovsky set down the fundamental rocket equation, relating a rocket's change in velocity to its exhaust velocity and to its initial and final masses. Engineers still use this Tsiolkovsky rocket equation to find the total potential change in velocity, and it remains a key concept of spaceflight. Robert H. Goddard pushed the idea toward reality with his 1919 paper A Method of Reaching Extreme Altitudes. By applying the de Laval nozzle to liquid-fuel rockets, he improved efficiency enough that interplanetary travel became possible. Goddard tried to secure an Army contract for a rocket-propelled weapon during the First World War. The armistice with Germany on the 11th of November 1918 foiled those plans. Working instead with private financial support, he became the first to launch a liquid-fueled rocket on the 16th of March 1926.

• 3. Weapons Into Vehicles

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  The V-2, developed and used as a weapon by Nazi Germany during World War II, was the first guided rocket. At the war's end most of the V-2 team, including its head Wernher von Braun, surrendered to the United States. They were brought over to work on American missiles at what became the Army Ballistic Missile Agency, producing missiles such as Juno I and Atlas. The Soviet Union captured several V-2 production facilities and built replicas, with 5 of their 11 rockets successfully reaching their targets. That rate was relatively consistent with Nazi Germany's own success rate. During the 1950s the Soviet Union developed intercontinental ballistic missiles to carry nuclear weapons, a counter to United States bomber planes. The Tsiolkovsky-influenced Sergey Korolev became the chief rocket designer. Derivatives of his R-7 Semyorka missiles launched the world's first artificial Earth satellite, Sputnik 1, on the 4th of October 1957. After Sputnik and two embarrassing failures of Vanguard rockets, the U.S. launched Explorer 1 on the 1st of February 1958. The line from battlefield weapon to orbital launcher ran straight through the same engines and the same engineers.

• 4. The Race To Orbit

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  Vostok 1 carried cosmonaut Yuri Gagarin into orbit, the first human spaceflight, on the 12th of April 1961, with Gagarin making one orbit around the Earth. Official Soviet documents make no mention that Gagarin parachuted the final seven miles of his descent. The United States answered with the suborbital launch of Alan Shepard on the 5th of May 1961, and the orbital flight of John Glenn on the 20th of February 1962. U.S. President John F. Kennedy then pledged to go to the Moon, and the Gemini and Apollo programs were created. The Gemini program performed a rendezvous, a docking, and an EVA before ending just ahead of the Apollo 1 tragedy. After uncrewed test flights of the Saturn 1B and Saturn V, Apollo 7 flew crewed into low Earth orbit. Apollo 8 became the first mission to orbit the Moon, Apollo 9 the first to launch with both the CSM and the LEM, and Apollo 10 the first to nearly land. Apollo 11 achieved the first crewed Moon landing, followed by six more missions, five of which landed successfully.

• 5. Falling Around Earth

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  Rockets are the only means currently capable of reaching orbit or beyond, because chemical propulsion can sustain thrust even as the atmosphere thins. Conventional spaceflight uses multistage rockets, which provide the thrust to overcome gravity and push a spacecraft onto a suborbital trajectory. For an orbital mission, the spacecraft separates its first stage and ignites the second, reaching speeds high enough to attain orbit. Once in orbit, a spacecraft moves fast enough that it falls around the Earth rather than back to the surface. The most common definition of outer space is everything beyond the Kármán line, 100 km above the Earth's surface, though the United States defines space as everything above 50 mi in altitude. Passing the Kármán line is the easy part. The increase in potential energy needed to cross it is only about 3% of the orbital energy required by the lowest possible Earth orbit. To reach a space station, a spacecraft must arrive at the same orbit and close to within visual contact through maneuvers called space rendezvous. It then docks, joining two free-flying vehicles, or berths, where a robotic arm places an inactive vehicle into a mating interface.

• 6. Coming Home

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  Vehicles in orbit hold large amounts of kinetic energy, and that energy must be discarded for a safe landing without vaporizing in the atmosphere. Harry Julian Allen developed the theory behind reentry. From his theory came the insight that reentry vehicles should present blunt shapes to the atmosphere. A blunt shape means less than 1% of the kinetic energy ends up as heat reaching the vehicle, while the rest heats the air. The Mercury, Gemini, and Apollo capsules splashed down in the sea, slowed by parachutes for relatively low landing speeds. Soviet and Russian Soyuz capsules use a big parachute plus braking rockets to touch down on land, while spaceplanes like the Space Shuttle land like a glider. Sometimes recovery happened before landing entirely. A specially designed aircraft could snag a spacecraft while it was still descending on its parachute. This mid-air retrieval technique recovered the film canisters from the Corona spy satellites.

• 7. From Suborbital To Interstellar

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  A suborbital spaceflight reaches space and then returns after following a primarily ballistic trajectory, often lasting only a few minutes. Pioneer 1, NASA's first space probe intended to reach the Moon, suffered a partial failure and instead flew suborbital to an altitude of 113854 km. It reentered the atmosphere 43 hours after launch. Point-to-point transport is a suborbital category offering rapid travel between two terrestrial locations. A London to Sydney trip that normally lasts over twenty hours could be crossed in less than one hour, and SpaceX has revealed plans to attempt this using Starship. Interplanetary spaceflight, in practice, means travel between the planets of the Solar System. New Horizons is the fifth spacecraft put on an escape trajectory leaving the Solar System, after Voyager 1, Voyager 2, Pioneer 10, and Pioneer 11. Voyager 1 is the farthest, more than 100 AU from the Sun and moving at 3.6 AU per year. Proxima Centauri, the closest star other than the Sun, lies 267,000 AU away. Voyager 1 would take over 74,000 years to reach that distance.

• 8. The Price Of Reuse

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  The X-15, the first reusable spacecraft, was air-launched on a suborbital trajectory on the 19th of July 1963. The first partially reusable orbital spacecraft, the Space Shuttle, launched on the 12th of April 1981, the 20th anniversary of Yuri Gagarin's flight. Six orbiters were built during the Shuttle era. Enterprise flew only approach and landing tests, launching from the back of a Boeing 747 and gliding to deadstick landings at Edwards AFB, California. Columbia flew first into space, followed by Challenger, Discovery, Atlantis, and Endeavour. Endeavour was built to replace Challenger, lost in January 1986, and Columbia broke up during reentry in February 2003. The USSR launched its automatic Buran spaceplane on the 15th of November 1988, but it flew only once before lack of funding and the dissolution of the USSR ended the program. Private reuse advanced quickly. SpaceX achieved the first vertical soft landing of a reusable orbital rocket stage on the 21st of December 2015, after delivering 11 Orbcomm OG-2 satellites into low Earth orbit. As of April 2025, three Super Heavy boosters, the first stage of Starship, have been recovered.

  When a Delta II rocket exploded 13 seconds after launch on the 17th of January 1997, store windows 10 mi away were reported broken by the blast. Launch vehicles carry enormous energy, and that energy can release prematurely with significant effects. In April 2004 the International Association for the Advancement of Space Safety was established in the Netherlands to advance international cooperation in space systems safety. Humans in orbit face their own dangers in a microgravity environment. Short-term exposure causes space adaptation syndrome, a self-limiting nausea from derangement of the vestibular system. Long-term exposure causes bone loss, some of it permanent, plus deconditioning of muscular and cardiovascular tissue. Above the atmosphere, radiation from the Van Allen belts, the Sun, and cosmic sources increases. Solar flares can deliver a fatal radiation dose in minutes. To keep people alive, NASA's Environmental Control and Life-Support System, or ECLSS, must supply air, water, and food while managing temperature, pressure, and waste. A worsening hazard sits in orbit itself. When large objects break up or collide, they create hundreds of small, hard-to-find pieces, a chain of continuous collisions known as Kessler syndrome, which could one day make orbit inaccessible for generations.