Since such a ship might take centuries to thousands of years to reach even nearby stars, the original occupants of a generation ship would grow old and die, leaving their descendants to continue traveling.
The concept of a generation starship is a good example of how science and fiction influence each other. Many space scientists and engineers who contributed to the concept of a generation starship were also science fiction writers. Perhaps the earliest description of a generation ship is in the 1929 essay "The World, The Flesh, & The Devil" by J. D. Bernal.
Robert H. Goddard, the rocket pioneer, was the first to write about very long duration interstellar journeys in his "The Last Migration" (1918).[note 1] In this he described the death of the Sun and the necessity of an "interstellar ark". The crew would face the centuries of travel by sleeping and would be awakened when they reached another star system.
Konstantin E. Tsiolkovsky, father of astronautic theory, first described the need for multiple generations of passengers in his essay, "The Future of Earth and Mankind" (1928), a space colony equipped with engines that travels thousands of years which he called "Noah's Ark".
Bernal's essay was the first publication to reach the public and influence other writers. He wrote about the concept of human evolution and mankind's future in space through methods of living that we now describe as a generation starship, and which could be seen in the generic word "globes".
The Enzmann starship is categorised as "slow boat" because of the Astronomy Magazine title “Slow Boat to Centauri” (1977). Gregory Matloff's concept is called a "colony ship" and Alan Bond called his concept a "world ship".
Such a ship would have to be entirely self-sustaining, providing energy, food, air, and water for everyone on board. It must also have extraordinarily reliable systems that could be maintained by the ship's inhabitants over long periods of time. This would require testing whether thousands of humans could survive on their own before sending them beyond the reach of help. Small artificial closed ecosystems, such as the Biosphere 2, have been built in an attempt to work out the engineering difficulties in such a system, with mixed results. 
Generation ships would have to anticipate possible biological, social and morale problems, and would also need to deal with matters of self-worth and purpose for the various crews involved. As an example, a moral quandary exists regarding how intermediate generations, those destined to be born and die in transit without actually seeing tangible results of their efforts, might feel about their forced existence on such a ship.
Estimates of the minimum reasonable population for a generation ship vary. Anthropologist John Moore has estimated that, even in the absence of cryonics or sperm banks, a population capacity of 160 people would allow normal family life (with the average individual having ten potential marriage partners) throughout a 200-year space journey, with little loss of genetic diversity; social engineering can reduce this estimate to 80 people. In 2013 anthropologist Cameron Smith reviewed existing literature and created a new computer model to estimate a minimum reasonable population in the tens of thousands. Smith's numbers were much larger than previous estimates such as Moore's, in part because Smith takes the risk of accidents and disease into consideration, and assumes at least one severe population catastrophe over the course of a 150-year journey.
In light of the multiple generations that it could take to reach even our nearest neighboring star systems such as Proxima Centauri, further issues on the viability of such interstellar arks include:
In order for a spacecraft to maintain a stable environment for multiple generations, it would have to be large enough to support a community of humans and a fully recycling ecosystem. However, a spacecraft of such a size would require a lot of energy to accelerate and decelerate. A smaller spacecraft, while able to accelerate more easily and thus make higher cruise velocities more practical, would reduce exposure to cosmic radiation and the time for malfunctions to develop in the craft, but would have challenges with resource metabolic flow and ecologic balance.
Generation ships travelling for long periods of time may see breakdowns in social structures. Changes in society (for example, mutiny) could occur over such periods and may prevent the ship from reaching its destination. This state was described by Algis Budrys in a 1966 book review:
The slower-than-light interstellar spaceship, pursuing its way through the weary centuries, its crew losing touch with all reality save the interior of the vessel ... Well, you know the story, and its unhappy downhill round, its exciting struggles between the barbarian tribes which develop in its disparate compartments, and then, if the writer is so minded, the ultimate flash of hope as the good guys win out and prepare to meet their future on some noble, if erroneous basis.
The radiation environment of deep space is very different from that on the Earth's surface, or in low earth orbit, due to the much larger influx of high-energy galactic cosmic rays (GCRs). Like other ionizing radiation, high-energy cosmic rays can damage DNA and increase the risk of cancer, cataracts, and neurological disorders. One known practical solution to this problem is surrounding the crewed parts of the ship with a thick enough shielding such as a thick layer of maintained ice as proposed in The Songs of Distant Earth, a science fiction novel by Arthur C. Clarke (note: in this book the ship's mammoth ice shield is only in the forward part of the ship, preventing micrometeors from damaging the ship during its interstellar journey).
If a generation ship is sent to a star system 20 light years away, and is expected to reach its destination in 200 years, a better ship may be later developed that can reach it in 50 years. Thus, the first generation ship may find a century-old human colony after its arrival at its destination.
Across the Universe is a trilogy of young adult science fiction novels written by American author Beth Revis. Chronicling the life of Amy Martin aboard a generation ship hundreds of years in the future, Across the Universe, the first novel published in 2011 by Penguin Books, received a starred Kirkus review and made the New York Bestseller List for Children's Chapter Books.Ascension (miniseries)
Ascension is a 2014 Canadian/American science fiction mystery drama television miniseries which aired on CBC in Canada and Syfy in the United States. It consists of six 43 minute episodes. The show was created by Philip Levens and Adrian A. Cruz. The pilot was written and executive produced by Philip Levens, who served as the showrunner.
On July 9, 2014, CBC added Ascension to its fall programming roster. It was originally scheduled to premiere in November 2014. In October 2014, CBC announced that the premiere date had been moved to January 2015.
It started airing on CBC on Monday nights starting February 9, 2015. Syfy had originally announced plans to debut the show on November 24, 2014, airing one episode per week for six weeks. Instead the series premiered on December 15, 2014, and aired two episodes each night for three consecutive nights.The story takes place aboard a generation ship originally launched in the 1960s and now half-way into its 100-year journey to Proxima Centauri. A murder onboard sparks off a series of events that leads some of the crew to begin second-guessing their real mission.Aurora (novel)
Aurora is a 2015 novel by American science fiction author Kim Stanley Robinson. The novel concerns a generation ship traveling to Tau Ceti in order to begin a human colony. The novel's primary narrating voice is the starship's artificial intelligence. The novel was well received by critics.Evacuate Earth
Evacuate Earth is a National Geographic Channel documentary that portrays the hypothetical scenario of humans evacuating the planet Earth before it is destroyed by a rogue neutron star. The documentary details the technical and social complications of building a generation ship to save humanity and other Earth organisms by relocating to a planet in another solar system.For the World Is Hollow and I Have Touched the Sky
"For the World is Hollow and I Have Touched the Sky" is the eighth episode of the third season of the American science fiction television series Star Trek. It was aired by NBC on November 8, 1968 and was written by Rik Vollaerts, and directed by Tony Leader.
In the episode, the crew of the Enterprise rush to stop an asteroid from colliding with a Federation world, but discover the asteroid is actually an inhabited generation ship.Hull Zero Three
Hull Zero Three is a science fiction novel by American author Greg Bear. It was published on November 22, 2010. It is set on a generation ship that has lost its way under mysterious circumstances.Interstellar ark
An interstellar ark or generation ship is a conceptual space vehicle designed for interstellar travel. Interstellar arks may be the most economically feasible method of traveling such distances. The ark has also been proposed as a potential habitat to preserve civilization and knowledge in the event of a global catastrophe.
Such a ship would have to be large, requiring a large power plant. The Project Orion concept of propulsion by nuclear pulses has been proposed. The largest spacecraft design analyzed in Project Orion had a 400 m diameter and weighed approximately 8 million tons. It could be large enough to host a city of 100,000 or more people.Journey into Space (book)
Journey into Space is a 2009 British science fiction novel by Toby Litt about people living on a generation ship which is bound for another planet. It was Litt's tenth novel and was published by Penguin Books.List of science fiction themes
The following is a list of articles about recurring themes in science fiction.Methuselah's Children
Methuselah's Children is a science fiction novel by American writer Robert A. Heinlein, originally serialized in Astounding Science Fiction in the July, August, and September 1941 issues. It was expanded into a full-length novel in 1958.
The novel is usually considered to be part of Heinlein's Future History series of stories. It introduces the Howard families, a fictional group of people who achieved long lifespans through selective breeding. The space ship in this novel, the New Frontiers, is described in the Future History timeline as a second generation ship, following the Vanguard, the vehicle for Heinlein's paired novellas "Universe" and "Common Sense".
According to John W. Campbell, the novel was originally to be called While the Evil Days Come Not. This provisional title stems from a quotation from Ecclesiastes that was used as a password on the second page of the story.
The novel was the origin of the word "masquerade" as a term for a fictional trope of a hidden society within the real world.Orphans of the Sky
Orphans of the Sky is a science fiction novel by American writer Robert A. Heinlein, consisting of two parts: "Universe" (Astounding Science Fiction, May 1941) and its sequel, "Common Sense" (Astounding Science Fiction, October 1941). The two novellas were first published together in book form in 1963. "Universe" was also published separately in 1951 as a 10¢ Dell paperback. These works contain one of the earliest fictional depictions of a generation ship.Orthogonal (series)
Orthogonal is a science fiction trilogy by Australian author Greg Egan taking place in a universe where, rather than three dimensions of space and one of time, there are four fundamentally identical dimensions. While the characters in the novels always perceive three of the dimensions as space and one as time, this classification depends entirely on their state of motion, and the dimension that one observer considers to be time can be seen as a purely spatial dimension by another observer.
The plot involves the inhabitants of a planet that comes under threat from a barrage of high-velocity meteors known as 'hurtlers', who launch a generation ship that exploits the distinctive relativistic effects present in this universe which allow far more time to elapse on the ship than passes on the home world, in order for the ship's inhabitants to have enough time to develop the technology needed to protect the planet. The three novels deal with a succession of increasingly advanced scientific discoveries, as well as a number of radical social changes in the culture of the generation ship's passengers.
Technically, the space-time of the universe portrayed in the novels has a positive-definite Riemannian metric, rather than a pseudo-Riemannian metric, which is the kind that describes our own universe.
The first novel of the trilogy, The Clockwork Rocket, was published in 2011, the second, The Eternal Flame, in 2012, and the third, The Arrows of Time, in 2013.Paradises Lost
Paradises Lost is a science fiction novella by American author Ursula K. Le Guin. It was first published in 2002 as a part of the collection The Birthday of the World. It is set during a multigenerational voyage from Earth to a potentially habitable planet. The protagonists, Liu Hsing and Nova Luis, are members of the fifth generation born on the ship. The story follows them as they deal with members of religious cult who do not believe in the ship stopping at its intended destination. They also face a crisis brought on by a drastic change in the ship's schedule. The novella has since been anthologized as well as adapted into an opera of the same name.
The novella explores the isolation brought on by space travel, as well as themes of religion and utopia. It contains elements of ecocriticism, or a critique of the idea that human beings are altogether separate from their natural environment. The novella and the collections it was published in received high praise from commentators. For its generation ship setting and examination of utopia, critics compared it to other Le Guin works such as "Newton's Sleep", and The Telling, as well as to the works of Gene Wolfe and Molly Gloss. Scholar Max Haiven described the novella as "a chastening lesson in both the potential and the perils of freedom", while author Margaret Atwood said that it "shows us our own natural world as a freshly discovered Paradise Regained, a realm of wonder".Ring (Baxter novel)
Ring is a 1994 science fiction novel by British author Stephen Baxter. The novel tells the story of the end of the universe and the saving of mankind from its destruction. Two parallel plots are followed throughout the novel: that of Lieserl, an AI exploring the interior of the sun, and that of the Great Northern, a generation ship on a five-million-year journey.Space Mutiny
Space Mutiny (also known as Mutiny in Space) is a 1988 South African space opera action film about a mutiny aboard the generation ship known as the Southern Sun. The film has since developed a cult following after being featured in a popular episode of the television show Mystery Science Theater 3000.The Ark (Doctor Who)
The Ark is the fifth serial of the third season of the British science fiction television series Doctor Who, which was first broadcast in four weekly parts from 5 to 26 March 1966.
The serial is set in the far distant future, at least ten million years. In the first two episodes of the serial, the time traveller the First Doctor (William Hartnell) and his travelling companions Steven Taylor (Peter Purves) and Dodo Chaplet (Jackie Lane) arrive on a generation ship Dodo names "the Ark", where the Doctor searches for a cure for a fever that has spread across the human and Monoid races on board who have no immunity to it. The last two episodes are set 700 years later, and involve the Doctor, Steven and Dodo working with the Refusian race to stop the Monoids from wiping out the last of humanity with a bomb.
The story constitutes Dodo's first journey with the Doctor as a travelling companion. It is also the earliest serial of the third season to exist in its entirety.The Book of the New Sun
The Book of the New Sun (1980 – 1983) is a series of four science fantasy novels or one four-volume novel written by American author Gene Wolfe. Alternatively, it is a series comprising the original tetralogy, a 1983 collection of essays, and a 1987 sequel. Either way, it inaugurated the so-called "Solar Cycle" that Wolfe continued after 1987 by setting other multi-volume works in the same universe.Gene Wolfe had originally intended the story to be a 40,000-word novella called "The Feast of Saint Catherine", meant to be published in one of the Orbit anthologies, but during the writing it continued to grow in size. Despite being published with a year between each book, all four books were written and completed during his free time without anyone's knowledge when he was still an editor of Plant Engineering, allowing him to write at his own pace and take his time.The tetralogy chronicles the journey of Severian, a disgraced journeyman torturer who is exiled and forced to travel to Thrax and beyond. It is a first-person narrative, apparently translated by Wolfe into contemporary English, set in the distant future when the Sun has dimmed and Earth is cooler (a "Dying Earth" story). Severian claims to have a "perfect memory", but at multiple occasions admits leaving out details and confides in the readers that he may be insane, making him an unreliable narrator.
In 1998, Locus magazine ranked the tetralogy number three among 36 all-time best fantasy novels before 1990, based on a poll of subscribers.Since the original four-volume novel, Wolfe has also written three short fictions and two book series that are set in Severian's universe.
The Internet Speculative Fiction Database catalogues it all as the "Solar Cycle" comprising the short works and three sub-series.The two later subseries are The Book of the Long Sun (1993–1996, four volumes) and The Book of the Short Sun (1999–2001, three volumes). Long Sun is set on a generation ship and Short Sun features the inhabitants of that generation ship after their long journey. Two of the Long Sun books were nominated for Nebula Awards.Voyage from Yesteryear
Voyage from Yesteryear is a 1982 science fiction novel by British writer James P. Hogan.