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The generation ship is currently humanity’s only technically feasible idea for interstellar travel. Perhaps this is why, as a science fiction subgenre, it cross-pollinates to such an extent with scientific thinking around the concept. Most stories in the subgenre draw from contemporary ideas on propulsion, shielding, computing, suspended animation, etc., while scientists borrow freely from science fiction writers when discussing physics, technology, sociological issues, and so on.

Types, Size and Speed of Generation Ships

In 2012, Andreas M. Hein, et al., produced a paper called ‘World Ships – Architectures & Feasibility Revisited’, which lays out a taxonomy of ‘interstellar arks’. Under the ‘arks’ are ‘sleeper ships’, which are manned starships where most, or all, of the crew travel in some form of suspended animation; ‘seed ships’, generally unmanned (or with a small crew) starships which carry embryos, gametes, or recorded genetic materials in order to transplant humanity and other lifeforms on to a distant colony world; and ‘generation ships’, enormous, self-sustaining ships that allow for manned interstellar travel at sub-light speed. The name comes from the fact that travelling between the stars would take many years, such that generations of the starship’s crew and passengers would be born, live and die along the way. Generation ships are further subdivided by capacity and speed: ‘world ships’ with crews of 100,000 or more and ‘colony ships’ with less than 100,000 people, ‘slow boats’, which travel less than .10C (1C being light speed) and ‘sprinters’, which travel faster than .10C.

To give some idea of the distances between stars and the length of time it would take to reach even some of our closer stellar neighbours, the Voyager 2 probe, one of the fastest man-made objects ever, will reach the area of the star Sirius, 8.6 light years away, in about 160,000 years. If humanity could build a ship that could go .10C, it would still take over 40 years, or two generations, to reach our closest neighbour, Proxima Centuri.

Generation ships crewed by 1,000 or fewer people would be significantly smaller than those crewed by more people but still giant compared to today’s spaceships. For example, the Project Orion ship design from the 1960s would have been about the size of a 16-story skyscraper, weighing 40,000 tonnes, with a crew of 70, whereas a ship crewed by 700 would be 400,000 tons. For comparison, a Nimitz-class aircraft carrier with a crew of some 5,000 is about 102,000 tonnes, but, of course, the aircraft carrier is not self-sustaining.

Some scientists have envisioned generation ships as spheres 10 miles in diameter with a surface area of 314 square miles. Others have proposed hollowing out asteroids, spinning them to create gravity, and using them as starships. Such world ships would be on the order of 14 to 20 km in diameter with a total mass of 168 to 480 billion tons and a habitable area of between 615 km2 (roughly the size of St. Petersburg, Russia) to 1810 (roughly the size of São Paulo, Brazil). Such world ships could support a population of several thousand people for hundreds of years.

However, a generation ship’s crew would not have to be in the thousands. One scientist calculated that a starting population of between 80 to 160 screened, unrelated individuals with an even sex ratio would be enough to maintain a stable population for some 10 generations. Other thinkers have suggested space colonies of some 100 pregnant women as the starting population, an all-female crew with a sperm bank, or even a male-to-female ratio of one man to five or more women. The population is, of course, a function of how many generations are needed and therefore linked to the speed of the ship and its destination.

History of the Concept

The concept of the generation ship goes back to before the Space Age. In 1918, Robert Goddard, then six years before he started his liquid fuel rocket experiments, wrote an essay called ‘The Ultimate Migration’. In this brief treatise, the rocket pioneer suggested that ‘an asteroid or a small moon’ could be turned into a starship, with ‘radioactivity furnishing light and heat.’ Goddard goes on to suggest that a possible voyage of ‘perhaps of 10,000 years for a passage to the nearest stars’ and he states ‘the possibility that after many thousands of years, the characteristics and natures of the passengers might change, with the succeeding generations.’ Therefore, one could argue that the sociological and ecological concerns were being considered just as carefully as the technological ones from the beginning.

In 1928, the Russian father of astronautic theory, Konstantin E. Tsiolkovsky, suggested in his essay ‘The Future of Earth and Mankind’, a fleet of ‘Noah’s Arks’, that is to say self-sufficient, man-made ships the size of small planets. These ‘arks’ would travel to distant star systems for hundreds or thousands of years; during the voyage, the crew would live out their lives while maintaining and piloting the vessels. They would meanwhile have children who would crew the ships in their turn.

Just a year after the publication of this essay, J. D. Bernal published the ‘The World, the Flesh & the Devil’. In the ‘World’ section, Bernal outlines in some detail the design of his idea of generation ships, later referred to as ‘Bernal spheres’. Amongst the details are how large the ship would be—a ‘spherical shell about ten miles or so in diameter” with a population/crew of about 20,000 people; he also outlined what materials could be used to build the ships and specified that light sails would be the means of propulsion. With Bernal, the concept of ‘generation ship’ and ‘world ship’ became roughly, but not exactly, synonymous.

After World War II, the British Interstellar Society (BIS) took the lead in conceptualising generation ships. In 1953, physicist and future chairman of the BIS, Leslie R. Shepherd laid out his ideas on generation ships in his article ‘Interstellar Flight’. First, the maximum time of a voyage would be about 1,000 years, or 30 generations, which he describes as equivalent to the ship launching under ‘command of King Canute and…[arriving] with President Truman in control.’ The population would have to be strictly controlled, and the ship would have to be ‘a veritable Noah’s Ark’ filled with plants and other animals. The vehicle would be huge, ‘in fact…a very small planetoid.’ For thrust, Shepard suggested that either nuclear, ion, fusion, or antimatter engines could provide sufficient velocity.
Up to the present day, BIS continues to produce scholarly and scientific works on the subject of interstellar travel using generation ships, such as Hein’s aforementioned ‘World Ships’.

In Written Fiction

Arguably the first generation ship in sci-fi appeared in the March 1935 issue of Astounding Stories. Murray Leinster’s ‘Proxima Centauri’ gave us the Adastra (Latin: to the stars), a spherical starship that ‘could subsist her crew forever’; made up of families, said crew ‘could perpetuate to make a voyage of a thousand years.’ But in the story, the voyage took only seven years. This unflinching confidence is characteristic of pre-World-War-II stories in the genre but is tempered by threads of growing worry about a future stripped of unique American values.

These societal concerns come further into focus five years later, in October 1940, when Amazing Stories published the first fully-realised generation ship story, Don Wilcox’s ‘The Voyage That Lasted 600 Years’. Its tagline was, ‘Thirty generations would live and die before the Flashaway reached its destination. Could the one man who was to live on keep them to their purpose?’ In the story, the ‘Keeper of Tradition’ is placed in hibernation, waking up every hundred years to check on the progress of the ship and the crew. Every time he awakes, he is greeted by pronounced societal change among the crew, culminating in their sinking into barbarity. Finally, the Keeper discovers that Faster Than Light (FTL) Earth ships have beaten the Flashaway to their target. In this very early story of the subgenre, Wilcox is already exploring the two main themes of generation ship stories: societal change and degeneration among the crew, and technology advancing on Earth so that the generation ship is beaten to its target planet.

The theme of societal decay, often accompanied by the development of a belief that ritualises and mythologises the ship, its creators, and its mission, is further explored in what is perhaps the classic generation ship tale: Robert Heinlein’s ‘Universe’ (Astounding Stories, May 1941) and its sequel, ‘Common Sense’ (Astounding Stories, October 1941), published in book form as Orphans of the Sky in 1963. ‘The World, the Flesh & the Devil’ likely inspired the two stories, in which the starship Vanguard’s company have not only forgotten they are even on a spaceship but have degenerated into a superstitious and pre-technical society, much like medieval Europe. The ‘crew’ are the peasants doing the menial work, and the ‘officers’ are the ruling lords. This is the result of a long-ago mutiny that killed most of the officers.

Perhaps because of the fear of societal decay, both Heinlein’s Orphans of the Sky and Wilcox’s ‘The Voyage That Lasted 600 Years’ focus on the acts of the individual. In Heinlein’s case, in particular, we see the idea that one extraordinary person using intellect and determination can solve any problem.

Arthur C. Clarke’s first professionally-sold story, ‘Rescue Party’ (Astounding Stories, May 1946) deals with an alien starship coming to rescue humanity from the sun going nova. They find Earth empty, as humanity has left the planet in a fleet of generation ships. The story doesn’t detail life aboard the human ships, though it does note that the fleet uses rockets for power. Like the ships in other stories of this period, they reflect the technologies of their time, are relatively primitive, and lack life support features such as recycling and greenhouses.

Clifford D. Simak’s ‘Spacebred Generations’ (Science-Fiction Plus, August 1953) plays an interesting variation on the degeneration and forgetfulness theme. In this story, the generation ship’s builders purposely produced a culture of ignorance, backed up by a religious system designed to keep the population peaceful and docile. For Simak, only ignorance about Earth, history, and the voyage itself could allow the ship’s population to deal with the stress of the long trip.

Published in 1953, Milton Lesser’s The Star Seekers is notable as being perhaps the first book-length treatment of the concept. The book has a four-way division of the society—again, degenerated and superstitious—in a hollowed-out asteroid at the end of its voyage. Mikal, the protagonist, is another example of the sole hero who must make a difference to save society.

In Frank M. Robinson’s ‘The Oceans Are Wide’ (Science Stories, April 1954), the crew know they are on a ship and continue to function through strict inheritance of positions. The story is a political thriller about a son struggling to take over as chairman of the ruling committee of the ship from his dying father. Arthur Sellings’s ‘A Start in Life’ (Galaxy, September 1954) has the crew of a generation ship decimated by a plague, the only survivors being two five-year-olds, one boy and one girl, being reared by robots. Depictions of generation ships are here becoming more advanced, incorporating more imagined and extrapolated technologies.

Throughout the ’50s and ’60s, the subgenre began to reflect growing fears of worldwide catastrophe, such as nuclear war. One example is Brian W. Aldiss’s first novel, Non-Stop (1958), released as Starship in the States, a masterful reworking of the themes from ‘Universe’ and ‘Common Sense’. The outlook tends toward the dark and unforgiving, a direct contrast to Heinlein’s earlier stories. Another is E.C. Tubb’s The Space-Born (1956), originally published as a serial called ‘Star Ship’ in the April and June 1955 issues of New Worlds, which tells the story of starship on a 300-year flight to Pollux. Life on the ship is nasty, brutish, and short; people are born, learn a job, reproduce, and are sentenced to death at age 40.

Societal concerns and thought experiments continue to feature. John Brunner’s ‘Lungfish’ (Science Fantasy #26, 1957) plays on the theme of what happens when those people born on the generation ship, called ‘tripborn’ in this story, don’t wish to leave the only world they have ever known and refuse to land on the colony planet. Chad Oliver’s ‘The Wind Blows Free’ (Fantasy & Science Fiction, July 1957) explores similar ideas with a man driven to the edge of insanity by the crowded and claustrophobic culture of a ship. He finally opens an airlock only to find that the ship had landed on a planet ages before. Published a year later, Judith Merril’s ‘Wish Upon a Star’ (Fantasy & Science Fiction, December 1958) presents a feminist approach to the subject: a ship originally crewed by 20 women and just four men, which results in a strict matriarchy as society on the ship grows.

Throughout the late 1950s and into the mid-1970s, authors continued to produce generation ship stories, most fitting neatly into the well-developed themes of social and cultural decay and incorporating developing technologies into their narratives. J. T. Macintosh’s novel 200 Years to Christmas (1961) is a good example of such rather conventional stories. Harry Harrison’s noteworthy Captive Universe (1969) has the asteroid Eros converted into a world ship in which the crew and colonists have been rather crazily forced into the roles of medieval monks and Aztec peasants to maintain stability until they reach their destination. While not all generation ships in this period are made from asteroids, many are self-sustaining, with recycling, hydroponics, and advanced propulsion systems—things unimagined in earlier tales.

The advent of the counter-culture New Wave movement in the 1960s overlaid another set of ideas on the generation ship stories. Works such as Kevin O’Donnell Jr’s Mayflies (1979) reflect a more artistic sensibility, with less focus on technology and more on people and society. In this case, a nearly-immortal human brain is connected to the generation ship. The brain has some control over the humans in the ship but generally sees the crew as living short, meaningless lives, thus the title of the book.

From the mid-1970s on, the subject fell out of favour with science fiction writers. There are notable exceptions, however. Pamela Sargent’s juvenile novel Earthseed (1983) has a seed ship that is a hollowed-out asteroid nearing the end of its voyage, now birthing and raising a generation of teenagers to colonise the new world. Gene Wolfe’s massive, four-volume work, The Book of the Long Sun (1993-1996), takes place in a world ship called the Whorl.

In 2002, Ursula K. Le Guin published a generation ship novella, Paradises Lost, which tells the story of 5-Liu Hsing and 5-Nova Luis, two members of the fifth generation on the Discovery as they struggle with religious cultists and a change in the ship’s itinerary. The novella was adapted into an opera in 2005 and premiered in 2012

Slow Train to Arcturus (2008) by Eric Flint and David Freer gives the reader some new ideas about a generation ship. The ship Slowtrain doesn’t have a single destination but instead drops off human habitation spheres in the Goldilocks zone of each star it passes. The ship will not slow down and the suns visited don’t even need to have planets to be colonised. Additionally, the ship is loaded with ‘nutters’ and ‘oddballs’ and ‘a bunch of fanatics and lunatics’, which allows the Earth to be rid of these troublesome types as well as colonising nearby stars.

New stories in the subgenre will continue to be written especially as new technologies, such as the ion engine, are discussed and developed.

Film and TV

Generation ships are by no means limited to the page. The first example on the big screen is the 1961 Italian film Il Pianeta Degli Uomini Spenti (English: The Planet of Extinct Men), released in America as Battle of the Worlds. This film has a huge world ship whose alien crew have all died while in flight, entering our solar system, its automated systems putting it in orbit around Earth.

Star Trek, likewise, has featured multiple generation ships and accompanying themes throughout the years. In 1968, the original Star Trek dealt with a generation ship in which the inhabitants have forgotten they are on a spaceship in ‘For the World is Hollow and I Have Touched the Sky’. Later, Star Trek: Voyager addressed themes of dissent amidst generation ship descendants in ‘The Disease’ (1999). This is an arguable inversion of the ‘tripborn’ in Brunner’s ‘Lungfish’.

The 1973 television series The Starlost, created by Harlon Ellison, explores many common themes of the generation ship subgenre. In the series, the Earthship Ark is carrying the last survivors of Earth. Some inhabitants are aware they are on a spaceship while others are not. To maintain separated cultures, the passengers are kept in sealed domes and do not generally interact with each other. In Ellison and Edward Bryant’s 1975 novelisation of the pilot script, Phoenix without Ashes, an Amish community, the entire city of San Francisco, and many other distinct cultures are loaded on the ship.

The film Pandorum (2009) explores some aspects of a generation ship voyage gone wrong and belongs more to the horror genre than to sci-fi. In 2014, the Syfy Channel aired the mini-series Ascension, in which a generation ship originally launched in secret in the 1960s and is now halfway into its century-long voyage to Proxima Centauri.

The science fiction comedy-drama The Orville, an homage to the original Star Trek, broadcast its generation ship story, ‘If the Stars Should Appear’, in 2017. In the episode, the crew of the Orville finds a generation ship ruled by a theocratic dictator and whose passengers are unaware they are on a ship. The Orville’s crew repairs the craft and opens its windows, enabling the populace to see the stars for the first time.

In Conclusion

In science fiction, each successive generation of writers have used the concepts, ideas, and fears that are uppermost in the zeitgeist at the time they are writing, so each successive wave of generation ship stories have reflected those conceptions and uncertainties. Also, as scientific and technological knowledge has advanced, so have the portrayals of the generation ships. Until new discoveries or technological advances provide a better option for interstellar travel, we will likely continue to encounter these ideas and stories.