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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.
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 reach 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".
Neither of these two publications received sufficient publicity to gain widespread public awareness at the time.
John D. Bernals'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 slow boat because of the Astronomy Magazine title “Slow Boat to Centauri” (1977). Gregory Matloffs concept is called colony ship and Alan Bond called his concept 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 test whether thousands of humans can survive on their own before sending them beyond the reach of help. There are also the concerns of immune systems atrophying in the ship's environment. Small artificial closed ecosystems, including Biosphere 2, have been built in an attempt to work out the engineering difficulties in such a system with mixed results.
Biology and society
Generation ships would also have to solve major biological, social, moral problems and would also need to deal with complex 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 of the viability of such interstellar arks include:
- the possibility of humans dramatically evolving in directions unacceptable to the sponsors
- the minimum population required to maintain in isolation a culture acceptable to the sponsors; this could include such aspects as
- ability to maintain and operate the ship
- ability to accomplish the purpose (planetary colonization, research, building new interstellar arks) contemplated
- sharing the values of the sponsors, which are not likely to be empirically demonstrated to be viable beyond the home planet unless once the ship is away from Earth and on its way, survival of one's offspring until the ship reaches the target star is one motivation.
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. Robert A. Heinlein's novel Orphans of the Sky and Brian Aldiss's novel Non-Stop discussed such a society.
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 flux of high-energy galactic cosmic rays (GCRs) along with radiation from solar proton events and the radiation belts. Like other ionizing radiation high-energy cosmic rays can damage DNA, increase the risk of cancer, cataracts, neurological disorders, and non-cancer mortality risks. The only 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 front of the ship, preventing micrometeors 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.
Generation ships are often found in science fiction stories.
Perhaps their earliest description is in the 1929 essay "The World, The Flesh, & The Devil" by J. D. Bernal. The first fiction dealing with one is the 1940 story "The Voyage That Lasted 600 Years" by Don Wilcox.
Beginning with the 1941 stories "Universe" and "Common Sense" by Robert A. Heinlein, combined in 1963 into the novel Orphans of the Sky, a common theme is that inhabitants of a generation ship have forgotten they are on a ship at all and believe their ship to be the entire universe. French writer Léon Groc wrote the first complete novel on this theme in the 1950 book L'Univers Vagabond. In the anglophone world, Brian Aldiss is attributed with the first complete novel dealing exclusively with the theme in the 1958 book Non-Stop. By 1959 Edmund Cooper's Seed of Light was being criticized for dealing with an old-hat subject though it is often accounted the author's best novel. Harry Harrison's novel Captive Universe (1969) and James Follett's Earthsearch radio serials deal with similar themes. The 2008 Pixar film WALL-E contains a subplot in which a generation ship containing humans returns to Earth after many centuries. Toby Litt's 2009 novel Journey into Space is about people living on a generation ship and deals with how people cope with the fact that they have never set foot on the Earth and will never set foot on their destination planet.
The novelization to the movie After Earth and the back story for the TV show Firefly have humanity abandoning Earth for a new home in generation ships. John Kenneth Muir in his review of the film Pandorum pointed out its many elements from previous generation ship stories such as The Ark in Space, The Starlost, Mission of the Darians, and Orphans of The Sky.
- Embryo space colonization
- Interstellar ark
- O'Neill cylinder
- Self-replicating spacecraft
- Sleeper ship
- Simone Caroti (2011). The Generation Starship in Science Fiction: A Critical History, 1934-2001. Mcfarland. p. 275. ISBN 978-0-7864-6067-0.
- J. D. Bernal. "The World, the Flesh & the Devil - An Enquiry into the Future of the Three Enemies of the Rational Soul". Retrieved 20 January 2016.
- K.F.Long, A.Crowl, R.Obousy. "The Enzmann Starship: History & Engineering Appraisal" (PDF). Retrieved 7 February 2013.
- Hein, Andreas; et al. "World Ships – Architectures & Feasibility Revisited". Retrieved 7 February 2013.
- Malik, Tariq (27 January 2005). "Sex and Society Aboard the First Starships". Space Adventures. Retrieved 13 February 2015. [Original reference is dead link: Space.com, 19 March 2002.]
- Damian Carrington (15 February 2002). ""Magic number" for space pioneers calculated". NewScientist.
- "Smith, C.M., "Estimation of a genetically viable population for multigenerational interstellar voyaging: Review and data for project Hyperion"". ScienceDirect. 2013-12-13. Retrieved 2013-02-18.
- "NASA Facts: Understanding Space Radiation" (PDF). Retrieved 2010-04-01.
- Isaac Asimov, Charles; nbsp; G. Waugh, Martin; nbsp; H. Greenberg, eds. (1984). Isaac Asimov Presents the Best Science Fiction Firsts. New York: Beaufort Books, Inc. p. 95. ISBN 0-8253-0184-X.
- Gary K. Wolfe: Cooper, Edmund. In: Jay P. Pederson: St. James Guide to Science Fiction Writers. 4. edition. St. James Press, New York 1996, p. 206-208; p. 207
- Firefly (TV series)#cite note-9
- Niall Alexander. "Behind the Simulated Sky: The Forever Watch by David Ramirez". Tor. Retrieved 11 May 2016.
- Aurora by Kim Stanley Robinson review – ‘the best generation starship novel I have ever read', Adam Roberts, The Manchester Guardian, July 8, 2015
- Caroti, Simone (2011). “The Generation Starship in Science Fiction: A Critical History, 1934-2001” Mcfarland. ISBN 978-0-7864-6067-0.
- Andreas Hein; et al. "World Ships – Architectures & Feasibility Revisited". Retrieved 7 February 2013.
- "Gilgamesh" (14 February 2007). "Interstellar Ark". Strange Paths: Physics, computation, philosophy. Retrieved 13 February 2015.
- Gilster, Paul (17 August 2011). "Worldships: A Interview with Greg Matloff". Centauri Dreams: Imagining and Planning Interstellar Exploration. Retrieved 9 February 2013.
- Hein, Andreas (13 May 2012). "Project Hyperion: The Hollow Asteroid Starship – Dissemination of an Idea". Icarus Interstellar. Retrieved 13 February 2015. Brief summary of the evolution of generation ship concepts.
- Nicholls, Peter; Langford, David (5 April 2014). "Generation Starships". The Encyclopedia of Science Fiction. London: Gollancz. Retrieved 13 February 2015.