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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 travelling.
The concept of generation starship is a good example of how science and fiction influence each other, because many space scientists and engineers who contributed to the concept of a generation starship were also science fiction writers. The first written thoughts can be dated back to Robert H. Goddard, the rocket pioneer who wrote "The Last Migration" (1918).[note 1] In this manuscript 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 (cryo sleep). This concept is not the same as the generation starship concept because the crew is sleeping during its trip. The concept as it is known today was first published by Konstantin E. Tsiolkovsky, father of the astronautic theory. He described in his essay "The Future of Earth and Mankind" (1928) a space colony equipped with engines which 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 influenced other writers. He wrote about the concept of human evolution and our future in space through methods of living which we now describe as generation starship, and which could be seen in the generic word "globes".
Hein et al. have categorized the different concepts of generation starships that have emerged since the 1970s. The parameters for categorization are cruise velocity and population size. The categorization (table 1) is shown in the following table and a part of figure 1 is shown on the right.
|Cruise velocity||Population size||Population size||Population size|
|% of c||< 1,000||< 100,000||> 100,000|
|> 10||Sprinter||Colony ship||-|
|< 10||Slow boat||Colony ship||World ship|
|< 1||-||Colony ship||World ship|
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. Beside these different characteristics and names there are lots of similarities.
Such a ship would have to be almost 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. Large, self-sustaining space habitats would be needed. For gaining experience before sending generation ships "to the stars", such a habitat could be effectively isolated from the rest of humanity for a century or more, but remain close enough to Earth for help. 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 and 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 might exist regarding how intermediate generations (for example, those destined to be born, reproduce, 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 viable population vary. The results of a 2005 study from Rutgers University theorized that the native population of the Americas are the descendants of only 70 individuals who crossed the land bridge between Asia and North America. However, anthropologist Dr. John Moore estimated in 2002 that a population of 150 to 180 would allow normal reproduction for 60 to 80 generations, equivalent to 2000 years. In 2013, anthropologist Dr. Cameron Smith estimated a minimum viable population of 14,000 to 44,000, greatly exceeding previous estimates. These numbers take the risk of accidents, diseases etc. into consideration. This has been neglected in previous studies. His analysis is based on an extensive literature review and modelling of genetic effects in populations over time.
Generation ships are based on the human life span not changing dramatically. Even though people are living longer and longer it would take a lifespan extension beyond most scientists' forecasts for any one individual to live throughout the entire trip.
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).
Generation ships travelling for long periods of time may see breakdowns in social structures. Changes in society (for example, mutiny) typically occur over such periods and may prevent the ship from reaching its destination.
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, increasing 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 science fiction novel by Arthur C. Clarke: "The Songs of Distant Earth".
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) deals with similar themes.
In the Star Trek: The Original Series episode "For the World Is Hollow and I Have Touched the Sky" (1968) the Enterprise encounters a computer-controlled generation ship whose inhabitants do not know they are within a ship traveling through space, but who believe themselves to be on a solid world and that the artificial sky is real; the David Gerrold tie-in novel The Galactic Whirlpool had the Enterprise encounter another generation ship on a collision course with a black hole whose crew also has the same the-ship-is-the-whole-universe mentality. Harlan Ellison's The Starlost, a 1973 Canadian TV series, is set aboard the giant spaceship called The ARK. In the Space: 1999 episode "Mission of the Darians" (1975) the Alphans encounter the heavily damaged but still populated generation ship Daria, whose inhabitants bear an evil secret.
Gene Wolfe's tetralogy The Book of the Long Sun (1993) deals directly with the challenges facing the inhabitants of the starcrosser Whorl and the continuing challenges after planetfall in The Book of the Short Sun (1999). 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. This method of slow interstellar travel is hinted at in Arthur C. Clarke's Rendezvous With Rama (1972) as the spacecraft Rama is analyzed, and this theme continues in the book's sequels. The 1999 Star Trek: Voyager episode "The Disease" features a generation ship of a species called the Varro. The 2010 Doctor Who episode, "The Beast Below", centers on a generation ship known as "Starship UK", which contains the entire future population of the United Kingdom (except for Scotland, which opted for its own ship) fleeing the deadly solar flares on the Earth in the 29th century.
Rob Grant's Colony, published in 2000, is a science fiction comedy farce which deals with a generation ship in which breeding is strictly controlled and a crew member's offspring automatically inherit their parent's role on the ship. Several generations on, the Captain is struggling with puberty, the Chief Science Officer is a fundamentalist Christian, the security officers have become so inbred as to be barely functional and the ship's chaplain is a pervert who spies on other crewmembers' quarters. The colonists have forgotten how to read and the ship is falling apart because nobody knows how to repair anything.
In Analogue: A Hate Story, a generation ship from the Republic of Korea called the Mugunghwa is lost hundreds of years after it leaves Earth. Thousands of years later, after FTL travel had been invented, an investigator is sent to find out what happened on the ship. The ship's social structure had changed from 21st-century South Korea into a feudal society with similarities to the Joseon Dynasty of Korean history. All of the people on the ship die hundreds of years before it is found.
John Thornton's Recovery of a Colony Ship (Colony Ship Eschaton) Volume 1 (2013) (ISBN 1482720442) and the three novel sequels all take place on a gigantic generational ship while it is on its journey to another solar system. The Eschaton's inhabitants have lost much of their technological knowledge through disasters and conflict. The last remnants of humanity on Earth teleport on board the Eschaton.
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 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 3 February 2013.
- Hein, Andreas; et al. "World Ships – Architectures & Feasibility Revisited". Retrieved 7 February 2013.
- K.F.Long, A.Crowl, R.Obousy. "The Enzmann Starship: History & Engineering Appraisal". Retrieved 7 February 2013.
- Malik, Tariq. "Sex and Society Aboard the First Starships." Space.com, 19 March 2002.
- "North America Settled by Just 70 People, Study Concludes". LiveScience. 2005-05-25. Retrieved 2010-04-01.
- 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. Retrieved 2013-02-18.
- "NASA Facts: Understanding Space Radiation" (PDF). Retrieved 2010-04-01.
- Isaac Asimov, Charles G. Waugh, Martin H. Greenberg, ed. (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
- 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.
- Interstellar Ark
- Brief summary of the evolution of generation ship concepts
- Paul Gilster. "Worldships: A Interview with Greg Matloff". Retrieved 9 February 2013.