Generation ship

A generation ship, or generation starship, is a hypothetical type of interstellar ark starship that travels at sub-light speed.

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.

In science

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. Other than different characteristics and names there are lots of similarities.

Obstacles

Biosphere

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. 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, 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. 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. 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.

Social breakdown

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.

Cosmic rays

Main article: Health threat from cosmic rays

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.

Technological progress

Main article: Wait Calculation

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.

In fiction

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.

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. Star Trek: Voyager episode The Disease features a generation ship of a species called the Varro. In the Star Trek: Enterprise series, the episode E² a space-time anomaly caused another Enterprise (NX-01) to travel 117 years back into the past and made itself into a generation ship in order to wait for the Xindi crisis and avoid timeline contamination.

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 Babylon 5 episode "The Long Dark" (1994) features a generation ship as a major plot element. 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.

Ascension is set aboard a generation ship launched during the John F. Kennedy Administration.

Rendezvous with Rama by Arthur C. Clarke describes the encounter with an alien ship, which, although its full purpose cannot be investigated, is best characterized as a huge generation ship of an alien race.

Kim Stanley Robinson's novel Aurora is set on a generation ship.

See also

• Embryo space colonization
• Interstellar ark
• O'Neill cylinder
• Self-replicating spacecraft
• Sleeper ship

Further reading

• 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.

External links

• "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.