Ageneration ship,generation starship orworld ship,[1] is a hypothetical type ofinterstellar arkstarship that travels at sub-light speed. Since such a ship might require hundreds to thousands of years to reach nearby stars, the original occupants of a generation ship would grow old and die, leaving their descendants to continue traveling.
Rocket pioneerRobert H. Goddard was the first to write about long-duration interstellar journeys in his "The Ultimate Migration" (1918).[2] In this he described the death of the Sun and the necessity of an "interstellar ark". The crew would travel for centuries insuspended animation and be awakened when they reached another star system. He proposed to use small moons or asteroids as ships, and speculated that the crew would endure psychological and genetic changes over the generations.[3]
Konstantin Tsiolkovsky, considered a father ofastronautic theory, first described the need for multiple generations of passengers in his essay, "The Future of Earth and Mankind" (1928), outlining a space colony equipped with engines that travels thousands of years which he called "Noah's Ark". In the story, the crew had changed so much over the generations at so many levels that they did not even acknowledge Earth as their home planet.[4]
Another early description of a generation ship is in the 1929 essay "The World, the Flesh, & the Devil" byJohn Desmond Bernal.[5] 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".[5]
The 2012 paperWorld Ships – Architectures & Feasibility Revisited differentiated several types of interstellar spacecraft: those with a population bigger than 100,000 are calledworld ships, while those with a population between 1,000 and 100,000 are calledcolony ships. Interstellar spacecraft with a population below 1,000 are calledsprinter if their cruise velocity is bigger than 10% ofc, andslow boat if it's smaller.
The paper also described a proposed world ship, having the minimal population to be considered as such (100,000), and consisting of 4 stackedStanford Torus colonies (with some changes from the original, such as having 2.5 times its population, and a 10% bigger mass), and a propulsion and power generation system based onProject Daedalus. The Stanford torus was chosen because of its detailed design, that covers in-depth aspects such as life support systems and wall thickness.[1]
Project Hyperion, launched in December 2011 by Andreas M. Hein, intends to perform a preliminary study that defines integrated concepts for a crewed interstellar generation ship. It has led to the most detailed designs of generation ships to date.[7] The project is associated with theInitiative for Interstellar Studies and has its origins with theWARR student group at theTechnical University of Munich. The study aims to assess the feasibility of crewed interstellar flight using current and near-future technologies. It also aims to guide future research and technology development plans as well as to inform the public about crewed interstellar travel.[8][9] Notable results of the project include an assessment of world ship system architectures and adequate population size.[1][10] A survey paper on generation ships has been presented at theESA Interstellar Workshop in 2019 as well as inESA's Acta Futura journal.[11][12][13] An interdisciplinary design competition was launched in 2024.[14][15][16][17] Results were announced in July 2025 with the Italian Chrysalis team on the 1st place, the Polish WFP Extreme 2nd, and the Malaysian Systema Stellare Proximum on 3rd place.[7][18][19][20]
According to Hein et al., a "generation ship" is a spacecraft on which a crew is living on board for at least several decades, such that it comprises multiple generations.[1] Several sub-categories of generation ships are distinguished: sprinter, slow boat, colony ship, world ship.[1]TheEnzmann starship is categorised as "slow boat" because of theAstronomy Magazine title "Slow Boat to Centauri" (1977).[21] Gregory Matloff's concept is called a "colony ship" andAlan Bond called his concept a "world ship".[1] These definitions are essentially based on the velocity of the ship and population size.[11]
The first generation ships need to balance high cost with the uncertain probability that a destination star system is sufficiently hospitable.
Such a ship would have to be entirely self-sustaining, providinglife support for everyone aboard. It must 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 asBiosphere 2, have been built in an attempt to examine the engineering challenges of such a system, with mixed results.[22]
Generation ships would have to anticipate possible biological, social and morale problems,[23] and would also need to deal with matters of self-worth and purpose for the various crews involved.
Estimates of the minimum reasonable population for a generation ship vary. Anthropologist John Moore has estimated that, withoutgenetic testing of people before boarding the ship,social control and / orsocial engineering (such as requiring people to wait until their thirties to have children), norcryopreservation of eggs, sperm, or embryos (as is done insperm banks), a minimum of 160 people boarding the ship would allow normal family life (with the average individual having ten potential marriage partners) throughout a 200-year space journey, with little loss ofgenetic diversity. If the people who board the ship are couples, presumably in their early twenties, and everybody who lives in the ship is required to wait until their mid to late thirties before having children, then the minimum would be just 80 people. However, many variables are not accounted for in the estimate, including the higher chance of health problems for both the woman who is pregnant and the fetus or baby because of thepregnant woman's age.[24] 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.[25]
In light of the multiple generations that it could take to reach even our nearest neighboring star systems such asProxima Centauri, further issues on the viability of such interstellar arks include:
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.[26] A spacecraft of such a size would require much 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.[27]
Generation ships traveling 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 byAlgis Budrys in a 1966 book review:[28]
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.
Robert A. Heinlein'sOrphans of the Sky (the "impeccable statement of this theme", Budrys said)[28] andBrian Aldiss'sNon-Stop (U.S. title:Starship) discussed such societies.
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-energygalactic cosmic rays (GCRs). Like otherionizing radiation, high-energy cosmic rays can damage DNA and increase the risk of cancer, cataracts, and neurological disorders.[29]
The success of a generation ship depends on children born aboard taking over the necessary duties, as well as having children themselves. Even if their quality of life might be better than, for example, that of people born into poverty on Earth, philosophy professor Neil Levy has raised the question of whether it is ethical to severely constrain life choices of individuals by locking them into a project they did not choose.[30] 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.