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 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 pioneer Robert 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 in suspended 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 of astronautic 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" by John 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]
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] The Enzmann starship is categorised as "slow boat" because of the Astronomy Magazine title "Slow Boat to Centauri" (1977). [6] Gregory Matloff's concept is called a "colony ship" and Alan Bond called his concept a "world ship". [1] These definitions are essentially based on the velocity of the ship and population size. [7]
Such a ship would have to be entirely self-sustaining, providing life 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 as Biosphere 2, have been built in an attempt to examine the engineering challenges of such a system, with mixed results. [8]
Generation ships would have to anticipate possible biological, social and morale problems, [9] 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, without genetic testing of people before boarding the ship, social control and / or social engineering (such as requiring people to wait until their thirties to have children), nor cryopreservation of eggs, sperm, or embryos (as is done in sperm 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 of genetic 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 the pregnant woman's age. [10] 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. [11]
In light of the multiple generations that it could take to reach even our nearest neighboring star systems such as Proxima 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. [12] 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. [13]
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.
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-energy galactic cosmic rays (GCRs). Like other ionizing radiation, high-energy cosmic rays can damage DNA and increase the risk of cancer, cataracts, and neurological disorders. [14]
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. [15] 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.
Project Hyperion, launched in December 2011 by Icarus Interstellar, was to perform a preliminary study that defines integrated concepts for a crewed interstellar generation ship. This was a two-year study mainly based out of the WARR student group at the Technical University of Munich. The study aimed to provide an assessment of the feasibility of crewed interstellar flight using current and near-future technologies. It also aimed to guide future research and technology development plans as well as to inform the public about crewed interstellar travel. [16] [17] Notable results of the project include an assessment of world ship system architectures and adequate population size. [1] [18] The core team members have transferred to the Initiative for Interstellar Studies's world ship project and a survey paper on generation ships has been presented at the ESA Interstellar Workshop in 2019 as well as in ESA's Acta Futura journal. [7] [19] [20]
Interstellar travel is the hypothetical travel of spacecraft from one star system, solitary star, or planetary system to another. Interstellar travel is expected to prove much more difficult than interplanetary spaceflight due to the vast difference in the scale of the involved distances. Whereas the distance between any two planets in the Solar System is less than 55 astronomical units (AU), stars are typically separated by hundreds of thousands of AU, causing these distances to typically be expressed instead in light-years. Because of the vastness of these distances, non-generational interstellar travel based on known physics would need to occur at a high percentage of the speed of light; even so, travel times would be long, at least decades and perhaps millennia or longer.
A starship, starcraft, or interstellar spacecraft is a theoretical spacecraft designed for traveling between planetary systems. The term is mostly found in science fiction. Reference to a "star-ship" appears as early as 1882 in Oahspe: A New Bible.
A sleeper ship is a hypothetical type of crewed spacecraft, or starship in which most or all of the crew spend the journey in some form of hibernation or suspended animation. The only known technology that allows long-term suspended animation of humans is the freezing of early-stage human embryos through embryo cryopreservation, which is behind the concept of embryo space colonization.
An interstellar ark is a conceptual starship designed for interstellar travel. Interstellar arks may be the most economically feasible method of traveling such distances. The ark has also been proposed as a potential habitat to preserve civilization and knowledge in the event of a global catastrophe.
The concept of self-replicating spacecraft, as envisioned by mathematician John von Neumann, has been described by futurists and has been discussed across a wide breadth of hard science fiction novels and stories. Self-replicating probes are sometimes referred to as von Neumann probes. Self-replicating spacecraft would in some ways either mimic or echo the features of living organisms or viruses.
Project Longshot was a conceptual interstellar spacecraft design. It would have been an uncrewed starship, intended to fly to and enter orbit around Alpha Centauri B powered by nuclear pulse propulsion.
Embryo space colonization is a theoretical interstellar space colonization concept that involves sending a robotic mission to a habitable terrestrial planet, dwarf planet, minor planet or natural satellite transporting frozen early-stage human embryos or the technological or biological means to create human embryos. The proposal circumvents the most severe technological problems of other mainstream interstellar colonization concepts. In contrast to the sleeper ship proposal, it does not require the more technically challenging 'freezing' of fully developed humans.
An interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar space, which is typically defined as the region beyond the heliopause. It also refers to probes capable of reaching other star systems.
Ark is a 2009 hard science fiction novel by English author Stephen Baxter. It is a sequel to his 2008 novel Flood. Ark deals with the journey of the starship Ark One, and the continuing human struggle for survival on Earth after the catastrophic events of Flood. The series continues in three pendant stories, which are described in the plot summary below.
Project Icarus is a theoretical engineering design study aimed at designing a credible, mainly nuclear fusion-based, unmanned interstellar space probe. Project Icarus was an initiative of members of the British Interplanetary Society (BIS) and the Tau Zero Foundation (TZF) started in 2009. The project was under the stewardship of Icarus Interstellar until 2019. It remains a BIS project.
The 100 Year Starship project (100YSS) was a one-year joint U.S. Defense Advanced Research Projects Agency (DARPA) and National Aeronautics and Space Administration (NASA) effort "to take the first step in the next era of space exploration—a journey between the stars". The study explored development of a viable and sustainable model for persistent, long-term, private-sector investment into the myriad of disciplines needed to make interstellar space travel practicable and feasible. The goal was to examine what it would take — organizationally, technically, sociologically and ethically — to develop the ability to send humans to another star within 100 years. The study culminated in a $500,000 grant awarded to a consortium under the lead of the Dorothy Jemison Foundation for Excellence, which led to the creation of an independent organization inheriting the name 100 Year Starship from DARPA. Annual 100YSS symposia were organized from 2011 to 2015, and again in 2023.
The Enzmann starship is a concept for a crewed interstellar spacecraft proposed in 1964 by Dr. Robert Enzmann. A three million ton ball of frozen deuterium would fuel nuclear fusion rocket engines contained in a cylindrical section behind that ball with the crew quarters. The craft would be about 2,000 feet (600 m) long overall.
The Initiative for Interstellar Studies (i4is) is a UK-registered not-for-profit company, whose objectives are education and research into the challenges of Interstellar Travel. It pioneered small-scale laser sail interstellar probes and missions to interstellar objects. Several of its principals were involved in the 100 Year Starship winning team originated by NASA and DARPA.
Evacuate Earth is a National Geographic Channel documentary that portrays the hypothetical scenario of humans evacuating the planet Earth before it is destroyed by a rogue neutron star. The documentary details the technical and social complications of building a generation ship to save humanity and other Earth organisms by relocating to a planet in another solar system.
Breakthrough Initiatives is a science-based program founded in 2015 and funded by Julia and Yuri Milner, also of Breakthrough Prize, to search for extraterrestrial intelligence over a span of at least 10 years. The program is divided into multiple projects. Breakthrough Listen will comprise an effort to search over 1,000,000 stars for artificial radio or laser signals. A parallel project called Breakthrough Message is an effort to create a message "representative of humanity and planet Earth". The project Breakthrough Starshot, co-founded with Mark Zuckerberg, aims to send a swarm of probes to the nearest star at about 20% the speed of light. The project Breakthrough Watch aims to identify and characterize Earth-sized, rocky planets around Alpha Centauri and other stars within 20 light years of Earth. Breakthrough plans to send a mission to Saturn's moon Enceladus, in search for life in its warm ocean, and in 2018 signed a partnership agreement with NASA for the project.
Project Dragonfly is the first conceptual design study that assesses the feasibility of a laser-propelled interstellar probe, conducted by the Initiative for Interstellar Studies. Contrary to past unmanned interstellar mission studies such as Project Daedalus and Project Icarus, the focus is particularly on a small spacecraft. The project was founded in 2013 by the Initiative for Interstellar Studies (i4is).
Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail interstellar probes named Starchip, to be capable of making the journey to the Alpha Centauri star system 4.34 light-years away. It was founded in 2016 by Yuri Milner, Stephen Hawking, and Mark Zuckerberg.
Project Hyperion, launched in December 2011 by Andreas M. Hein in the context of Icarus Interstellar, was a project aimed at performing a preliminary study that defined integrated concepts for a crewed interstellar starship or generation ship. This was a two-year study mainly based out of the WARR student group at the Technical University of Munich (TUM). The study aimed to provide an assessment of the feasibility of crewed interstellar flight using current and near-future technologies. It also aimed to guide future research and technology development plans as well as to inform the public about crewed interstellar travel.