Space advocacy: Space advocacy is a political position that favors the exploration, utilization, and colonization of outer space. There are many different organizations dedicated to space advocacy. They are usually active in lobbying governments for increased funding in space-related activities. They also recruit members, fund projects, and provide information for their membership and interested visitors. They are sub-divided into three categories depending on their primary work: practice, advocacy, and theory. These organizations are noted for developing theories and actually putting them into practice through projects, as well as space advocacy: The Mars Society, founded by Robert Zubrin, studies and advocates for the exploration and settlement of Mars, and has many international volunteer-run projects - The Space Studies Institute was founded by Gerard O'Neill to fund the study of space habitats, built several mass driver prototypes - The Planetary Society, founded by Carl Sagan and two of his colleagues, claims to be the largest space interest group, with about 100,000 members; emphasis on robotic exploration and the search for extraterrestrial life, recent solar sail construction and attempted launch.

Gravitational lensing: A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is "bent" around a massive object (such as a massive galaxy) between the source object and the observer. The process is known as gravitational lensing, and is one of the predictions of Albert Einstein's general relativity theory. Gravitational microlensing can provide information on comparatively small astronomical objects, such as MACHOs within our own galaxy, or extrasolar planets (planets beyond the solar system). Three extrasolar planets have been found in this way, and this technique has the promise of finding Earth-mass planets around sunlike stars within the 21st century. Gravitational lensing can be used to calculate an estimate of the amount of dark matter contained in the lensing body.

Astronomical interferometer: An astronomical interferometer or hypertelescope is an array of telescopes or mirror segments acting together to probe structures with higher resolution. Astronomical interferometers are widely used for optical astronomy, infraredastronomy, submillimetre astronomy and radio astronomy. Aperture synthesis can be used to perform high-resolution imaging using astronomical interferometers. Projects are now beginning that will use interferometers to search for extrasolar planets, either by astrometric measurements of the reciprocal motion of the star (as used by the Palomar Testbed Interferometer and the VLTI), through the use of nulling (as will be used by the Keck Interferometer and Darwin) or through direct imaging (as proposed for Labeyrie's Hypertelescope).

Nulling interferometry: Nulling interferometry is a type of interferometry in which two or more signals are mixed to produce observational regions in which the incoming signals cancel themselves out. This creates a set of virtual 'blind spots' which prevent unwanted signals from those areas from interfering with other, possibly much weaker signals that are nearby. This technique is used by SIM, and is being considered for use by the Terrestrial Planet Finder, both NASA missions. Also the ESA Darwin mission is considering the use of it. It is being used on the Keck Interferometer.

Extraterrestrial life: Extraterrestrial life is life that may exist and originate outside the planet Earth, the only place in the universe currently known to support life. Its existence is currently purely hypothetical as there is yet no evidence of any other planets that can support life, or actual extraterrestrial life that has been widely accepted by the scientific community. Most scientists believe that if extraterrestrial life exists, its evolution occurred independently, in different places. An alternative hypothesis, held by a minority, is panspermia. This suggests that life could have been created elsewhere and spread across the universe, between habitable planets. The putative study and theorisation of extraterrestrial life is known as astrobiology or exobiology or xenobiology. Speculative forms of extraterrestrial life range from sapient beings, to life at the scale of bacteria.

Astrobiology: Astrobiology is the study of life in space, combining aspects of astronomy, biology and geology. It is focused primarily on the study of the origin, distribution and evolution of life. Some major astrobiological research topics include addressing the following questions. What is life? How did life arise on Earth? What kind of environments can life tolerate? How can we determine if life exists on other planets? How often can we expect to find complex life? What will life consist of? Is it always DNA-based? Carbon based? What is the physiology of life on other planets?

Extremophiles (organisms able to survive in extreme environments) are a core research element for astrobiologists. Such organisms include biota able to survive kilometers below the ocean's surface near hydrothermal vents and microbes that thrive in highly acidic environments. Characterization of these organisms—their environments and their evolutionary pathways—is considered a crucial component to understanding how life might evolve elsewhere in the universe. Recently, a number of astrobiologists have teamed up with marine biologists and geologists to search for extremophiles and other organisms living around hydrothermal vents on the floors of our own oceans. Scientists hope to use their findings to help them create hypotheses on whether life could potentially exist on certain moons in our own solar system.

Extremophiles: An extremophile is an organism, usually unicellular, which thrives in or requires 'extreme' conditions that would exceed optimal conditions for growth and reproduction in the majority of mesophilic terrestrial organisms. Most extremophiles are microbes. The domain Archaea is known for widespread extremophily, but extremophiles are present in numerous and diverse genetic lineages of both the bacteria and archaea. Although the terms archaea and extremophile are occasionally used interchangeably, there are many mesophile archaeans and many extremophile bacteria. Additionally, not all extremophiles are unicellular. Examples of extremophilic metazoa are the Pompeii worm, the psychrophilic Grylloblattodea (insects), antarctic krill (crustaceans) and the Tardigrade. Extremophiles and astrobiology: Astrobiologists are particularly interested in studying extremophiles, as many organisms of this type are capable of surviving in environments similar to those known to exist on other planets. For example, Mars may have regions in its deep subsurface permafrost that could harbor endolith communities. The subsurface water ocean of Jupiter's moon Europa may harbor life, especially at hypothesized hydrothermal vents at the ocean floor.

Panspermia: Panspermia is the hypothesis that the seeds of life are in the Universe, that they may have delivered life to Earth, and that they may deliver or have delivered life to other habitable bodies; also the process of such delivery. Exogenesis is a related, but less radical, hypothesis that simply proposes that life did not originate on Earth, but was transferred to Earth from elsewhere in the Universe, with no prediction about how widespread life is. The term 'panspermia' is more well-known, however, and tends to be used in reference to what would properly be called exogenesis, too. Space is a damaging environment for life, as it would be exposed to radiation, cosmic rays and stellar winds. However, some bacteria may be able to survive these conditions. Also, environments may exist within meteorites or comets that are somewhat shielded from these hazards.

SETI: SETI is the acronym for Search for Extra-Terrestrial Intelligence; organized efforts to detect intelligent aliens. A number of efforts with 'SETI' in the project name have been organized, including projects funded by the United States Government. The generic approach of SETI projects is to survey the sky to detect the existence of transmissions from a civilization on a distant planet - an approach widely endorsed by the scientific community as hard science. There are great challenges in searching across the sky to detect a first transmission that can be characterised as intelligent, since its direction, spectrum and method of communication are all unknown beforehand.

Zoo hypothesis: The zoo hypothesis is one of a number of suggestions that have been advanced in response to the Fermi paradox, regarding the apparent absence of evidence in support of the existence of advanced extraterrestrial life. According to this hypothesis, aliens would generally avoid making their presence known to humanity, or avoid exerting an influence on human development, somewhat akin to zookeepers observing animals in a zoo. Adherents of the hypothesis consider that Earth and humans are being secretly sureveyed using equipment located on Earth or elsewhere in the solar system which relays information back to the observers. It is also suggested that overt contact will eventually be made with humanity once they reach a certain level of development.

Drake equation: The Drake equation (also known as the Green Bank equation or the Sagan equation) is a famous result in the speculative fields of xenobiology, astrosociobiology and the search for extraterrestrial intelligence. This equation was devised by Dr Frank Drake (now Emeritus Professor of Astronomy and Astrophysics at the University of California, Santa Cruz) in the 1960s in an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact. The main purpose of the equation is to allow scientists to quantify the uncertainty of the factors which determine the number of extraterrestrial civilizations. In recent years, the Rare Earth hypothesis, which posits that conditions for intelligent life are quite rare in the universe, has been seen as a possible refutation of the equation. The Drake equation is closely related to the Fermi paradox.

Rare Earth Hypothesis: In planetary astronomy and astrobiology, the Rare Earth hypothesis asserts that the emergence of complex multicellular life (metazoa) on Earth required an extremely unlikely combination of astrophysical and geological events and circumstances. The Rare Earth hypothesis is explained in detail in the book Rare Earth: Why Complex Life Is Uncommon in the Universe, by Peter Ward, a geologist and paleontologist, and Donald Brownlee, an astronomer and astrobiologist. The Rare Earth hypothesis is the contrary of the principle of mediocrity (also called the Copernican principle), whose best known recent advocates include Carl Sagan and Frank Drake. The principle of mediocrity maintains that the Earth is a typical rocky planet in a typical planetary system, located in an unexceptional region of a large but conventional barred-spiral galaxy. Ward and Brownlee argue to the contrary: planets, planetary systems, and galactic regions that are as friendly to complex life as are the Earth, the solar system, and our region of the Milky Way are probably extremely rare.

Habitable zone: In astronomy a habitable zone (HZ) is a region of space where conditions are favorable for the creation of life. There are two regions that must be favorable, one within a solar system and the other within the galaxy. Planets and moons in these regions are the likeliest candidates to be habitable and thus capable of bearing extraterrestrial life. Astronomers believe that life is most likely to form within the circumstellar habitable zone (CHZ) within a solar system, and the galactic habitable zone (GHZ) of the larger galaxy (though research on the latter point remains nascent). The HZ may also be referred to as the 'life zone', 'Green Belt' or the 'Goldilocks Zone'. Within a solar system, it is believed a planet must lie within the habitable zone in order to sustain life. The circumstellar habitable zone (or ecosphere) is a notional spherical shell of space surrounding stars where the surface temperatures of any planets present might maintain liquid water. Many believe liquid water is vital because of its role as the solvent needed for biochemical reactions. The location of a solar system within the galaxy must also be favorable to the development of life, and this leads to the concept of a galactic habitable zone. To harbor life, a solar system must be close enough to the galactic center that a sufficiently high level of heavy elements exist to favor the formation of rocky planets, and heavier elements are also necessary to form complex molecules of life. On the other hand, the solar system must be far enough from the galaxy center to avoid hazards such as impacts from comets and asteroids, close encounters with passing stars, and outbursts of radiation from supernovae and from the black hole at the center of the galaxy.

Fine-tuned universe: The term fine-tuned universe refers to the idea that conditions that allow life in the universe are the result of the exact values of the universal physical constants, and that small changes in these constants would correspond to a very different universe, not conducive to the establishment and development of matter, astronomical structures, or life as we know them. The arguments relating to the fine-tuned universe concept are related to the weak anthropic principle, which states that any valid theory of the universe must be consistent with our existence as human beings at this particular time and place in the universe. The premise of the fine-tuned universe assertion is that any small change in the approximately 26 dimensionless fundamental physical constants would make the universe radically different: if, for example, the strong nuclear force were 2% stronger than it is (i.e. if the constant representing its strength were 2% larger), diprotons would be stable and hydrogen would fuse into them instead of deuterium and helium. This would drastically alter the physics of stars, and presumably prevent the universe from developing life as we know it.

Trans-Neptunian objects: A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. The Kuiper belt, Scattered disk, and Oort cloud are names for three divisions of this volume of space. The orbit of each of the planets is affected by the gravitational influences of all the other planets. Discrepancies in the early 1900s between the observed and expected orbits of the known planets suggested that there were one or more additional planets beyond Neptune. The search for these led to the discovery of Pluto. It took more than 60 years to discover another TNO. Since 1992 however, more than 1000 objects have been discovered, differing in sizes, orbits and surface composition. Notable trans-Neptunian objects: Pluto (dwarf planet), Charon (largest moon of Pluto), Eris (dwarf planet, currently the largest known TNO with one known satellite, Dysnomia), Varuna and Quaoar, Orcus and Ixion, Sedna, 2005 FY9 (third largest known TNO) and 2003 EL61.

Eris: Eris, also designated 136199 Eris, is the largest known dwarf planet in the solar system. It is a trans-Neptunian object (TNO), orbiting the Sun in a region of space known as the scattered disc, just beyond the Kuiper belt, and accompanied by at least one moon, Dysnomia. Mike Brown, who led the Mount Palomar-based discovery team, announced in April 2006 that the Hubble Telescope has measured Eris's diameter to be 2400 km, slightly larger than that of Pluto. Eris' size resulted in its discoverers and NASA labelling it the solar system's tenth planet. This, along with the prospect of other similarly sized objects being discovered in the future, stimulated the International Astronomical Union (IAU) to define the term 'planet' more precisely. Under a new definition approved on August 24, 2006, Eris was designated a 'dwarf planet' along with Pluto and Ceres.

Oort cloud: The Oort cloud is a postulated spherical cloud of comets situated about 50,000 to 100,000 AU from the Sun. This is approximately 2000 times the distance from the Sun to Pluto or roughly one light year, almost a quarter of the distance from the Sun to Proxima Centauri, the star nearest the Sun. The Oort cloud would have its inner disk at the ecliptic from the Kuiper belt. Although not confirmed direct observations have been made of such a cloud, astronomers believe it to be the source of most or all comets entering the inner solar system (some short-period comets may come from the Kuiper belt), based on direct observations of the orbits of comets.

Brown dwarf: Brown dwarfs are sub-stellar objects with a mass below that necessary to maintain hydrogen-burning nuclear fusion reactions in their cores, as do stars on the main sequence, but which have fully convective surfaces and interiors, with no chemical differentiation by depth. Brown dwarfs occupy the mass range between that of large gas-giant planets and the lowest mass stars (anywhere between 75 and 80 Jupiter masses). Currently there is a large ambiguity as to what separates a brown dwarf from a giant planet at very low brown dwarf masses (approx. 13 Jupiter masses). For most stars, gas and radiation pressure generated by the thermonuclear fusion reactions within the core of the star will support it against any further gravitational contraction. Hydrostatic equilibrium is reached and the star will spend most of its lifetime burning hydrogen to helium as a main-sequence star. If, however, the mass of the protostar is less than about 0.08 solar mass, normal hydrogen thermonuclear fusion reactions will not ignite in the core. Gravitational contraction does not heat the small protostar very effectively, and before the temperature in the core can increase enough to trigger fusion, the density reaches the point where electrons become closely packed enough to create quantum electron degeneracy pressure.

Yellow dwarf: A yellow dwarf or G-type star is a small (about 0.9 to 1.4 solar masses), yellow main sequence star that is in the process of converting hydrogen to helium in its core by means of nuclear fusion. Our Sun is the most well-known example of a yellow dwarf. A yellow dwarf's lifespan is about 10 billion years, until its supply of hydrogen runs out. When this happens, the star expands to many times its previous size and becomes a red giant. The star Aldebaran is an example of a red giant. Eventually the red giant sheds its outer layers of gas, which become a planetary nebula, while the core collapses into a small, dense white dwarf.

Orange dwarf: Orange dwarfs are main sequence stars of spectral type K. These stars are intermediate in size between M class red dwarf stars and yellow G class stars such as the Earth's Sun. Orange dwarfs vary from 0.5 to 0.9 times the mass of the Sun and have a surface temperature between 4000 and 5200 degrees Celsius. Examples include Alpha Centauri B and Epsilon Indi. These stars are of particular interest in the search for extraterrestrial life because they are stable on the main sequence for a very long time (15 to 30 billion years, compared to 10 billion for the Earth's Sun). This may create an opportunity for life to evolve on terrestrial planets orbiting such stars.

Supernova: A supernova (pl. supernovae) is a stellar explosion which produces an extremely bright object made of plasma that declines to invisibility over weeks or months. A supernova briefly outshines its entire host galaxy. It would take 10 billion years for the Sun to produce the energy output of an ordinary Type II supernova. Stars beneath the Chandrasekhar limit, such as the Sun, are too light to ever become supernovae and will evolve into white dwarfs. There are several different types of supernovae and two possible routes to their formation. A massive star may cease to generate fusion energy from fusing the nuclei of atoms in its core, and collapse under the force of its own gravity to form a neutron star or black hole. A widely-observed supernova in the year 1054 produced the Crab Nebula.

Survivalism: A survivalist is a person who anticipates and prepares for a future disruption in local, regional or worldwide social or political order. Survivalists often prepare for this anticipated disruption by learning skills (e.g., emergency medical training), stockpiling food and water, or building structures that will help them to survive (e.g., an underground shelter). The specific preparations made by survivalists depend on the nature of the anticipated disruption, some of the most commonly anticipated being

• Natural disasters, such as tornadoes, hurricanes, earthquakes, blizzards, and severe thunderstorms
• A disaster brought about by the activities of humankind: chemical spills, release of radioactive materials, or war.
• General collapse of society, resulting from the unavailability of electricity, fuel, food, and water.
• Widespread chaos, or some other apocalyptic event.

Space and survival: Space and survival is the relationship between space and the long-term survival of the human species and civilization. It is based on the observation that space colonization and space science would prevent many human extinction scenarios. A related observation is the limited time and resources available for the colonization of space. Extinction can be prevented by improving the physical barrier or increasing the distance between people and the potential extinction event. For example, people survive imminent explosions by being in a bunker or evacuating. Pandemics are controlled by putting exposed people in quarantine and moving healthy people away. Life support systems that enable people to live in space may also allow them to survive hazardous events. For example, an infectious disease or biological weapon that transmits through the air could not infect a person in a life support system. There is an internal supply of air and a physical barrier between the person and the environment. Increasing the number of places where humans live also prevents extinction. For example, if a massive impact event occurred on Earth without warning, the human species would probably become extinct, and its art, culture and technology would be lost. However, if humans had previously colonized locations outside Earth, the species would survive and possibly recover. do not currently exist. There is a concern that the human species may lose its technological knowledge, use up required resources or become extinct before it colonizes space.

The author Sylvia Engdahl wrote about the 'Critical Stage', a period of time when a civilization has both the technology to expand into space and the technology to destroy itself. Engdahl states that the human civilization is at a Critical Stage, but that the funding for space exploration and colonization is minuscule compared to the funding for weapons of mass destruction and military forces. NBC News space analyst James Oberg commented that "It's just a matter of waiting until we get some kind of cosmic 9/11 that will make everyone say 'why didn't we see this before,' and then we'll have enough money to afford these programs."

Terraforming: Terraforming (literally, 'Earth-shaping') is the theoretical process of modifying a planet, moon, or other body to a more habitable atmosphere, temperature, or ecology. It is a type of planetary engineering. The term is sometimes used broadly as a synonym for planetary engineering in general. The concepts of terraforming are rooted both in science fiction and actual science. The term was probably coined by Jack Williamson in a science-fiction story published in 1942.

Nanotechnology: Nanotechnology is a field of applied science and technology covering a broad range of topics. The main unifying theme is the control of matter on a scale below 100 nanometers, as well as the fabrication of devices on this same length scale. It is a highly multidisciplinary field, drawing from fields such as colloidal science, device physics, and supramolecular chemistry. Much speculation exists as to what new science and technology might result from these lines of research. Some view nanotechnology as a marketing term that describes pre-existing lines of research. Despite the apparent simplicity of this definition, nanotechnology actually encompasses diverse lines of inquiry. Nanotechnology cuts across many disciplines, including colloidal science, chemistry, applied physics, biology. It could variously be seen as an extension of existing sciences into the nanoscale, or as a recasting of existing sciences using a newer, more modern term. Two main approaches are used in nanotechnology: one is a 'bottom-up' approach where materials and devices are built from molecular components which assemble themselves chemically using principles of molecular recognition; the other being a "top-down" approach nano-objects are constructed from larger entities without atomic-level control.

Carbon nanotube: Carbon nanotubes (CNTs) are an allotrope of carbon. They take the form of cylindrical carbon molecules and have novel properties that make them potentially useful in a wide variety of applications in nanotechnology, electronics, optics and other fields of materials science. They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat. Inorganic nanotubes have also been synthesized. Nanotubes are members of the fullerene structural family, which also includes buckyballs. Whereas buckyballs are spherical in shape, a nanotube is cylindrical, with at least one end typically capped with a hemisphere of the buckyball structure. Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers (approximately 50,000 times smaller than the width of a human hair), while they can be up to several millimeters in length.

Redundancy in engineering: Redundancy in engineering is the duplication of critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe. In many safety-critical systems, such as fly-by-wire aircraft, some parts of the control system may be triplicated. An error in one component may then be out-voted by the other two. In a triply redundant system, the system has three sub components, all three of which must fail before the system fails. Since each one rarely fails, and the sub components are expected to fail independently, the probability of all three failing is calculated to be extremely small.

Faster-than-light starship: Faster-than-light (also superluminal or FTL) communications and travel refer to the propagation of information or matter faster than the speed of light. This concept is a staple of the science fiction genre, but is generally considered impossible by the mainstream physics community, due to special relativity. In the context of this article, FTL refers to transmitting information or matter faster than c, a constant equal to the speed of light in a vacuum, 299,792,458 meters per second, or roughly 186,000 miles per second. This is the simplest solution, and is particularly popular in science fiction. However, empirical evidence unanimously support Einstein's theory of special relativity as the correct description of high-speed motion, which reduces in the low-speed case to Galilean relativity, which is an approximation only valid for slow speeds. Similarly, general relativity is unanimously supported as the correct theory of gravitation in the regime of very large masses and long distances. Unfortunately, general relativity breaks down at small distances and is no longer valid in the quantum regime. Special relativity is easily incorporated into nongravitational quantum field theories, however it only applies to a flat Minkowski universe.

Time dilation: Time dilation is the phenomenon whereby an observer finds that another's clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. This is often taken to mean that time has "slowed down" for the other clock, but that is only true in the context of the observer's frame of reference. Locally, time is always passing at the same rate. The time dilation phenomenon applies to any process that manifests change over time. Time dilation would make it possible for passengers in a fast moving vehicle to travel into the further future while aging very little, in that their great speed retards the rate of passage of onboard time. That is, the ship's clock (and according to relativity, any human travelling with it) shows less elapsed time than stationary clocks. For sufficiently high speeds the effect is dramatic. For example, one year of travel might correspond to ten years at home. Indeed, a constant 1 g acceleration would permit humans to circumnavigate the known universe (with a radius of some 13.7 billion light years) in one human lifetime. A more likely use of this effect would be to enable humans to travel to nearby stars without spending their entire lives aboard the ship. However, any such application of time dilation would require the use of some new, advanced method of propulsion.

Fusion rocket: A fusion rocket is a rocket that is driven by fusion power. The process of nuclear fusion is well understood and recent developments indicate this technology will be able to provide terrestial based power within 30 years. However, the proposed reactor vessels are prohibitively large and heavy making them unsuitable to use on spacecraft until at least next century. A smaller and lighter fusion reactor might be possible in the future when better methods have been devised to control magnetic confinement and prevent plasma instabilities. For space flight, the main advantage of fusion would be the very high specific impulse, the main disadvantage the (probable) large mass of the reactor. A tokamak is a machine producing a toroidal (doughnut-shaped) magnetic field for confining a plasma. It is one of several types of magnetic confinement devices and the leading candidate for producing fusion energy.

Generation starship: A generation ship is a hypothetical starship that travels across great distances between stars at a speed much slower than that of light (see interstellar travel). Since such a ship might take hundreds to tens of thousands of years to reach even nearby stars, the original occupants might die during the journey and leave their descendants to continue traveling, depending on the life span of its inhabitants and relativistic effects. It is estimated that, in order to assure genetic diversity during a centuries-long trip, a generation starship would require at least 500 inhabitants. Sperm banks or egg banks can drastically reduce the requisite number. Additionally, the ship would have to be almost entirely self-sustaining (see Biosphere and life support), providing 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.

Self-replicating spacecraft: A von Neumann probe is a specific example of a hypothetical concept based on the work of mathematician and physicist John von Neumann. Von Neumann rigorously studied the concept of self-replicating machines that he called "Universal Assemblers", which are most often referred to as von Neumann machines. While von Neumann never applied his work to the idea of spacecraft, theoreticians since then have done so. The idea of self-replicating spacecraft has been applied (in theory) to several distinct 'tasks', and the particular variant of this idea applied to the idea of space exploration is known as a von Neumann probe. Other variants include the Berserker and an automated seeder ship.

Sleeper ship: A sleeper ship is a hypothetical type of manned spaceship in which most or all of the crew spends the journey in some form of hibernation or suspended animation. As there is currently no known technology that allows for long-term suspended animation of humans, the term is usually only found in science fiction. One alternative may be cryogenic freezing of the crew, though that would not be true suspended animation. The most common role of sleeper ships in fiction is for interstellar travel, usually at slower-than-light speed. Travel times for such journeys could reach into the hundreds or thousands of years, making some form of life extension such as suspended animation necessary for the original crew to live to see their destination. Suspended animation is also required on ships which cannot be used as generation ships, for whatever reason. Suspended animation can also be useful to reduce the consumption of life support resources by crewmembers who are not needed during the trip, and for this reason sleeper ships sometimes also make an appearance in the context of purely interplanetary travel.

Suspended animation: Suspended animation is the slowing of life processes by external means without termination. Breathing, heartbeat, and other involuntary functions may still occur, but they can only be detected by artificial means. Extreme cold is used to precipitate the slowing of an individual's functions; use of this process has led to the developing science of cryonics. Outside of science fiction, the technique has never been applied to humans for more than a few hours. Placing astronauts in suspended animation has been proposed as one way for an individual to reach the end of an interplanetary or interstellar journey, avoiding the necessity for a gigantic generation ship; occasionally the two concepts have been combined, with generations of "caretakers" supervising a large population of frozen passengers. Since the 1970s hypothermia has been induced for some open-heart surgeries as an alternative to heart-lung machines. Hypothermia though only provides a limited amount of time to operate and there has been some evidence of risk of tissue and brain damage. An article in the April 22, 2005 issue of the scientific journal Science, reports success towards inducing suspended animation in mice. The findings are significant, as mice do not hibernate in nature. The breakthrough was achieved when the laboratory of Mark Roth placed mice in a chamber containing 80 ppm hydrogen sulfide, and the test was conducted for 6 hours. The mice's core body temperature dropped to 13 degrees Celsius and metabolism.

Cryonics: Cryonics is the practice of cryopreserving humans or animals that can no longer be sustained by contemporary medicine until resuscitation may be possible in the future. The largest current practitioners are two member-owned, non-profit organizations, the Alcor Life Extension Foundation in Scottsdale, Arizona, with 74 cryopreserved patients and the Cryonics Institute in Clinton Township, Michigan with 75. The process is not currently reversible. Cryonics can only be performed on humans after clinical death, and a legal determination that further medical care is not appropriate (legal death). The rationale for cryonics is that the process may be reversible in the future if performed soon enough, and that cryopreserved people may not really be dead by standards of future medicine (see information theoretic death).

Embryo space colonization: Embryo space colonization is a theoretical interstellar space colonization concept that involves sending a robotic mission to a terrestrial planet (having a biosphere) transporting frozen early-stage embryos. This circumvents the problem of freezing fully developed humans (which is not technologically feasible today and is regarded by many scientists as never feasible; see cryonics) for the hundreds or thousands of years required for interstellar journeys. Instead, it would use currently available technology to preserve viable human embryos in a frozen state. Upon arrival at the target planet, fully autonomous robots or androids would build the first settlement on the planet and start growing crops. Thereafter the first embryos could be unfrozen and would develop in artificial uteri. In contrast to a generation ship, an Embryo-carrying Interstellar Starship (EIS) would have feasible small dimensions in the range of today's spacecraft. Major difficulties with the idea being implemented in reality include: the development of fully autonomous robots, Artificial Wombs, and computer hardware that can function reliably over long periods of time. Furthermore, a propulsion system would be required that could accelerate the EIS to (at least) around one percent of light speed and slow it down again upon nearing the destination. Finally this depends on the existence of an exoplanet qualifying for colonization within a few hundred light years of Earth.

Artificial womb: In the field of ectogenesis, an artificial uterus (or womb) is a mechanism that is used to grow an embryo outside of the body of a female organism that would normally internally carry the embryo to term. An artificial uterus, as a replacement organ, could also be used to assist women with damaged or diseased uteri to be able to conceive to term. Since the uterus is grown from the woman's own endometrial cells, there would be minimal chance of organ rejection. Primary research into the engineering of an artificial uterus was conducted at the Cornell University Center for Reproductive Medicine and Infertility. In the year 2002 Dr. Liu announced that she and her team had grown tissue samples from cultured endometrial cells removed from a human donor. The tissue sample was then engineered to form the shape of a natural uterus, human embryos were implanted into the tissue. The researchers found that the embryos correctly implanted into the artificial uterus' lining and started to grow. Dr. Liu's experiments were halted after six days, to stay within the permitted legal limits of in vitro fertilisation (IVF) legistation in the United States.

Surrogacy: Surrogacy is a third party reproduction arrangement whereby a woman agrees to become pregnant for the purpose of gestating and giving birth to a child for others to raise. She may be the child's genetic mother or not, depending on the type of arrangement agreed to. A surrogate mother is a woman who carries a child for a couple or single person with the intention of giving that child to that person/people once the being is born (also called surrogate pregnancy). The surrogate mother may be the baby's biological mother (traditional surrogacy) or she may be implanted with someone else's fertilized egg (gestational surrogacy).

Transhumanism: Transhumanism is an international intellectual and cultural movement supporting the use of new sciences and technologies to enhance human cognitive and physical abilities and ameliorate what it regards as undesirable and unnecessary aspects of the human condition, such as disease, aging, and death. Transhumanist thinkers study the possibilities and consequences of developing and using human enhancement techniques and other emerging technologies for these purposes. Possible dangers, as well as benefits, of powerful new technologies that might radically change the conditions of human life are also of concern to the transhumanist movement. Although the first known use of the term 'transhumanism' dates from 1957, the contemporary meaning is a product of the 1980s, when a group of scientists, artists, and futurists based in the United States began to organize what has since grown into the transhumanist movement. Transhumanist thinkers postulate that human beings will eventually be transformed into beings with such greatly expanded abilities as to merit the label 'posthuman'.

Proteomics: Proteomics is the large-scale study of protein, particularly their structures and functions. This term was coined to make an analogy with genomics, and while it is often viewed as the "next step", proteomics is much more complicated than genomics. Most importantly, while the genome is a rather constant entity, the proteome differs from cell to cell and is constantly changing through its biochemical interactions with the genome and the environment. One organism has radically different protein expression in different parts of its body, in different stages of its life cycle and in different environmental conditions. The proteome refers to all the proteins produced by an organism, much like the genome is the entire set of genes. The human body may contain more than 2 million different proteins, each having different functions. Thus, proteomics is the study of the composition, structure, function, and interaction of the proteins directing the activities of each living cell. As the main components of the physiological pathways of the cells, proteins serve as vital functions in the body.

Rational-emotive therapy: Rational Emotive Behavior Therapy (REBT) is an active-directive, solution-oriented therapy which focuses on resolving emotional, cognitive and behavioral problems in clients, originally developed by the American psychotherapist Albert Ellis. REBT is one of the first forms of Cognitive Behavior Therapy and was first expounded by Ellis in 1953. Fundamental to REBT is the concept that emotional suffering results primarily, though not completely, from our evaluations of a negative event, not solely by the events per se. In other words, human beings on the basis of their belief system actively, though not always consciously, disturb themselves, and even disturb themselves about their disturbances. The REBT framework assumes that humans have both rational and irrational tendencies. Irrational thought/images prevent goal attainment, lead to inner conflict, lead to more conflict with others and poor mental health. Rational thought/images lead to goal attainment and more inner harmony. In other words rational beliefs reduce conflicts with others and improved health.

Virtual reality: Virtual reality (VR) is a technology which allows a user to interact with a computer-simulated environment, be it a real or imagined one. Most current virtual reality environments are primarily visual experiences, displayed either on a computer screen or through special stereoscopic displays, but some simulations include additional sensory information, such as sound through speakers or headphones. Some advanced, haptic systems now include tactile information, generally known as force feedback, in medical and gaming applications. Users can interact with a virtual environment or a virtual artifact (VA) either through the use of standard input devices such as a keyboard and mouse, or through multimodal devices such as a wired glove, the Polhemus boom arm, and/or omnidirectional treadmill. The simulated environment can be similar to the real world, for example, simulations for pilot or combat training, or it can differ significantly from reality, as in VR games. In practice, it is currently very difficult to create a high-fidelity virtual reality experience, due largely to technical limitations on processing power, image resolution and communication bandwidth. However, those limitations are expected to eventually be overcome as processor, imaging and data communication technologies become more powerful and cost-effective over time.

Head-mounted display: A head-mounted display (HMD) is a display device that a person wears on the head to have video information directly displayed in front of the eyes. An HMD has either one or two small CRT, LCD, LCoS (Liquid Crystal on Silicon), or OLED displays with magnifying lenses embedded in a helmet, glasses or visor. With two displays, the technology can be used to show stereoscopic images by displaying an offset image to each eye. Lenses are used to give the perception that the images are coming from a greater distance, to prevent eye strain. One company, Sensics, makes an HMD with 24 OLED displays, with the lenses designed to combine 12 displays into a seamless image for each eye. Head-mounted displays may also be coupled with head-movement tracking devices to allow the user to "look around" a virtual reality environment naturally by moving the head without the need for a separate controller. Performing this update quickly enough to make the experience immersive requires a great amount of computer image processing. If six axis position sensing (direction and position) is used then the wearer may physically move about and have their movement translated into movement in the virtual environment.

Wired glove: A wired glove is a glove-like input device for virtual reality environments. Various sensor technologies are used to capture physical data such as bending of fingers. Often a motion tracker, such as a magnetic tracking device or inertial tracking device, is attached to capture the global position / rotation data of the glove. These movements are then interpreted by the software that accompanies the glove, so any one movement can mean any number of things. Gestures can then be categorized into useful information, such as to recognize American Sign Language or other symbolic functions. Expensive high-end wired gloves can also provide haptic feedback, which is a simulation of the sense of touch. This allows a wired glove to also be used as an output device. Traditionally, wired gloves have only been available at a huge cost, with the finger bend sensors and the tracking device having to be bought separately.

Holography: Holography is the science of producing holograms; it is an advanced form of photography that allows an image to be recorded in three dimensions. The technique of holography can also be used to optically store, retrieve, and process information. A volumetric display device is a graphical display device that forms a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects. One definition offered by pioneers in the field is that volumetric displays create 3-D imagery via the emission, scattering, or relaying of illumination from well-defined regions in (x,y,z) space.

Quantum computer: A quantum computer is any device for computation that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. In a classical (or conventional) computer, the amount of data is measured by bits; in a quantum computer, the data is measured by qubits. The basic principle of quantum computation is that the quantum properties of particles can be used to represent and structure data, and that quantum mechanisms can be devised and built to perform operations with these data. Though quantum computing is still in its infancy, experiments have been carried out in which quantum computational operations were executed on a very small number of qubits. It is widely believed that if large-scale quantum computers can be built, they will be able to solve certain problems asymptotically faster than any classical computer. Quantum computers are different from other computers such as DNA computers and computers based on transistors, even though these may ultimately use some kind of quantum mechanical effect (for example covalent bonds). Some computing architectures such as optical computers may use classical superposition of electromagnetic waves, but without some specifically quantum mechanical resource such as entanglement, they do not share the potential for computational speed-up of quantum computers.