Interstellar space travel is unmanned or manned travel between stars. Travel is the change in location of people on a trip through the means of Transport from one location to another A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth The concept of interstellar travel in starships is a staple in science fiction. A starship is a theoretical Spacecraft designed for traveling between the stars, as opposed to a vehicle designed for Orbital spaceflight or Interplanetary Interstellar travel is tremendously more difficult than interplanetary travel. Intergalactic travel, the travel between different galaxies, is even more difficult. Intergalactic travel is travel between galaxies, and is considered much more technologically demanding than even Interstellar travel.
Many scientific papers have been published about related concepts. Given sufficient travel time and engineering work, both unmanned and generational interstellar travel seem possible, though representing a very considerable technological and economic challenge unlikely to be met for some time, particularly for crewed probes. NASA has been engaging in research into these topics for several years, and has accumulated a number of theoretical approaches. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program
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The difficulties of interstellar travel
The main difficulty of interstellar travel is the vast distances that have to be covered and therefore the time it takes with most realistic propulsion methods - from decades to millennia. A decade is a period of 10 Years (since 1594 a factor of 10 difference between two numbers, or sometimes a set or a group of ten (since 1451 A millennium (pl millennia) is a period of Time equal to one thousand Years (from Latin la mille, thousand and la annum Hence an interstellar ship would be much more severely exposed to the hazards found in interplanetary travel, including hard vacuum, radiation, weightlessness, and micrometeoroids. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation Weightlessness is a phenomenon experienced by people during Free-fall. A Micrometeoroid (also micrometeorite, micrometeor) is a tiny Meteoroid; a small particle of rock in space usually weighing less than a Gram The long travel times make it difficult to design manned missions, and make economic justification of any interstellar mission nearly impossible, since benefits that do not become available for decades or longer have a present value close to zero. Present value is the value on a given date of a future payment or series of future payments discounted to reflect the Time value of money and other factors such as Investment
It has been argued that an interstellar mission which cannot be completed within 50 years should not be started at all. Instead, the money should be invested in designing a better propulsion system. This is because a slow spacecraft would probably be passed by another mission sent later with more advanced propulsion. [1]
Intergalactic travel involves distances about a million-fold greater than interstellar distances, making it radically more difficult than even interstellar travel. Intergalactic travel is travel between galaxies, and is considered much more technologically demanding than even Interstellar travel.
Interstellar distances
Astronomical distances are sometimes measured in the length of time it would take a beam of light to travel between two points (see lightyear). Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by Light in a vacuum travels 299,792,458 meters per second or 186,282. 37 miles per second.
The distance from Earth to the Moon is 1. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 3 light-seconds. A light-second is a Unit of length. It is defined as the Distance Light travels in an absolute Vacuum in one Second or 299792458 With current spacecraft propulsion technologies, a trip to the moon will typically take about three days. The distance from Earth to other planets in the solar system ranges from three light-minutes to about four light-hours. Depending on the planet and its alignment to Earth, for a typical unmanned spacecraft these trips will take from a few months to a little over a decade.
The nearest known star to the Sun is Proxima Centauri, which is 4. The Sun (Sol is the Star at the center of the Solar System. Proxima Centauri ( Latin la ''proximus proxima proximum'' meaning 'next to' or 'nearest to' is a Red dwarf Star approximately 4 23 light-years away. The fastest outward-bound spacecraft yet sent, Voyager 1, has covered 1/600th of a light-year in 30 years and is currently moving at 1/18000 the speed of light. The Voyager 1 spacecraft is a 722-kilogram robotic Space probe of the outer Solar system and beyond launched September 5, At this rate, a journey to Proxima Centauri would take 72,000 years. Of course, this mission was not specifically intended to travel fast to the stars, and current technology could do much better. The travel time could be reduced to a few millennia using lightsails, or to a century or less using nuclear pulse propulsion (Orion).
No current technology can propel a craft fast enough to reach other stars in under 50 years' time. Current theories of physics indicate that it is impossible to travel faster than light, and suggest that if it were possible, it might also be possible to build a time machine using similar methods. This article details time travel itself For other uses see Time Traveler.
However, special relativity offers the possibility of shortening the apparent travel time: if a starship with sufficiently advanced engines could reach velocities approaching the speed of light, relativistic time dilation would make the voyage seem much shorter for the traveller. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial This article discusses a concept in physics For the concept in sociology see Time displacement. However, it would still take many years of elapsed time as viewed by the people remaining on Earth, and upon returning to Earth, the travellers would find that far more time had elapsed on Earth than had for them. (This effect is referred to as the twin paradox. In physics the twin paradox is a thought experiment in Special Relativity, in which a person who makes a journey into space in a high-speed rocket will return home to find he )
General relativity offers the theoretical possibility that faster than light travel may be possible without violating fundamental laws of physics, for example, via wormholes, although it is still debated whether this is possible in the real world. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 In Physics, a wormhole is a hypothetical topological feature of Spacetime that is fundamentally a 'shortcut' through Space and Time Proposed mechanisms for faster than light travel within the theory of General Relativity require the existence of exotic matter. Exotic matter is a hypothetical concept of Particle physics. It covers any material which violates one or more classical conditions or is not made of known baryonic particles
Manned missions
The mass of any craft capable of carrying humans would inevitably be several orders of magnitude greater than that necessary for an unmanned interstellar probe. An interstellar probe is a Space probe which has left -- or is expected to leave -- the Solar system and enter interstellar space (typically defined as For instance, the first space probe, Luna 1, had a payload of 361 kg; while the first spacecraft to carry a living passenger (Laika the dog), Sputnik 2, had a payload over 20 times that at 7,314 kg. Luna 1 (E-1 series also known as Mechta (Мечта lit: Dream) was the first Spacecraft to reach the vicinity Laika (from the Лайка, a breed of dog, literally meaning "Barker" or "Howler" was a Soviet space dog (c Mission profile Sputnik 2 was launched into a 212 x 1660 km (132 x 1031 mile orbit with a period of 103 This in fact severely underestimates the difference in the case of interstellar missions, given the vastly greater travel times involved and the resulting necessity of a closed-cycle life support system. Controlled (or Closed) Ecological Life Support Systems (acronym CELSS) are a type of scientific endeavor to create a self-supporting Life support In Human spaceflight, the life support system is a group of devices that allow a human being to survive in outer space
Proposed methods of interstellar travel
If a spaceship could average 10 percent of light speed, this would be enough to reach Proxima Centauri in forty years. Proxima Centauri ( Latin la ''proximus proxima proximum'' meaning 'next to' or 'nearest to' is a Red dwarf Star approximately 4 Several propulsion systems are able to achieve this, but none of them is reasonably cheap.
Nuclear pulse propulsion
Since the 1960s it has been technically possible to build spaceships with nuclear pulse propulsion engines, i. e. ships driven by a series of nuclear explosions. This propulsion system contains the prospect of very high specific impulse (space travel's equivalent of fuel economy) and high speed, and therefore of reaching the nearest star in decades rather than centuries; construction and operational costs per unit of Payload (air and space craft) were expected to be similar to those of ships using chemical rockets. Specific impulse (usually abbreviated I sp is a way to describe the efficiency of rocket and jet engines In military aircraft or space exploration the payload is the carrying capacity of an aircraft or space ship including as Cargo, Munitions scientific instruments [2]
Proposed interstellar spacecraft using nuclear pulse propulsion include Project Orion and Project Longshot. Project Orion was the first engineering design study of a Spacecraft powered by Nuclear pulse propulsion, an idea first proposed by Stanisław Ulam Project Longshot is a design for an interstellar Spacecraft, an unmanned probe intended to fly to Alpha Centauri powered by Nuclear pulse propulsion. Using miniature nuclear bombs as fuel, Orion would be able to reach a velocity of 3% of the speed of light. It is one of very few known interstellar spacecraft proposals that could be constructed entirely with today's technology.
Fusion rockets
Fusion rocket starships, using foreseeable fusion reactors, should be able to reach speeds of approximately 10 percent of that of light. 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 These would "burn" deuterium. One proposal using a fusion rocket is Project Daedalus. Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible interstellar Unmanned spacecraft
The problem with all traditional rocket propulsion methods is that the spacecraft would need to carry its fuel with it, thus making it quite heavy. The following three methods attempt to solve this problem.
Interstellar Ramjets
In 1960 Robert W. Bussard proposed the Bussard ramjet, a fusion rocket in which a huge scoop would collect the diffuse hydrogen in interstellar space, "burn" it on the fly using a proton-proton fusion reaction, and expel it out of the back. The Bussard ramjet is a theoretical method of Spacecraft propulsion proposed in 1960 by the physicist Robert W The proton-proton chain reaction is one of several fusion reactions by which Stars convert Hydrogen to Helium, the primary alternative being the Though later calculations with more accurate estimates suggest that the thrust generated would be less than the drag caused by any conceivable scoop design, the idea is attractive because, as the fuel would be collected en route, the craft could theoretically accelerate to near the speed of light.
Antimatter rockets
An Antimatter rocket would have a far higher energy density and specific impulse than any other proposed class of rocket. An antimatter rocket is a proposed class of Rockets that use Antimatter as their power source If energy resources and efficient production methods are found to make antimatter in the quantities required, theoretically it would be possible to reach speeds near that of light, where time dilation would shorten perceived trip times for the travelers considerably. In Particle physics and Quantum chemistry, antimatter is the extension of the concept of the Antiparticle to Matter, where antimatter is composed This article discusses a concept in physics For the concept in sociology see Time displacement.
Beamed Propulsion
A light sail or magnetic sail powered by a massive laser or particle accelerator in the home star system could potentially reach even greater speeds, because it would not need reaction mass and therefore would not need to accelerate that as well as the payload. Solar sails (also called light sails or photon sails, especially when they use Light sources other than the Sun) are a proposed form of A magnetic sail or magsail is a proposed method of Spacecraft propulsion which would use a static magnetic field to deflect charged particles radiated by the A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. Working mass is a mass against which a system operates in order to produce Acceleration. In military aircraft or space exploration the payload is the carrying capacity of an aircraft or space ship including as Cargo, Munitions scientific instruments In theory a lightsail driven by a laser or other beam from Earth can be used to decelerate a spacecraft approaching a distant star or planet, by detaching part of the sail and using it to focus the beam on the forward-facing surface of the rest of the sail. [3] A magnetic sail could also decelerate to its destination without fuel, by interacting with the plasma found in the solar wind of the destination star and the interstellar medium.
Beamed propulsion seems to be the best interstellar travel technique presently available, since it uses known physics and known technology that is being developed for other purposes. Beam-powered propulsion is a class of Spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant [4]
Further speculative methods
Light speed travel
Interstellar travel via transmission
If physical entities could be transmitted as information and reconstructed at a destination, travel precisely at the speed of light would be possible. Teleportation is the movement of objects from one place to another more or less instantaneously either by Paranormal means or through technological artifice Note that, under General Relativity, information cannot travel faster than light. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 The speed increase when compared to near-light-speed travel would therefore be minimal for outside observers, but for the travelers the journey would become instantaneous.
Encoding, sending and then reconstructing an atom by atom description of (say) a human body is a daunting prospect, but it may be sufficient to send software that in all practical purposes duplicates the neural function of a person. Presumably, the receiver/reconstructor for such transmissions would have to be sent to the destination by more conventional means. Tachyons could not be used for communication. A tachyon (from the Greek, takhyónion, from, takhýs, ie swift fast is any hypothetical particle that travels at Faster-than-light
Faster than light travel
Scientists and authors have postulated a number of ways by which it might be possible to surpass the speed of light. Even the most serious-minded of these are speculative.
Warped Spacetime
According to Einstein's equation of General Relativity, spacetime is curved:
General relativity may permit the travel of an object faster than light in curved spacetime. The Einstein field equations ( EFE) or Einstein's equations are a set of ten equations in Einstein 's theory of General relativity in which the General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS [5] One could imagine exploiting the curvature to take a "shortcut" from one point to another. This is one form of the Warp Drive concept. Warp drive is a form of Faster-than-light propulsion in the Fictional universe of Star Trek, capable of propelling spacecraft or objects to many multiples
In physics, the Alcubierre drive is based on an argument that the curvature could take the form of a wave in which a spaceship might be carried in a "bubble". The Alcubierre metric, also known as the Alcubierre drive or Warp Drive, is a speculative mathematical model of a spacetime exhibiting features reminiscent of Space would be collapsing at one end of the bubble and expanding at the other end. The motion of the wave would carry a spaceship from one space point to another in less time than light would take through unwarped space. Nevertheless, the spaceship would not be moving faster than light within the bubble. This concept would require the spaceship to incorporate a region of exotic matter, or "negative mass". Exotic matter is a hypothetical concept of Particle physics. It covers any material which violates one or more classical conditions or is not made of known baryonic particles As a practical means of interstellar transportation, this idea has been criticized; see Alcubierre Drive. The Alcubierre metric, also known as the Alcubierre drive or Warp Drive, is a speculative mathematical model of a spacetime exhibiting features reminiscent of
Wormholes
Wormholes are conjectural distortions in space-time that theorists postulate could connect two arbitrary points in the universe, across an Einstein-Rosen Bridge. In Physics, a wormhole is a hypothetical topological feature of Spacetime that is fundamentally a 'shortcut' through Space and Time In Physics, a wormhole is a hypothetical topological feature of Spacetime that is fundamentally a 'shortcut' through Space and Time It is not known whether or not wormholes are possible in practice. Although there are solutions to the Einstein equation of general relativity which allow for wormholes, all of the currently known solutions involve some assumption, for example the existence of negative mass, which may be unphysical. Exotic matter is a hypothetical concept of Particle physics. It covers any material which violates one or more classical conditions or is not made of known baryonic particles [6] However, Cramer et al. argue that such wormholes might have been created in the early universe, stabilized by cosmic string. A cosmic string is a hypothetical 1-dimensional (spatially Topological defect in various fields [7] The general theory of wormholes is discussed by Visser in the book Lorentzian Wormholes[8]
Methods for slow manned missions
Slow interstellar travel designs such as Project Longshot generally use near-future spacecraft propulsion technologies. Project Longshot is a design for an interstellar Spacecraft, an unmanned probe intended to fly to Alpha Centauri powered by Nuclear pulse propulsion. Spacecraft propulsion is any method used to change the velocity of Spacecraft and artificial Satellites There are many different methods As a result, voyages are extremely long, starting from about one hundred years and reaching to thousands of years. Crewed voyages might be one-way trips to set up colonies. This article is about a type of political territory For other uses see Colony (disambiguation. The duration of such a journey would present a huge obstacle in itself. The following are the major proposed solutions to that obstacle:
Generation ships
A generation ship is a type of interstellar ark in which the travellers live normally (not in suspended animation) and the crew who arrive at the destination are descendants of those who started the journey. 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 An interstellar ark is a conceptual space vehicle that some have speculated could be used to traverse the distances between stars Suspended animation is the slowing of life processes by external means without termination
Generation ships are not currently feasible, both because of the enormous scale of such a ship and because such a sealed, self-sustaining habitat would be difficult to construct. 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. An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( Biosphere 2 is a 314-acre (127 ha) structure originally built to be an artificial closed ecological system in Oracle, Arizona ( USA
Generation ships would also have to solve major biological and social problems. [9] Estimates of the minimum viable population vary - 180 is about the lowest, but such a small population would be vulnerable to genetic drift, which might reduce the gene pool below a safe level. Minimum viable population (MVP is a lower bound on the population of a species such that it can survive in the wild In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time In Population genetics, a gene pool is the complete set of unique Alleles in a Species or Population. A generation ship in fiction typically takes thousands of years to reach its destination, i. e. longer than most human civilizations have lasted. Hence there is a risk that the culture which arrives at the destination may be incapable of doing what is needed - in the worst case it may have fallen into barbarism. Also they may forget that they are on a generation ship. Stephen Baxter's story "Mayflower II" (in the collection Resplendent) explores both of these risks as does Robert A. Heinlein's two-part 1941 novel Orphans of the Sky. Stephen Baxter (born 13 November 1957 is a British Hard science fiction Author. Resplendent was released on 21 September 2006 in the UK and in the US on September 13, 2007. Robert Anson Heinlein (July 7 1907 – May 8 1988 was an American Novelist and Science fiction Writer. Orphans of the Sky is a 1963 Science fiction Novel by Robert A
Suspended animation
Scientists and writers have postulated various techniques for suspended animation. Suspended animation is the slowing of life processes by external means without termination These include human hibernation and cryonic preservation. For the ability of certain operating systems see Hibernate (OS feature Hibernation is a state of inactivity and metabolic depression Cryonics is the low-temperature Preservation of Humans and other Animals that can no longer be sustained by contemporary Medicine until While neither is currently practical, they offer the possibility of sleeper ships in which the passengers lie inert for the long years of the voyage. 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 However, even assuming all relevant space-faring and suspended animation technologies could be developed, an automated means of guiding the ship to its destination with little or no human influence would be required.
Extended human lifespan
A variant on this possibility is based on the development of substantial human life extension, such as the "Engineered Negligible Senescence" strategy of Dr. Aubrey de Grey. Dr Aubrey David Nicholas Jasper de Grey (born 20 April 1963 in London, England) is a British biomedical gerontologist If a ship crew had lifespans of some thousands of years, they could traverse interstellar distances without the need to replace the crew in generations. The psychological effects of such an extended period of travel would potentially still pose a problem.
Frozen embryos
A robotic space mission carrying some number of frozen early stage human embryos is another theoretical possibility. See also Robot Robotics is the science and technology of Robots and their design manufacture and application An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular This method of space colonization requires, among other things, the development of a method to replicate conditions in a uterus, the prior detection of a habitable terrestrial planet, and advances in the field of fully autonomous mobile robots. Space colonization (also called space settlement, space humanization, Space habitation, etc The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the A terrestrial planet, telluric planet or rocky planet is a Planet that is primarily composed of Silicate rocks Within our See also Robot Robotics is the science and technology of Robots and their design manufacture and application (See embryo space colonization. Embryo space colonization is a Theoretical interstellar Space colonization concept that involves sending a robotic mission to a habitable Terrestrial )
NASA research
The NASA Breakthrough Propulsion Physics Project identified two breakthroughs which are needed for interstellar travel to be possible [10]:
- A method of propulsion able to reach the maximum speed which it is possible to attain
- A new method of on-board energy production which would power those devices. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program
In other words, any engine short of the best conceivable engine won't work, and that engine cannot be powered by currently known energy sources. Analogies for 'breakthroughs' in technology are steam engines supplanting sailing ships, and jet aircraft replacing propeller aircraft.
Geoffery A. Landis, of NASA's Glenn Research Center, says that a laser-powered interstellar sail ship could possibly be launched within 50 years, utilizing new methods of space travel. "I think that ultimately we're going to do it, it's just a question of when and who," Landis said in an interview. Rockets are too slow to send humans on interstellar missions. Instead, he envisions interstellar craft with gigantic sails, propelled by laser light to about one tenth the speed of light. It would take such a ship about 43 years to reach Alpha Centauri, if it passed through the system. Slowing down to stop at Alpha Centauri could increase the trip to 100 years. [9]
References
- ^ Yoji Kondo: Interstellar Travel and Multi-generation Spaceships, p. 31
- ^ General Dynamics Corp. General Dynamics Corporation ( is a defense conglomerate formed by Mergers and Divestitures and as of 2008 it is the fifth largest Defense contractor (Jan 1964). Nuclear Pulse Vehicle Study Condensed Summary Report (General Dynamics Corp.). U. S. Department of Commerce National Technical Information Service.
- ^ Forward, R. L. (1984). "Roundtrip Interstellar Travel Using Laser-Pushed Lightsails". J Spacecraft 21 (2): 187-195.
- ^ Bob Forward: Ad Astra, in Journal of the British Interplanetary Society (Vol. 49, pp. 23-32, 1996)
- ^ Remote Sensing Tutorial Page A-10
- ^ (http://www.nasa.gov/centers/glenn/research/warp/ideachev.html#worm)
- ^ John G. Cramer, Robert L. Forward, Michael S. Morris, Matt Visser, Gregory Benford, and Geoffrey A. Landis, "Natural Wormholes as Gravitational Lenses," Phys. Rev. D51 (1995) 3117-3120
- ^ M. Visser (1995) Lorentzian Wormholes: from Einstein to Hawking, AIP Press, Woodbury NY, ISBN 1-56396-394-9
- ^ a b [1] Malik, Tariq, "Sex and Society Aboard the First Starships. " Science Tuesday, Space. com March 19, 2002.
- ^ Warp Drive, When? Breakthrough Technologies
- Eugene Mallove and Gregory Matloff (1989). The Starflight Handbook. John Wiley & Sons, Inc. ISBN 0-471-61912-4.
- Zubrin, Robert (1999). Entering Space: Creating a Spacefaring Civilization. Tarcher / Putnam. ISBN 1-58542-036-0.
- Eugene F. Mallove, Robert L. Forward, Zbigniew Paprotny, Jurgen Lehmann: "Interstellar Travel and Communication: A Bibliography," Journal of the British Interplanetary Society, Vol. 33, pp. 201-248, 1980.
- Geoffrey A. Landis, "The Ultimate Exploration: A Review of Propulsion Concepts for Interstellar Flight," in Interstellar Travel and Multi-Generation Space Ships, Kondo, Bruhweiller, Moore and Sheffield. , eds. , pp. 52-61, Apogee Books (2003), ISBN 1-896522-99-8.
- Zbigniew Paprotny, Jurgen Lehmann: "Interstellar Travel and Communication Bibliography: 1982 Update," Journal of the British Interplanetary Society, Vol. 36, pp. 311-329, 1983.
- Zbigniew Paprotny, Jurgen Lehmann, John Prytz: "Interstellar Travel and Communication Bibliography: 1984 Update" Journal of the British Interplanetary Society, Vol. 37, pp. 502-512, 1984.
- Zbigniew Paprotny, Jurgen Lehmann, John Prytz: "Interstellar Travel and Communication Bibliography: 1985 Update" Journal of the British Interplanetary Society, Vol. 39, pp. 127-136, 1986.
See also
- Interstellar communication
- Interstellar travel and the Wait Calculation
- Project Daedalus
- Project Orion
- Fusion rocket
- Spaceship
- Starwisp
- Eugen Sänger
- Robert Bussard
- Robert L. Forward
- Freeman Dyson
- Carl Sagan
- Tau Zero
- Gliese 581c
External links
- Links gathered by Mark Tomion, including Practical Design of a Spacewarp, by Mohammad Mansouryar
- NASA Breakthrough Propulsion Physics Program
- Centauri Dreams
- "Atomic rockets" SF spacecraft fan site
- Sex and Society Aboard the First Starships
- Bibliography of Interstellar Flight
- Extensive list of sources Science and Science Fiction for Interstellar Flight
- [2]
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