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52-977: In 1987, the L5 Society merged with the National Space Institute to form the National Space Society . The name comes from the L 4 and L 5 Lagrangian points in the Earth – Moon system proposed as locations for the huge rotating space habitats that O'Neill envisioned. L 4 and L 5 are points of stable gravitational equilibrium located along the path of the Moon's orbit , 60 degrees ahead or behind it. An object placed in orbit around L 5 (or L 4 ) will remain there indefinitely without having to expend fuel to keep its position, whereas an object placed at L 1 , L 2 or L 3 (all points of unstable equilibrium) may have to expend fuel if it drifts off

104-461: A "characteristic length", L c , which is also known as its "self-support length" and is the length of untapered cable it can support in a constant 1 g gravity field. where σ is the stress limit (in pressure units) and ρ is the density of the material. Hypersonic skyhook equations use the material's "specific velocity" which is equal to the maximum tangential velocity a spinning hoop can attain without breaking: For rotating tethers (rotovators)

156-710: A Skyhook, while spacecraft bound for higher orbit, or returning from higher orbit, would use the upper end. In 2000, NASA and Boeing considered a HASTOL concept, where a rotating tether would take payloads from a hypersonic aircraft (at half of orbital velocity) to orbit . A tether satellite is a satellite connected to another by a space tether. A number of satellites have been launched to test tether technologies, with varying degrees of success. There are many different (and overlapping) types of tether. Momentum exchange tethers are one of many applications for space tethers. Momentum exchange tethers come in two types; rotating and non-rotating. A rotating tether will create

208-426: A controlled force on the end-masses of the system due to centrifugal acceleration. While the tether system rotates, the objects on either end of the tether will experience continuous acceleration; the magnitude of the acceleration depends on the length of the tether and the rotation rate. Momentum exchange occurs when an end body is released during the rotation. The transfer of momentum to the released object will cause

260-407: A current that can generate either thrust or drag from a planetary magnetic field , in much the same way as an electric motor does. These can be either rotating tethers, or non-rotating tethers , that capture an arriving spacecraft and then release it at a later time into a different orbit with a different velocity. Momentum exchange tethers can be used for orbital maneuvering , or as part of

312-403: A modular staged tether system maybe used to achieve the same goal. Multiple tethers would be used between stages. The number of tethers would determine the strength of any given cross-section. For rotating tethers not significantly affected by gravity, the thickness also varies, and it can be shown that the area, A, is given as a function of r (the distance from the centre) as follows: where R

364-582: A paper on "Closed Ecosystems of High Agricultural Yield" at the 1975 Princeton Conference on Space Manufacturing Facilities, which was organized by O'Neill. At this conference, O'Neill merged the Solar Power Satellite (SPS) ideas of Peter Glaser with his space habitat concepts. The Hensons incorporated the L5 Society in August 1975, and sent its first 4-page newsletter in September to a sign up list from

416-682: A planetary-surface-to-orbit / orbit-to-escape-velocity space transportation system. This is typically a non-conductive tether that accurately maintains a set distance between multiple space vehicles flying in formation. A form of solar wind sail with electrically charged tethers that will be pushed by the momentum of solar wind ions . A concept for suspending an object from a tether orbiting in space. Many uses for space tethers have been proposed, including deployment as space elevators , as skyhooks , and for doing propellant-free orbital transfers. Konstantin Tsiolkovsky (1857–1935) once proposed

468-531: A protective coating is needed, including relative to UV and atomic oxygen . For applications that exert high tensile forces on the tether, the materials need to be strong and light. Some current tether designs use crystalline plastics such as ultra-high-molecular-weight polyethylene , aramid or carbon fiber . A possible future material would be carbon nanotubes , which have an estimated tensile strength between 140 and 177  GPa (20.3 and 25.7 million psi; 1.38 and 1.75 million atm), and

520-547: A proven tensile strength in the range 50–60 GPa (7.3–8.7 million psi; 490,000–590,000 atm) for some individual nanotubes. (A number of other materials obtain 10 to 20 GPa (1.5 to 2.9 million psi; 99,000 to 197,000 atm) in some samples on the nano scale, but translating such strengths to the macro scale has been challenging so far, with, as of 2011, CNT-based ropes being an order of magnitude less strong, not yet stronger than more conventional carbon fiber on that scale). For some applications,

572-399: A specific height above the surface of the celestial body, but lower than (A). Instead of rotating end for end, tethers can also be kept straight by the slight difference in the strength of gravity over their length. A non-rotating tether system has a stable orientation that is aligned along the local vertical (of the earth or other body). This can be understood by inspection of the figure on

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624-459: A tether satellite, which can operate on electromagnetic principles as generators , by converting their kinetic energy to electrical energy , or as motors , converting electrical energy to kinetic energy. Electric potential is generated across a conductive tether by its motion through the Earth's magnetic field. The choice of the metal conductor to be used in an electrodynamic tether is determined by

676-401: A tower so tall that it reached into space, so that it would be held there by the rotation of Earth . However, at the time, there was no realistic way to build it. In 1960, another Russian, Yuri Artsutanov , wrote in greater detail about the idea of a tensile cable to be deployed from a geosynchronous satellite , downwards towards the ground, and upwards away, keeping the cable balanced. This

728-574: A variety of factors. Primary factors usually include high electrical conductivity and low density . Secondary factors, depending on the application, include cost, strength, and melting point. An electrodynamic tether was profiled in the documentary film Orphans of Apollo as technology that was to be used to keep the Russian space station Mir in orbit. This is the use of a (typically) non-conductive tether to connect multiple spacecraft. Tethered Experiment for Mars inter-Planetary Operations (TEMPO³)

780-402: Is a proposed 2011 experiment to study the technique. A theoretical type of non-rotating tethered satellite system, it is a concept for providing space-based support to things suspended above an astronomical object. The orbital system is a coupled mass system wherein the upper supporting mass (A) is placed in an orbit around a given celestial body such that it can support a suspended mass (B) at

832-460: Is the space elevator idea, a type of synchronous tether that would rotate with the Earth. However, given the materials technology of the time, this too was impractical on Earth. In the 1970s, Jerome Pearson independently conceived the idea of a space elevator, sometimes referred to as a synchronous tether, and, in particular, analyzed a lunar elevator that can go through the L1 and L2 points , and this

884-585: Is the radius of tether, v is the velocity with respect to the centre, M is the tip mass, δ {\displaystyle \delta } is the material density, and T is the design tensile strength. Integrating the area to give the volume and multiplying by the density and dividing by the payload mass gives a payload mass / tether mass ratio of: where erf is the normal probability error function . Let V r = V / V c {\displaystyle V_{r}=V/V_{c}\,} , then: This equation can be compared with

936-412: Is theorized to be significantly less expensive than spaceflight using rocket engines . Tether satellites might be used for various purposes, including research into tether propulsion , tidal stabilization and orbital plasma dynamics. Five main techniques for employing space tethers are in development: Electrodynamic tethers are primarily used for propulsion. These are conducting tethers that carry

988-411: Is very unlikely that multiple redundant cables would be damaged near the same point on the cable, and hence a very large amount of total damage can occur over different parts of the cable before failure occurs. Beanstalks and rotovators are currently limited by the strengths of available materials. Although ultra-high strength plastic fibers ( Kevlar and Spectra ) permit rotovators to pluck masses from

1040-563: The Omni arrangement was discontinued and an agreement was made with Palmer Publications to make their monthly general space interest magazine Space World the official NSI member magazine. When von Braun died in June 1977, Hugh Downs became Chairman of the Board and, after a time, Ben Bova assumed the presidency. After Hewitt departed in 1980, Courtney Stadd served for a period as General Manager. The Institute

1092-598: The Van Allen belts can have markedly lower life than those that stay in low earth orbit or are kept outside Earth's magnetosphere. Tether properties and materials are dependent on the application. However, there are some common properties. To achieve maximum performance and low cost, tethers would need to be made of materials with the combination of high strength or electrical conductivity and low density. All space tethers are susceptible to space debris or micrometeoroids. Therefore, system designers will need to decide whether or not

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1144-401: The lunar surface. It would also be able to hold 100 cargo vehicles, each with a mass of 580 kg (1,280 lb), evenly spaced along the length of the elevator. Other materials that could be used are T1000G carbon fiber, Spectra 2000, or Zylon. For gravity stabilized tethers, to exceed the self-support length the tether material can be tapered so that the cross-sectional area varies with

1196-460: The rocket equation , which is proportional to a simple exponent on a velocity, rather than a velocity squared. This difference effectively limits the delta-v that can be obtained from a single tether. In addition the cable shape must be constructed to withstand micrometeorites and space junk . This can be achieved with the use of redundant cables, such as the Hoytether ; redundancy can ensure that it

1248-516: The NSI board of directors and governors were a veritable "Who's Who" list that included comedian and entertainer Bob Hope , singer/songwriter John Denver , oceanographer Jacques-Yves Cousteau , "Original 7" Project Mercury astronaut and Senator John H. Glenn Jr. , Apollo 8 astronaut Frank Borman , Apollo 11 astronauts Buzz Aldrin and Michael Collins , Michael DeBakey , Star Trek creator Gene Roddenberry and actress Nichelle Nichols . Toward

1300-476: The National Space Institute will be that of a catalyst between the space techonologist and the user. It will attempt to bring to the attention of people the new opportunities offered by advances made in space experiments and space techniques. It will study the feasibility of the application, and the potential uses of space technology as it relates to other human activities." Initial members serving on

1352-554: The November/December 1994 issue of Ad Astra , the magazine of the NSS. Tether propulsion Space tethers are long cables which can be used for propulsion, momentum exchange, stabilization and attitude control , or maintaining the relative positions of the components of a large dispersed satellite/ spacecraft sensor system. Depending on the mission objectives and altitude, spaceflight using this form of spacecraft propulsion

1404-614: The SPS/space colony concept had merit, it foundered on short political and economic horizons and the fact that the transport cost to space was about 300 times too high for individuals to fund when compared to the Plymouth Rock and Mormon colonies . In 1986, the L5 Society, which had grown to about 10,000 members, merged with the 25,000 member National Space Institute , to form the present-day National Space Society . The National Space Institute had been founded in 1972 by Wernher von Braun ,

1456-589: The conference and O'Neill's mailing list. The first newsletter included a letter of support from Morris Udall (then a contender for US president) and said "our clearly stated long range goal will be to disband the Society in a mass meeting at L 5 ." The peak of L5's influence was the defeat of the Moon Treaty in the U.S. Senate in 1980 ("... L-5 took on the biggest political fight of its short life, and won"). Specifically, L5 Society activists campaigned for awareness of

1508-568: The end of 1975, von Braun commented on the state of the general public's interest in the space program. "I'm fully aware that public interest is a very fickle thing. One day, the word is 'Moon or bust,' and the next day it is 'let's clean up the rivers.' People get so much information today that the priorities in [their] minds swing back and forth. The Apollo flights to the Moon were demonstrations of immense capabilities and potential, but in some respect they may be compared with Lindbergh's flight across

1560-406: The feasibility of the idea and gave direction to the study of tethered systems, especially tethered satellites. In 1990, Eagle Sarmont proposed a non-rotating Orbiting Skyhook for an Earth-to-orbit / orbit-to-escape-velocity Space Transportation System in a paper titled "An Orbiting Skyhook: Affordable Access to Space". In this concept a suborbital launch vehicle would fly to the bottom end of

1612-619: The former German rocket engineer of the WW II Nazi V-2 rocket/ballistic missile program , and of NASA 's Marshall Space Flight Center and Project Apollo program manager. While the L5 Society failed to achieve the goal of human settlements in space, it served as a focal point for many of the people who later became known in fields such as nanotechnology , memetics , extropianism , cryonics , transhumanism , artificial intelligence , and tether propulsion , such as K. Eric Drexler , Robert Forward , and Hans Moravec . The L5 News

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1664-404: The fruits of the trees we have planted. I think the silliest part of the dacay of the public interest in space is that ... we planted the orchard, and we nourished it and fertilized it and watered it and gave it all our tender loving care. And now, the time comes when the fruits can be picked – and they don't want to play the fruit pickers! That is where I think the young generation can make

1716-511: The greatest contribution – pick the fruits." After some years of publishing a newsletter that became known as I NSI ght , the Institute entered into an arrangement with the publishers of Omni magazine whereby all members except life members would receive that magazine as part of their membership. Omni editor Ben Bova joined the NSI board, then became vice president and finally succeeded Downs as president. He continued as president after

1768-421: The historical record to the contrary is clear. Following the merger, Wilson was succeeded by his assistant, Lori Garver . The merged organization has continued to use the NSS name and logo after a joint membership vote was taken in 1987 to determine whether or not to change it to the "Space Frontier Society." A more complete history of the National Space Institute is contained in a series of articles published in

1820-409: The improved versions listed here, but these are currently tracked on radar and have predictable orbits. Although thrusters could be used to change the orbit of the system, a tether could also be temporally wiggled in the right place, using less energy, to dodge known pieces of junk. Radiation, including UV radiation tend to degrade tether materials, and reduce lifespan. Tethers that repeatedly traverse

1872-468: The last [Apollo] Moon mission, Wernher von Braun recognized that something had to be done to keep the importance of ongoing space activity before the public mind. The sort of organization that could do such a job would need to be independent enough to view critically all aspects of NASA policy and implementation." At the first annual meeting of the organization, in July 1975, von Braun said: "The main role of

1924-413: The lower mass. The system must move at a single speed, so the tether must therefore slow down the lower mass and speed up the upper one. The centrifugal force of the tethered upper body is increased, while that of the lower-altitude body is reduced. This results in the centrifugal force of the upper body and the gravitational force of the lower body being dominant. This difference in forces naturally aligns

1976-646: The more efficient and lighter the tether can be in relation to the payloads that they can carry. Eventually however, the mass of the tether propulsion system will be limited at the low end by other factors such as momentum storage. Proposed materials include Kevlar , ultra-high-molecular-weight polyethylene , carbon nanotubes and M5 fiber . M5 is a synthetic fiber that is lighter than Kevlar or Spectra. According to Pearson, Levin, Oldson, and Wykes in their article "The Lunar Space Elevator", an M5 ribbon 30 mm (1.2 in) wide and 0.023 mm (0.91 mils) thick, would be able to support 2,000 kg (4,400 lb) on

2028-414: The ocean. I think space is now entering a maturing period where it will be less gee-whiz, less sensational, but it will become more a part of everyday life -- just like the airlines. ... There were great men long before the first big rockets were built. And we are just building on their legacy. We want to make sure that this legacy can now be passed on to the next generation, the people who will really pick

2080-420: The point. O'Neill's first published paper on the subject, "The Colonization of Space", appeared in the magazine Physics Today in September 1974. A number of people who later became leaders of the L5 Society got their first exposure to the idea from this article. Among these were a couple from Tucson, Arizona, Carolyn Meinel and Keith Henson . The Hensons corresponded with O'Neill and were invited to present

2132-469: The provisions against any form of sovereignty or private property in outer space that would make space colonization impossible and the provisions against any alteration of the environment of any celestial body prohibiting terraforming . Leigh Ratiner [a Washington lawyer/lobbyist] "played the key role in the lobbying effort, although he had energetic help from L-5 activists, notably Eric Drexler and Christine Peterson ." Although economic analysis indicated

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2184-408: The right where two spacecraft at two different altitudes have been connected by a tether. Normally, each spacecraft would have a balance of gravitational (e.g. F g1 ) and centrifugal (e.g. F c1 ) forces, but when tied together by a tether, these values begin to change with respect to one another. This phenomenon occurs because, without the tether, the higher-altitude mass would travel slower than

2236-621: The rotating tether to lose energy, and thus lose velocity and altitude. However, using electrodynamic tether thrusting, or ion propulsion the system can then re-boost itself with little or no expenditure of consumable reaction mass. A skyhook is a theoretical class of orbiting tether propulsion intended to lift payloads to high altitudes and speeds. Proposals for skyhooks include designs that employ tethers spinning at hypersonic speed for catching high speed payloads or high altitude aircraft and placing them in orbit. Electrodynamic tethers are long conducting wires, such as one deployed from

2288-509: The system along the local vertical, as seen in the figure. Objects in low Earth orbit are subjected to noticeable erosion from atomic oxygen due to the high orbital speed with which the molecules strike as well as their high reactivity. This could quickly erode a tether. Simple single-strand tethers are susceptible to micrometeoroids and space junk . Several systems have since been proposed and tested to improve debris resistance: Large pieces of junk would still cut most tethers, including

2340-493: The tensile force on the tether is projected to be less than 65 newtons (15 lbf). Material selection in this case depends on the purpose of the mission and design constraints. Electrodynamic tethers, such as the one used on TSS-1R, may use thin copper wires for high conductivity (see EDT ). There are design equations for certain applications that may be used to aid designers in identifying typical quantities that drive material selection. Space elevator equations typically use

2392-415: The total load at each point along the length of the cable. In practice this means that the central tether structure needs to be thicker than the tips. Correct tapering ensures that the tensile stress at every point in the cable is exactly the same. For very demanding applications, such as an Earth space elevator, the tapering can reduce the excessive ratios of cable weight to payload weight. In lieu of tapering

2444-403: The value used is the material's 'characteristic velocity' which is the maximum tip velocity a rotating untapered cable can attain without breaking, The characteristic velocity equals the specific velocity multiplied by the square root of two. These values are used in equations similar to the rocket equation and are analogous to specific impulse or exhaust velocity. The higher these values are,

2496-589: Was a space advocacy group, the first of its kind, established by Wernher von Braun to help maintain the public's support for the United States space program . It has since merged, in 1987, with the L5 Society founded by fans of the Space Colonization and Industrialization work of Gerard K. O'Neill , to become the present-day National Space Society . In its earliest stages of formation in June 1974, NSI

2548-465: Was first known as the "National Space Association", but was renamed from "Association" to "Institute" in April 1975. Von Braun was the NSI's first president, but shortly became chairman, with journalist and former ABC-TV 20/20 host Hugh Downs as president. Charles C. Hewitt was the first executive director. Downs later recalled the beginning of the organization: "Long before the launch of Apollo 17,

2600-433: Was found to be possible with materials then existing. In 1977, Hans Moravec and later Robert L. Forward investigated the physics of non-synchronous skyhooks , also known as rotating skyhooks, and performed detailed simulations of tapered rotating tethers that could pick objects off, and place objects onto, the Moon , Mars and other planets , with little loss, or even a net gain of energy. In 1979, NASA examined

2652-400: Was the newsletter of the L5 Society reporting on space habitat development and related space issues. The L5 News was published from September 1975 until April 1987, when the merger with the National Space Institute was completed and the newly formed National Space Society began publication of its own magazine, Ad Astra . National Space Institute The National Space Institute

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2704-404: Was then led until 1984 by executive director Mark R. Chartrand, followed by Glen P. Wilson . Under Bova and Wilson, the arrangements for merger with the L5 Society were concluded, and the name change to National Space Society was announced in advance of the merger, with vague explanations to the members. Since the merger, it has been claimed that the name change took place upon the merger, but

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