Diagram showing equatorial and polar Lunar space elevators running past L1. An L2 elevator would mirror this arrangement on the Lunar far side, and cargo dropped from its end would be flung outward into the solar system.
A lunar space elevator or lunar spacelift is a proposed transportation system for moving a mechanical climbing vehicle up and down a ribbon-shaped tethered cable that is set between the surface of the Moon "at the bottom" and a docking port suspended tens of thousands of kilometers above in space at the top.
It is similar in concept to the better known Earth-based space elevator idea, but since the Moon's surface gravity is much lower than the Earth's, the engineering requirements for constructing a lunar elevator system can be met using materials and technology already available. For a lunar elevator, the cable or tether extends considerably farther out from the lunar surface into space than one that would be used in an Earth-based system. However, the main function of a space elevator system is the same in either case; both allow for a reusable, controlled means of transporting payloads of cargo, or possibly people, between a base station at the bottom of a gravity well and a docking port in outer space.
A lunar elevator could significantly reduce the costs and improve reliability of soft-landing equipment on the lunar surface. For example, it would permit the use of mass-efficient (high specific impulse), low thrust drives such as ion drives which otherwise cannot land on the Moon. Since the docking port would be connected to the cable in a microgravity environment, these and other drives can reach the cable from low Earth orbit (LEO) with minimal launched fuel from Earth. With conventional rockets, the fuel needed to reach the lunar surface from LEO is many times the landed mass, thus the elevator can reduce launch costs for payloads bound for the lunar surface by a similar factor.
Location
There are two points in space where an elevator's docking port could maintain a stable, lunar-synchronous position: the Earth-Moon Lagrange pointsL1 and L2. The 0.055 eccentricity of the lunar orbit means that these points are not fixed relative to the lunar surface: the L1 is 56,315km +/- 3,183km away from the Earth-facing side of the Moon (at the lunar equator) and L2 is 62,851km +/- 3,539km from the center of the Moon's far side, in the opposite direction. At these points, the effect of the Moon's gravity and the effect of the centrifugal force resulting from the elevator system's synchronous, rigid body rotation cancel each other out. The Lagrangian points L1 and L2 are points of unstable gravitational equilibrium, meaning that small inertial adjustments will be needed to ensure any object positioned there can remain stationary relative to the lunar surface.
Both of these positions are substantially farther up than the 36,000km from Earth to geostationary orbit. Furthermore, the weight of the limb of the cable system extending down to the Moon would have to be balanced by the cable extending further up, and the Moon's slow rotation means the upper limb would have to be much longer than for an Earth-based system, or be topped by a much more massive counterweight. To suspend a kilogram of cable or payload just above the surface of the Moon would require 1,000kg of counterweight, 26,000km beyond L1. (A smaller counterweight on a longer cable, e.g., 100kg at a distance of 230,000km — more than halfway to Earth — would have the same balancing effect.) Without the Earth's gravity to attract it, an L2 cable's lowest kilogram would require 1,000kg of counterweight at a distance of 120,000km from the Moon. The average Earth-Moon distance is 384,400km.
The anchor point of a space elevator is normally considered to be at the equator. However, there are several possible cases to be made for locating a lunar base at one of the Moon's poles; a base on a peak of eternal light could take advantage of near-continuous solar power, for example, or small quantities of water and other volatiles may be trapped in permanently shaded crater bottoms. A space elevator could be anchored near a lunar pole, though not directly at it. A tramway could be used to bring the cable the rest of the way to the pole, with the Moon's low gravity allowing much taller support towers and wider spans between them than would be possible on Earth.
Fabrication
Because of the Moon's lower gravity and lack of atmosphere, a lunar elevator would have less stringent requirements for the tensile strength of the material making up its cable than an Earth-tethered cable. An Earth-based elevator would require high strength-to-weight materials that are theoretically possible, but not yet fabricated in practice (e.g., carbon nanotubes). A lunar elevator, however, could be constructed using commercially available mass-produced high-strength para-aramid fibres (such as Kevlar and M5) or ultra-high-molecular-weight polyethylene fibre.
Compared to an Earth space elevator, there would be fewer geographic and political restrictions on the location of the surface connection. The connection point of a lunar elevator would not necessarily have to be directly under its center of gravity, and could even be near the poles, where evidence suggests there might be frozen water in deep craters that never see sunlight; if so, this might be collected and converted into rocket fuel.
Cross-section profile
Space elevator designs for Earth typically have a taper of the tether that provides a uniform stress profile rather than a uniform cross-section. Because the strength requirement of a lunar space elevator is much lower than that of an Earth space elevator, a uniform cross-section is possible for the lunar space elevator. The study done for NASA's Institute of Advanced Concepts states "Current composites have characteristic heights of a few hundred kilometers, which would require taper ratios of about 6 for Mars, 4 for the Moon, and about 6000 for the Earth. The mass of the Moon is small enough that a uniform cross-section lunar space elevator could be constructed, without any taper at all."[1] A uniform cross-section could make it possible for a lunar space elevator to be built in a double-tether pulley configuration. This configuration would greatly simplify repairs of a space elevator compared to a tapered elevator configuration. However a pulley configuration would require a strut at the counterweight hundreds of kilometers long to separate the up-tether from the down-tether and keep them from tangling. A pulley configuration might also allow the system capacity to be gradually expanded by stitching new tether material on at the Lagrange point as the tether rotated.
History
The idea of space elevators has been around since 1960 when Yuri Artsutanov wrote a Sunday supplement to Pravda on how to build such a structure and the utility of geosynchronous orbit. His article however, was not known in the West.[citation needed] Then in 1966, John Isaacs, a leader of a group of American Oceanographers at Scripps Institute, published an article in Science about the concept of using thin wires hanging from a geostationary satellite. In that concept, the wires were to be thin (thin wires/tethers are now understood to be more susceptible to micrometeoroid damage). Like Artsutanov, Isaacs’ article also was not well known to the aerospace community.[citation needed]
In 1972, James Cline submitted a paper to NASA describing a "mooncable" concept similar to a lunar elevator.[2] NASA responded negatively to the idea citing technical risk and lack of funds.[3]
In 1975, Jerome Pearson independently came up with the Space elevator concept and published it in Acta Astronautica. That made the aerospace community at large aware of the space elevator for the first time. His article inspired Sir Arthur Clarke to write the novel The Fountains of Paradise (published in 1979, almost simultaneously with Charles Sheffield's novel on the same topic, The Web Between the Worlds). In 1978 Pearson extended his theory to the moon and changed to using the Lagrangian points instead of having it in geostationary orbit.[4]
In 1977, some papers of Soviet space pioneer Friedrich Zander were posthumously published, revealing that he conceived of a lunar space tower in 1910.[5]
In 2005 Jerome Pearson completed a study for NASA Institute of Advanced Concepts which showed the concept is technically feasible within the prevailing state of the art using existing commercially available materials.[6]
In October 2011 on the LiftPort website Michael Laine announced that LiftPort is pursuing a Lunar space elevator as an interim goal before attempting a terrestrial elevator. At the 2011 Annual Meeting of the Lunar Exploration Analysis Group (LEAG), LiftPort CTO Marshall Eubanks presented a paper on the prototype Lunar Elevator co-authored by Laine.[7] In August 2012, Liftport announced that the project could actually start near 2020.[8][9][10] In April 2019, LiftPort CEO Michael Laine reported no progress beyond the lunar elevator company's conceptualized design.[11]
Materials
Unlike earth-anchored space elevators, the materials for lunar space elevators will not require a lot of strength. Lunar elevators can be made with materials available today. Carbon nanotubes aren’t required to build the structure.[1] This would make it possible to build the elevator much sooner, since available carbon nanotube materials in sufficient quantities are still years away.[12]
One material that has great potential is M5 fiber. This is a synthetic fiber that is lighter than Kevlar or Spectra.[13] According to Pearson, Levin, Oldson, and Wykes in their article The Lunar Space Elevator, an M5 ribbon 30mm wide and 0.023mm thick, would be able to support 2000kg on the lunar surface (2005). It would also be able to hold 100 cargo vehicles, each with a mass of 580kg, evenly spaced along the length of the elevator.[1] Other materials that could be used are T1000G carbon fiber, Spectra 200, Dyneema (used on the YES2 spacecraft), or Zylon. All of these materials have breaking lengths of several hundred kilometers under 1g.[1]
The materials will be used to manufacture the ribbon-shaped, tethered cable which will connect from the L1 or L2 balance points to the surface of the moon. The climbing vehicles which will travel the length of these cables in a finished elevator system will not move very fast, thus simplifying some of the challenges of transferring cargo and maintaining structural integrity of the system. However, any small objects suspended in space for extended periods of time, like the tethered cables would be, are vulnerable to damage by micrometeoroids, so one possible method of improving their survivability would be to design a "multi-ribbon" system instead of just a single-tethered cable.[1] Such a system would have interconnections at regular intervals, so that if one section of ribbon is damaged, parallel sections could carry the load until robotic vehicles could arrive to replace the severed ribbon. The interconnections would be spaced about 100km apart, which is small enough to allow a robotic climber to carry the mass of the replacement 100km of ribbon.[1]
Climbing vehicles
One method of getting materials needed from the moon into orbit would be the use of robotic climbing vehicles.[1] These vehicles would consist of two large wheels pressing against the ribbons of the elevator to provide enough friction for lift.[1] The climbers could be set for horizontal or vertical ribbons.
The wheels would be driven by electric motors, which would obtain their power from solar energy or beamed energy. The power required to climb the ribbon would depend upon the lunar gravity field, which drops off the first few percent of the distance to L1.[1] The power that a climber would require to traverse the ribbon drops in proportion to proximity to the L1 point. If a 540kg climber traveled at a velocity of fifteen meters per second, by the time it was seven percent of the way to the L1 point, the required power would drop to less than a hundred watts, versus 10 kilowatts at the surface.
One problem with using a solar powered vehicle is the lack of sunlight during some parts of the trip. For half of every month, the solar arrays on the lower part of the ribbon would be in the shade.[1] One way to fix this problem would be to launch the vehicle at the base with a certain velocity then at the peak of the trajectory, attach it to the ribbon.[1]
Possible uses
Materials from Earth may be sent into orbit and then down to the Moon to be used by lunar bases and installations.[1]
Former U.S. PresidentGeorge W. Bush, in an address about his Vision for Space Exploration, suggested that the Moon may serve as a cost-effective construction, launching and fueling site for future space exploration missions. As President Bush noted,[14]"(Lunar) soil contains raw materials that might be harvested and processed into rocket fuel or breathable air." For example, the proposed Ares V heavy-lift rocket system could cost-effectively[15] deliver raw materials from Earth to a docking station, (connected to the lunar elevator as a counterweight,)[16] where future spacecraft could be built and launched, while extracted lunar resources could be shipped up from a base on the Moon's surface, near the elevator's anchoring point. If the elevator was connected somehow to a lunar base built near the Moon's north pole, then workers could also mine the water ice which is known to exist there, providing an ample source of readily accessible water for the crew at the elevator's docking station.[17] Also, since the total energy needed for transit between the Moon and Mars is considerably less than for between Earth and Mars, this concept could lower some of the engineering obstacles to sending humans to Mars.
The lunar elevator could also be used to transport supplies and materials from the surface of the moon into the Earth's orbit and vice versa. According to Jerome Pearson, many of the Moon's material resources can be extracted and sent into Earth orbit more easily than if they were launched from the Earth's surface.[1] For example, lunar regolith itself could be used as massive material to shield space stations or crewed spacecraft on long missions from solar flares, Van Allen radiation, and other kinds of cosmic radiation. The Moon's naturally occurring metals and minerals could be mined and used for construction. Lunar deposits of silicon, which could be used to build solar panels for massive satellite solar power stations, seem particularly promising.[1]
One disadvantage of the lunar elevator is that the speed of the climbing vehicles may be too slow to efficiently serve as a human transportation system. In contrast to an Earth-based elevator, the longer distance from the docking station to the lunar surface would mean that any "elevator car" would need to be able to sustain a crew for several days, even weeks, before it reached its destination.[12]
Interplanetary spaceflight or interplanetary travel is the crewed or uncrewed travel between stars and planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System. Uncrewed space probes have flown to all the observed planets in the Solar System as well as to dwarf planets Pluto and Ceres, and several asteroids. Orbiters and landers return more information than fly-by missions. Crewed flights have landed on the Moon and have been planned, from time to time, for Mars and Venus. While many scientists appreciate the knowledge value that uncrewed flights provide, the value of crewed missions is more controversial. Science fiction writers propose a number of benefits, including the mining of asteroids, access to solar power, and room for colonization in the event of an Earth catastrophe.
A space elevator is a proposed type of planet-to-space transportation system. The main component would be a cable anchored to the surface and extending into space. The design would permit vehicles to travel up the cable from a planetary surface, such as the Earth's, directly into orbit, without the use of large rockets. An Earth-based space elevator could not feasibly be simply a tall tower supported from below, due to the immense weight - instead it would consist of a cable with one end attached to the surface near the equator and the other end attached to a counterweight in space beyond geostationary orbit. The competing forces of gravity, which is stronger at the lower end, and the upward centrifugal force, which is stronger at the upper end, would result in the cable being held up, under tension, and stationary over a single position on Earth. With the tether deployed, climbers could repeatedly climb up and down the tether by mechanical means, releasing their cargo to and from orbit.
A space habitat is a more advanced form of living quarters than a space station or habitation module, in that it is intended as a permanent settlement or green habitat rather than as a simple way-station or other specialized facility. No space habitat has been constructed yet, but many design concepts, with varying degrees of realism, have come both from engineers and from science-fiction authors.
Gemini 11 was the ninth crewed spaceflight mission of NASA's Project Gemini, which flew from September 12 to 15, 1966. It was the 17th crewed American flight and the 25th spaceflight to that time. Astronauts Charles "Pete" Conrad Jr. and Richard F. Gordon Jr. performed the first direct-ascent rendezvous with an Agena Target Vehicle, docking with it 1 hour 34 minutes after launch; used the Agena rocket engine to achieve a record high-apogee Earth orbit; and created a small amount of artificial gravity by spinning the two spacecraft connected by a tether. Gordon also performed two extra-vehicular activities for a total of 2 hours 41 minutes.
A skyhook is a proposed momentum exchange tether that aims to reduce the cost of placing payloads into low Earth orbit. A heavy orbiting station is connected to a cable which extends down towards the upper atmosphere. Payloads, which are much lighter than the station, are hooked to the end of the cable as it passes, and are then flung into orbit by rotation of the cable around the center of mass. The station can then be reboosted to its original altitude by electromagnetic propulsion, rocket propulsion, or by deorbiting another object with the same kinetic energy as transferred to the payload.
The Vision for Space Exploration (VSE) was a plan for space exploration announced on January 14, 2004 by President George W. Bush. It was conceived as a response to the Space Shuttle Columbia disaster, the state of human spaceflight at NASA, and as a way to regain public enthusiasm for space exploration.
Yuri Nikolaevich Artsutanov was a Russian engineer born in Leningrad. He was one of the pioneers of the idea of a space elevator.
A momentum exchange tether is a kind of space tether that could theoretically be used as a launch system, or to change spacecraft orbits. Momentum exchange tethers create a controlled force on the end-masses of the system due to the pseudo-force known as centrifugal force. 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 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.
An orbital ring is a concept of an artificial ring placed around a body and set rotating at such a rate that the apparent centrifugal force is large enough to counteract the force of gravity. For the Earth, the required speed is on the order of 10 km/sec, compared to a typical low Earth orbit velocity of 8 km/sec. The structure is intended to be used as a space station or as a planetary vehicle for very high-speed transportation or space launch.
Lunar habitation is any human social and material structure and activity on the Moon making human habitation on the Moon. Therefore, it is more than the particular surface space habitats and more specific than the moonbases which can consist of any facility.
The X Prize Cup is a two-day air and space exposition which was the result of a partnership between the X Prize Foundation and the State of New Mexico that began in 2004 when the Ansari X-Prize was held. This led to plans to build the world's first true rocket festival. Three X-Prize Cups have been held: in 2005, 2006 and 2007. Each X Prize Cup hosts different events and demonstrations, such as rocket-powered bicycles, rocket jet packs; but particularly notable are the Lunar Lander Challenge and the Space Elevator Games. 85,000 visitors attended the 2007 X Prize Cup. Although there was no X Prize Cup in 2009, there was a Lunar Lander Challenge.
Space-based solar power is the concept of collecting solar power in outer space by solar power satellites (SPS) and distributing it to Earth. Its advantages include a higher collection of energy due to the lack of reflection and absorption by the atmosphere, the possibility of no night, and a better ability to orient to face the sun. Space-based solar power systems convert sunlight to some other form of energy which can be transmitted through the atmosphere to receivers on the Earth's surface. It is attractive to those seeking large-scale solutions to anthropogenic climate change or fossil fuel depletion.
Jerome Pearson was an American engineer and space scientist best known for his work on space elevators, including a lunar space elevator. He was president of STAR, Inc., and has developed aircraft and spacecraft technology for the United States Air Force, DARPA, and NASA. He held several patents and was the author of nearly 100 publications in aircraft, spacecraft, electrodynamic tethers, SETI, and global climate control.
Non-rocket spacelaunch refers to concepts for launch into space where much of the speed and altitude needed to achieve orbit is provided by a propulsion technique that is not subject to the limits of the rocket equation. A number of alternatives to rockets have been proposed. In some systems, such as a combination launch system, skyhook, rocket sled launch, rockoon, or air launch, a portion of the total delta-v may be provided, either directly or indirectly, by using rocket propulsion.
There are risks associated with never-done-before technologies like the construction and operation of a space elevator. A space elevator would present a navigational hazard, both to aircraft and spacecraft. Aircraft could be dealt with by means of simple air-traffic control restrictions. Impacts by space objects such as meteoroids, satellites and micrometeorites pose a more difficult problem for construction and operation of a space elevator.
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 is theorized to be significantly less expensive than spaceflight using rocket engines.
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A space elevator is a theoretical system using a super-strong ribbon going from the surface of the Earth to a point beyond Geosynchronous orbit. The center of gravity of the ribbon would be exactly in geosynchronous orbit, so that the ribbon would always stay above the anchor point. Vehicles would climb the ribbon powered by a beam of energy projected from the surface of the Earth. Building a space elevator requires materials and techniques that do not currently exist. A variety of Space Elevator competitions have been held in order to stimulate the development of such materials and techniques.
Hypothetical technology is technology that does not exist yet, but that could exist in the future. This article presents examples of technologies that have been hypothesized or proposed, but that have not been developed yet. Some examples of hypothetical technology are flying cars, jetpacks, teleportation or robot helpers.
Bi-sat Observations of the Lunar Atmosphere above Swirls (BOLAS) is a spacecraft mission concept that would orbit the Moon at very low altitude in order to study the lunar surface. The concept, currently under study by NASA, involves two small identical CubeSat satellites connected vertically above the lunar surface by a 25 km long tether. The mission goal would be to understand the hydrogen cycle on the Moon, dust weathering, and the formation of lunar swirls.
↑ Pearson, J., "Lunar space elevators for cislunar space development", NASA NIAC Phase I Final Technical Report, under NASA Grant #07605-003-034, 2 May 2005
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