Lunar space elevator
Encyclopedia
It is similar in concept to the better known Earth space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
idea (a cable suspended above Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, with its center of gravity
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
slightly above geostationary orbit
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
). It would instead be constructed with its center of gravity in a stationary position above the surface of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
, providing a controlled means to transport people and/or materials between the surface and lunar orbit.
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 cable would possess a microgravity point, these and other drives can reach the cable from low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
(LEO) with very minimal launched fuel from Earth. With conventional rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
s, the fuel needed to reach the lunar surface from LEO is many times the landed mass, thus the elevator can slash launch costs for payloads bound for the lunar surface by a similar factor.
Location
There are two lunar-synchronous points where an elevator could be placed that would be stable: the libration points and . on the Earth side of the Moon is 56,000 km up from the surface, and on the far side is 67,000 km up. In these positions, the forces of gravity and centrifugal forceCentrifugal force
Centrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
are equal, and as long as the system remained balanced ( and are in unstable equilibrium along the line between Earth and Moon), it would remain stationary.
Both of these positions are substantially farther up than the 36,000 km 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. To suspend a kilogram of cable or payload just above the surface of the Moon would require 1,000 kg of counterweight, 26,000 km beyond . (A smaller counterweight on a longer cable, e.g., 100 kg at a distance of 230,000 km — more than halfway to Earth — would have the same balancing effect.) Without the Earth's gravity to attract it, an cable's lowest kilogram would require 1,000 kg of counterweight at a distance of 120,000 km from the Moon.
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
Peak of Eternal Light
Peak of Eternal Light describes a point on a body within the Solar System which is eternally bathed in sunlight. This is due to both the bodies' rotation and the point's altitude...
could take advantage of 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 nanotubeCarbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
s). Whereas, a lunar elevator could be constructed using high-strength commercially available materials such as Kevlar
Kevlar
Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...
or Spectra.
Compared to Earth, 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.
Jerome Pearson
Jerome Pearson
Jerome Pearson is an American engineer and space scientist best known for his work on space elevators and lunar space elevator. He is president of STAR, Inc., and has developed aircraft and spacecraft technology for the United States Air Force, DARPA, and NASA...
has proposed a cable design using M5 fiber (See Materials, below) that would have a mass of 6,100 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s including a massive counterweight, that would be capable of lifting or depositing loads of 2,000 newtons (450 lbf, or at lunar surface gravity, masses of 1233 kg / 2700 lbm) at the base. The counterweight could potentially be lifted from the lunar surface.
History
The idea of space elevators has been around since 1960 when Yuri ArtsutanovYuri Artsutanov
Yuri N. Artsutanov is a Russian engineer born in Leningrad. A graduate of Leningrad Technological Institute, he is best known for being one of the pioneers of the idea of space elevator.In 1960 he wrote an article "V Kosmos na Electrovoze Yuri N. Artsutanov (born 1929) is a Russian engineer born...
wrote a Sunday supplement to Pravda
Pravda
Pravda was a leading newspaper of the Soviet Union and an official organ of the Central Committee of the Communist Party between 1912 and 1991....
on how to build such a structure and the utility of geosynchronous orbit. His article however, was not known in the West. Then in 1966, John Isaacs
John Isaacs
John Isaacs was an early African-American professional basketball player. Born in Panama but raised in New York City, he was a member of the New York Renaissance, the Washington Bears, and various other teams....
, a leader of a group of American Oceanographers at Scripps Institute
Scripps Institution of Oceanography
Scripps Institution of Oceanography in La Jolla, California, is one of the oldest and largest centers for ocean and earth science research, graduate training, and public service in the world...
, published an article in Science
Science (magazine)
Science was a general science magazine published by the American Association for the Advancement of Science . It was intended to "bridge the distance between science and citizen", aimed at a technically literate audience who may not work professionally in the sciences...
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
Micrometeoroid
A micrometeoroid is a tiny meteoroid; a small particle of rock in space, usually weighing less than a gram. A micrometeor or micrometeorite is such a particle that enters the Earth's atmosphere or falls to Earth.-Scientific interest:...
damage). Like Artsutanov, Isaacs’ article also wasn’t well known to the aerospace community.
In 1972, James Cline submitted a paper to NASA describing a lunar elevator concept . NASA responded negatively to the idea citing technical risk and lack of funds.
In 1975, Jerome Pearson
Jerome Pearson
Jerome Pearson is an American engineer and space scientist best known for his work on space elevators and lunar space elevator. He is president of STAR, Inc., and has developed aircraft and spacecraft technology for the United States Air Force, DARPA, and NASA...
independently came up with the Space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
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
Arthur C. Clarke
Sir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,...
to write the novel The Fountains of Paradise
The Fountains of Paradise
The Fountains of Paradise is a Hugo and Nebula Award–winning 1979 novel by Arthur C. Clarke. Set in the 22nd century, it describes the construction of a space elevator. This "orbital tower" is a giant structure rising from the ground and linking with a satellite in geostationary orbit at the...
. Later, Pearson extended his theory to the moon and changed to using the Lagrangian points instead of having it in geostationary orbit.
In October 2011 on the the LiftPort website Laine announced that LiftPort is pursuing a Lunar space elevator
Lunar space elevator
A lunar space elevator is a proposed cable running from the surface of the Moon into space.It is similar in concept to the better known Earth space elevator idea...
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 Michael Laine.
Materials
Unlike earth-anchored space elevators, the materials for lunar space elevators won’t require a lot of strength. Lunar elevators can be made with materials available today. Carbon nanotubes aren’t required to build the structure. This would make it possible to build the elevator much sooner, since available carbon nanotube materials in sufficient quantities are still years away.One material that has great potential is M5 fiber
M5 fiber
M5 fiber is a high-strength synthetic fiber first developed by Dr. Doetze Sikkema and his team at the Dutch chemical firm Akzo Nobel...
. This 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 wide and 0.023 mm thick, would be able to support 2000 kg on the lunar surface (2005). It would also be able to hold 100 cargo vehicles, each with a mass of 580 kg, evenly spaced along the length of the elevator. Other materials that could be used are T1000G carbon fiber, Spectra 200, or Zylon. All of these materials have breaking lengths of several hundred kilometers under 1g.
| Material | Density ρ kg/m3 |
Stress Limit σ GPa |
Breaking height (h = σ/ρg, km) |
|---|---|---|---|
| Single-wall carbon nanotubes (laboratory measurements) | 2266 | 50 | 2200 |
| Toray Carbon fiber (T1000G) | 1810 | 6.4 | 361 |
| Aramid, Ltd. polybenzoxazole fiber (Zylon PBO) | 1560 | 5.8 | 379 |
| Honeywell extended chain polyethylene fiber (Spectra 2000) | 970 | 3.0 | 316 |
| Magellan honeycomb polymer M5 (with planned values) | 1700 | 5.7(9.5) | 342(570) |
| DuPont Aramid fiber (Kevlar 49) | 1440 | 3.6 | 255 |
| Glass fibre (Ref Specific strength Specific strength The specific strength is a material's strength divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity is the usual measure of specific strength... ) |
2600 | 3.4 | 133 |
The materials will be used to build the ribbons which will connect from the and balance points to the surface of the moon. The ribbons would be used by the robotic climbing vehicle to get from the surface into orbit. The vehicles would be slow, compared to chemical rockets, but it is a good speed for transferring cargo.
The ribbons are going to be prone to damage by micrometeoroids from space so one way to improve their survivability is to make a multi-ribbon system instead of one. They will have interconnections at regular intervals, so that if one section is damaged, the parallel sections would carry the load until robotic vehicles can come and replace the missing ribbon. The interconnections would be spaced about 100 km apart, which is small enough to allow a robotic climber to carry the mass of the replacement 100 km of ribbon.
Climbing vehicles
One method of getting materials needed from the moon into orbit would be the use of robotic climbing vehicles. These vehicles would consist of two large wheels pressing against the ribbons of the elevator to provide enough friction for lift. 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 . The power that a climber would require to traverse the ribbon drops in proportion to proximity to the point. If a 540 kg climber traveled at a velocity of fifteen meters per second, by the time it was seven percent of the way to the 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. 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.
Possible uses
Materials from Earth may be sent into orbit and then down to the Moon to be used by lunar bases and installations.Former U.S. President George W. Bush
George W. Bush
George Walker Bush is an American politician who served as the 43rd President of the United States, from 2001 to 2009. Before that, he was the 46th Governor of Texas, having served from 1995 to 2000....
, addressing his Vision for Space Exploration
Vision for Space Exploration
The Vision for Space Exploration is the United States space policy which was announced on January 14, 2004 by President George W. Bush. It is seen as a response to the Space Shuttle Columbia disaster, the state of human spaceflight at NASA, and a way to regain public enthusiasm for space...
, noted that the Moon may serve as a cost-effective construction, launching and fueling site for future space exploration missions
Space exploration
Space exploration is the use of space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft....
. As President Bush
George W. Bush
George Walker Bush is an American politician who served as the 43rd President of the United States, from 2001 to 2009. Before that, he was the 46th Governor of Texas, having served from 1995 to 2000....
announced, "Its soil contains raw materials that might be harvested and processed into rocket fuel or breathable air." For example, future Ares V
Ares V
The Ares V was the planned cargo launch component of the Constellation program, which was to have replaced the Space Shuttle after its retirement in 2011. Ares V was also planned to carry supplies for a human presence on Mars...
missions could cost-effectively deliver raw material
Raw material
A raw material or feedstock is the basic material from which a product is manufactured or made, frequently used with an extended meaning. For example, the term is used to denote material that came from nature and is in an unprocessed or minimally processed state. Latex, iron ore, logs, and crude...
s from Earth for future spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
and missions
Space exploration
Space exploration is the use of space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft....
to a Moon-based space dock positioned as a counterweight
Counterweight
A counterweight is an equivalent counterbalancing weight that balances a load.-Uses:A counterweight is often used in traction lifts , cranes and funfair rides...
to a lunar space elevator, while fuel and breathable air could be shipped up from the Moon's surface to the same Moon-based dock along the same lunar space elevator. As well, the total energy needed for transit between the Moon and Mars is actually much less than between the Moon and Earth, so lunar base activity could make a large impact on building a Mars base. Since millions of tonnes of water ice have been found on the moon's poles, there is a much more accessible form of water than the regolith. The proximity of the polar base on the lunar space elevator to the water ice could make mining the ice far more efficient.
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, there are plenty of resources on the moon that would be easier to gather and send into Earth orbit rather than launch from Earth. He claims that one such material which would be very valuable is lunar regolith
Regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...
, also known as moon dirt. One particular use for the regolith would be for massive material to shield space stations or crewed deep space missions against solar flare
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...
s, Van Allen trapped or cosmic radiation. Other materials such as metals and minerals could be mined and sent up for construction. Silicon for solar cells, as would be needed for the construction of massive satellite solar power stations, seems particularly promising.
One disadvantage of the lunar elevator is that it may not be able to carry human passengers. The rate at which cargo is transferred would be too slow, normally taking weeks to reach its destination. Humans would be able to get there faster by using rockets to and from the moon.
External links
- An introductory review of the whole gamut of skyhookSkyhookSkyhook or sky hook may refer to:- Technology :* Skyhook , explanation of design complexity in the universe that does not build on lower, simpler layers* Skyhook , "hook" used to lift an object on a long cable hanging from the sky...
contraptions by Arthur C. ClarkeArthur C. ClarkeSir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,... - Universe Today article on a Lunar space elevator
- Jerome Pearson's company website on Space Elevators
- Elevator Proposal by Jerome Pearson
- Simulations of lunar space elevators in samples 95 and 96 of spacetethers.com simulator