Space elevator

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A space elevator is a proposed type of planet-to-space transport system. Its main component is a cable (also called a tether) that is mounted to the surface and extends into space. This design will allow the vehicle to travel along wires from the planet's surface, such as Earth, directly into space or orbit, without the use of large rockets. An Earth-based space elevator will consist of a cable with one end attached to the surface near the equator and the other end in space outside the geostationary orbit (altitude 35.786 km). The competing force of gravity, which is stronger at the lower end, and a stronger upward/upward centrifugal force at the upper end, results in a retained, under pressure, and stationary cable above a position on Earth.. With the landing deployed, climbers can repeatedly climb the moorings into space in a mechanical way, releasing their charge into orbit. Climbers can also lower the moorings to restore the charge to the surface of the orbit.

The concept of a tower that reached geosynchronous orbit was first published in 1895 by Konstantin Tsiolkovsky. The proposal is for free-standing towers that reach from the Earth's surface to the top of a geostationary orbit. Like all buildings, the structure of Tsiolkovsky will be under pressure, supporting its weight from below. Since 1959, most of the ideas for space elevators have focused on fully tensile structures, with system weights held from the top by centrifugal force. In drag concepts, the mooring of space reaches from a large mass (counterweight) outside the geostationary orbit to the ground. This structure is held in the tension between the Earth and the balancing like a perpendicular bob.

To build space elevators on Earth, the cable material must be stronger and lighter (has greater specific strength) than the material is known. The development of new materials that meet the urgent specific strength requirements must occur before design can evolve beyond the discussion stage. Carbon nanotubes (CNTs) have been identified as being able to meet specific power requirements for an Earth space elevator. Other materials are considered to have boron nitride nanotubes, and diamond nanothreads, which were first built in 2014.

This concept applies to other planets and celestial bodies. For locations in the solar system with weaker gravity than Earth (like Moon or Mars), the strength-to-density requirements for tethering materials are not problematic. Currently available material (such as Kevlar) is strong enough and light enough that it can be used as anchoring material for elevators there.

Video Space elevator

Histori

Konsep awal

The key concept of the space elevator appeared in 1895 when Russian scientist Konstantin Tsiolkovsky was inspired by the Eiffel Tower in Paris. He considers a similar tower that reaches all the way into space and is built from the ground to a height of 35,786 kilometers, the height of a geostationary orbit. He noted that such a spire would surround the Earth as in geostationary orbit. The objects will reach horizontal speed as they climb the tower, and the objects released above the tower will have sufficient horizontal velocity to remain in geostationary orbit. The conceptual tower of Tsiolkovsky is a compression structure, whereas the modern concept requires a pull structure (or "tethering").

20th century

Building a compression structure from bottom to top proved to be an unrealistic task because no material existed with sufficient compressive strength to support its own weight in such conditions. In 1959, another Russian scientist, Yuri N. Artsutanov, proposed a more feasible proposal. Artsutanov suggests using geostationary satellites as a basis for deploying structures down. By using a counterweight, the wires will be lowered from geostationary orbit to the Earth's surface, while the balancer is extended from satellites away from Earth, keeping wires constantly above the same spot on the Earth's surface. The idea of ​​Artsutanov was introduced to the Russian-speaking public in an interview published in Sunday's Komsomolskaya Pravda supplement in 1960, but it was not available in English until much later. He also proposed a reduction in the thickness of the cable so that the voltage across the cable was constant. This gives the thinner cable at the thickest ground level at the geostationary orbit level.

Both tower and cable ideas were proposed in the quasi-humor column Ariadne in New Scientist , December 24, 1964.

In 1966, Isaacs, Vine, Bradner and Bachus, four American engineers, rediscovered the concept, named it "Sky-Hook," and published their analysis in Science. journals. They decided to decide what kind of material was needed to build the space elevator, assuming it was a straight wire with no variation on the transverse cross section, and found that the required power would be twice that of existing materials including graphite. , quartz, and diamonds.

In 1975, an American scientist, Jerome Pearson, rediscovered the concept again, publishing his analysis in the journal Acta Astronautica. He designed a cross section that was better suited for building elevators. Completed cables will be the thickest in geostationary orbit, where the tension is greatest, and will be the most narrow at the end to reduce the amount of weight per unit of cross-sectional area that each point of the cable must bear. He suggested using a counterweight that would slowly extend to 144,000 kilometers (89,000 miles), almost half the distance to the Moon when the bottom of the lift was built. Without a large counterweight, the top of the cable must be longer than the lower because the force of gravity and centrifugal change with distance from Earth. His analysis included disruptions such as Moon's gravity, wind and moving up and down wires. The weight of material needed to build an elevator will require thousands of Space Shuttle journeys, although parts of the material can be transported up the elevator when the minimum strand reaches the ground or is made in the space of an asteroid or lunar ore.

Following the development of carbon nanotubes in the 1990s, engineer David Smitherman of the NASA/Marshall Advanced Projects Office noticed that the high strength of this material could make the space elevator concept feasible, and set up a workshop at Marshall Space Flight Center, inviting many scientists and engineers to discuss concept and devise a plan for elevators to turn the concept into reality.

In 2000, another American scientist, Bradley C. Edwards, suggested making a 100,000 km (62,000 mile) thick paper ribbon using a carbon nanotube composite material. He chose a wide-band cross-section rather than a previously circular cross-section concept because the shape would have a greater chance of surviving the meteoroid impact. The ribbon sectional shape also provides a large surface area for climbers with simple rollers. Supported by the NASA Institute for Advanced Concepts, Edwards's work is expanded to include dispersion scenarios, climber designs, power delivery systems, orbital orbital debris, anchor systems, surviving atomic oxygen, avoiding lightning and hurricanes by placing anchors on the west equator. Pacific, construction costs, construction schedules, and environmental hazards.

21st century

To accelerate the development of elevator space, supporters have organized several competitions, similar to Ansari X Prize, for relevant technology. Among them are Elevators: 2010, which organizes annual competitions for climbers, ribbons, and power-beaming systems from 2005 to 2009, the Robogames Space Elevator Ribbon Climbing competition, as well as the NASA Challenge Hundred program, which, in March 2005, announced a partnership with the Spaceward Foundation (operator Elevator: 2010), increasing the total prize value to US $ 400,000. The first European Space Elevator Challenge (EuSEC) to build the climbing structure took place in August 2011.

In 2005, the LiftPort Group space elevator company announced that it will build a carbon nanotube manufacture plant in Millville, New Jersey, to supply a variety of glass, plastic and metal companies with strong materials.Although LiftPort hopes to eventually use carbon nanotubes in the construction of a 100,000km (62,000 mi) space elevator, this will enable it to make money in the short run and conduct research and development into new production methods. "Their stated goal is to launch space in 2010. On February 13, 2006, the Group LiftPort announced that, at the beginning of the same month, they had tested a mile of "elevator-room support" made of carbon fiber composite strings and fiberglass bands measuring 5 cm (2.0 inches) wide and 1 mm (about 13 sheets of paper ) thick, lifted with a balloon.

In 2007, Elevator: 2010 hosted the 2007 Space Lift game, which featured USD500,000 awards for each of the two competitions, (total USD1,000,000) as well as an additional USD4,000,000 to be awarded over the next five years for the elevator-related technology room. No team won the competition, but the MIT team entered the first 2 grams (0.07 oz), 100 percent of the carbon nanotubes entered into the competition. Japan held an international conference in November 2008 to devise a schedule for building elevators.

In 2008 the book Leaving the Planet by Space Elevator by Dr. Brad Edwards and Philip Ragan were published in Japanese and included in Japan's bestseller list. This led to Shuichi Ono, chairman of the Japan Space Association, launching a space-lift plan, putting what observers consider to be a very low cost estimate of one trillion yen (Â¥ 5 billion/$ 8 billion) to build it.

In 2012, Obayashi Corporation announces that in 38 years it can build elevator space using carbon nanotube technology. At 200 kilometers per hour, 30-passenger designer climber will be able to reach the GEO level after 7.5 days of travel. No cost estimates, financial plans, or other specifics are made. This, along with time and other factors, suggests that the announcement was made largely to provide publicity for the opening of one of the other company's projects in Tokyo.

In 2013, the International Academy of Astronautics publishes a technological feasibility assessment that concludes that the required critical capability improvement is a constraining material, which is projected to achieve the required strength-to-weight ratio in 20 years. The four-year study looked at many aspects of elevator space development including missions, development schedules, financial investments, income streams, and profits. It was reported that it is possible to operate operationally from smaller impacts and avoid greater impacts, with meteors and space debris, and that cost estimates lift a kilogram of payload to GEO and beyond will be $ 500.

In 2014, the Rapid Evaluation R & D team of Google X embarked on the Space Elevator design, eventually finding that no one has produced a perfectly formed carbon nanotube strand longer than a meter. Thus they decided to put the project in "deep freezing" and also oversee any progress in the carbon nanotube field.

Maps Space elevator

In fiction

In 1979, space elevators were introduced to a wider audience with the simultaneous publication of the novel Arthur C. Clarke, The Fountains of Paradise , in which engineers built the space elevator at the top of a mountain peak in the fictional island nation Taprobane (loosely based on Sri Lanka, though moved south to the Equator), and Charles Sheffield's first novel, The Web Between the Worlds , also features a space elevator building. Three years later, in the 1982 Robert A. Heinlein novel Friday the main character used "Nairobi Nut Tree" on his way. In the 1993 novel Kim Stanley Robinson Red Mars, the colonists built a space elevator on Mars that made it possible for more colonies to arrive as well as the natural resources mined there to get to Earth. In David Gerrold's 2000 novel, Jumping Off The Planet, the family outing on Ecuador's "bean" tree is actually a kidnapping of children. Gerrold's book also examines some of the applications of the mature elevator technology industry. In the biology version, Joan Slonczewski's 2011 novel The Highest Frontier describes a student riding a space elevator built from a self-healing cord from an anthrax bacillus. Engineered bacteria can regenerate wires when disconnected by space remains.

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Physics

A clear gravity field

A space elevator cable spins along with the Earth's rotation. Therefore, the objects attached to the cable will experience an upward centrifugal force in the opposite direction with the downward force of gravity. The higher the object wire is, the less the Earth's gravitational pull, and the stronger the centrifugal force upward because of the rotation, so that the centrifugal force favors the less gravity. Centrifugal force and gravity are balanced in geosynchronous equatorial orbit (GEO). Above GEO, the centrifugal force is stronger than gravity, causing objects to stick to the cable there to pull up above it.

The total force for the object attached to the cable is called the visible gravitational field . The clear gravitational field for attached objects is gravity (down) minus centrifugal force (upward). The obvious gravity experienced by the object on the cable is zero in GEO, down below GEO, and up above GEO.

Medan gravitasi yang tampak dapat direpresentasikan dengan cara ini:

Gaya ke bawah gravitasi aktual menurun dengan tinggi: ${\ displaystyle g_ {r} = - GM/r ^ {2}}  ÂÂ$

Gaya sentrifugal ke atas karena rotasi planet meningkat dengan tinggi: ${\ displaystyle a = \ omega ^ {2} r}  ÂÂ$

Bersama-sama, medan gravitasi tampak adalah penjumlahan dari keduanya:

${\ displaystyle g = - {\ frac {GM} {r ^ {2}}} \ omega ^ {2} r}  ÂÂ$

Where

g is a clear, or downward (negative) gravity acceleration (positive) along the vertical cable (ms ^-2 ),

g _r is the acceleration of gravity due to the pull of the Earth, downward (negative) (ms ^-2 ),

a is a centrifugal acceleration, pointing upward (positive) along the vertical cable (m s ^-2 ),

G is the gravity constant (m ³ s ^-2 kg ^-1 )

M is the mass of the Earth (kg)

r is the distance from that point to the center of Earth (m),

? is the rotational speed of the Earth (radians/s).

At some point the cable, the two terms (gravity down and centrifugal force upward) are the same and opposite. The objects that are attached to the cable at that point do not put a load on the wires. This height (r ₁ ) depends on the mass of the planet and its rate of rotation. The actual gravity arrangement is equal to the centrifugal acceleration giving:

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{         r              Â 1                          =                           Â (                ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ...
                  G         Â Â¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ...                 ?                                      2     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,    ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                       Â )                                     Â 1     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ...      ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                                {\ displaystyle r_ {1} = \ left {{\ frac {GM} {\ omega ^ {2}}} \ right) ^ {\ frac { 1} {3}}}  Â}

On Earth, this distance is 35,786 km (22,236 mi) above the surface, the height of geostationary orbit.

In the cable below geostationary orbit, the downward gravity will be greater than the upward centrifugal force, so gravity will obviously attract objects that attach to the cable downward. Any object that is released from the cable below that level will initially accelerate downward along the length of the cable. Then gradually it will turn eastward from the cable. In the cable above the stationary orbital level, the upward centrifugal force will be greater than the downward gravity, so the visible gravity will draw objects attached to the cable up . Any object that is released from the cable above the geosynchronous level will initially speed up up along the cable. Then gradually it will veer west of the cable.

Cable section

Historically, a major technical problem has been considered the ability of the cable to withstand, with tension, the weight itself below a certain point. The greatest strain on the space lift cable is at the geostationary orbit point, 35,786 km (22,236 mi) above the Earth's equator. This means that the cable material, combined with the design, must be strong enough to withstand its own weight from the surface of up to 35,786 km (22,236 mi). Thicker wires at cross sections at that height than on the surface can be better to hold their own weight longer. How the cross-sectional area slopes from the maximum at 35,786 km (22,236 mi) to the minimum on the surface because it is an important design factor for elevator space cables.

To maximize the excess strength that can be used for a certain number of cable materials, the cross-sectional area of ​​the cable needs to be designed to a large extent such that the voltage (ie, the voltage per unit cross-sectional area) is constant throughout the length of the cable. The constant voltage criterion is the starting point in the cable cross-section design as it changes with altitude. Other factors considered in the more detailed design include thickening at the higher altitude places space space is present, the point pressure considerations imposed by climbers, and the use of varying materials. To account for these and other factors, a detailed modern cross-sectional design seeks to achieve the greatest possible safety margin possible, with slight variation over altitude and time. In the design of a simple starting point, which is equivalent to constant stress.

Dalam kasus tegangan konstan, penampang melintang mengikuti persamaan diferensial ini:

${\ displaystyle \ sigma dS = g \ rho Sdr}  ÂÂ$

atau

${\ displaystyle {\ frac {dS} {S}} = {\ frac {g \ rho} {\ sigma}} dr}  ÂÂ$

atau

${\ displaystyle {\ frac {dS} {S}} = {\ frac {\ rho} {\ sigma}} \ kiri ({\ frac {GM} {r ^ {2}}} - \ omega ^ {2} r \ right) dr}  ÂÂ$

Where

g is accelerated along the radius (mÃ, Â · s ^-2 ),

S is the cable cross-section area at a point r, (m ² ) and dS variations (m ² as well),

? is the density of the material used for the cable (kgÃ, Â · m ^-3 ).

? is the stress that the cross-sectional area can generate without producing (NÃ, Â · m ^-2 = kgÃ, Â · m ^-1 Â · S ^{- 2} ), the elastic limit.

Nilai g diberikan oleh persamaan pertama, yang menghasilkan:

${\ displaystyle \ Delta \ left [\ ln (S) \ right] _ {r_ {0}} ^ {r_ {1}} = - {\ frac {\ rho } {\ sigma}} \ Delta \ kiri [{\ frac {GM} {r}} {\ frac {\ omega ^ {2} r ^ {2}} {2}} \ right] _ {r_ {0 }} ^ {r_ {1}}}  ÂÂ$ ,

variations taken between r ₀ (ground) and r ₁ (geostationary).

Di antara dua poin ini, kuantitas ini dapat dinyatakan sebagai:

${\ displaystyle \ Delta \ left [\ ln (S) \ right] = {\ frac {\ rho} {\ sigma}} g_ {0} r_ {0} \ kiri (1 {\ frac {x} {2}} - {\ frac {3} {2}} x ^ {\ frac {1} {3}} \ right),}  ÂÂ$

atau

${\ displaystyle S_ {1} = S_ {0}.e ^ {{\ frac {\ rho} {\ sigma}} g_ {0} r_ {0} \ kiri (1 {\ frac {x} {2}} - {\ frac {3} {2}} x ^ {\ frac {1} {3}} \ right)}}  ÂÂ$

di mana ${\ displaystyle x = \ omega ^ {2} r_ {0}/g_ {0} \ thicksim 0,0035}  ÂÂ$ adalah rasio antara gaya sentrifugal di khatulistiwa dan gaya gravitasi.

Bahan kabel

To compare materials, the special strength of the material for the space elevator can be expressed within the characteristic length or "free breaking length": the length of the unprotected cylindrical cable where it will broken under its own weight under constant gravity. For the given material, the length is ${\ textstyle L_ {c} = \ sigma/(\ rho g_ {0})}$ , where ${\ textstyle \ sigma}$ ${\ textstyle \ rho}$ and ${\ textstyle g_ {0}}$ as defined above.

Panjang pemutusan bebas yang dibutuhkan diberikan oleh persamaan

${\ displaystyle \ Delta \ left [\ ln (S) \ right] = {\ frac {r_ {0}} {L_ {0}}} \ kiri (1 {\ frac {x} {2}} - {\ frac {3} {2}} x ^ {\ frac {1} {3}} \ right)}  ÂÂ$ .

There are various elevator room designs. Almost every design includes base stations, cables, climbers, and balancers. The earth's rotation creates an upward centrifugal force on counterweight. Counterweight is retained by cable when cable is retained and strained by counterweight. The base station anchors the entire system to the surface of the Earth. Climbers go up and down cable with payload.

Base station

Modern concepts for base stations/anchors are usually mobile stations, large oceangoing vessels or other mobile platforms. The mobile base station will have advantages over the previous stationary concept (with ground-based anchors) by being able to maneuver to avoid strong winds, storms, and space debris. Oceanic anchor points are also common in international waters, simplifying and reducing the cost of using negotiating areas for base stations.

Stationary land-based platforms will have simpler and cheaper logistics access to the base. They will also have the advantage of being at an altitude, like on a mountain. In alternative concepts, the base station can be a tower, forming a space elevator comprising a compression tower near the surface, and a fastening structure at higher altitudes. Combining the compression structure with the voltage structure will reduce the load from the atmosphere at the end of the Earth tether, and reduce the distance to the Earth's gravitational field which needs to be extended cable, and thus reduce the critical power-to-density requirements for cable materials, all other design factors are considered equal.

Cable

A space elevator cable should carry its own weight as well as additional weight of climbers. The required cable strength will vary along its length. This is because at various points it should carry the weight of the cable below, or give the power down to maintain the wires and balancers above. The maximum tension on the space lift cable will be at geosynchronous altitude so that the cable should be thick there and taper carefully as it approaches Earth. Each potential cable design can be characterized by a taper factor - the ratio between cable radius at geosynchronous and Earth-level altitudes.

Cables need to be made from materials with a large tensile strength/density ratio. For example, the Edwards elevator room design assumes a cable material with a specific strength of at least 100,000 kN/(kg/m). This value considers all the weight of the space elevator. The non-stunned space elevator cables will require materials capable of maintaining a length of 4,960 km (3,080 mi) of own weight at sea level to achieve geostationary heights of 35,786 km (22,236 mi) without producing. Therefore, materials with very high strength and light are required.

By comparison, metals such as titanium, steel or aluminum alloys have a length of only 20-30 km. Modern fiber materials such as kevlar, fiberglass and carbon fiber/graphite have a termination length of 100-400 km. Nanoengineered materials such as carbon nanotubes and, recently discovered, graphene ribbons (perfectly two-dimensional carbon sheets) are expected to have a breaking length of 5000-6000 km at sea level, and are also capable of performing electrical power.

For space elevators on Earth, with relatively high gravity, the cable material must be stronger and lighter than the material currently available. For this reason, there is a focus on developing new materials that meet the urgent specific strength requirements. For high specific strengths, carbon has the advantage of being only the sixth element in the periodic table. Carbon has relatively few of the protons and neutrons that contribute most of the deadweight of any material. Most of the interatomic bonding forces of any element are only influenced by some of the outer electrons. For carbon, the bond strength and stability are high compared to the atomic mass. The challenge in using carbon nanotubes remains to extend the macroscopic size of the production of the material is still perfect on a microscopic scale (such as the microscopic defect that is most responsible for material weakness). In 2014, carbon nanotube technology allows tubes to grow up to a few tenths of a meter.

By 2014, nanothread diamonds were first synthesized. Because they have similar strength properties to carbon nanotubes, diamond nanothreads are quickly seen as a candidate cable material as well.

Climbers

A space elevator can not be an elevator in the general sense (with moving cables) because the need for wires becomes significantly wider in the center than at the end. While various designs using moving cables have been proposed, most cable designs call "elevators" to climb stationary cables.

Climbers cover a wide range of designs. In the design of elevators whose cables are planar bands, most propose to use roller pairs to hold the cable with friction.

Climbers need to be applied to optimum timings to minimize cable tension and oscillation and maximize throughput. Lighter climbers can be sent more often, with some riding at the same time. This will increase throughput, but will decrease the mass of each individual payload.

Horizontal velocity, that is, because of the orbital rotation, each part of the cable increases with altitude, proportional to the distance from the center of the Earth, achieves a low orbital velocity at a point about 66 percent of the height between the surface and the geostationary orbit, or an altitude of about 23,400 km. A payload released at this point would be a very eccentric elliptical orbit, remaining almost obscure from the atmospheric reentry, with periapsis at the same height as LEO and apoapsis at the release height. With the increased height of orbit release will become less eccentric as periapsis and apoapsis increase, becoming a circle at the geostationary level. When the load has reached the GEO, the horizontal speed is exactly the velocity of the circular orbit at that level, so if it is released it will stay close to that point on the cable. Payloads can also continue to climb further up the cable beyond GEO, allowing it to gain higher speeds when disposing of it. If released from 100,000 km, the charge will have sufficient speed to reach the asteroid belt.

As the load is raised to the space elevator, it will not only increase the height, but also the horizontal speed (angular momentum). Angular momentum is taken from Earth's rotation. When the climber rises, it initially moves slower than each part of the cable that gradually moves. This is Coriolis strength: climbers "drag" (westward) on the cable, as they climb, and slightly reduce the rotational speed of the Earth. The opposite process will occur for a declining load: the cable is tilted to the east, thus sl

Source of the article : Wikipedia