Space elevator
A space elevator , also space elevator ( engl. Space Elevator ) is a hypothetical transporter in the outer space without a rocket engine along a tensioned guide cable between a base station at the equator, and a space station behind the geostationary orbit in 35,786 km altitude. The competing forces of gravity, which is stronger on earth, and centrifugal force , which is stronger at the top end, are intended to tension the rope and a self-propelled or externally driven lift to lift a payload or move it in both directions.
history
In 1895, the Eiffel Tower- inspired Russian space pioneer Konstantin Ziolkowski devised a 35,786 kilometer high tower into space.
In 1959, the Soviet scientist Yuri Arzutanov suggested lowering a rope from a geostationary satellite . The rope should be thickest at geostationary orbit and thinner towards the ends. It should be taut between the ground and a large counterweight behind the geostationary orbit. An interview was published in Russian in 1960 and his work on it was unknown abroad for a long time.
In 1966, American engineers calculated the tensile strength required for a rope of constant thickness and found that the materials known at the time were unsuitable.
In 1975, the American Jerome Pearson, like Arzutanow, proposed a lift with an uneven cable cross-section. The rope should be thickest at the site of construction in geostationary orbit and taper towards the ends. The transportation of materials required thousands of space flights on a space shuttle .
In 2000, David Smitherman of the US space agency NASA published a report based on the results of a conference held in 1999 at the Marshall Space Flight Center . He suggested using carbon nanotubes .
In 2004 a group of scientists led by Alan Windle at Cambridge University made a 100 meter long thread from carbon nanotubes. The ratio of tensile strength to weight was up to 100 times better than that of steel. Since carbon is oxidized in the atmosphere, the material must be coated.
At the end of June 2004, the leader of the space elevator project Bradley Edwards in Fairmont , West Virginia announced that a prototype could be ready in 15 years. NASA is supporting the research project through its Institute for Advanced Concepts (NIAC) with 500,000 US dollars . According to Edwards, a rope would behave like a hammer throw up to 100,000 kilometers and he suggested making it out of a composite material made of carbon nanotubes.
From 2005 to 2009, NASA and the Spaceward Foundation organized funded Elevator: 2010 competitions.
Transportation costs
It is estimated that traditional transportation costs could be reduced from $ 12,000 to $ 80,000 to $ 200 per kilogram.
To lift one kilogram of mass from the earth's equator to a height of 35,786 km above the earth's equator, 48,422 kJ (approx. 13 kWh) are required. If the rope is extended to a height of 143,780 km above the earth's equator, this energy can be recovered.
By decoupling from the space elevator at different heights, spacecraft can be brought onto numerous different flight paths and orbits without any further drive.
technology
Enormous technical demands are made on the lift, the rope and the base station. The NASA has announced contests with high prize money on this. A distinction is made between the following five problem areas, for which there are several possible solutions.
Material for the rope
Each segment of the rope must be able to hold at least the weight of the underlying rope segments plus the payload capacity. The higher the considered rope segment, the more rope segments it has to hold. An optimized rope therefore has a larger cross-section with increasing height, until this trend is reversed on geostationary orbit, since from there the resulting force of the rope segments acts away from the earth.
For a given specific tensile strength of a material, the minimum cross-section at the base station is determined solely by the payload capacity. The optimal further cross-sectional development is then also determined. The ratio of the largest cable cross-section to the smallest is called the taper ratio . You and the payload capacity ultimately determine the total mass of the rope.
Basically, a space elevator can be built with any material with an optimized rope cross-section by selecting the corresponding rapid increase in cross-section or by using a large taper ratio . The economy ultimately dictates the limit of the still meaningful values in this size.
A normal steel cable of constant cross-section would tear under its own weight from a length of four to five kilometers (material- specific tear length ), high-performance steel cables for cable cars, whose tear strength is comparable to Kevlar , would come to around 30 km. New materials, whose tear strength is far beyond that of Kevlar, are therefore a decisive factor for the future realization of this company. According to the research so far, there are three possible options:
- Carbon nanotubes seem to exceed the breaking length of Kevlar by a factor of five, but calculations by Nicola Pugno of the Polytechnic in Turin have shown that when carbon nanotubes are woven into longer ropes, the tensile strength of the rope decreases by around 70% compared to the tensile strength of individual nanotubes . The reason for this are inevitable crystal defects which, according to Pugnos' model, reduce the load-bearing capacity of the rope to about 30 gigapascals . According to calculations by NASA, however, a material with a load capacity of around 62 gigapascals would be necessary to withstand the forces that occur. In addition, no laboratory has yet succeeded in creating a coherent rope that is longer than 100 meters. The coating of the rope represents an additional cost and weight factor, because carbon nanotubes oxidize and erode in the atmosphere.
- Also very promising is the UHMW polyethylene fiber Dyneema , which, when hung vertically, reaches a tearing length of 400 km and thus exceeds all conventional materials many times over, and even spider silk by a factor of two. What speaks against the use of Dyneema, however, is that the melting point of Dyneema is between 144 ° C and 152 ° C, that the strength of Dyneema decreases significantly between 80 ° C and 100 ° C, and that Dyneema becomes brittle below −150 ° C, because all of these temperatures are common in space.
- A new, as yet little researched material is graphene . The modulus of elasticity of approx. 1020 GPa corresponds to that of normal graphite along the basal planes and is almost as large as that of diamond. Scientists at New York's Columbia University published further measurement results in 2008, in which they emphasized that graphene has the highest tear strength that has ever been determined. Its tensile strength of 1.25 × 10 5 N / mm 2 or 125 gigapascals is the highest that has ever been determined and around 125 times as high as that of steel . At 7874 kg / m³, steel has a density around 3.5 times higher than graphene with 2260 kg / m³, so that the tear length of graphene is around 436 times as great as that of steel. In a gravitational field of 9.81 m / s² assumed to be homogeneous, graphene would have a tear length of around 5655 km. In fact, however, the acceleration due to gravity becomes significantly lower with increasing altitude, which increases the tear length. A band of graphene with a constant cross-sectional area ( taper ratio = 1) would only be loaded to 87% of its tear strength at the height of the geostationary orbit of 35,786 km above the earth's equator (see the picture). At an even greater height, the tensile load would then decrease again. If the graphene rope were 143,780 km long with a constant cross-sectional area, then it would be in complete equilibrium with the gravitational acceleration of the earth and the centrifugal acceleration due to the rotation of the earth. At a height of 143,780 km above the Earth's equator, a net acceleration of 0.78 m / s² would act upwards, and a tangential velocity of 10,950 m / s would be present, which would favor the launch of space probes. Graphene and graphite have a melting point of around 3700 ° C. 76 cm wide, endless graphene ribbons are produced by applying a monoatomic layer of carbon to a foil made of inert carrier material, such as copper, by chemical vapor deposition (CVD), and then dissolving the carrier material. A protective coating is probably also necessary for graphene.
Erection of the rope
So far it is only conceivable to lower the rope from a geostationary satellite . The behavior of long ropes in space is the subject of current research. It is conceivable that initially only a minimally load-bearing rope is started, which is then gradually reinforced until the final payload thickness is reached.
Construction of the tower as a base station
The base station also has to withstand heavy loads, because according to NASA, up to 62 gigapascals can be loaded on the connection between the cable and the base station. This means that the base station needs to be anchored deeply, complexly and expensive in the ground. This is because the space elevator has to have an excess of centrifugal force in the vertical direction compared to the gravitational force in order to tension the rope, and because the space elevator in the horizontal direction transfers the Coriolis force of the loads going up or down to the earth. A space elevator that would be in complete equilibrium between centrifugal force and gravitational force would be disturbed in its stability by even minimal loads, and could therefore not transfer any torque between the earth and the load by the Coriolis force. When the space elevator is taut, it only costs energy to overcome the weight of the load along the height difference , because the Coriolis force is always at right angles to the movement of the load. That part of the energy that is needed to overcome the Coriolis force comes from the deceleration of the earth's rotation.
Propulsion of the satellite
A rocket drive is not required for the satellite, because as soon as the Coriolis force of a load transported upwards pulls the satellite backwards, the rope forms a small angle to the vertical, and thereby accelerates the satellite while braking the earth's rotation. For this purpose it is beneficial if the satellite orbits a little higher above the earth's surface than 40,000 km, so that although it is geosynchronous, it tensions the rope through its centrifugal force. This functional principle can be illustrated by the hammer throw . As long as the hammer thrower rotates at a constant speed, the rope of the hammer points radially away from the axis of rotation. As the hammer thrower increases its speed of rotation, the hammer lags behind radial alignment and kinetic energy is transferred from the hammer thrower to the hammer. The transport of the load is hardly hindered by the Coriolis force, since it is practically at right angles to the movement of the load.
Expansion of general space infrastructure and the space industry
It is believed that a space elevator could drastically reduce transport costs into space. With typical payloads for individual transports on the order of tons and transport times on the order of individual weeks, a space elevator would achieve a considerable transport capacity over a year. Since the final parameters of the lift such as speed, tensile strength and costs have not yet been determined, it is currently difficult to estimate the effects. However, there is agreement that because of the lower acceleration forces that occur compared to a rocket launch, it is possible to transport mechanically sensitive workpieces such as telescope mirrors into space.
Space elevator on the moon
Technically, Jerome Pearson's suggestion is already in the realm of possibilities: he would like to install a space elevator on the moon. Because of the lower gravity in comparison with the earth , the required rope would be exposed to lower loads. Due to the slow rotation of the moon, a rope to the luna-stationary orbit would be much longer at almost 100,000 km than with an earth space elevator. However, the Pearson space elevator would tie in at Lagrange point L1 or L2 in the Earth-Moon system. L1 is at a distance of approx. 58,000 km from the center of the moon in the direction of the earth, the point L2 facing away from the earth is approx. 64,500 km from the center of the moon. With rope materials available today, a taper by a factor of 2.66 is sufficient.
The necessary rope with an estimated mass of seven tons could be carried into space with a single rocket. Jerome Pearson is the managing director of Star Technology and Research , which also provides information about the moon lift on its website. Pearson's research on the project is currently supported by NASA with $ 75,000.
Space elevator as a motif in literature, film and television
In his Mars trilogy ( Red Mars , Green Mars , Blue Mars ), Kim Stanley Robinson depicts the space elevator as a key technology for colonizing Mars. In the novels, Earth and Mars have space elevators, but the elevator on Mars is used by the planet's separatists Destroyed by blowing up the anchor point to prevent further immigration of inhabitants of the earth.
In his children's book Charlie and the Big Glass Elevator (1972), a successor to the classic Charlie and the Chocolate Factory (1964), Roald Dahl describes an elevator that reaches freely around the world and (inadvertently) into space , in which the elevator has also already been mentioned.
In construction game Anno 2205 from Ubisoft from the year 2015, the space elevator will be addressed as a central element of the game.
The idea of the space elevator became known to the public when Arthur C. Clarke and Charles Sheffield used it independently in 1978/79 as the central theme of their novels The Fountains of Paradise and The Web between the Worlds (German : Elevator to the Stars ) .: A network of a thousand stars) processed.
In the manga classic Battle Angel Alita (from 1991) by Yukito Kishiro , the main storyline also revolves around a space elevator with an end in orbit and a stopover in the manner of a city in the clouds.
In the episode Die Asteroiden ( English Rise , season 3, episode 19, 1997) of the TV series Star Trek: Spaceship Voyager , the crew of Voyager meets a planet on which a space elevator exists.
The authors Terry Pratchett , Ian Stewart and Jack Cohen take up the concept of the space elevator both as a metaphor and as a physically feasible device in their book The Scholars of Discworld (2000) .
Frank Schätzing dealt with the topic of the space elevator in his novel Limit , published in 2009 .
In the third volume of the Airborn series, Sternenjäger , by Kenneth Oppel , the protagonists use a space elevator to be the first humans to get into space.
Alastair Reynolds depicts in his novel Chasm City what happens when the rope of a space elevator breaks.
Julia Reda suggested building a space elevator for the Pirate Party in the European election campaign.
In Liu Cixin's novel The Three Suns , nanotechnology, which the protagonist Wang Miao is researching, is recognized as the key to building a space elevator.
literature
- Chapter: The Space Elevator. In: Eugen Reichl: Typenkompass: Zukunftsprojekte der Raumfahrt , Motorbuch Verlag, Stuttgart 2012, ISBN 978-3-613-03462-4 , pp. 105–111
Web links
- Scientific Working Group for Rocket Technology and Space Travel ( WARR Space Elevator )
- Space Elevator Website from SpaceRef with current news about the project, presentations, lectures and links
- German Space Elevator (Max Born Team 2006) Space Elevator Construction (Schoolchildren / Young Students Project)
- ESA portal
- Elevator to space. The eight millionth floor . Article about space elevators in the online edition of the FAZ ( Frankfurter Allgemeine ). Ulf von Rauchhaupt, October 2, 2014.
Individual evidence
- ↑ National Space Society: Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium (pdf)
- ↑ Success story of space transport: Like Phoenix from the ashes.
- ↑ Peter Odrich: The Japanese want to build a space elevator by 2050. In: Ingenieur.de. October 1, 2014, accessed October 7, 2014 .
- ↑ Changgu Lee, Xiaoding Wei, Jeffrey W. Kysar, James Hone: Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene . In: Science . tape 321 , no. 5887 , 2008, p. 385-388 , doi : 10.1126 / science.1157996 .
- ↑ Sukang Bae, Hyeongkeun Kim, Youngbin Lee, Xiangfan Xu, Jae-Sung Park, Yi Zheng, Jayakumar Balakrishnan, Tian Lei, Hye Ri Kim, Young Il Song, Young-Jin Kim, Kwang S. Kim, Barbaros Ozyilmaz, Jong- Hyun Ahn, Byung Hee Hong, Sumio Iijima: Roll-to-roll production of 30-inch graphene films for transparent electrodes . In: Nat Nano . tape 5 , no. 8 , 2010, p. 574-578 , doi : 10.1038 / nnano.2010.132 ( PDF [accessed October 5, 2010]). PDF ( Memento of the original from July 10, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Jerome Pearson, Eugene Levin, John Oldson, and Harry Wykes: The Lunar Space Elevator (PDF; 365 kB), STAR Inc., Mount Pleasant, SC USA, 55th International Astronautical Congress, Vancouver, Canada, October 4-8, 2004.
- ↑ http://www.star-tech-inc.com/id4.html
- ^ Original edition The Science of Discworld , 1999
- ↑ Jolinde Hüchtker, Cyrill Callenius, David Fresen, Max Deibert, Simon Grothe, Xenia Heuss, Antonia Bretschkow: A space elevator and crooked cucumbers. In: tagesspiegel.de. May 24, 2014, accessed September 30, 2015 .
