Space elevator

A space elevator, also called space elevator, is theoretically possible, but with today 's technology makes unrealizable elevator system of a planet's surface into space. A gondola for example, could go from the ground up to a geostationary space station. Orbits in lower tracks are also theoretically impossible because of the necessary high rotational speed.

History

The idea of ​​the space elevator appeared for the first time in 1895, when the Russian space pioneer Konstantin Tsiolkovsky proposed inspired by the Eiffel Tower, to build a space tower - which means a tower that reaches directly into space. He introduced himself to bring at the end of a rope a kind of suspension of the elevator directly into geostationary orbit.

A tower or elevator of this type would be able to get without rocketry objects into orbit. As an object in the ascent must win at the same time the tangential velocity, it would have the same time to remain the necessary energy and speed in a geostationary orbit at reaching the target.

To erect a building of this kind was impossible since no material was known with the required compressive strength. In 1957 the Soviet scientists suggested Yuri Arzutanow before an alternative variant of this idea. A satellite should be placed in a geostationary orbit and serve as a suspension of the elevator. From there you could then let down a rope to the surface. The focus of the design should lie on the geostationary orbit such that at an angular velocity corresponding to the Earth's rotation, the centrifugal force compensates for the gravitational force. A rope of 35,786 km length is, however, difficult to realize.

1966 examined four American engineers, which material would be required for the creation of such rope. They came to the conclusion that new materials would be required that would have to be at least twice as powerful pull as all the known materials. 1975 suggested the Americans Jerome Pearson to use a cone-shaped structure. The cable would have to be thickest in the vicinity of the center of gravity, as it has to withstand the highest voltage there. The construction of the lift would start at the center of gravity. From there, be applied in both directions so that the focus of the system is constantly on the geostationary orbit. The rope could be extended as a counterweight into space, while one would build on the near-Earth half a tower.

Current

In recent years, greater efforts to implement this plan one day into reality. David Smitherman published by the U.S. space agency NASA, for example, in 2000 a report based on the results of 1999 in the Marshall Space Flight Center conference held.

Since the beginning of the 21st century with the carbon nanotubes, a material known, which could meet the requirements. In early 2004, it is a group of scientists led by Alan Windle at Cambridge University have succeeded in producing on the basis of this technology an approximately 100 -meter-long thread. Carbon nanotubes have an up to 100 times better ratio of tensile strength to weight than steel, so this material is a potential candidate for the space elevator. However, the technology is far from mature: carbon nanotubes can so far only be produced in very limited numbers and are therefore very expensive. Ropes of nanotubes must be coated because carbon is oxidized and eroded.

End of June 2004, the Head of the Space Elevator project Bradley Edwards in Fairmont, West Virginia, that even in 15 years, a prototype could be ready. NASA supported the research project through their NASA Institute for Advanced Concepts ( NIAC ) with U.S. $ 500,000.

The U.S. company lift Port Group has set itself the goal of building such a space elevator. The first sub-goal in the summer of 2012 neugesetzt to build an elevator between lunar surface and there in 55,000 km altitude (in the future ) stationary space station - this was added - after the first attempt on the earth's surface. For this purpose, a 250,000 km long rope should be anchored in the lunar surface and led to a located in the orbit equilibrium point. In addition, the Japanese construction company Obayashi had announced in early 2012, also to build a lift from the earth into space, with a station at 36,000 km.

The Space Foundation Ward organized, together with NASA Elevator :2010- competitions.

Effects

It is believed that a space elevator could reduce transportation costs, currently 20,000 to 80,000 U.S. dollars per kilogram up to 100 U.S. dollars per kilogram. Scientific research would benefit greatly into space by the much cheaper transport of laboratories and telescopes. The industrial research can develop by working in zero gravity new processes and new manufacturing technologies; last but not least, it would be possible to develop this technology for space tourism.

The energy balance during transport to the space elevator is not necessarily negative. To lift one kilogram mass from the Earth's equator to a height of 35,786 km above the earth's equator, one needs 48 422 kJ (about 13 kWh). If a rope is extended up to an altitude of 143,780 km above the Earth's equator, then this amount of energy can be recovered. The reason is that the sum of the gravitational potential difference between the Earth's equator and Zentrifugalkraftpotentialdifferenz and 143,780 km height is equal to zero. This recovery is only possible when transporting a body from the geostationary orbit at an even greater height, for example, to launch an interplanetary probe by centrifugal force.

Technology

On the lift, the rope and the base station enormous technical demands are made. NASA has announced contests on this topic, which are crowned with high prize money and have great success. We distinguish between the following five problem areas where there are already several solutions.

Material for the rope

Each segment of the cable must be at least the weight of the underlying rope segments plus the payload capacity can hold. The higher the rope segment is considered, the more cable segments must keep it. Thus, an optimized cable has height increases a larger cross section until this trend reverses at geostationary orbit, because from there the resultant force of the rope segments acts erdabgewandt.

At a given specific tensile strength of a material that is the minimum cross-section at the base station is determined solely by the load capacity. Next then the optimal another cross-sectional development is fixed. The ratio of the largest to the smallest cable cross section is called the taper ratio. You and the payload capacity lay ultimately determine the total mass of the rope.

Basically it can be optimized with rope mean using any material, a space elevator built by the cross-sectional growth is chosen according to rapid or a large taper ratio will be used. The economics dictates this finally the limit of still meaningful values ​​in this size.

An ordinary steel cable of constant cross -section would already from a length of four to five kilometers tear under its own weight, high performance steel wire ropes for ropeways, whose tensile strength is similar to Kevlar, would come to around 30 km. New materials whose tensile strength far beyond that of Kevlar, so are a crucial factor for a future realization of this company. According to previous research, three options are:

• Carbon nanotubes seem to be the tenacity of Kevlar again to exceed by a factor of five, calculations by Nicola Pugno of the Polytechnic in Turin revealed, however, that in the interweaving of carbon nanotubes to long ropes the tensile strength of the rope by about 70 % compared to the tensile strength of individual nanotubes decreases. This is due to unavoidable crystal defects, which reduced according Pugnos model the load of the rope to about 30 Gigapascal. Calculations according to NASA, however, a material with a capacity of about 62 Gigapascal would be necessary to withstand the forces that occur. In addition, there is no laboratory yet been able to create a coherent cable that is longer than 100 meters. An additional cost factor represents the coating of the rope, because carbon nanotubes oxidize and erode.

• Another promising approach is the UHMW polyethylene fiber Dyneema, with vertical suspension a breaking length of 400 km of the hotel and therefore all conventional materials exceeds many times and even spider silk by a factor of two the. Against the use of Dyneema speaks however, that the melting point of Dyneema between 144 ° C. and 152 ° C, the strength of Dyneema between 80 ° C and 100 ° C decreases significantly, and that Dyneema below -150 ° C is brittle, for all these temperatures occur in space to frequently.

• A new, yet little -researched material is graphene. The elastic modulus corresponds with about 1020 GPa 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 in 2008, further measurements, in which they stressed that graphene having the highest tensile strength that has ever been determined. Its tensile strength of 1.25 × 105 N · mm -2 or 125 Giga Pascal is the highest that has ever been found, and about 125 times higher than steel. Steel has to 7874 kg · m -3, a roughly 3.5 times higher than density graph 2260 kg · m -3, so that the tear length of the graph is about 436 times greater than that of steel. In an assumed to be homogeneous gravitational field of 9.81 m · s-2 graphs would have a breaking length of around 5655 km. In fact, the acceleration of gravity is considerably lower with increasing height, which increases the tenacity. A band of graphs with constant cross- sectional area ( taper ratio 1 ) would be charged at the height of the geostationary orbit 35,786 km above the Earth's equator by only about 87 % of its tensile strength (see the picture). In still greater height the tensile load would then drop again. If the graph cable at constant cross-sectional area would be 143,780 km long, then it would be in full equilibrium with the gravitational acceleration of the earth and the centrifugal acceleration due to the Earth's rotation. At the height of 143,780 km above the Earth's equator, a net acceleration of 0.78 m · s-2 would act up, and a tangential velocity of 10,950 m · s- 1 to be present, which would promote the launch of space probes. Graphene and graphite have a melting point of about 3700 ° C. 76 cm wide endless strips of the graph represents one characterized ago that applying a mono-atomic layer of carbon on a sheet of inert support material, such as copper, by chemical vapor deposition (CVD), and then dissolving the carrier material.

Construction of the rope

So far, the rope of a geostationary satellite is only conceivable down permit. The behavior of long ropes in the universe is the subject of current research. It is conceivable that initially only a minimal viable rope is started, which is then gradually increased until the final payload thickness is achieved.

Erection of the tower as a base station

The base station has to withstand heavy loads, because of the connection between the cable and base station loads according to NASA up to 62 Gigapascal. This required a sufficiently deep, complex and expensive to be built anchoring the base in the ground. The reason is that the space elevator in the vertical direction must prevail, an excess of centrifugal force against the force of gravity to pull the string, and the fact that the space elevator in the horizontal direction, the Coriolis force the up or down moving loads is transferred to the earth. A space elevator, which would be in stark balance between the centrifugal force and the gravitational force would be already disturbed by minimal expense in its stability, and therefore could be transmitted by the Coriolis force between the Earth and the load no torque. When taut space elevator costs only overcome the weight of the load along the height difference energy, because the Coriolis force is always transverse 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.

Power supply to the lift

A further problem would be the energy supply of the actual lift. Can not be secured by a power line is integrated in the cable, the power supply as the electrical resistance at up to 36,000 km in length is too large and the energy loss would be too high. However, there are several ways to eliminate the problem:

• The supply is ensured by a laser station to the base station. The laser is very precise irradiated to a photovoltaic surface and the lift will draw from his energy. But there is no laser that is so strong that it can compensate for the enormous loss of energy.

• The sunlight that is particularly strong in space is captured using solar panels and converted to electrical energy. However, the solar panels have to be very large, so that they can produce enough energy to accelerate the lift at about 200 km / h.

• One could construct a hybrid solution. In the Earth's atmosphere the solar radiation is lower than in space. The hybrid solution of the lift, is supplied to the point at which it leaves the earth's atmosphere by a laser station on the ground of energy. From about 100 km altitude, the sun is large enough to supply the lift good enough. Then solar panels are extended and switched off the laser.

• A maser generates microwaves that are cast with a very high concentration in the direction of the lift, which then converts this into electrical energy. Here there is the same problem as with the laser power, namely that there still is no grain that can create such a concentration.

• You could use a small nuclear reactor to generate electricity. When some 100 m behind the lift cabin forth pulling the nuclear reactor on the power cables, then you can do without the heavy radiation shielding of the reactor. While staying in the ground station of the nuclear reactor rests in an appropriately deep shaft.

A rocket engine is not required for the satellite, because as soon as the Coriolis force a transported upward load pulls the satellite towards the rear, the rope forms a small angle to the vertical, and thereby accelerates the satellites under braking the rotation of the earth. For this purpose, it is advantageous if the satellite is slightly higher above the Earth orbits 40,000 km, so it is geosynchronous, but the rope spanned by its centrifugal force. This operating principle can be illustrated by the hammer throw. As long as the hammer thrower rotates at a constant speed, the rope of the hammer faces radially away from the axis of rotation. When the hammer thrower increases its speed of rotation, then the hammer behind the radial alignment is lagging behind, and kinetic energy is transferred from the hammer thrower on the hammer. The transport of the load is hardly hindered by the Coriolis force, as it is practically transverse to the movement of the load.

Developing educational space infrastructure and space industry

It is believed that transport costs could be reduced dramatically into space by a space elevator. In typical payloads for individual transports in the order of tons and transport durations on the order of individual weeks, a space elevator would be seen for over a year to reach a considerable transport capacity. Since not even the final parameters of the lift as speed, strength and costs are known, is currently an assessment of the impact remains difficult. There is general agreement that because of the lower occurring G- forces, opening the possibility to transport sensitive workpieces such as telescope mirrors into space.

Space elevator on the moon

Technically already in the realm of possibility is the proposal of Jerome Pearson: He wants to install a space elevator on the moon. Because of the smaller compared to the earth gravity, the required rope would be exposed to lower stresses. Due to the slow rotation of the Moon a rope to the luna- stationary orbit, however, with just under 100,000 km would be much longer than in a natural space elevator. The Pearson's space elevator would, however, build on the Lagrangian point L1 or L2 in the Earth- Moon system. L1 is located at a distance of 58,000 km from the center of the Moon towards the Earth, the Earth facing away from the L2 point is approximately 64,000 miles from the Moon's center. With rope materials available today rejuvenation by a factor of 2.66 is sufficient.

The necessary rope with an estimated weight of seven tons could be carried by a single rocket into space. Jerome Pearson is the managing director of the company Star Technology and Research, which provides information on its website also over the moon lift. The research of Pearson on the project are currently supported by NASA with $ 75,000.

Space elevator as a motif in literature, film and television

Kim Stanley Robinson states in his Mars trilogy ( Red Mars, Green Mars, Blue Mars) the space elevator dar. as a key technology for the colonization of Mars in the novels include Earth and Mars on space elevators, the elevator on Mars is of the separatists of the planet Bursting Mars - Phobos at which it was attached, destroyed to prevent further migration of the inhabitants of the earth.

A lift, ranging freely around the world and ( accidentally) in the space, Roald Dahl describes in his children's book Charlie and the great glass elevator (1972 ), a sequel to the classic Charlie and the Chocolate Factory ( 1964), in which the lift also already been mentioned.

The idea of ​​the space elevator in the public became known as Arthur C. Clarke and Charles Sheffield them 1978/79 independently to the central theme of her novels The Fountains of Paradise (German: Elevator to the stars ) and The Web Between The Worlds ( dt. : A network of thousands of stars ) processed.

Also in the manga classic Battle Angel Alita (from 1991) by Yukito Kishiro, the main storyline revolves around a space elevator with the end in orbit and stopover in the manner of a city in the clouds.

As a result, the asteroid (English Rise, Season 3, Episode 19, 1997) of the television series Star Trek: Voyager meets the crew of Voyager to a planet on which a space elevator exists.

The authors Terry Pratchett, Ian Stewart and Jack Cohen draw on the concept of the space lift both as metaphor and as a physically realizable device The Science of Discworld (2000) in her book.

Frank Schätzing processed the issue to the space elevator in his 2009 novel erschienenem limit.