Space Elevator Systems Architecture
In , another American scientist, Bradley C.
The ribbon cross-section shape also provided large surface area for climbers to climb with simple rollers. Supported by the NASA Institute for Advanced Concepts , Edwards' work was expanded to cover the deployment scenario, climber design, power delivery system, orbital debris avoidance, anchor system, surviving atomic oxygen , avoiding lightning and hurricanes by locating the anchor in the western equatorial Pacific, construction costs, construction schedule, and environmental hazards.
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To speed space elevator development, proponents have organized several competitions , similar to the Ansari X Prize , for relevant technologies. In , "the LiftPort Group of space elevator companies announced that it will be building a carbon nanotube manufacturing plant in Millville, New Jersey , to supply various glass, plastic and metal companies with these strong materials. Brad Edwards and Philip Ragan was published in English, a comprehensive coverage of space elevator issues. In , the Obayashi Corporation announced that in 38 years it could build a space elevator using carbon nanotube technology.
This, along with timing and other factors, hinted that the announcement was made largely to provide publicity for the opening of one of the company's other projects in Tokyo. In , the International Academy of Astronautics published a technological feasibility assessment which concluded that the critical capability improvement needed was the tether material, which was projected to achieve the necessary strength-to-weight ratio within 20 years.
The four-year long study looked into many facets of space elevator development including missions, development schedules, financial investments, revenue flow, and benefits. They thus decided to put the project in "deep freeze" and also keep tabs on any advances in the carbon nanotube field. In , a Japanese prototype was launched as a testing bed for a larger structure.
In , space elevators were introduced to a broader audience with the simultaneous publication of Arthur C. Clarke 's novel, The Fountains of Paradise , in which engineers construct a space elevator on top of a mountain peak in the fictional island country of Taprobane loosely based on Sri Lanka , albeit moved south to the Equator , and Charles Sheffield 's first novel, The Web Between the Worlds , also featuring the building of a space elevator.
Three years later, in Robert A. Heinlein 's novel Friday the principal character makes use of the "Nairobi Beanstalk" in the course of her travels. In Kim Stanley Robinson 's novel Red Mars , colonists build a space elevator on Mars that allows both for more colonists to arrive and also for natural resources mined there to be able to leave for Earth.
In David Gerrold 's novel, Jumping Off The Planet , a family excursion up the Ecuador "beanstalk" is actually a child-custody kidnapping. Gerrold's book also examines some of the industrial applications of a mature elevator technology. In a biological version, Joan Slonczewski 's novel The Highest Frontier depicts a college student ascending a space elevator constructed of self-healing cables of anthrax bacilli.
The engineered bacteria can regrow the cables when severed by space debris. A space elevator cable rotates along with the rotation of the Earth. Therefore, objects attached to the cable would experience upward centrifugal force in the direction opposing the downward gravitational force. The higher up the cable the object is located, the less the gravitational pull of the Earth, and the stronger the upward centrifugal force due to the rotation, so that more centrifugal force opposes less gravity.candsbrokerage.com/images/46-chloroquine-phosphate-cheap.php
Space Elevator Systems Architecture
The centrifugal force and the gravity are balanced at geosynchronous equatorial orbit GEO. Above GEO, the centrifugal force is stronger than gravity, causing objects attached to the cable there to pull upward on it. The net force for objects attached to the cable is called the apparent gravitational field. The apparent gravitational field for attached objects is the downward gravity minus the upward centrifugal force. The apparent gravitational field can be represented this way: Ref  Table 1.
At some point up the cable, the two terms downward gravity and upward centrifugal force are equal and opposite.
Objects fixed to the cable at that point put no weight on the cable. This altitude r 1 depends on the mass of the planet and its rotation rate. Setting actual gravity equal to centrifugal acceleration gives: Ref  page On the cable below geostationary orbit, downward gravity would be greater than the upward centrifugal force, so the apparent gravity would pull objects attached to the cable downward.
Any object released from the cable below that level would initially accelerate downward along the cable. Then gradually it would deflect eastward from the cable. On the cable above the level of stationary orbit, upward centrifugal force would be greater than downward gravity, so the apparent gravity would pull objects attached to the cable upward.
Any object released from the cable above the geosynchronous level would initially accelerate upward along the cable. Then gradually it would deflect westward from the cable. Historically, the main technical problem has been considered the ability of the cable to hold up, with tension, the weight of itself below any given point.
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A cable which is thicker in cross section at that height than at the surface could better hold up its own weight over a longer length. To maximize the usable excess strength for a given amount of cable material, the cable's cross section area would need to be designed for the most part in such a way that the stress i.
Other factors considered in more detailed designs include thickening at altitudes where more space junk is present, consideration of the point stresses imposed by climbers, and the use of varied materials. To compare materials, the specific strength of the material for the space elevator can be expressed in terms of the characteristic length , or "free breaking length": There are a variety of space elevator designs. Almost every design includes a base station, a cable, climbers, and a counterweight.
Earth's rotation creates upward centrifugal force on the counterweight. The counterweight is held down by the cable while the cable is held up and taut by the counterweight. The base station anchors the whole system to the surface of the Earth. Climbers climb up and down the cable with cargo. Mobile base stations would have the advantage over the earlier stationary concepts with land-based anchors by being able to maneuver to avoid high winds, storms, and space debris. Oceanic anchor points are also typically in international waters , simplifying and reducing cost of negotiating territory use for the base station.
Stationary land based platforms would have simpler and less costly logistical access to the base. They also would have an advantage of being able to be at high altitude, such as on top of mountains. In an alternate concept, the base station could be a tower, forming a space elevator which comprises both a compression tower close to the surface, and a tether structure at higher altitudes.
A space elevator cable would need to carry its own weight as well as the additional weight of climbers. The required strength of the cable would vary along its length. This is because at various points it would have to carry the weight of the cable below, or provide a downward force to retain the cable and counterweight above. Maximum tension on a space elevator cable would be at geosynchronous altitude so the cable would have to be thickest there and taper carefully as it approaches Earth.
Any potential cable design may be characterized by the taper factor — the ratio between the cable's radius at geosynchronous altitude and at the Earth's surface. For a space elevator on Earth, with its comparatively high gravity, the cable material would need to be stronger and lighter than currently available materials.
For high specific strength, carbon has advantages because it is only the 6th element in the periodic table. Carbon has comparatively few of the protons and neutrons which contribute most of the dead weight of any material. Most of the interatomic bonding forces of any element are contributed by only the outer few electrons. For carbon, the strength and stability of those bonds is high compared to the mass of the atom. The challenge in using carbon nanotubes remains to extend to macroscopic sizes the production of such material that are still perfect on the microscopic scale as microscopic defects are most responsible for material weakness.
In , diamond nanothreads were first synthesized. A space elevator cannot be an elevator in the typical sense with moving cables due to the need for the cable to be significantly wider at the center than at the tips. While various designs employing moving cables have been proposed, most cable designs call for the "elevator" to climb up a stationary cable.
Climbers cover a wide range of designs. On elevator designs whose cables are planar ribbons, most propose to use pairs of rollers to hold the cable with friction. Climbers would need to be paced at optimal timings so as to minimize cable stress and oscillations and to maximize throughput. Lighter climbers could be sent up more often, with several going up at the same time. This would increase throughput somewhat, but would lower the mass of each individual payload. The horizontal speed, i.
A payload released at this point would go into a highly eccentric elliptical orbit, staying just barely clear from atmospheric reentry, with the periapsis at the same altitude as LEO and the apoapsis at the release height. With increasing release height the orbit would become less eccentric as both periapsis and apoapsis increase, becoming circular at geostationary level. The payload can also continue climbing further up the cable beyond GEO, allowing it to obtain higher speed at jettison. As a payload is lifted up a space elevator, it would gain not only altitude, but horizontal speed angular momentum as well.
The angular momentum is taken from the Earth's rotation. As the climber ascends, it is initially moving slower than each successive part of cable it is moving on to. This is the Coriolis force: The opposite process would occur for descending payloads: The overall effect of the centrifugal force acting on the cable would cause it to constantly try to return to the energetically favorable vertical orientation, so after an object has been lifted on the cable, the counterweight would swing back towards the vertical like an inverted pendulum.
Lift and descent operations would need to be carefully planned so as to keep the pendulum-like motion of the counterweight around the tether point under control. Climber speed would be limited by the Coriolis force, available power, and by the need to ensure the climber's accelerating force does not break the cable. Climbers would also need to maintain a minimum average speed in order to move material up and down economically and expeditiously. Both power and energy are significant issues for climbers—the climbers would need to gain a large amount of potential energy as quickly as possible to clear the cable for the next payload.
Unused energy would need to be re-radiated away with heat-dissipation systems, which add to weight. Yoshio Aoki, a professor of precision machinery engineering at Nihon University and director of the Japan Space Elevator Association, suggested including a second cable and using the conductivity of carbon nanotubes to provide power.
Extending the cable has the advantage of some simplicity of the task and the fact that a payload that went to the end of the counterweight-cable would acquire considerable velocity relative to the Earth, allowing it to be launched into interplanetary space. Its disadvantage is the need to produce greater amounts of cable material as opposed to using just anything available that has mass. That is more than enough to escape Earth's gravitational field and send probes at least as far out as Jupiter.
Once at Jupiter, a gravitational assist maneuver could permit solar escape velocity to be reached. Transferring from earth's one bar pressure environment into the zero pressure of space means you are shifting into a vacuum and require a pressure chamber. Travellers would enter the elevator and as they slowly became weightless would have to fasten their seat belts.
Space Elevator Architecture Note #14
To have an operating space elevator would mean that we could transport people and goods into low earth orbit on a continuous basis, and then launch spacecraft from here. Having orbital platforms to launch further into space would significantly cut down costs as it is extremely expensive to lift large masses off of earth's gravity due to having to overcome the gravity. A futuristic concept, the idea of a space elevator is not entirely far-fetched if the architectural community are already dreaming up these designs.
As Rousek, founder of international design company XTEND and space architect at ESTEE , has said, 'we're currently in the medieval ages' of space design and exploration, therefore perhaps we should look at it from the bigger picture. The world's 10 best green universities. Upfest street art festival wrap up.
Space Elevator Systems Architecture: Peter Swan, Cathy Swan: qexefiducusu.tk: Books
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