space elevator

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SPACE ELEVATOR Climb to the sky:

SPACE ELEVATOR Climb to the sky By RAKESH.B 096Q1A2107

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It is a type of space transportation system by using cables (Tether). Tether is anchored to surface and extend to space. An Earth-based space elevator would consist of a cable with one end attached to the surface near the equator and the other end in space beyond geostationary orbit (35,800 km altitude).

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How it works? Space elevator is made off CARBON NANO TUBES COMPOSITE RIBBON anchored to an offshore sea platform would stretch to small counter weight approximately 62,000 miles(100,000Km) into space. Mechanical lifters attached to the ribbon would then climb the ribbon carrying cargo and human into space at the price of only about $220 to $800 per kg. The competing force of gravity, which is stronger at the lower end and outward centrifugal force is stronger at upper end would result in the cable being held up under tension, and stationary over a single position on earth.

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History In 1895 Russian scientist Konstantin Tsiolkovsky considered a tower similar to Eiffel Tower that reached all the way into space and was built from ground up to altitude 35,790km(Geosynchronous orbit). Tsiolkovsky conceptual tower was a compression structure, while modern concepts call for a tensile structure In 1979, space elevators were introduced to a broader audience with the simultaneous publication of Arthur C. Clarke's novel, The Fountains of Paradise. In 1990 Sumio Linjima discovered the Carbon nano tubes and Bradly Edward’s engineering research in 2001 is clearing the road map to space elevator’s construction.

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Physics of space elevator A space elevator cable rotates along with the rotation of the Earth. Objects fastened to the cable will experience upward centrifugal force that opposes some of, all of, or more than, the downward gravitational force at that point. The higher up the cable, the stronger is the upward centrifugal force and the more it opposes the downward gravity. Eventually it becomes stronger than gravity above the geosynchronous level.] Along the length of cable apparent gravitational field is activated.

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Apparent gravitation = Actual gravitation- Centrifugal force Actual gravity decreases with height g= -G.M / r^2 Upward centrifugal force increases with height a= ω ^2 . r Therefore apparent gravitation= g= (-G.M/r^2)+(w^2.r) Where g is the acceleration of actual gravity or apparent gravity a is the centrifugal acceleration G is the gravitational constant M is the mass of the Earth r is the distance from that point to Earth's center ω is Earth's rotation speed

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At some point the downward gravity and the centrifugal force equal to each other so objects fixed to the cable have no weight on the cable. actual gravity = centrifugal force (G.M/r^2) = ( ω^2.r) r1 = [G.M/ ω^2]^(1/3) On Earth, this level is 35,786 km (22,236 mi) above the surface, the level of geostationary orbit. From geosynchronous station, any object dropped off the tether from a point closer to Earth will initially accelerate downward. If dropped from any point above a geosynchronous station, the object would initially accelerate up toward space.

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Outline of system

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Space elevator components Base station Cable Climbers Powering climbers Counter weight

Base station:

Base station Base station/Anchor is a mobile, oceangoing platform identical to once used in oil drilling. Anchor is located in Eastern equatorial pacific. Weather and mobility are primary factors .

Climbers:

Climbers Climbers built with current satellite technology. Drive system build with DC electric motor. Photovoltaic array receives power from Earth. 7-ton climbers carry 13-ton payloads. Climbers ascend at 200km/hr or more. 8 day trip from earth to geosynchronous altitude.

Powering climbers:

Powering climbers Power is sent to deployment spacecraft and climbers by laser. Solid-state disk laser produces kW of power and being developed for MW. Mirror is the same design as conventional astronomical telescopes (Hobby- Eberly , Keck).

Counter weight:

Counter weight It is a weight at outer end of the cable to balance support on earth. Several solutions have been proposed for counter weight Heavy or captured asteroid( practically not possible as per current technology) Space station

Cable:

Cable A space elevator cable must carry its own weight as well as the additional weight of climbers. Maximum tension is at geosynchronous altitude so the cable must be thickest there and taper carefully as it approaches Earth. a specific strength of cable at least 100,000 kN /(kg/m)

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For comparison metals like titanium, steel or aluminium have breaking lengths of only 20-30km . Fiber materials like kevlar , fiberglass and carbon/graphite fiber have breaking strength 100-200km. Nanoengineered materials such as carbon nanotubes , graphene ribbons are expected to have breaking strength 5000-6000km.

Carbon nano tubes:

Carbon nano tubes CNT made the space elevator closer to reality. Young’s modulus of CNT is more than 1000GPa. It is apprx 5 times double than steel. Tensile strength is 63Gpa, which is 50x than steel.

Challenges:

Challenges Induced oscillations: 7 hour natural frequency couples poorly with moon and sun, active damping with anchor Radiation: carbon fiber composites good for 1000 years in Earth orbit (LDEF) Atomic oxygen: <25 micron Nickel coating between 60 and 800 km (LDEF) Environmental Impact: Ionosphere discharging not an issue Malfunctioning climbers: up to 3000 km reel in the cable, above 2600 km send up an empty climber to retrieve the first Lightning, wind, clouds: avoid through proper anchor location selection Meteors: ribbon design allows for 200 year probability-based life LEOs: active avoidance requires movement every 14 hours on average to avoid debris down to 1 cm Health hazards: under investigation but initial tests indicate minimal problem Damaged or severed ribbons: collatoral damage is minimal due to mass and distribution

Estimated Budget:

Estimated Budget Component Cost Estimate (US$) Launch costs to GEO 1.0B Ribbon production 400M Spacecraft 500M Climbers 370M Power beaming stations 1.5B Anchor station 600M Tracking facility 500M Other 430M Contingency (30%) 1.6B TOTAL ~6.9B Costs are based on operational systems or detailed engineering studies. Additional expenses will be incurred on legal and regulatory issues. Total construction should be around US$10B. Recommend construction of a second system for redundancy: US$3B

Advantages:

Advantages Low operations costs - US$250/kg to LEO, GEO, Moon, Mars, Venus or the asteroid belts No payload envelope restrictions No launch vibrations Safe access to space - no explosive propellants or dangerous launch or re-entry forces Easily expandable to large systems or multiple systems Easily implemented at many solar system locations.

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Reference Wikipedea Arthur C. Clarke's novel, The Fountains of Paradise

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