--------- #1263 - Can We Replace the Space Shuttle with a Kite on a String?
- The Space Shuttle will be making its last flight into outer space. Would it be possible to attach a tether to a satellite and then simply run payloads up the line into orbit? This review explores how this idea could happen. It would be 100 times cheaper than using rockets to get spacecraft into orbit.
- Attachments - none
- To attach a tether to a satellite would require a very strong material. Technology is getting close to something that might do the job. It is multiwalled carbon fiber nanotubes in a long ribbon. The ribbon would have to be 60,000 miles long. That is a very high orbit but the longer length is needed to connect to the counterweight that is keeping the line tight during its geosynchronous orbit. The orbiting satellite stays in the same spot above the Earth because its orbit matches the Earth’s speed of rotation. One end is attached to a base station on the surface, most likely a floating base station in the Pacific Ocean.
- Carbon nanotubes are molecular strands of carbon atoms that are many times stronger than steel. They would be manufactured into a long ribbon that a space station could climb. The counter weight would be higher and heavier in order to create tensile force on the cable. The tensile strength of the cable would need to be 19 million pounds per square inch, psi. Today, carbon nanotubes have been tested to have up to 9 million psi. By constructing multiwalled nanotubes a strong enough cable could be manufactured.
- The space vehicle would start at the base station attached to the ribbon with rollers. Multiple wheels on either side of the ribbon that would spin as it climbed the ribbon.
- The space vehicle rollers would be powered by electric motors attached to a solar panel. Photovoltaic cells would be mounted on the underside of the vehicle. A laser would shoot a beam from the station to the climbing vehicle to power the photovoltaic cells. The photovoltaic cells would be tuned to the frequency of the laser for maximum efficiency. Other solar cells on the top side would us the Sun’s energy to provide additional climbing power.
- The cargo would weigh up to 14 tons and be about the size of an 18 wheeler truck. It would be constructed out of aluminum much like airplanes are today. Lighter climbers could be sent up more often with several going up at the same time.
- The cargo could go back and forth an unlimited number of times. It could even be hauling people up to the orbiting space station. In this way extremely large space vehicles could be constructed in space. Large missions could be launched from orbit to visit the planet Mars.
- If the climber could get out to 90,000 miles on the tether it would have a tangential velocity of 24,400 miles per hour and could escape Earth’s gravity and reach as far as Jupiter.
- Today’s conventional rockets cost $11,000 per pound to launch payloads into geostationary orbits. A space elevator should be able to do the job for $100 per pound.
- How to get a cable that can support 22,000 miles of itself? The gravitational pull of the Earth is pulling the payload back to the surface. The centripetal force of the spinning Earth and satellite are pushing the payload into space. The two forces acting on the payload are in balance when the satellite reaches geostationary orbit.
- The pull of gravity is strongest at the surface where the acceleration of gravity is proportional to mass of the Earth and inversely proportional to the square of the radius of the Earth.
-------------- Acceleration of gravity = - G * M / r^2
-------------- “G” is the gravitational constant of proportionality = 6.67*10^-11 m^3 / kg*sec^2
-------------- “M” is the mass of the Earth = 5.97 * 10^24 kilograms
-------------- “r” is the radius of the Earth = 6.378*10^6 meters
-------------- “r^2” = 40.7 *10^12 meters^2
-------------- Acceleration of gravity = - 9.8 meters / sec^2
-------------- Acceleration of gravity = - 32 feet / sec / sec
- The higher the elevation above the surface of the Earth the weaker the gravity. When the payload is 26,400 miles from the center of the Earth ( 35,786,000 meters ) the acceleration of gravity is 0.189 meters /second^2. ( - 0.62 feet / sec /sec )
- The push of centripetal force is equal to the square of the angular velocity times the radius of the orbit.
-------------- Acceleration of angular velocity = w^2 * r
-------------- “w” is one rotation every 24 hours = 2* pi radians / 86,400 seconds = 0.727*10^-4 radians per second.
-------------- “w^2” = 0.528*10^-8 radians^2 / sec^2
--------------- “r” = 35*786*10^6 meters
-------------- Acceleration of centripetal force = 0.189 meters / second^2
- Therefore at 26,400 miles from the center of the Earth the pull of gravity and the push of centripetal force are exactly equal, 0.189 m/sec^2. A space elevator is not as far fetched as it first seems. It could actually be an economic and practical solution to getting spacecraft on their mission. Announcements will be made soon, stay tuned.
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707-536-3272, Sunday, June 26, 2011
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