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Is the Space Elevator Even Theoretically Possible? Yes and the lunar elevator = skyhook can likely be built with 2007 materials. There is lots of correct info at www.liftport.com There is also a forum which has some errors at www.liftport.com look for word forum about 80% of the way down the main page. Let's focus on the Edwards space elevator in this article and a separate article about a bolo = rotating tether and rotovator. Edwards proposed 91,000 kilometers = 60,000 miles of ribbon. 60% of the ribbon is above GEO altitude, and a modest counter-weight is still needed at the far end. This is because Earth's gravity decreases with altitude. Edwards starts with a ribbon that can only lift one ton with a breaking strength of two tons. The climber = lifter has pinch rollars powered by electric motors to climb the ribbon. The electricity is delivered by laser beams to two photovoltaic panels. Other methods of propelling the climber run out of fuel before reaching GEO altitude, even with no payload. The payload is a reel of very thin CNT thread, at least 60,000 miles long, which the climber attaches to the ribbon to increase the strength of the ribbon. Several hundred of these threads are needed to increase the ribbon strength to 20 tons = break at 40 tons. Climbers that have layed thread are stored at the far end to serve as the counter-weight. If the CNT has a working strength of 60 GPa, the cross sectional area at GEO altitude needs to be about double the cross sectional area at the top and bottom end = the ribbon is tapered. The required taper ratio increases rapidly with slightly weaker material, quickly making the ribbon too costly, and the number of strengthening threads required increases rapidly until the construction time exceeds the 10 or 20 years before the ribbon is excesssively lumpy from patches due to space junk damage. It is thought that the ribbon can dodge the pieces of space junk which are large enough to have known orbits, by moving the anchor ship a few kilometers per day. One gram and smaller pieces will make small holes in the ribbon, some of which will need to be patched before the ribbon can operate at full capacity.
CNT has a theroretical strength of 1000 GPa and several other materials are almost as good. So far, the macro strength of actual ribbon has been much less, but hopes are still high for 60GPa working strength or more. Funding is needed to advance several other possible show stoppers. DSS = darkskystation or equivelent kites such as www.skywindpower.com are also short of funding. Generally an anchor at 20 to 40 kilometers is not thought to be enough help to justify the extra complications, but that thinking could change, if a long term demonstration of an upper atmosphere station actually flew.
The space elevator has some dangers, some of which are avoided with a lunar skyhook.
The ribbon is black, so night flying birds will likely be killed, if they hit the sharp edge of the ribbon, but the anchor ship will be far from land, so birds will be rare.
The airspace can be restricted to craft on official business.
People who work with CNT will be trained to be careful not to eat nor inhale the fibers. It appears that the hazard is similar to rockwool and fiberglass, but much less than asbestos.
The lunar space elevator will extend from a winch near the center of the side of the Moon visable from Earth though the Earth-Moon L1 plus perhaps 50,000 more kilometers. Climbers powered by lasers will drop their cargo at or near the end and it will fall rapidly toward Earth where it will do a sling shot manuver = gravity assist manuver to other locations in the solar system. Some delta v is needed for this manuver or to do areobreaking in Earth's atmosphere for a soft landing on Earth. The reverse direction will take almost as much fuel as landing on the moon directly, so pay loads will rarely use the skyhook for deliveries to the moon, but deliveries to L1 from the moon will likely be done with the Skyhook.
- http://www.treitel.org/Richard/rass/stalk05.html Would a beanstalk (or "skyhook") be possible on the moon?
- http://www.star-tech-inc.com/papers/als/lunar.pdf - Anchored Lunar Satellites for Cislunar Transportation and Communication - Jerome Pearson