Designing a space elevator
From the table above both Steel and Titanium are unrealistic, with Kevlar and Carbon Fibre better, but still costing more than we can afford. However, there is a futuristic material called Carbon Nanotubes that has a taper ratio of only 1.62. This could solve all our problems, but Carbon Nanotubes are ridiculously expensive and the technology we currently have is not good enough to produce thousands of kilometres of it. Therefore, the construction of the tether is one of the hardest engineering challenges in developing a functional space elevator because without a safe tether the elevator would not run.
Secondly, the forces acting on the space elevator are another major engineering challenges to overcome, in particular, atomic oxygen. Therefore, engineers must formulate a protective coating for the tether. Atomic oxygen is a very corrosive substance found in the upper atmosphere between 60 and
800km, with the highest density near 100km altitude. According to NASA's Long Duration Exposure Facility (LDEF) mission, atomic oxygen etches into materials such as carbon fibre composites at a rate of up to one μm/month. The rate of corrosion on the cable would destroy it in a matter of weeks. Nevertheless, Bradley Edwards in The Space Elevator illustrates two viable solutions to this problem. The first is the concept of coating the cable with anti-corrosive materials, such as gold, platinum and nickel plus SiO2. While both gold and platinum are good materials for the job, studies show that nickel plus SiO2 is the most efficient method, as a marginal 0.16 microns could protect the
Diagram from the paper by Bradley Edwards titled ‘The Space Elevator’
composite from the effects of atomic oxygen. With the use of carbon nanotubes in this cable, it is unclear how corrosive atomic oxygen would be to the cable and several tests need to be conducted to determine the exact effects on the cable. Consequently, the protective covering for the cable is an engineering challenge in the of building a functioning lift, because otherwise the elevator would not be able to run. The last significant engineering challenge is avoiding space debris in orbit travelling fast enough to destroy the space elevator. Space debris is a big problem for NASA and they have spent thousands of hours trying to reduce the amount of space debris. It is highly likely that a still immobile object like the space elevator will be hit by one of the 500,000 pieces in orbit. Space debris can vary in size, the largest
being a satellite called Envisat, once operated by the European Space Agency. All space debris orbits the Earth at speeds of up to 18,000 miles per hour. This is a high enough velocity for even the smallest particles to damage satellites and the space elevator. This also has the potential to unbalance the lift and disrupt its geosynchronous orbit. Such a catastrophe would cause the space elevator to spin out of control and make it impossible to operate. Bradley Edwards devotes a separate
Diagram from the paper by Bradley Edwards titled ‘The Space Elevator’
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