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Space elevator safety
There are risks associated with never-done-before technologies like the construction and operation of a space elevator. A space elevator would present a navigational hazard, both to aircraft and spacecraft. Aircraft could be dealt with by means of simple air-traffic control restrictions. Impacts by space objects such as meteoroids, satellites and micrometeorites pose a more difficult problem for construction and operation of a space elevator.
If nothing were done, essentially all satellites with perigees below the top of the elevator would eventually collide with the elevator cable.
For stability, it is not enough that other fibers be able to take over the load of a failed strand — the system must also survive the immediate, dynamical effects of fiber failure, which generates projectiles aimed at the cable itself. For example, if the cable has a working stress of 50 gigapascals (7,300,000 psi) and a Young's modulus of 1,000 gigapascals (150,000,000 psi), its strain will be 0.05 and its stored elastic energy will be 1/2 × 0.05 × 50 GPa = 1.25 billion joules per cubic meter. Breaking a fiber will result in a pair of de-tensioning waves moving apart at the speed of sound in the fiber, with the fiber segments behind each wave moving at over 1,000 metres per second (3,300 ft/s) (more than the muzzle velocity of a standard .223 caliber (5.56 mm) round fired from an M16 rifle). Unless these fast-moving projectiles can be stopped safely, they will break yet other fibers, initiating a failure cascade capable of severing the cable. The challenge of preventing fiber breakage from initiating a catastrophic failure cascade seems to be unaddressed in the current literature on terrestrial space elevators.[citation needed] Problems of this sort would be easier to solve in lower-tension applications (e.g., lunar elevators). This problem has been described by physicist Freeman Dyson.
Corrosion is thought by some to be a risk to any thinly built tether (which most designs call for). In the upper atmosphere, atomic oxygen steadily eats away at most materials.
Other analyses show atomic oxygen to be a non-problem in practice.
Most of the space elevator structure would lie inside the Van Allen radiation belt, and the space elevator would run through the Van Allen belts. This is not a problem for most freight, but the amount of time a climber spends in this region would cause radiation poisoning to any unshielded human or other living things. The inner belt would have to be crossed, where—behind a shield of three millimetres (0.12 in) of aluminium—the dose rate can reach 465 mSv/h.
Furthermore, the effectiveness of the magnetosphere to deflect radiation emanating from the sun decreases dramatically after rising several earth radii above the surface. This ionising radiation may cause damage to materials within both the tether and climbers.
For a space elevator to be used by human passengers, the Van Allen radiation belt must therefore be emptied of its charged particles. This has been proposed by the High Voltage Orbiting Long Tether project.
Space elevator safety
There are risks associated with never-done-before technologies like the construction and operation of a space elevator. A space elevator would present a navigational hazard, both to aircraft and spacecraft. Aircraft could be dealt with by means of simple air-traffic control restrictions. Impacts by space objects such as meteoroids, satellites and micrometeorites pose a more difficult problem for construction and operation of a space elevator.
If nothing were done, essentially all satellites with perigees below the top of the elevator would eventually collide with the elevator cable.
For stability, it is not enough that other fibers be able to take over the load of a failed strand — the system must also survive the immediate, dynamical effects of fiber failure, which generates projectiles aimed at the cable itself. For example, if the cable has a working stress of 50 gigapascals (7,300,000 psi) and a Young's modulus of 1,000 gigapascals (150,000,000 psi), its strain will be 0.05 and its stored elastic energy will be 1/2 × 0.05 × 50 GPa = 1.25 billion joules per cubic meter. Breaking a fiber will result in a pair of de-tensioning waves moving apart at the speed of sound in the fiber, with the fiber segments behind each wave moving at over 1,000 metres per second (3,300 ft/s) (more than the muzzle velocity of a standard .223 caliber (5.56 mm) round fired from an M16 rifle). Unless these fast-moving projectiles can be stopped safely, they will break yet other fibers, initiating a failure cascade capable of severing the cable. The challenge of preventing fiber breakage from initiating a catastrophic failure cascade seems to be unaddressed in the current literature on terrestrial space elevators.[citation needed] Problems of this sort would be easier to solve in lower-tension applications (e.g., lunar elevators). This problem has been described by physicist Freeman Dyson.
Corrosion is thought by some to be a risk to any thinly built tether (which most designs call for). In the upper atmosphere, atomic oxygen steadily eats away at most materials.
Other analyses show atomic oxygen to be a non-problem in practice.
Most of the space elevator structure would lie inside the Van Allen radiation belt, and the space elevator would run through the Van Allen belts. This is not a problem for most freight, but the amount of time a climber spends in this region would cause radiation poisoning to any unshielded human or other living things. The inner belt would have to be crossed, where—behind a shield of three millimetres (0.12 in) of aluminium—the dose rate can reach 465 mSv/h.
Furthermore, the effectiveness of the magnetosphere to deflect radiation emanating from the sun decreases dramatically after rising several earth radii above the surface. This ionising radiation may cause damage to materials within both the tether and climbers.
For a space elevator to be used by human passengers, the Van Allen radiation belt must therefore be emptied of its charged particles. This has been proposed by the High Voltage Orbiting Long Tether project.