Comment Re:Way too long. (Score 1) 422
Actually to return an object you only need to return it close enough to Earth for gravity to do the rest. From the ISS this is just a slight push down or opposite of your angular velocity. For an object at the end of a 100,000 km space elevator the story is quite different.
At 100,000 km from the center of the Earth (about 94,000 km from the surface) the geosynchronous velocity would be 7,270 m/s. In order for gravity to overcome centrifugal force and pull the object back down it has to be slowed to just under 2,000 m/s. For a 1-ton object, this requires a kinetic energy change of 3,480 kWh. At 3 cents per kWh that means a cost of over $100 just to bring the object back, which is assuming you don't want it back in a more timely manner or precise location.
At 100,000 km from the center of the Earth (about 94,000 km from the surface) the geosynchronous velocity would be 7,270 m/s. In order for gravity to overcome centrifugal force and pull the object back down it has to be slowed to just under 2,000 m/s. For a 1-ton object, this requires a kinetic energy change of 3,480 kWh. At 3 cents per kWh that means a cost of over $100 just to bring the object back, which is assuming you don't want it back in a more timely manner or precise location.
