Example of an asymmetric platform. The total number of External Tanks used Is 36; 24 of them are assembled to form the upper deck, 12 the lower deck. The two decks arc linked by 8 cables, 0.5 cm diameter, of 45 km length. The system 1n circular orbit at 400-500 km has the mean motion of the center of mass of the system which lays roughly 15 km below the upper deck and 30 km above the lower deck. The total tension Is of the order of 5 tons distributed In the 0 cables. The asymmetric configuration has the following advantages: a) The upper and lower platforms may be designed so that the atmospheric drag gives a zero torque with respect to G. b) We have larger acceleration at both the upper and lower levels. In particular, at the lower deck it may be advantageous to have a larger acceleration for simplifying operations there. c) The lower platform has lower velocity, much lower than the local circular velocity and the Shuttle may dock there with zero relative velocity from an eccentri' it with much lower perigee.
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