8.46 The truss is sized by applying this load in the middle of the longest unsupported span, the 300m lengthwise span of the frame. The truss is modeled as a square hollow beam with an equal concentration of material in each corner. The design stress level is chosen low, at 140 MN/m 2 (20,000 psi) so as to avoid fatigue problems. Using the imposed loading and working stress, each corner must have an area of .027m 2 or 160 mm x 160 mm. Several other loading conditions were checked including the loading of the cranes assuming the same cross section as was found necessary for the frame. In all cases, the resulting stresses were below (but not greatly below) the design stress. Therefore, the trusswork structures are modeled as square hollow beams made up of four .027m 2 corners for a total cross sectional area of .108m 2 . While this probably leads to a conservative value for the structural mass, it is probably a reasonable estimate of the effective cross sectional area since none of the masses of the detailed elements, such as the hoist, cabs, electric drive motors or busbars have been included. The construction site is made up of the 400m long mast,four 150m long booms, a frame with two 310m sides and one 220m side, and two cranes of 220m diameter, for a total of 3222m of truss with a cross sectional area of .10Bm 2 . The total mass of steel needed is 2740 tons. Power requirements for this structure include those for hoist and crane motions, manipulators, damping mechanisms (if required), lighting, and measurement systems. This electrical consumption is estimated at 1000 kW. The crew quarters are one of the first things to arrive at the colony site and should therefore be completely preassembled and carried in the Shuttle. The Shuttle bay is roughly 4.Sm in diameter and 18m long. A cylinder of this size has a volume of 286m 3 Assuming 20m 3 per man, 14 people could live in a cylinder. Therefore,four cylinders would be needed for the initial crew of about 50 workers. As the work force builds up to the peak of 140-160 people, additional space is needed. If one 18m diameter shack is built according to the same design as the work shacks (Section VIII.6.1), it can add 7600m 3 for
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