In terms of g's and rpm's, It has sometimes been viewed as desirable to provide one g at no more than one rpm. This is possible only in exceedingly large habitats, e.g., 100,000 people with slightly more than 10,000 m3/person, in a spherical geometry. The toroidal geometry, i.e., the Stanford Torus, allows this idea to be approached with much smaller total enclosed volume, but the ratio of shield area to enclosed volume is much greater. A further design consideration is heat rejection. If the habitat must reject its net internal heat load from its surface, its size is limited. (External radiators or refrigeration machinery can ameliorate this limitation, but these are undesirable complications.) For a sphere, Crew Requirements Estimates of the construction crew complement for early commercial SPS construction have converged on a figure of roughly 500. In the reference scenario, this grows to about 2000 people in 30 years due to growth in maintenance workload. A slightly conservative allowed delta cost of $100/kg yields a volume of 200 m3/person and a radius of roughly 35 m. To provide even 0.5 g, the required spin rate is about 3.6 rpm. Rotating room studies have found that people can adapt to rotating environments up to 3 rpm, and that below 1 rpm little adaption is required. People in rotating rooms are subject to “weird” fields . . . one experiences Coriolis forces walking across the floor; the local vertical is not normal to the floor. By comparison, the field in a rotating habitat free of Earth's permanent gravitation field is less weird. Nonetheless, 3 rpm has generally been adopted as an upper limit for rotating habitats. Thus, the 500-person habitat seems marginal. Moreover, the construction in space of a large habitat pressure vessel is likely a challenge that would best be deferred to a later time than the challenges faced in getting SPS production underway. Projecting further in time to a work force of 2000, and adopting a slightly more bullish cost of $50/kg, yields an allowable volume of 1000 m3/person and a radius of 80 m. With 0.5 g, the required spin is 2.4 rpm. This case meets the thermal and spin rate criteria and provides relatively generous volume. The $50/kg target may be attainable by Earth launch and is almost certainly or P = (3/R)( V)(0.3), roughly P = V/R. A typical heat load is 10 kWth/person; for V = 104, a radius up to 1000 m can be accommodated; for V = 103, a radius of 100 m is allowable. The heat rejection capability of its surface at room temperature is roughly 0.3 kWth/m2. We can employ a set of ratios:
RkJQdWJsaXNoZXIy MTU5NjU0Mg==