redundancy) can be achieved by placing four thrusters around the rim at 90-degree intervals. Consider the "pin-wheel" arrangement in Figure 5. The SPS mass is supported against thruster action by the four-strut arrangement shown. These struts are at right angles to each other, meet at the SPS Center of Mass (CM) and each has a gimbaled thruster on the end farthest from the CM. Each thruster can apply thrust perpendicular to the local strut (Tt) and parallel to that strut (Tl). SPS rotation is modeled using the moment of inertia (I) for a thin bar rotating about a perpendicular through its center: Furthermore, Table 2 shows that a 2000-meter diameter bicycle wheel has an array mass of roughly 50 tonnes. However, due to the light weight of the structural material, it was considered worthwhile to "overengineer" the support struts to support additional weight.) If all SPS mass must (in worst-case scenario) be supported by each leg of the structure, I Previous calculations have implicitly assumed Tt, thrust applied perpendicular to the strut. Maximum strut mass can be estimated by assuming that this maximum thruster force Conservatively assume that the specific gravity of the strut material is 10 (density = 10,000 kg/m3). Because each strut has a length of 1000 m and there are 4 struts, the total structural mass required to support thruster-caused rotations of the SPS is about 0.12 kg.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==