The final design configuration is a backboard of inflatable struts, as seen in Figure 5.
Figure 7: Inflatable Strut Configuration
The inflatable structure is constructed of 0.27 mm thick Kevlar with Neoprene coating. Each strut is 10 meters in diameter. Perpendicular to the primary axis of rotation are two struts, 1 km long, to counteract the forces caused by the rotation. All four corners are supported by the double criss-cross design. Each criss-crossed strut is 1.4 km long. The solar cells are attached to the face of the structure. Like a sheet, the solar cell array covers the entire side of the inflated backbone.
The distribution of the mass in the structure is symmetric about both axes of rotation. The symmetry is important for balance purposes. If the structure becomes unbalanced the effects of the Earth's gravitational pull could become disastrous.
Kevlar tubes are easy to manufacture. The manufacturing process is much like that of textile fabrics. Current techniques can produce the necessary dimensions required for the structure on current machines. Recent trials of an inflated Kevlar craft have been successful. The Spartan STS-77 mission deployed an inflatable antenna 50 meters in diameter on three 92 ft struts 14 inches in diameter. Though the inflated antenna tumbled violently end over end, the inflated struts did not buckle or fold.