Desktop Prototyping, Trade Studies and Refined Prototype Design
At the start of the project, some pre-prototype studies and tests were conducted to help evolve a preferred prototype design, to fulfill goal 1 of the Project Goals. The first pre-prototype approach involved evaluation of the feasibility of an inflatable heliostat support comprising a base balloon, which rolls on the ground surface to accomplish orientation control in elevation and azimuth. A “blue balloon” desktop prototype was used for this purpose, and is illustrated in Figure 3.
The “blue balloon” model is a 15-inch heavy-duty child’s play ball. A toroidal balloon for supporting a reflective surface, is represented in this pre-prototype by a circular wood structure, to which the stranded wire tethers are attached. The tethers are steel wire, and are wrapped on “winches” made from half-inch diameter bolts. The winches are turned with a ratchet wrench that provides 10 deg increments, or about 0.04 inches of cable movement per ratchet click. The tether cables were typically tensioned to 20 to 30 lbs. The balloon was typically inflated to 50 to 70 inches of water (1.8 to 2.5 psi) – similar to heavy-duty rubber rafts. Inflation pressure was measured using a water manometer.
Figure 3 – “Blue Balloon” Desktop Prototype
November 24, 2002