This section provides some detail on the construction of the final version of the heliostat
prototype. mid-plane supported rotated by
The heliostat consists of an inflated sphere with a membrane mirror mounted at the of the sphere. The mirror is supported by an extruded aluminum ring, which in turn is
by the two Polar Arms.
The Polar Arms rest on an Azimuth Platform that can be
the azimuth drive to provide pointing in the azimuth direction.
Pointing the elevation
direction is accomplished by turning the sphere about Polar Arms. The inflatable sphere is supported by a Rollers. Figures 6a and 6b provide an overview of the below for each component.
bearings located at the upper end of the combination of the Polar Arms and Ball heliostat. Additional details are provided
It should be noted that in a number of cases materials and construction techniques used for the prototype would not meet production design requirements. These compromises in materials and construction techniques were made to keep the cost and construction time within the scope of the project. None of the project goals were sacrificed to any significant degree by the compromises.
Domes: The upper dome is constructed from heat seamed Vinyl. The upper dome and Mylar mirror form the upper airtight chamber. The lower dome is constructed from PVC coated Polyester fabric. A latex bladder is used inside the lower dome to provide an airtight chamber. Each of the domes is constructed from 12 panels that are cut beach-ball-style to form a sphere. The air pressure in each
of the domes can be maintained in the upper approximately 4 inches
In operation a slightly higher pressure is
dome to focus the Mylar film mirror. The domes of water. The differential pressure to maintain
are normally inflated to focus is small – of the
order of 0.1 inches of water. It should be noted that the production single piece, thermoformed dome constructed from a material with Tefzel).
design will probably utilize a a longer life (such as DuPont
Polar Arms: The polar arms support the sphere formed by the two domes, and allow rotation of the domes in elevation. The lower ends of the polar arms are rigidly attached to the Azimuth Platform. The upper end of the arms each have a bearing that carries a shaft mounted to the mirror support ring. This allows the sphere to be rotated in elevation about the top of the polar arms. The bearings
quality, dimensionally stable plywood that is overlain on both sides with resin membrane for strength and stability). Two aluminum braces between the azimuth each polar arm stiffen the polar arms.
impregnated platform and
Azimuth Platform: The Azimuth Platform provides the support base for the polar arms and for the ball rollers. The entire Azimuth Platform is supported on edge rollers and is free to rotate about a vertical axis through the center of the Azimuth Platform – this provides for aiming the heliostat in the azimuth direction. The Azimuth Platform is shown in figure 6c. A detail of the edge rollers is shown in Fig. 6d. The Azimuth Platform is also constructed from MDO.
November 24, 2002