Thermal considerations for hydroformed reflectors

One antenna design under consideration for both the next generation Deep Space Network (DSN) array and the Square Kilometer Array (SKA) project is a hydroformed symmetrically shaped dual reflector system. Hydroforming is the process of forming aluminum to a rigid and precise mold by using a fluid or gas under pressure. Three 6-meter hydroformed reflectors with rms less than 8 mils (0.2 mm) have been delivered to JPL. One concern about the high-frequency performance of these antennas is the surface deformation caused by thermal gradients. The rms surface requirement for the combined as manufactured shape plus thermal and gravity deformations is 10.7 mils (0.27mm). The first assembled dish was not painted (bare aluminum only) and measurements of surface rms under mid-day sun showed an rms exceeding 14 mils (0.36mm) rms. After application of the triangle no. 6 diffusive white paint typically used on JPL reflectors, the rms under similar conditions was reduced to less than the 10.7 mil (0.27mm) specification. This paper discussed the thermal design and performance of the 6-meter hydroformed reflector as well as projecting the performance of the SKA 12-meter antenna.