Full Moon Flux Mapping the 400 m 2 “ Big Dish ” at the Australian National University

Videographic flux mapping of a lunar image has been used to characterize the focal flux distribution of the ANU 400m “Big Dish” solar collector. This technique was undertaken by using a CCD video camera to capture the image of the moon focal flux projected onto a planar target. The advantage of this technique is that the moon has a very similar angular width to the solar image and the high heat flux associated with the solar insolation that would require a complex cooling system with complicated target structure is avoided. Conventional flux mapping was used to characterize the optical performance of the dish when it was first built. The aim of this investigation was to see if the optical performance had changed in the intervening years. In this experiment a light weight target was placed in front of the monotube boiler receiver that is currently fitted to the dish for the display of the flux image. Comparison of ray trace predictions and the measured flux indicated that the dish surface has a mean surface error of 7.5 ± 0.3 milliradian.