APEX

5 years ago, CMA produced the first 0.75m subreflector for the 12-m Atacama Pathfinder Experiment (APEX) telescope, located at 16,000 ft elevation on the Atacama Plateau in Chile. Produced entirely from replicated carbon composites, the subreflector was in operation for over 3 years on the telescope and was recently shipped back to CMA for an improved coating.

Testing of the surface quality shows no measurable degradation in optical performance in that time. With the replication mandrel accuracy of 6.1µm rms, the initial carbon composite subreflector measurement was 7.5µm rms in 2004 before shipment. The latest data in October 2008 shows a surface rms of 7.0, indicating a high degree of stability for the APEX subreflector.

CBI

As a side note, the Cosmic Background Imager (CBI) telescope, located at the same site as APEX, uses 13 carbon composite replicated hyperbolic secondary mirrors. CMA produced the mirrors 14 years ago for Caltech and CBI. The subreflectors initially measured out to 1µm rms and have performed nominally for the past 14 years.