Secondary mirror for MRO
Thales SESO has manufactured (i.e. grinding, polishing and coating) the secondary ULE mirror of the Magdalena Ridge Observatory (MRO). This is a challenging highly off axis convex aspherical mirror.
The main characteristics and specifications of this mirror are:
• Substrate: Lightened ULE structure with Corning fusion process
• Size : circular Φ690mm
• Shape: hyperbolic Convex with about 50µm asphericity from best fit sphere
• Optical quality required: WFE < 40nm RMS for full Clear Aperture
• Coating: protected aluminum
One of the main challenges of this mirror was the optical control because we are facing simultaneously different problems: a large mirror, an aspherical surface are, moreover, a convex one. Thales SESO has developed for this mirror a full aperture interferometric bench using a large sized Hindle corrector. Errors due to Hindle corrector itself and WFE distortions induced by the natural gravity were managed and compensated thanks to a specific control iteration process.