GMT ASM status and phasing test results

Le résumé fourni par la source

The Giant Magellan Telescope utilizes a segmented adaptive secondary mirror subsystem for correction of atmospheric wavefront error (r0=7cm), wind-induced telescope vibrations up to 17 m/s wind speed, and M1 and M2 alignment errors. Each of the 7 segments is a 1.05 m diameter concave circular segment with a 2mm thick facesheet driven by 675 voice coil motors to provide wavefront and phasing control. Hexapod positioners maintain a 7 Hz bandwidth alignment within the capture range of the wavefront control system. The first off-axis ASM segment is currently being manufactured by the AdOptica Consortium. To provide diffraction limited optical performance for Natural Guidestar and Laser Tomography AO modes, the 7 ASM and 7 M1 segment sub-apertures must be phase matched at the image plane. Wavefront and phasing correction commands are issued by the AO system to the ASM segments. The phasing corrections are augmented using Edge Sensors to maintain optical vertex alignment during periods of latency in the phasing control system. Phasing is recognized as a high risk for GMT performance. Under the NSF Optical Performance and Risk Reduction Cooperative Agreement, GMTO, working with AdOptica, has designed and built an ASM Phasing Testbed utilizing one operational ASM segment mounted within a reference frame simulating three adjacent ASM segments. Disturbances representing median wind condition are injected using the ASM hexapod positioner. Edge Sensors measure the motion of the segment relative to the reference frame, and feedforward corrections are sent to a 2000 Hz bandwidth facesheet control system to compensate the simulated wind disturbances. Key terms in the phasing error budget are measured and used to correlate finite element models, used in turn to improve accuracy of the ASM full array phasing performance model and analysis. Future ASM testbeds, with increasing levels of fidelity, are being planned.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.