Design of the infrared fast steering mirror chopping control system for the Keck II Telescope

Jean-Noel Aubrun; Kenneth R. Lorell; Gregory J. Feher; Ernesto O. Perez; Paul J. Reshatoff Jr.; Donald F. Zacharie

doi:10.1117/12.319278

25 August 1998 Design of the infrared fast steering mirror chopping control system for the Keck II Telescope

Jean-Noel Aubrun, Kenneth R. Lorell, Gregory J. Feher, Ernesto O. Perez, Paul J. Reshatoff Jr., Donald F. Zacharie

Proceedings Volume 3352, Advanced Technology Optical/IR Telescopes VI; (1998) https://doi.org/10.1117/12.319278
Event: Astronomical Telescopes and Instrumentation, 1998, Kona, HI, United States

Abstract

The Keck 2 ten meter telescope will utilize an advanced chopping secondary mirror in order to enhance observations in the infrared. The Infrared Fast Steering Mirror (IFSM) can execute a square-wave chop at frequencies as high as 25 Hz with an accuracy of +/- 0.1 arcsec. Chopping can be synchronized by focal plane instruments, and the system can simultaneously perform high-performance chopping as well as beam-steering (for atmospheric correction), providing the Keck telescope with greatly enhanced capability. Details of design, testing, and performance of the Keck 2 IFSM are presented in this paper. The mirror is controlled by three voice coil actuators. Reaction forces generated by the actuators are absorbed by a reaction mass suspended from the main IFSM structure. Motor driven springs are used to minimize power dissipation in the actuators. The IFSM all- digital control system uses a unique adaptive algorithm that forces the mirror to precisely follow the commanded chop waveform. Tests use various computerized instruments: a three-axis laser interferometer for calibration and stability, a 6-axis dynamometer to evaluate reaction forces transmitted to the telescope. In addition to specifics of the design, performance, and testing, a video illustrating details of the IFSM hardware and showing it in operation will be presented.

Citation Download Citation

Jean-Noel Aubrun, Kenneth R. Lorell, Gregory J. Feher, Ernesto O. Perez, Paul J. Reshatoff Jr., and Donald F. Zacharie "Design of the infrared fast steering mirror chopping control system for the Keck II Telescope", Proc. SPIE 3352, Advanced Technology Optical/IR Telescopes VI, (25 August 1998); https://doi.org/10.1117/12.319278

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