AAS 207th Meeting, 8-12 January 2006
Session 26 LSST
Poster, Monday, 9:20am-7:00pm, January 9, 2006, Exhibit Hall

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[26.21] LSST Wavefront and Alignment Sensing

W.J. Gressler, C.F. Claver (NOAO), W.P. Kuhn (Optical Perspectives Group), S. Olivier, D. Phillion (LLNL), J. Richards (CTIO/NOAO), J. Sebag (NOAO), H.E. Schwarz (CTIO/NOAO), LSST Collaboration

The proposed Large Synoptic Survey Telescope (LSST) has developed a concept for optical wavefront and system alignment control that includes direct wavefront sensing and separate rigid body position sensing. The telescope optical system has three reflective surfaces based on a Paul-Baker three element design and three refractive lenses feeding the single flat focal plane in the dedicated instrument. The large mirrors, an 8.4 m diameter primary, 3.4 m secondary, and 5.0 m tertiary, require active control of figure and all the optics and camera assembly must be actively positioned in rigid body to maintain performance of this 3.5 degree field of view system. The LSST concept uses a distributed set of wavefront sensors in the 65cm diameter focal plane with adequate spatial frequency to resolve the wavefront control for each of the three reflective surfaces. Optical reconstruction analysis, wavefront sensor performance, and star density statistics have been used to define the necessary field dependant sensing to meet the LSST requirements. An active alignment system using laser tracker technology has been defined to address the rigid body position control. The 30 second cadence of the LSST and the wavefront sensing intermittency associated with full camera exposures demands a separate system to keep the optical elements and camera within alignment specification. These two systems, working in concert with each other, sense the LSST wavefront and alignment at spatial and temporal rates necessary to support the LSST science mission.

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