LBT AGW units Design Review Mar.2001 General Concept Performance specifications and goals The off-axis unit The mechanical support structure The control system, electronics/software The on-axis AO system

Goals for this meeting Prepare list of modifications (off- axis) Freeze off-axis design Discuss on-axis AO design Can we proceed w. outer structure and/or baseplate? Prepare tentative timetable for design and review

Performance specs & goals Baseline Science FOV 4'x4' Guiding (seeing limit) AO (diff. AO w. optical light reflected off 15deg inclined entrance window Operating temperature range -5 to +15C w. possibly degraded performance -20 to -5C and +15 to +25C Performance maintained for dT/dt < 1deg/h Performance maintained over 30deg rotation of derotator

Performance specs & goals Off-axis system centroid to 1/10x0.4=0.04arcsec Camera FOV >20arcsec, patrol area > 15sq.arcmin On-axis access for acquisition WFS on natural stars for active optics (>10sec) WFS w. 4x4 and 12x12 Shack-Hartmann lenslet arrays Guider camera provides high res. curvature sensing

Performance specs & goals On-axis tip-tilt system Tip-tilt camera FOV > 1' Tip-tilt signal > 100Hz APD (STRAP) instead of CCD...

Performance specs & goals On-axis WFS system WFS on natural and sodium laser (589nm) reference stars WFS signals at >100Hz Pyramid/SH sensor? Atmospheric Dispersion Corrector? Filter wheel?

Performance specs & goals Control system CCDs running over SDSU GenII controllers Industry standard computers VxWorks environment TCP/IP, RPC (remote procedure call) interfaces 120V 60Hz UPS powered

The off-axis unit Optical layout Guider camera w. focal reducer (x2), 22x22" FOV Patrol field 18 sq. arcmin 98% chance of finding R<18mag guidestar (1Hz guiding) Filterwheel Keep FM4 small for stability and vignetting (<50mm) Shack-Hartmann WFS 2 lenslet arrays 4x4 and 12x12 lenslets 1.9mm pupils 2 pinholes and collimators Dichroic reflects red light into WFS arm

The off-axis unit Mechanical layout X  stage for patrol Common focus stage for the cameras Optics separate from unit Shack-Hartmann WFS 2 lenslet arrays 4x4 and 12x12 lenslets 2 pinholes and collimators Dichroic reflects red light into WFS arm

The off-axis unit Mechanical tolerances IQ better than 1/10th of the seeing limit: 0.4arcsec Platescale 1.67"/mm gives about 0.025mm tolerance w. respect to science focal plane In X and theta we then have 0.013mm tolerance Tilt of FM4 less than 5 arcsec Tilt of complete unit less than 10 arcsec Positioning better than 0.1arcsec (0.06mm) Focus range +-20mm (focal plane curvature=+-10mm)

The off-axis unit Detectors  Guiding 512x1k frame-trans. Marconi mm/pix, 0.04"/pix QE: 45% at 700nm RON: 20kHz : 2e-; 1MHz: 6e- Dark 1e-/s/pix at -60C 0.03 e-/s/pix at -80C Shutter less  Wavefront Sensing 512x1k frame-trans. Marconi " FOV, 4x4 SH sensor: 0.08"/pix 12x12 SH sensor: 0.25"/pix Steward dewars for both CCDs Cooling critical for >30s exp.

The mechanical support structure Connects derotator w. instrument FE analysis of different truss designs Within 0.055mm shift, well within 0.2mm tolerance Stress analysis looks fine Baseplate stability driven by tip- tilt camera (mass) FE analysis of opto-mechanical system in progress Image motion < mm =0.04" over 60deg turn Still to be optimized Steel structure

The control system VME+PMAC2-UltraLite Macro fiber optic link UMAC local control unit (3U Eurocard format) Very few connectors! VME-VxWorks interface Stepper motors 12 axes total Encoders on position stages Brakes on position stages Power switched off while observing Single wire Temp. and humidity sensing system

The on-axis AO system tip-tilt camera Most critical mechanical stability, drives mechanical design High speed essential as tip-tilt error dominates budget APDs superior to CCDs at low light level (no RON) 10mu gap = 0.1" gap in present camera, too big, pyramid? STRAP unit w. VME local control unit (big+15m limit)

The on-axis AO system wavefront sensor Shack-Hartmann or Pyramid or curvature? Pyramid gains almost 2mag for natural guidestar Can the pyramid be made to specs? Is the actuated mirror rugged enough? System analysis needed to establish requirements 80x80 frame-transfer Marconi CCD mm pix, quad read QE=90% at 500nm RON: 3e- at 20kHz 7e- at 1MHz Dark: 8e-/s/pix at -60C 0.2e-/s/pix at -80C