1. GRIPS Imaging Subsystem Gordon Hurford GRIPS Kickoff Meeting 22-Sept-08

2. Outline Review of proposed imager Imager issues Aspect issues Priorities and schedule

3. GRIPS Imaging Principle Rotating mask casts a corresponding x-ray shadow on detector. Back-projecting location of successive counts enables image reconstruction 1 3 10 30 100 1000

4. Multi-pitch Rotating Modulator (MPRM) Quasi-continuous range of grid pitch provides good point response function Grid pitches: 1 to 13 mm 12.9 – 168 arcsec FWHM (with 8 m boom) Requires spatial resolution = 0.5 * pitch Grids thick enough for 2.2 MeV (2 cm W) Images reconstructed from any selected subset of counts defined by (x,y,t)  imaging spectroscopy and imaging polarimetry

5. Inputs to Imager Design Imaging goals (13-169 arcsec, up to 2.2 MeV, full Sun FOV & Crab) Detector layout (4 x 7.5x7.5 cm active within 19x19cm envelope) –drives mask size) Detector spatial resolution and profile –Expected performance drives grid design –Failure to achieve expected performance gracefully reduces angular resolution and imaging sensitivity. –Knowledge of inflight performance needed for size measurement  calibration masks ? Pointing accuracy (+- 0.5 degrees, 3 sigma) –drives mask size Upper limit to boom length (8m) –If boom ‘shrinks’ during development, spatial resolution just scales Upper limit to mask weight (48 kg) - If upper limit shrinks during development, grid redesign may be reqd.

6. Grid Fabrication and Calibration Issues Cut individual grid slats from tungsten sheet of different thickness Options other than EDM? Purchase slats precut Subcontract cutting In house Purchase tungsten sheet in ‘standard’ thicknesses ? Standard or custom thickness requirements Flatness requirement Alloy ? Calibration For 5 arcsec locations, need 0.2 mm metrology Error budget includes, grid, aspect, detector & system level components Hardware options ?

7. Imager – Next steps Consensus on design inputs Optimize grid design Develop error budget Investigate tungsten options Document imaging concept

8. GRIPS Aspect Requirements Absolute pitch and yaw (<3 arcsec) Relative orientation of detector and mask Absolute orientation of detector Aspect for both solar and Crab viewing Required cadence >> pendulation & ACS timescales –Resonance frequency of boom?

9. Solar Pitch-Yaw Aspect Grid-embedded lens forms solar image on diffuse reflecting screen Viewed by boom- mounted camera

10. Crab Pitch and Yaw Motor-operated beam- steering prisms and second lens cast solar image on screen Supports offsets > 20 degrees Provides relative pitch and yaw only Heritage from HEIDI balloon project

11. Detector-mask relative twist Laser diodes mounted on back of grid mount. Viewed by camera mounted on detector

12. Absolute detector roll aspect Electronic level compensates for balloon balance errors – enables absolute source placement on Sun Crab observations require additional aspect to correct for balloon pendulation –Options: Side-viewing star camera (HEIDI heritage) Horizon sensor?

13. GRIPS Aspect Subsystems Gondola-related –Solar acquisition –Real-time for pointing control Image reconstruction SolarCrab Pitch/yawEmbedded lens in grid + detector screen Motorized prism + 2 nd lens Detector-mask rollEmbedded laser diodes in grid or 2 nd lens Embedded laser diodes Absolute detector rollElectronic level (for only) Horizon sensor or star camera

14. Aspect – next steps Get confirmation of expected pendulation properties, balance and ACS dynamics Achieve consensus on aspect approach Quantify aspect performance and design parameters Identify potential camera/data options Aspect testbed by summer 09 ?

16. Other to-do’s Modify schedule –match budget and other subsystem schedules Need to identify personnel –camera subsystems and data recording –role of students?