SECCI/COR2Status Report

SECCHI CONSORTIUM MEETING

D. Socker, S. Plunkett,

A. Vourlidas

Science Objectives

• 3D structure of CMEs.• CME evolution (speed, mass, etc).• Structure of outer corona (streamers, plumes).

Performance Specifications

Field of View 2-15 R (nominal)

Pixel resolution 14"/pixel

Exposure Time 4 seconds,

(3 exposures /19 sec)

Image Cadence 30 minutes (synoptic)

22 seconds (max for pB)

Passband ~600-700 nm

Observing Modes

• pB sequence– Three (0, 120, 240 deg) polarizer position image set.

– Three images transmitted to the ground.

• Total B sequence– Two (0, 90 deg) polarizer position image set.

– On-board processing of images.

– Single processed image transmitted .

• ROI (Region Of Interest)– Selected sub-fields processed and transmitted.

Observing Modes

• Sum/Difference– On board comparison of two (or more) images.

– Sum or difference transmitted.

• Calibration– Lamp and dark images for CCD calibration.

– Images in several (~18) redundant polarizer positions from 0º-360º.

• Pixel binning– In SEB (digital) or (analog) CCD.

COR2 Layout

Design Status

• Significant changes from proposal level concept– Vignetting in 12R-15R region eliminated.– Singlet objective replaced with doublet (“air”

spaced).– Halfwave retarder plate replaced by polarizer

(Polarcor or polaroid,TBD)

Design Status

• Mechanical– Layout level complete– Design level in progress

• Optical– Still using proposal singlet design as

placeholder.– Intermediate level design initiated.

Design Status

• Thermal– Critical locations (A0, occulter, heat rejection mirror)

being modeled.– Thermal bending < 5”.

• Contamination control– Layout (for SCIP box case) completed.

• Radiation damage issues– Using same optical materials as LASCO C2.– Looking at some optical materials testing (glass,

cements, AR coatings).

Instrumental Backgrounds Studies

• A0– Modeling serrated and circular edge generated

backgrounds.

• A0-A1 tube section baffles– Modeling baffles to minimize machining cost without

degrading optical performance.

• Heat rejection mirror– Modeling to determine optical surface requirements.

Instrumental Backgrounds Studies

• A1/heat rejection mirror interface– Model details of design to avoid interface

becoming a significant background.

• Shutter leakage model.

• O1, O2 aberration modeling– Detailed ray trace studies to optimize rejection

at internal occulter and Lyot stop.

Instrumental Backgrounds Studies

• External occulter model and test– Straight edge (model & test)

• Point source, multiple wavelengths.• Edge bevel effects.• Polarization effects.

– Single circular disk (model & test)• Point and extended sources, multiple distances.• Fresnel model matches test results.

– Multiple (2/3) disks (model & test in LASCO/C3 EM).– Serrated disk (model & test in LASCO/C3 EM).– Smooth cone and tear-drop shapes (test in LASCO/C3 EM).

Instrumental Backgrounds Studies

• O1 Coating and Polish Scatter Tests– Flat glass samples

• Conventionally polished (fussed silica tested, BK7 future).

• Ion milled polish (fussed silica tested, BK7 future).

• AR & non AR coated (hard coating).

– Results to date• AR coating has negligible effect on scattering.

• Scattering from samples with conventional and ion-milled surface polish is similar.

• Near-specular angles dominated by point-like defects.

Instrumental Backgrounds Studies

• Future flats tests– Flat samples of radiation resistant BK7 will be

delivered to NRL by end of July.

• Future singlet & doublet objective tests.– Aberration optimized O1 lenses will be mounted in C3

EM and stray light measured in vacuum.

Calibration

• Based on LASCO experience– LASCO in-flight calibrations verified the ground

calibrations to within <10-30% overall.

• Ground-based calibrations– Measure expected flight performance and will provide

a baseline for comparison with in-flight calibrations.

• In-flight calibrations– Measure actual performance and monitor instrument

stability.

Ground Calibrations

• Ground-based calibrations will take place at NRL Solar Instrument Test facility (Building A13).

• Calibration products include:– Radiometric calibration.

– Stray light background.

– Vignetting and distortion function.

– Filter and CCD QE and spectral response.

– Polarization calibration (polarization analyzer and instrumental polarization).

In-flight Calibrations(Door Closed)

• Diffusing window in door for photometric calibrations, measurement of instrument polarization and stability checks.

• Three LED calibration lamps at TBD locations for CCD calibrations.

• Dark images for CCD calibrations and stability checks.

In-flight Calibrations(Door Open)

• Background stars.– Pointing, plate scale, time corrections, vignetting,

distortion, photometry.

• Spacecraft rolls.– Polarization and stray light.

• Time series of coronal images.– F-corona, stray light.

• Cross-calibration with COR1/HI, COR2 A/B, LASCO, and ground-based observations.