Full text
Miniature Coronagraph for Heliophysics Research Angelos Vourlidas, on behalf of the MiniCOR APL-Argotech-NRL Teams
The MiniCOR Project at aGlance Science Objectives: - What is the CME kinematical behavior in the middle corona? - What is the Small-Scale Nature of the Solar Wind? Technical Objectives - Are Miniature Imagers viable alternatives for cutting-edge science? - Develop the next-generation operational coronagraph (for SWx and cis-lunar PNT). Concept Description • Develop a miniature version (3U) of the STEREO COR2 coronagraph (demonstrator for science-grade imagers). • Develop a deployable occulter boom with precise positioning for coronagraphy (enabler for new compact imager designs) •Simplified electronics via FPGA-based image acquisition (enabler for new compact imager designs) miniCOR fits within a 2U box (2 x 7 x 17.5 cm), 3 kg Compatible with a 6U+ CubeSat bus MiniCOR Field of View compared to LASCO/C2+C3 Programmatic Value ØProves the science & operational value of miniaturized imagers ØEnables constellation-based mission architectures (e.g., NASA LWS Architecture Report) Teaming APL: project lead, instrument, SOC Argotec: spacecraft provider NRL: design support, testing facilities
Background • MiniCOR was conceived by Clarence Korendyke (NRL, ret); science and performance requirements were developed by Angelos Vourlidas (APL), and initial optical design by Arnaud Thernisien (NRL) • The mission concept was initially proposed in 2014 for EM-1 and in 2016 and 2022 for H-FORT. • The instrument aims to be the next-generation coronagraph concept for operational deployment (improving on CCOR) and for research constellation architectures. 0.63 m 0.18 m
What is MiniCOR about? Measurement Requirement Projected Performance Bandpass Visible 540-740 Field of View Inner:³ 2.5 Rs 3 - 20 Spatial Resolution <120” < 53” rms Cadence < 10 min 4 min Exposure <45 sec 20 sec SNR (at 3 Rs) >5 20 • MiniCOR captures science-grade images of CMEs with larger FOV than COR2, higher resolution that C3 and higher cadence than any currently-operating coronagraphs MiniCOR Objectives • Improve Measurements of CME Kinematics & CME-Shock Standoff Distances • Investigate the Small-Scale Nature of the Solar Wind? • Become the trailblazer for Future Miniature Coronagraphs.
MiniCOR meets or exceeds the performance of existing coronagraphs Parameter LASCO C2 LASCO C3 SECCHI COR2 CCOR MiniCOR Field of view (Rs) 2.5-6 4-30 2.5-15 4-19 3-20 EO to O1 distance (mm) 821 320 600 250 450 Entrance aperture diameter (mm) 19 934 16 14.5 Focal length (mm) 388 77.6 120 110 78 Spectral Range (nm) 540-640 400-850 660-750 450-750 540 – 740 Pass band (nm) 100 450 90 300 200 Spatial resolution (arcs) 24 120 30 50 53 Detector Front - side illum. Tek 1024x1024 CCD Back-side illum. e2V 2048x2048 CCD Front-side illum. SRI 1920x2048 APS Back - side illum. e2V 2048x2048 APS Throughput relative to C3 incl. detector QE/bandpass 1.0 1.0 7.1 2.1 2.7 - 3 Synoptic Cadence (min) 12 12 15 15 <4 Exposure time (sec) 25 45 625 20 Image Acquisition Single image Single image 2-image sum 3 x 8.5s img sum 3x6 img sum
Coronagraph Optical Train 175 mm 70 mm Parameter Design Value EPD 14.5 mm EFL 78 mm F/# 5.4 IFOV (pixel) 26.4 arcsec IFOV (cutoff) 0.8⁰ (3 Rs) HFOV 5.33⁰ (20 Rs) Pixel Pitch, # Pixels 10 µm, 2048 2 Spectral Range 540 -740 nm
Considerations for Earth orbits: Polar Sun-Sync (600km, 98º) Approach: • We created a 2-year ephemeris for a 600 km, 98º sun-sync orbit and modeled the illumination at the A0 aperture by sunlight reflecting off the Earth and Moon surfaces during a typical year. • We considered all reflected rays within +/- 90º (UFOV) of the MiniCOR boresight to obtain an estimate of the Earth/Moon-shine (EMS) in Mean Solar Brightness (MSB) at A0. • Then, we considered an aperture of decreasing diameter that reduced the UFOV to +/-40º and 20º, and estimated the resulting EMS. • Finally, we estimated the impact on the duty cycle by rejecting observations when EMS > 10-5 MSB or when Earth/Moon were in the FOV (+/- 5.3º). Results: • Earthshine affects MiniCOR observations throughout the orbit due to the Earth’s proximity. • A 40º aperture (7.5 cm OD) reduces EMS by x10 (duty cycle: 91%). • A 20º aperture (3.5cm OD) reduces EMS by x100 without improving duty cycle (91.4%). However, the lower stray light levels may allow observations even at 10-4 MSB at reduced quality but sufficient for operations with a different summing program. *Strong aurora could increase the background under certain geometries and for large field angles. This effect is not considered here given the relatively narrow miniCOR FOV For LEO orbits, the Earth-shine becomes the dominant stray light consideration*. We consider both Earth and Moonshine and their incursions in the FOV to estimate the impact on the monitoring duty cycle. Acceptable Earth/Moon-shine levels No aperture 40º Aperture 20º Aperture Earth-Shine (MSB) Earth-shine for a 600 km sun-sync orbit for different shade geometries at the entrance of the MiniCOR A0 aperture. CDRL 04
MiniCOR will leverage new image processing algorithms to remove straylight and Fcorona backgrounds Raw Divide w/ 27-day average Divide by image-specific background COR2-based example of expected MiniCOR observations (2.5 min cadence)
The MiniCOR spacecraft Argotec, Inc. 12U bus S/X-band transceiver BCT XACT-15 XACT in-orbit performance (CUTE) X-band antenna
