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Whipple: A Space-Based Occultation Survey of the Outer Solar System

Whipple: A Space-Based Occultation Survey of the Outer Solar System. Matthew J. Lehner Harvard-Smithsonian Center for Astrophysics. Proposed Discovery Mission for Survey of Outer Solar System. Smithsonian Astrophysical Observatory. Ball Aerospace. Jet Propulsion Laboratory. Collaborators.

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Whipple: A Space-Based Occultation Survey of the Outer Solar System

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  1. Whipple: A Space-Based Occultation Survey of the Outer Solar System Matthew J. Lehner Harvard-Smithsonian Center for Astrophysics

  2. Proposed Discovery Missionfor Survey of Outer Solar System Smithsonian Astrophysical Observatory Ball Aerospace Jet Propulsion Laboratory

  3. Collaborators Charles R. Alcock Len Andreozzi Roger J. Brissenden James L. Fanson Kathryn A. Flanagan Ronald L. Gilliland Matthew J. Holman Almus T. Kenter SAO Ball SAO JPL MIT STScI SAO SAO Scott J. Kenyon Ralph P. Kraft Matthew J. Lehner Harold F. Levison Stephen S. Murray Irene L. Porro Paul R. Weissman Michael W. Werner SAO SAO HCO SwRI SAO MIT JPL JPL

  4. Survey Goals: • Measure size distribution of KBOs down to 300 m • Map out spatial distribution of Kuiper Belt • Determine if a Sedna-like population exists • Determine number and distribution of objects in Inner and Outer Oort Clouds Whipple will expand horizon of Solar System science from ~100 AU out to 20,000 AU!

  5. KBO Size Distribution

  6. Sedna Population? • Perihelion at 70 AU • Mass ~10-3 Earth mass • How did it get there? • Encounter with passing star • Extra-solar planet exchanged with star in birth cluster? • What else is out there? • Brown et al. (2004) estimate 5 Earth masses! • Population formed while Sun in birth cluster? • (Morbidelli & Levison, 2006; • Brasser et al. 2006) Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

  7. 10 km Occultations of stars 3 km KBO at 43 AU

  8. Occultations of stars 10 km object at 10000 AU with a V=14 F0V star 40 Hz sampling Point source star Finite source star Added noise

  9. Occultations of stars 3 km at 42 AU, 40 Hz 10 km at 104 AU, 5 Hz 600 m at 42 AU, 40 Hz 4 km at 3000 AU, 10 Hz

  10. Spacecraft based on Kepler design • 95 cm Schmidt optical system • 100 square degree field of view • Articulated solar arrays • Hybrid CMOS focal plane array (Rockwell HyViSI/Hawaii-2RG) • 140,000 stars, 40 Hz readout

  11. Whipple will go into an Earth-trailing orbit, similar to Kepler. • Fields at all ecliptic longitudes and latitudes

  12. Hawaii-2RG Hybrid CMOS • 36 units of 2048×2048 pixels, 18µm • bump-bond every other pixel, get 1024×1024 36µm pixels • read out 3×3 aperture around each target star • each CMOS device is capable of reading out 4096 sub-apertures • devices packaged into 2×2 arrays

  13. FPUs placed on curved focal plane • Field flatteners added to surface of each FPU to provide uniform PSF across focal plane • Readout controllers placed directly behind focal plane • Low power devices, no thermal problems

  14. Data Rate • Raw data rate of ~1Gbps • Downlink capability ~5Gb per day • 5×1011 measurements per day • Can only download 10,000 events per day • Need significant on-board processing • Use field programmable gate arrays (FPGAs)

  15. FPGA Analysis • Use “equivalent width” algorithm (Roques et al. 2003) • Easily implemented in FPGA

  16. Focal plane Ring buffer FPGA SIDECAR™ ASIC Solid state recorder Downlink Instrument Control Computer Ground-based analysis Data Flow

  17. Expected Event Rates

  18. Expected Event Rates • Oort Cloud: • 1012 objects (D>3 km) each in Inner and Outer Oort Clouds • N(D) ~ D-1.8 • randomized eccentricities • Sednas: • same assumptions as in Oort Cloud • 100 AU < a < 1000 AU • q > 30 AU

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