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

2. Proposed Discovery Mission for 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
JPL
MIT
STScI
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
HCO
SwRI
MIT
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)

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

9. 10 km object at 10000 AU with a V=14 F0V star
Occultations of stars
10 km object at AU with a V=14 F0V star
Point source star
40 Hz sampling
Finite source star
Added noise

10. Occultations of stars 3 km at 42 AU, 40 Hz 10 km at 104 AU, 5 Hz

11. 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

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

13. Hawaii-2RG Hybrid CMOS
36 units of 2048×2048 pixels, 18µm
bump-bond every other pixel, get 1024× µm 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

14. 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

15. 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)

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

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

18. Expected Event Rates

19. 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