KOcnes instrument SNAP

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The SNAP Experiment

Current status: 

Current status JDEM (J= joint = DOE) 2003 An agreement between NASA/DOE = JDEM 2004 A ‘science definition team’ 2005 A ‘concept studies’ AO (NASA ROSES solicitation) Aug 2006 NASA selects advanced mission concept studies SNAP SELECTED with Destiny et Adept 2007 Nat’l Academy Sciences: Definition of priorities JDEM/LISA/constellation X… => choice for summer 2007 French involvement: CNES is interest for a SNAP cooperation and do a telescope assement study in 2007. Marseille, already in charge of the spectrograph, started devoting some workforce to help analyzing the WL requirements and their flow down to the telescope

Instrument: the telescope: 

SNAP concept eliminates complexity: telescope design withIR imaging Baseline = room temperature optics Instrument: the telescope

SNAP Observatory Cross Section: 

SNAP Observatory Cross Section All fixed, passively cooling

Payload Features: 

Payload Features 90 deg Symmetric Focal Plane allows continuous year round science data taking one side always sunward, allowing fixed solar panels hence a rigid spacecraft (resonances > 10Hz) other side always dark, allowing fixed passive thermal radiator serving sensor array Telescope assembly is thermally and structurally separate from surrounding outer baffle and from spacecraft maneuvers do not compromise PSF stability Innovative telescope design does IR imaging with room temperature optics three mirror anastigmat has accessible exit pupil and complete cold stop baffling Built in end-to-end optical test capability simplifies integration and testing The fixed telemetry antenna eliminates major mission risks and costs: no gimbals, no flex waveguide rigid spacecraft eases ACS task No onboard data analysis: all images are downlinked to Earth; 2:1 Rice compression assumed

Metering Configuration: 

Metering Configuration


Baseline SNAP telescope team lead M.Lampton Thermal (P. Jelinsky) Mechanical (D. Pankow, W. Whitehead) Strength and dynamics analysis (B. Besuner, T. Courri) Optics/stray light (M. Lampton, M. Sholl, M. Kaplan) Fabrication/testing (D. Pankow, J. Figoski, S. Kendrick) Many contributions by Ball Aerospace team since 1999 Selected as JDEM telescope partner in 2006 System baseline Mass, Source: 00004-ME02-E.xls Telescope primary structure 218kg upper outer barrel 154kg Lower outer barrel 74kg Cover 22kg Mirrors 264kg Power, Source: 00005-ME02-C.xls 125W (peak, mainly heater power) Optical performance, Source: 00008-MW02-F.doc Wavefront error Thermal stability Stray Light, Source: 00056-MW02.doc <10% Zodi

The focal plane: 

All instruments/detectors on single focal plane. Passively cooled to 140K 0.7 square degrees instrumented FOV 9 fixed filters from 350nm to 1700nm 36 CCDs. 36 HgCdTe detectors The focal plane

Focal Plane: 

Focal Plane Detectors and electronics operate at 140K CCDs for guiding from the focal plane. Exposure times of 300 s with four/eight exposures in CCDs/HgCdTe. 20 s readout slow enough for CCD noise and 4 post exposure and 4 pre exposure reads of HgCdTe. shield

An R&D effort: 

An R&D effort Quantum efficiency T operation = 140 K Traditional n-channel CCDs are sensitive to radiation damage due to loss of Charge Transfer Efficiency (CTE) P-channel CCDs are 10-50x more radiation tolerant Detectors have good performances High QE Noise reduced by a factor 100 2 vendors For IR detectors For CCD

The spectrograph: 

Visible and NIR resolution = 70 – 100 Compact, light Image slicer: 3 to 10 arcsec of imaging & spectra The spectrograph Marseille SNAP group is developing the spectrograph. IFU concept basé sur un slicer (expertise LAM, autre NIRSPEC/ MUSE..) A demonstrator currently under integration in Marseille


SNAP Walkthrough Through-The-Telescope guiding simplifies spacecraft requirements No onboard data analysis: all images are downlinked to Earth Science and Engineering Downlink 150 Mbit/sec Ka band at 26 GHz SNAP 35 W TWT transmitter 1.2m fixed dish Deep Space Network (DSN) / White Sands


SNAP Walkthrough L2 Orbit, puts most “work” in the Launch Vehicle, small fuel for injection, station keeping, angular momentum. Earth and Moon Illumination For direct injection L2 orbits: Atlas V or Delta 4040 lift capacity of ~2800Kg to L2 . Soyuz 2-1B with Fregat ~2020Kg to L2. (not including PAF) Total SNAP mass ~ 1950 Kg


Launch Vehicles Delta IV Soyuz-ST/Fregat (2-1B)

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