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ISWG - December 7, A Brief History of Destiny Astronomical community recognizes the potential of dark energy space probes. NASA & DOE propose a generic Joint Dark Energy Mission Initial Destiny concept for JDEM proposed in Wins initial concept study. GFSC, LMCO, & LANL partners. NASA creates general “Beyond Einstein” program for astrophysical missions: Con-X, LISA, CMB probes, etc. Includes JDEM. Destiny wins 1 of 3 JDEM concept studies in NRC BEPAC recommends JDEM for first BE start in Development continued to September 2008.
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ISWG - December 7, 2009 1
Destiny, The Dark Energy Space Telescope
ISWG - December 7, 2009 2
DESTINY Fact Sheet• 1.65m telescope at L2• 32 H2RG FPAs: 0.15” pixels• FOV: 0.18° x 0.72°• SN1a survey over > 3°2
• NIR imaging 0.85 m < 1.7 m
• “objective Prism” with ~ 75
ISWG - December 7, 2009 3
A Brief History of Destiny• Astronomical community recognizes the potential
of dark energy space probes.• NASA & DOE propose a generic Joint Dark Energy
Mission• Initial Destiny concept for JDEM proposed in 2003.
Wins initial concept study. GFSC, LMCO, & LANL partners.
• NASA creates general “Beyond Einstein” program for astrophysical missions: Con-X, LISA, CMB probes, etc. Includes JDEM .
• Destiny wins 1 of 3 JDEM concept studies in 2006. NRC BEPAC recommends JDEM for first BE start in 2007.
• Development continued to September 2008.
ISWG - December 7, 2009 4
DESTINY Philosophy• In 2003, SN Ia was the favored DE methodology - DETF
identified NIR observations of SN Ia as the sole “space unique” methodology.
• Do only in space what must be done in space - ground observations for low-redshift.
• Use the minimal instrument required.– Variable DE EOS observing over 0 < z < 1.7– Stage IV errors Sample ~ 3000+ SN Ia.– 5 day cadence 3 deg survey area for 2 year mission.– S/N requirements A product (detectors vs. Primary)
• All spectra all the time. Complete spectro- photometric time series on all SN events. One data set provides photometry, classification, redshifts, time decay, extinction, etc.
• Highly automated survey - no time critical operations.
ISWG - December 7, 2009 5
Supernovae
ISWG - December 7, 2009 6
Why go to high redshifts?
Dark energy can be detected at low redshift, but precise constraints on the DE Eos requires measurements over both the acceleration and deceleration epochs.
SpaceGround
ISWG - December 7, 2009 7
NIR available only in spaceCrucial near-infrared observations are impossible from the
ground for the required photometric accuracy• Sky is very bright in NIR: >100x brighter than in visible• Sky is not transparent in NIR: absorption due to water is
very strong and extremely variable
Data from Gemini Observatory & ATRAN: Lord (1992)
ISWG - December 7, 2009 8
Riess et al. (2004) obtain ACS grism spectra of
z ~ 1.3 SN Ia
ISWG - December 7, 2009 9
ACS Grism Images of SN2002FW (z = 1.30)
Riess et al. (2004)
ISWG - December 7, 2009 10
Supernova Observations
1.Filter: locate SN & host galaxy2.Dispersed mode: spectral time series3.Difference & extract SN spectrophotometry
ISWG - December 7, 2009 11
Supernovae Survey Schema
Survey area is a contiguousMosaic of Destiny FOVs.Orientation rolls by 90º every 3 months.Dithering will fill in chipgaps and ensure Nyquist sampling.
ISWG - December 7, 2009 12
Triprism for nearly constant dispersion
Comparison
30
40
50
60
70
80
90
100
110
800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800
Wavelength (nm)
Two-pixel Resolving Power
Al2O3 BaF2 sum(3.735, 11.564). "dark.16"MgO 7.59 degAl2O3 ZnSe sum(5.26, 0.40786, dark.15)R GrismR Grism, 75 @ 1700 nm
50
60
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80
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100
110
800 900 1000 1100 1200 1300 1400 1500 1600 1700
Wavelength (nm)
R (two-pixel)
dark.6, grism
dark.10, single prism
dark.16, dual prism
dark.18, tri-prism
-1.5
-1
-0.5
0
0.5
1
1.5
800 900 1000 1100 1200 1300 1400 1500 1600 1700
Wavelength (nm)
Y (mm)
dark.6, grism
dark.10, single prism
dark.16, dual prism
dark.18, tri-prism
ISWG - December 7, 2009 13
Sn Photometric Calibration
• Obtain high fidelity external and internal flats in ground tests.• Monitor with internal flats on orbit, plus field stars.• Absolute photometric calibration with DA white Dwarfs.• Sn spectra isolated with differencing. Ad hoc spectral flat
extracted from data cube of monochromatic flats.
ISWG - December 7, 2009 14
On-orbit calibration system (from Jason Budinoff)
Integrating Sphere
Shutter
MonochromatorFold MirrorDiffuser
Diffuser Mechanism
Diffuser Mirror
Baffle Box
F/8 Light Pipe
500 mm Light Pipe
ISWG - December 7, 2009 15
Supernova Survey
• Present day & ongoing surveys find hundreds
• Destiny will find >3000 SN in 2 yrs.
• Most at z~1; requires 3.2 deg2 survey area
ISWG - December 7, 2009 16
Focal Plane Layout• Science FPAs: HAWAII-2RG
2k x 2k arrays, 4 x 8 mosaic =128M pixels
• Guide FPAs:2k x 2k arrays, 2 x 2 sparse mosaic (dichroic overlay)
ISWG - December 7, 2009 17
Observatory• Lockheed Spacecraft
bus• Goodrich Optical
Telescope Assembly• GSFC Science
Instrument, Teledyne FPA
• GSFC Instrument Outer BaffleDestiny Observatory
Destiny OTA + Science Instrument Destiny Optics
Spacecraft BusFixed Solar Array
Instrument Radiators
Outer BaffleAssembly
Goodrich OTA GSFC Science Instrument
1.65m primary mirror
Telescope Optical Bench
ISWG - December 7, 2009 18
Optical layoutTertiary
Telescope Bench
Instrument Bench
Fold2 Cell
Filter/Prism Wheel
Primary Mirror
Secondary Mirror
Guider FPA
Science FPA
InternalThermal Enclosure
Interface Deck
Monochrometer
Central “Shark Mouth”
Baffle
ISWG - December 7, 2009 19
Destiny, The Dark Energy Space Telescope
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