ISWG - December 7, 20091 Destiny, The Dark Energy Space Telescope

ISWG - December 7, 2009 1

Destiny, The Dark Energy Space Telescope


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


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.


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.


Supernovae


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


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)


Riess et al. (2004) obtain ACS grism spectra of

z ~ 1.3 SN Ia


ACS Grism Images of SN2002FW (z = 1.30)

Riess et al. (2004)


Supernova Observations

1.Filter: locate SN & host galaxy2.Dispersed mode: spectral time series3.Difference & extract SN spectrophotometry


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.


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

70

80

90

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


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.


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


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


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)


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


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


Destiny, The Dark Energy Space Telescope

Documents

ISWG - December 7, 20091 Destiny, The Dark Energy Space Telescope