Destiny: a candidate architecture for the Joint Dark Energy Mission

Abstract

&lap;Destiny is a simple, direct, low cost mission to determine the properties of dark energy by obtaining a cosmologically deep supernova (SN) type Ia Hubble diagram. Its science instrument is a 1.65m space telescope, featuring a grism-fed near-infrared (NIR) (0.85-1.7 &#956;m) survey camera/spectrometer with a 0.12 square degree field of view (FOV) covered by a mosaic of 16 2k x 2k HgCdTe arrays. For maximum operational simplicity and instrument stability, Destiny will be deployed into a halo-orbit about the Second Sun-Earth Lagrange Point. During its two-year primary mission, Destiny will detect, observe, and characterize ~3000 SN Ia events over the redshift interval 0.4 < z < 1.7 within a 3 square degree survey area. In conjunction with ongoing ground-based SN Ia surveys for z < 0.8, Destiny mission data will be used to construct a high-precision Hubble diagram and thereby constrain the dark energy equation of state. The total range of redshift is sufficient to explore the expansion history of the Universe from an early time, when it was strongly matter-dominated, to the present when dark energy dominates. The grism-images will provide a spectral resolution of R&#8801;&#955;/&#916;&#955;=75 spectrophotometry that will simultaneously provide broad-band photometry, redshifts, and SN classification, as well as time-resolved diagnostic data, which is valuable for investigating additional SN luminosity diagnostics. Destiny will be used in its third year as a high resolution, wide-field imager to conduct a multicolor NIR weak lensing (WL) survey covering 1000 square degrees. The large-scale mass power spectrum derived from weak lensing distortions of field galaxies as a function of redshift will provide independent and complementary constraints on the dark energy equation of state. The combination of SN and WL is much more powerful than either technique on its own. Used together, these surveys will have more than an order of magnitude greater sensitivity (by the Dark Energy Task Force's (DETF) figure of merit) than will be provided by ongoing ground-based projects. The dark energy parameters, w₀ and w_a, will be measured to a precision of 0.05 and 0.2 respectively.