SPHEREx is based on a telescope with an effective 20 cm diameter and a 11°x3.5° field of view. The focal plane is split with a dichroic to three short-wavelength and three long-wavelength detector arrays. Two focal plane assemblies (FPAs) simultaneously image the sky through a dichroic beam splitter. This specialized optic behaves as a mirror to short wavelengths and a window to long. Each FPA contains three 2K x 2K detector arrays placed behind a set of linear variable filters, providing narrow-band response with a band center that varies along one axis of the array. SPHEREx obtains spectra through multiple exposures, placing a given source at multiple positions in the field of view, where it is measured at multiple wavelengths by repointing the spacecraft.
SPHEREx implements a simple and robust design that maximizes spectral throughput and efficiency. This is done in the absence of any moving parts, with the exception of a one-time ejection of an aperture cover.
Design features employed on SPHEREx have proven effective on previous missions, and include:
|Telescope Effective Aperture||20 cm|
|Pixel Size||6.2" x 6.2"|
|Field of View||2 x (3.5° x 11.3°); dichroic|
|Resolving Power and Wavelength Coverage||λ= 0.75- 2.42 µm; R=41
λ= 2.42 - 3.82 µm; R=35
λ= 3.82 - 4.42 µm; R=110
λ= 4.42 - 5.00 µm; R=130
|Arrays||3x Hawaii-2RG 2.5 µm
3x Hawaii-2RG 5.3 µm
|Point Source Sensitivity||>19.2 AB mag (5σ) per frequency bin referenced at 2 µm (MEV).|
|2.5 µm Array and Optics Temperature||<80K|
|5.3 µm Array Temperature||<55K|