SPHEREx will observe the entire sky multiple times during its planned two-year mission. Its overlapping scan strategy will obtain a minimum of four 0.75--5.0 µm spectra at every point along the ecliptic, with much greater redundancy in the deep survey fields near the North and South ecliptic poles. SPHEREx will achieve point source sensitivities magnitudes deeper than 2MASS in every SPHEREx spectral element. This is illustrated in Figure 1 below. The SPHEREx team is also making these files defining the performance specifications publicly available to the community. These forecasts will be updated as the instrument is assembled and tested.
The innovative SPHEREx field-of-view is comprised of rectangular linear variable filters (LVFs). The mission surveys the sky by pointing the LVF to tile the sky over successive orbits (Figure 3). This yields:
Four independent all-sky during the nominal 25-month mission
Every exposure images the sky with a central wavelength that varies across the field of view. For a given object, each exposure therefore provides photometry at one wavelength. The spacecraft executes a series of maneuvers to take multiple images. When complete, this ensemble of images gives a full spectrum of the object of interest.
Every exposure images the sky with a central wavelength that varies across the 3.5°x3.5° field of view. For a given object, each exposure therefore provides photometry at one wavelength. The spacecraft executes a series of maneuvers to take multiple images. When complete, this ensemble of images gives a full spectrum of the object of interest.
SPHEREx images the entire sky in over 100 bands across a key part of the infrared spectrum. Linear-Variable filter technology lets the telescope efficiently collect large quantities of both spectral and imaging data simultaneously. Since each pixel in the SPHEREx detector arrays measures a different infrared color, combing data taken across several exposures yields full imaging and spectral data for any galaxy or other target of interest on the sky.
This movie uses a very simple model of our instrument to illustrate how we take small steps in our pointing to move a source along our spectral filters and thus collect different wavelengths of data. The rainbow stripes represent the spectral elements into which we divide each linear variable filter. The small steps move a source onto different stripes of the rainbow. By moving a source onto each stripe, we collect a full set of spectral data for the object you see. In reality, our instrument is more complex than this, with multiple linear variable filters and detectors.
SPHEREx takes spectral imaging data across the entire sky while operating from low-earty orbit. The data gradually accumulates over time to cover the entire sky in 102 near-infrared colors. After 25 months of science operations, SPHEREx will deliver all-sky coverage in four independent surveys.