SPHEREx (for Spectro-photometer for the History of the Universe, epoch of reionization, and Ices Explorer) is a planned NASA space mission for a telescope and spectrograph to survey the whole sky in the near infrared. It is to be launched in 2023.
It is a NASA MIDEX (Medium-class Explorers Program) project for a 20-cm telescope and spectrograph with a wide field of view and an angular resolution of 6.2 arcseconds, with spectrography covering a wavelength-range of 0.75 to 5 micrometers with spectral resolutions ranging from 41 to 130. It would operate in a low, polar Earth orbit for two years, completing an all-sky survey each 6 months.
The spectrography is accomplished with filters effectively covering enough channels to produce the spectral resolution: they are linearly variable filters, which vary in the band they allow across one direction. The sky will be continuously scanned so that at any instant, portions of the captured image are capturing different wavelengths. The spacecraft design minimizes moving parts.
It is aimed at a number of scientific goals for which such a survey is helpful, including learning more of the history of large scale structures and galaxy formation as well as measurement of the water in molecular clouds that could contribute to habitable extra-solar planets. It is expected that it will pick up some gravitational lensing in its own regime, and that cross correlation with data from other surveys will confirm Sunyaev-Zel'dovich effects and gravitational lensing effects and use correlations to produce new information about large scale structure.