  We explore the possibility of detecting the first galaxies with the next
generation Origins Space Telescope (OST) by applying an analytical model of
primordial dust emission. By analysing source densities as a function of
redshift (z), and considering deep-field exposures with the Origins Survey
Spectrometer, we estimate that the redshift horizon for detecting one
individual source would be above z~7 for systems with dust-to-metal ratios
higher than those expected for typical primeval galaxies. On the other hand, if
confusion limits could be overcome, the Far-infrared Imager and Polarimeter
would enable the detection of more typical fainter systems at z>7. Given the
dependence of the obtained results with the properties of primeval dust, we
conclude that the OST could provide important clues to the nature of the
interestellar medium in the early Universe.
