1σ forecasts on the non-ionizing λ = 1500 Å continuum for (GALEX+ULTRASAT)×DESI (shaded area), with conservative and optimistic priors on the bias. To get GALEX×SDSS (C19) results, we propagated our “post-diction” in Sect. 4.2. We compare with available results in the literature. Schiminovich et al. (2005) data are based on the UV luminosity function of the galaxies in GALEX, Dahlen et al. (2006) on the GOODS survey from the Hubble Space Telescope, while Reddy et al. (2008) use a compilation of data from Hubble. The green line reproduces the fitting of Dominguez et al. (2011) over multiband data, while the dotted lines are the semi-analytical models obtained in Gilmore et al. (2012) with different dust prescriptions.