Following recommendations from the Decadal Survey report, "Pathways to Discovery in Astronomy and Astrophysics for the 2020s", NASA will limit the first generation of Probe mission concepts to far-infrared and x-ray observatories. The ATLAS team is now developing a new version of the ATLAS concept scaled to a NASA MIDEX mission. The science goals of ATLAS Explorer are the same as those for ATLAS Probe. ATLAS Explorer accomplishes most of the ATLAS Probe science, making it an extraordinarily capable MIDEX mission. 

ATLAS Explorer is a 1m telescope with FoV of 0.8 sq deg, for R=1000 slit spectroscopy over 1-4 microns. It has a spectroscopic multiplex factor of 12000 (3000 per DMD) using 4 Cinema DMDs (each a 1080×2048 micro-mirror array). The reflective slit size is 1.06”×1.06”.

Compared to ATLAS Probe, ATLAS Explorer will have 2 instead of 3 galaxy surveys: ATLAS Medium and ATLAS Wide. ATLAS Milky Way and ATLAS Solar System Surveys remain unchanged. 

ATLAS Medium Survey obtains 7.63M galaxy spectra over 50 sq deg to AB=24.2 (3σ), and 1.53×10-18 erg/s/cm2 (5σ), over ~ 2 years of observing time.

ATLAS Wide Survey obtains 144M galaxy spectra over 2000 sq deg to to AB=21.9 (3σ), and 1.36×10-17 erg/s/cm2 (5σ), over ~ 2 years of observing time.