  The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is designed to
identify the sources of Ultra-High-Energy Cosmic Rays (UHECRs) and to observe
cosmic neutrinos, both with full-sky coverage. Developed as a NASA Astrophysics
Probe-class mission, POEMMA consists of two spacecraft flying in a loose
formation at 525 km altitude, 28.5 deg inclination orbits. Each spacecraft
hosts a Schmidt telescope with a large collecting area and wide field of view.
A novel focal plane is optimized to observe both the UV fluorescence signal
from extensive air showers (EASs) and the beamed optical Cherenkov signals from
EASs. In POEMMA-stereo fluorescence mode, POEMMA will measure the spectrum,
composition, and full-sky distribution of the UHECRs above 20 EeV with high
statistics along with remarkable sensitivity to UHE neutrinos. The spacecraft
are designed to quickly re-orient to a POEMMA-limb mode to observe neutrino
emission from Target-of-Opportunity (ToO) transient astrophysical sources
viewed just below the Earth's limb. In this mode, POEMMA will have unique
sensitivity to cosmic neutrino tau events above 20 PeV by measuring the
upward-moving EASs induced by the decay of the emerging tau leptons following
the interactions of neutrino tau inside the Earth.
