EUSO-SPB2 is a mission to monitor the night sky of the Southern hemisphere by a second generation of instruments of the JEM-EUSO program.
This mission has been approved by NASA for a long duration flight aboard a Super-Pressure Balloon (SPB) in 2022.

EUSO-SPB2 will measure air-showers produced by cosmic rays in the energy range range 10⁷ GeV < E < 10⁸ GeV by viewing their Cherenkov light from high in the atmosphere. It should be able to discriminate among primary protons, heavy nuclei, and photons via their characteristic Cherenkov profiles. The instrument will be also capable to characterize the background for upward going showers initiated by the decay of tau leptons which are expected to be produced by Earth-skimming tau neutrinos.

EUSO-SPB2 is also intended to measure, by using fluorescence light, the evolution of nearly horizontal extensive air showers which develop at high altitude in a nearly constant density atmosphere. Such measurements will provide a unique channel to tune hadronic interaction models at ultrahigh energies, and may elucidate the reason why ultrahigh-energy cosmic ray (UHECR) showers observed by ground-based detectors contain more muons than expected from existing hadronic interaction models.

Two independent telescopes, based on Schmidt design reflecting telescope, will perform the specified measurements. One telescope will observe the Cherenkov signal from horizontal events and the upward directed Cherenkov signal from air showers produced in the atmosphere. The other telescope, with an smaller FoV, will measure the intensity of the slower fluorescence signals produced by extensive air showers, imaging the event trajectory as the cascade develops down through the atmosphere.

Reference: EUSO-SPB2 paper at ICRC2019: (https://pos.sissa.it/358/466/pdf)