Second from the Planetary Society.
"Measure electron cloud densities in Earth?s ionosphere, a layer high above Earth that affects long-range radio communications."
"One of the payloads is NASA's DSAC (Deep Space Atomic Clock), a technology demonstration mission to validate a miniaturized, ultra-precise mercury-ion atomic clock that is 100 times more stable than today?s best navigation clocks."
Research technologies needed to significantly advance Department of Defense (DoD) capabilities to operate spacecraft in the harsh radiation environment of MEO (Medium-Earth Orbits).