ExoCube: In-Situ Measurement of Composition in the Exosphere, Thermosphere and Topside Ionosphere

Abstract:

Quantification of neutral species densities in the upper thermosphere and lower exosphere remains elusive despite the analytical theories established by the pioneers of Aeronomy roughly fifty years ago, despite the evident requirements of Space Weather modeling, and despite the pragmatic reality of manned and unmanned spacecraft exploitation of the region. In fact, [O], [He] and [N2] have not been measured in-situ in the upper atmosphere since the era of DE-2, and then for only 18 months from 1981-1983 (near solar maximum). Prior to that, the Atmospheric Explorer program (AE-A launched in 1963, AE-E ended in 1980) provided the neutral density information upon which the MSIS model is largely based. No instrument has measured [H] in-situ, which is instead derived in MSIS by solution of the proton continuity equation.

The ExoCube satellite provides a long-overdue benchmark for the densities of significant neutral and ionized species in the upper atmosphere, on a global scale, for the Space Weather and Aeronomy communities. These will be the first in-situ global neutral density data since DE-2, including the first direct measurements of [H] using a mass spectrometer technique. Since roughly half of the total electron column content (TEC) arises from photoionization of H, reliable knowledge of exospheric [H] is a crucial requirement of realistic Space Weather modeling of TEC. To insure that this project has enduring impact beyond the projected two-year duration of the satellite mission, experimental interaction with ground-based ISR and optical facilities is integrated. The simultaneous collection of ion and neutral densities will facilitate the use of ExoCube data for studies of charge exchange processes. Overpasses with observatories will enable ExoCube measurements to be used as a constraint for retrieval of density information from forward modeling of ground-based observations. Presented here will be the first post-launch mission status and operations.