Exospheric and interplanetary hydrogen sensing from a translunar CubeSat platform by the Tomographic Hydrogen Emission Observatory (THEO)

Abstract:

The evaporation of neutral hydrogen (H) atmospheres into interplanetary space is a near-ubiquitous process in the universe that can be strongly perturbed by charge exchange coupling with ambient ions, influencing atmospheric evolution as well as the dissipation of plasma energy. Space-based observation of solar ultraviolet (UV) radiation scattered by H atoms is a powerful means to infer the underlying exospheric density distribution and thus unravel the competing effects of thermal and non-thermal processes on H energization and escape. Numerous past and present NASA missions have obtained measurements of terrestrial H emission at 121.6 nm (Lyman alpha) from earth-orbiting satellite platforms. However, their separate targeting of either the optically thick emission in the lower exosphere or the optically thin emission in the outer exosphere, together with their lack of independent measurement of the interplanetary emission that constitutes a significant background contamination, renders such data insufficient to advance exospheric science beyond current understanding. Here, we describe a new nano-satellite mission concept for exospheric H investigation that overcomes these historical measurement limitations. The mission, known as the Tomographic Hydrogen Emission Observatory (THEO), is designed to provide 3-D photometric measurements of terrestrial H Lyman alpha emission from a highly autonomous, three-axis-stabilized, 6U CubeSat platform along a trans-lunar trajectory that is ideal for the unambiguous estimation of H density from the exobase to the magnetopause and beyond. In particular, we will describe the feasibility of meeting operational challenges associated with satellite navigation and communication at such large distances.