Radio Instrument Package for Lunar Ionospheric Observation: A Concept Study

• Published in: Radio science Vol. 58; no. 7
• Main Authors: Watson, C., Jayachandran, P. T., Kashcheyev, A., Themens, D. R., Langley, R. B., Marchand, R., Yau, A. W.
• Format: Journal Article
• Language: English
• Published: 01.07.2023
• Subjects: CubeSats; ionosphere; lunar; radio occultation
• ISSN: 0048-6604; 1944-799X
• DOI: 10.1029/2023RS007666

The lunar ionosphere is a ∼100 km thick layer of electrically charged plasma surrounding the moon. Despite knowledge of its existence for decades, the structure and dynamics of the lunar plasma remain a mystery due to lack of consistent observational capacity. An enhanced observational picture of the lunar ionosphere and improved understanding of its formation/loss mechanisms is critical for understanding the lunar environment as a whole and assessing potential safety and economic hazards associated with lunar exploration and habitation. To address the high priority need for observations of the electrically charged constituents nikear the lunar surface, we introduce a concept study for the Radio Instrument Package for Lunar Ionospheric Observation (RIPLIO). RIPLIO would consist of a multi‐CubeSat constellation (at least two satellites) in lunar orbit for the purpose of conducting “crosslink” radio occultation measurements of the lunar ionosphere, with at least one satellite carrying a very high frequency (VHF) transmitter broadcasting at multiple frequencies, and at least one satellite flying a broadband receiver to monitor transmitting satellites. Radio occultations intermittently occur when satellite‐to‐satellite signals cross through the lunar ionosphere, and the resulting phase perturbations of VikHF signals may be analyzed to infer the ionosphere electron content and high‐ resolution vertical electron density profiles. As demonstrated in this study, RIPLIO would provide a novel means for lunar observation, with the potential to provide long‐term, high‐resolution observations of the lunar ionosphere with unprecedented pan‐lunar detail. Plain Language Summary The lunar ionosphere comprises electrically charged particles within the lunar atmosphere and is derived from a wide range of sources and formation mechanisms that are not fully resolved. Although extremely tenuous compared to that of Earth's, the lunar ionosphere plays an integral role in physical processes occurring within the lunar environment. The composition and dynamics of the lunar ionosphere are mostly unknown at this point and may be linked to the lunar surface and sub‐surface, solar wind, magnetosphere, and Earth's atmosphere. Observation of the lunar ionosphere is essential to develop a complete picture of its structure and dynamic behavior and how it is formed. This is a critical aspect of assessing its physical role within the lunar environment and potential safety hazards for future lunar exploration and habitation. This paper presents the concept of a radio‐based mission for lunar ionospheric observation called the Radio Instrument Package for Lunar Ionospheric Observation (RIPLIO). This mission would employ multiple CubeSats in lunar orbit, equipped with radio transmitters and receivers, to observe the lunar ionosphere with unprecedented detail. This paper presents preliminary simulations of radio measurements of the lunar ionosphere, and discusses requirements for a potential RIPLIO mission and relevance to international science objectives. Key Points We propose a “crosslink” radio occultation method of observing electrically charged constituents of the lunar exosphere Simulations demonstrate that two CubeSats in lunar orbit result in a substantial increase in lunar ionosphere observational capacity We demonstrate that a VHF transmitter‐receiver “crosslink” setup is ideal for making radio occultation observations of the lunar ionosphere