Lunar Near Surface Plasma Environment from Chandrayaan-2 Lander Platform:RAMBHA-LP payload

The near surface lunar plasma environment is modulated by important components like the photoelectron sheath, solar wind, lunar surface potential, etc. In situ measurements of lunar near surface plasma are not available as of now. Previous lunar missions which explored the near surface environment have arrived at estimates of lunar photo electron densities mainly from lunar sample returns. The Chandrayaan-2 lunar mission affords a unique opportunity to explore the near surface lunar plasma environment from the lunar lander platform. A Langmuir probe is developed indigenously for probing the tenuous lunar near surface plasma environment from the top deck of the lunar lander. The probe is designed to cater to a wide dynamic range of 10/cc to 10,000/cc. The probe behaviour is characterized in the ambient room conditions using a current source. The sensitivity of the probe to incoming ionized species is also characterized in a vacuum chamber. The Langmuir probe response is characterized such that the input current to the probe is correctly deciphered during the mission duration. The calibration of the present Langmuir probe is carried out using a standard calibrated Langmuir probe. The details of the theoretical simulations of the expected currents, the characterization and calibration activities are presented and discussed.