Lyman Alpha Photometer (LAP) for Water Evolution Studies in Planetary Atmospheres: Instrumentation, Experimentation and Performance Aspects

Raja V.L.N. Sridhar, M. Viswanathan , A.S. Laxmiprasad and LAP Development Team

Laboratory for Electro-Optics Systems (LEOS)

The evolutionary history of planetary atmospheres especially of non-magnetic planets such as Mars, Venus etc depends on how well one can understand their atmospheric escape process for different gases. Owing to very mild or absence of intrinsic magnetic field, the upper atmosphere of these planets is always exposed to solar wind that triggers photo-dissociation of water by producing hydrogen (H) and deuterium (D), which are subsequently lost to space over time. Measurements of the atmospheric deuterium to hydrogen (D/H) abundance ratio are vital to understand the escape process and further aid to infer the loss process of water in the evolutionary history of planet’s atmosphere. The team at ‘Laboratory for Electro-Optics Systems-LEOS’ developed a light-weighed (≤ 2 kg) and low power consumption (≤ 8 Watt) ultra-violet photometer; namely, ‘Lyman Alpha Photometer-LAP’ that is primarily dedicated for D/H measurements of planetary upper atmospheres. LAP has successfully qualified for space use and is one of the 5 scientific instruments flown in India’s maiden mission to the planet Mars, i.e., ‘Mars Orbiter Mission-MOM’. This paper primarily shares details in brief on the instrumentation, theory, and experimental investigations; finally presents the gist on the executed operations in cruise and Martian orbit phase