Development of Deployment Mechanism for RAMBHA-LP Payload Onboard Chandrayaan-3 Lander 2024-26-0455

RAMBHA-LP (Radio Anatomy of Moon Bound Hypersensitive Ionosphere and Atmosphere - Langmuir Probe) is one of the key scientific payloads onboard the Indian Space Research Organization’s (ISRO) Chandrayaan-3 mission. Its objectives were to estimate the plasma density and its variations on the near lunar surface. The probe was initially kept in a stowed condition attached to the lander. A mechanism was designed and realized to meet the functional requirement of deploying the probe at a distance of 1 meter, equivalent to the Debye length of the probe in the moon’s plasma environment. The probe deployment mechanism consists of the Titanium alloy spherical probe with a Titanium Nitride coating on its surface to achieve a constant work function, a long carbon-fiber-reinforced polymer boom, a double torsion spring, a dust-protection box, and a shape-memory alloy-based Frangibolt actuator for low-shock separation. The entire mechanism weighed less than 1.5 kilograms. The system had undergone a sufficiently large number of sub-system level and system level tests in ambient, dynamic, and thermo-vacuum environments experienced in an interplanetary mission. After completing all developmental, qualification, and acceptance level tests, the system was integrated with the lander and launched using ISRO’s Launch Vehicle Mark III (LVM 3). The Chandrayaan-3 lander made history by landing on the lunar south pole on 23rd September 2023. The RAMBHA-LP payload was successfully deployed the next day. The deployment of the probe was confirmed by the micro-switches present in the mechanism. The data provided by the probe indicates that the plasma encompassing the lunar surface is relatively sparse, characterized by a number density ranging from approximately 5 to 30 million electrons per cubic meter. This paper presents the design and development process of the probe deployment mechanism and the details of the various tests conducted to qualify it for the lunar landing mission.