Design and Development of Terminal Velocity Measurement System for Descending Modules

During landing of re-entry modules in manned missions, one of the most critical parameters to be monitored is its terminal velocity. As human safety is prioritized in manned missions, the module’s maximum permissible terminal velocity values are pre-determined based on the human tolerance levels. The entire deceleration system of the module is then optimized for achieving terminal velocities below these limits to ensure safe touchdown of the crew. In addition to vertical velocity, the module also experiences lateral and rotational velocities during its descent. Characterizing these velocities lead to a more comprehensive understanding of the dynamics faced by the module while landing. Therefore, acquiring accurate in-flight velocity data is a fundamental requirement for Gaganyaan missions. Existing methods for measuring terminal and lateral velocities have limitations in terms of accuracy, feasibility, and cost-effectiveness. In response to the need for an accurate and precise measurement of tri-axial velocities, Terminal Velocity Measurement System (TVMS) is developed. TVMS harnesses state-of-the-art Doppler radar technology to provide tri-axial velocity with a high update rate. Primarily, TVMS consists of Doppler radar sensors for measuring the Doppler shift due to deceleration. By employing three radar sensors, TVMS guarantees the measurement of both terminal and lateral velocities. Doppler frequency output is processed into velocity data by a microcontroller and associated electronics integrated onto a compact card. TVMS frequency-processing card was developed and subjected to rigorous testing which exhibited highly promising results. It offers both analog as well as digital outputs, enabling seamless telemetry to ground stations to meet mission requirements. Thus, TVMS ensures the precise measurement of tri-axial velocity, thereby enhancing the safety and reliability of manned missions. It promises to set a benchmark for other velocity measurement methods and offers immense potential in future space exploration endeavors.