PSLV-C61 mission fails: Former Isro scientist explains what happens next

India Today

18-05-2025

The Indian Space Research Organisation (Isro) launched the Polar Satellite Launch Vehicle at 5:59 a.m. IST from Sriharikota's Satish Dhawan Space Centre, but the rocket veered off trajectory during the critical third-stage burn ending up in a major failure.It was carrying the Earth Observation Satellite (EOS-09) to space in a bid to give India an all-weather imaging edge.advertisementWHAT HAPPENS NOW?When a space mission fails, Isro initiates a meticulous and systematic process to analyse the failure and identify its root cause. This process is critical to ensure future missions are safer and more reliable.Here's how Isro typically approaches the analysis of a lost mission, such as a launch failure. The first step is to form a Failure Analysis Committee (FAC), comprising experts from various Isro centers, including engineers, scientists, and mission specialists. This team is tasked with reviewing all available data from the mission.During a launch, Isro's telemetry systems collect vast amounts of real-time data, such as velocity, altitude, pressure, temperature, and engine performance. For instance, in the case of a failure like the PSLV-C61/EOS-09 mission, where velocity dropped unexpectedly, the FAC would examine telemetry graphs showing parameters like the sharp decline in relative velocity (from 6 km/s to 2.45 km/s) and the corresponding altitude and trajectory data.advertisementThe FAC will thoroughly review the flight data along with all data related to the activities ranging from the stage preparation at the launch complex, countdown to lift-off.Next, the committee analyses the flight data to pinpoint the exact moment of deviation.
With EOS-09, India aimed to strengthen its position in space-based earth observation. (Photo: Isro)
This involves comparing actual performance against the expected profile—such as the target velocity curve after satellite separation. If the data shows anomalies, like engine shutdowns or structural issues, the team cross-references it with ground-based radar and tracking station inputs to reconstruct the sequence of events. For example, if the third stage (PS3) malfunctioned, the team would investigate propulsion system logs and closed loop guidance telemetry.Isro also conducts simulations and reviews the rocket's design and manufacturing processes. This includes checking for potential flaws in components, such as engines, avionics, or guidance systems.Additionally, software algorithms controlling the rocket's navigation and control systems are audited for errors.The FAC then compiles a detailed report, identifying the root cause—be it a mechanical failure, human error, or external factors like weather.advertisementRecommendations are made to address the issue, such as design modifications or procedural changes.After the PSLV-C1 failure in 1993 due to a software glitch and EOS03 failure due to tank pressurization issue in GSLV CUS, Isro revamped its testing protocols and active mechanisms to attain required performance.This rigorous process ensures that each failure becomes a stepping stone for future success, enhancing Isro's reliability in space exploration.(Manish Purohit is a former Isro scientist with vast experience in managing critical space missions and solar energy projects, including Mangalyaan and Chandrayaan-2 missions.)