European Space Agency claims, that have discovered main reason for disaster of their EDM lander during descent maneuver over surface of the Mars on October 19, 2016. But still, for more detailed report with full analysis and case study we will have to wait for 2017.
First general analysis and first conclusions given by ESA few days after crashing Entry, Descent and Landing Demonstrator Module (EDM) pointed on successful separation from Schiaparelli orbiter and entering Martian atmosphere. It was not possible to evaluate any potential reason for crash due the slow pace of receiving and interpretation of telemetry data from EDM. After over one month ESA decided to announce possible reasons of disaster before giving official report from Schiaparelli mission.
According to ESA first phase of flight in Martian atmosphere went as it was planned. Extraction of the parachute on altitude of 12 km and releasing bottom heat shield on altitude of 7.8 km both went as it was planned. Doppler radar which was measuring altitude was working correctly, just as guidance, navigation and control systems. Inertial Measurement Unit (IMU) was also working correctly and was continuously providing data on rotation of EDM. Problems appeared later. Thrusters, which were designed to be used on altitude of 1100 m, were started on altitude of over 3.7 km; this caused, with too short time of burn, fatal problems with speed reducing and crashing EDM during first contact with the ground. As it was discovered, reason for preliminary initialization of braking thrusters for too short time, was problem with interpretation of data provided by onboard rolling sensor (IMU) of EDM. After releasing parachute, number of rotations per second reached peak value, but that moment last one second longer than it was originally planned. This situation has not been provided for in the algorithm of onboard computer. Data were interpreted as EDM was under sea level; Computer decided to release upper cover using parachute and quickly started thrusters. It also activated all ground systems necessary for resuming communication and first self tests. It was just ordinary procedure but conducted too early.
According to ESA this situation was simulated multiple times on computers and always result was exactly the same – lander reacted on prolonged spinning just like for reaching sea level and was always starting to perform all necessary procedures basing on data only from this one sensor. For the moment it is the most likely explanation for crash of the EDM. Still ESA is going to keep investigation conducted by board of independent specialists and release final report on EDM in the early 2017.
EDM lander was result of joined efforts of ESA and Thales Alenia Space. It was planned that after landing on Meridiani Planum, inside ellipse of 100 km x 15 km, EDM will operate for at least three days.