The cause of the failure of the ESA ExoMars mission’s Schiaparelli landing on the planet Mars has been found. It was the inertial measurement unit (IMU) what done it!
The investigation and computer simulation showed a satisfactory re-entry into the Martian atmosphere and the Schiaparalli lander’s parachute deploying on time at 12 km altitude. At 7.8 km the heat shield was ejected as planned. However, at this point a fault in the lander’s IMU led to an incorrect negative altitude reading being fed into the craft’s navigation system, so the craft’s guidance system actually believed it had landed.
This resulted in the premature release of the parachute and a very brief three-second firing of the thrusters, before the craft started to deploy its equipment as if it had landed. The net result was that the now parachute-less and engine-thrust-less craft fell onto the ground from an altitude of 3.7 km, instead of the planned 2m free fall drop. Not surprisingly the craft exploded on impact. The exact cause of the faulty IMU reading is still being investigated, but is thought to be related to the rotation of the craft exceeding limits, which caused a data saturation effect.
ESA’s leadership still hopes to convince its membership to finance the follow-on ExoMars rover mission. In fact, the Schiaparelli lander was designed to shake out faults in the landing system for that key mission.
