Official word has come from the ESA regarding the why and wherefore of Schiaparelli’s crash landing on the Martian surface. Mission scientists were able to recover data from the lander before its untimely demise, and that data has revealed much more about the sequence of events during Schiaparelli’s last moments.
The lander entered the Martian atmosphere and performed atmospheric braking just as expected. Its parachute and heatshield both released normally, too, at 12 km and 7.8km respectively. Up to this point, the radar altimeter was working just fine, and its feedback was being integrated in other systems. So too was the Inertial Measurement Unit, which measured the vehicle’s rate of rotation. But shortly after the parachute deployed, Schiaparelli’s IMU reached saturation (maximum inertia) — and the IMU reported at saturation for longer than the navigation system expected.
The Schiaparelli lander model
When the navigation system got wind of the IMU’s wacky output, it decided that meant the spacecraft had “an estimated altitude that was negative” — that is, below ground level. In its scramble, the system released the backshell too early, fired the braking thrusters, and finally flicked on the on-ground systems as if Schiaparelli had already landed. In reality, the unfortunate spacecraft was still in freefall more than two miles off the ground.
Plugging all this data into simulations of Schiaparelli’s control systems reproduces this fatal cascade of events.
“This is still a very preliminary conclusion of our technical investigations,” said David Parker, ESA’s Director of Human Spaceflight and Robotic Exploration. “The full picture will be provided in early 2017 by the future report of an external independent inquiry board, which is now being set up, as requested by ESA’s Director General, under the chairmanship of ESA’s Inspector General.”
Meanwhile in orbit around Mars, Schiaparelli’s parent Trace Gas Orbiter is starting its first series of science observations, sampling the Martian atmosphere to characterize the atmospheric chemistry. At the same time, the TGO is moving from its initial parking orbit into the aerobraking maneuvers that will deliver the spacecraft to its operational orbit towards the end of 2017. From there, the TGO expects to act as a communications hub for the ExoMars 2020 rover.