Last October, the European Space Agency’s ExoMars mission lost contact with its Schiaparelli lander as it attempted to land on Mars. As the agency began to investigate, it suspected that a computer problem or bad navigational data was to blame. Now, an independent investigation has issued its final report, confirming that software problems caused the capsule to crash, and provided recommendations for the 2020 ExoMars mission.
The report highlights reveals a timeline for the crash, noting that “between [Entry in the Mars atmosphere] and Parachute Deployment triggering, an unexpected evolution in the spin rate of the [Entry Demonstrator Module] was noticed.” The vehicle’s parachute deployed as expected, but its Inertial Measurement Unit detected that it detected a “larger than expected” angular pitch rate, which triggered a “saturation” alert. The Guidance Navigation and Control system believed that the angular rate was the same as the saturation threshold, which threw off the capsule’s calculated altitude.
That meant that the lander’s systems thought the spacecraft was closer to the ground, and released the capsule’s back-shell and parachute early and switching on the Reaction Control System for a handful of seconds. When the RCS shut down, the capsule was still just over two miles in the air, which led “to a free fall of Schiaparelli and to the impact on Mars surface about 34 seconds later.”
The final report concluded that insufficient parachute modeling, inadequate handling of alerts, an “insufficient approach to Failure Detection, Isolation and Recovery and design robustness,” and “mismanagement” with subcontractors and hardware were to blame for the crash, and provided a series of recommendations to avoid similar accidents in the future.
While the Schiaparelli lander was destroyed, the experience wasn’t a total loss: the landing was designed as a test before the ESA begins the next phase of its ExoMars mission, in which will land a larger payload on the surface in 2020. The mission also brought a spacecraft called the Trace Gas Orbiter (TGO) into Mars orbit, which will begin measuring the composition of the planet’s atmosphere later this year.