Accidents

Loss of Schiaparelli Mars Lander

High rates led to the saturation of the Inertial Measurement Unit (IMU); the lander prematurely believed it was on the ground and released its parachute; the lander was lost. The high rates should have been expected, but were not due to modelling deficiencies.

The Schiaparelli module, also known as the Entry Demonstrator Module (EDM), was part of the European  Space Agency (ESA)’s ExoMars 2016 mission. The objective was to validate and demonstrate entry, descent  and landing on Mars in preparation for the ExoMars 2020 mission.

On 19 October 2016, the EDM entered the Mars atmosphere at 14:42:07 (UTC). During its entry and  descent it constantly transmitted telemetry. Its signal was lost at 14:47:22 (UTC), about 43 seconds before  expected touchdown. On 20 October, a camera on NASA’s Mars Reconnaissance Orbiter imaged the  planned landing site and observed crash debris.

During entry, a parachute was deployed as planned. This triggered oscillations that saturated the IMU.  Integration of this saturated value caused a significant error in predicted attitude. As the descent  continued, a Radar Doppler Altimeter (RDA) was turned on. The significant attitude error led to large  discrepancies between the IMU and the RDA. The nature of the guidance and navigation control software  meant that this discrepancy led to a premature declaration of touchdown. As such, the parachute was  jettisoned too early, causing the EDM to crash into the planet’s surface.

The investigation determined the rates that saturated the IMU could have been predicted. Limitations in  the modelling of parachute dynamics meant they were not. The investigation also noted issues with the  persistence of the flag used to denote IMU saturation, as well as inadequate handling of this saturation by  the guidance software.

This incident illustrates the importance of the fidelity / representation Data Property, with respect to the  modelling, and the integrity Data Property, with respect to the persistence time of the saturation flag.

Links 

http://exploration.esa.int/mars/59176-exomars-2016-schiaparelli-anomaly-inquiry/
(accessed 29  November 2017).