Artist impression of the Schiaparelli module with parachute deployed.
Credit: ESA/ATG medialab

A European Space Agency (ESA) and industry inquiry into last year’s crash-landing of the ExoMars Schiaparelli module on the Red Planet has concluded that conflicting information in the onboard computer caused the descent sequence to end prematurely.

According to a just-released final report, the Schiaparelli demonstrator was very close to successfully landing on Mars at the planned location.

Six-minute descent

The Schiaparelli entry, descent and landing demonstrator module separated from its mothership — the now orbiting Mars, Trace Gas Orbiter — as planned on October 16, 2016 and coasted towards Mars for three days.

Much of the six-minute descent onto Mars on October 19 went as expected: the module entered the atmosphere correctly, with the heatshield protecting it at supersonic speeds. Sensors on the front and back shields collected useful scientific and engineering data on the atmosphere and heatshield.

Schiaparelli’s heatshield was equipped with a variety of sensors designed to take measurements as the module entered the atmosphere. The Combined Aerothermal and Radiometer Sensors Instrument Package, COMARS+, used sensors on the back heatshield to measure pressure, temperature and heat flux. System sensors on the front shield were monitored by the data housekeeping system.
Credit: ESA/ATG medialab

Real-time telemetry

Telemetry from Schiaparelli was relayed to the main craft, which was entering orbit around the Red Planet at the same time – the first time this had been achieved in Mars exploration. This real-time transmission proved invaluable in reconstructing the unfolding chain of events.

At the same time as the orbiter recorded Schiaparelli’s transmissions, ESA’s Mars Express orbiter also monitored the lander’s carrier signal, as did the Giant Meterwave Radio Telescope in India.

Root causes

In the report, the following root causes for the mishap have been identified:

– Insufficient uncertainty and configuration management in the modeling of the parachute dynamics which led to expect much lower dynamics than observed in flight;

– Inadequate persistence time of the craft’s inertial measurement unit (IMU) saturation flag and inadequate handling of IMU saturation by the guidance, navigation and control (GNC) hardware;

– Insufficient approach to Failure Detection, Isolation and Recovery and design robustness;

– Mishap in management of subcontractors and acceptance of hardware.

Planned descent sequence of Schiaparelli Mars lander.
Credit: ESA

Spin rate

Also noted in the report is an unexpected evolution of the spin rate of the Entry, descent and landing Demonstrator Module (EDM) with no apparent links to the landing failure. The root cause of this anomaly is believed to be linked with uneven degradation of thermal blankets during entry and a possible slight twist in the parachute riser after deployment.

Within this report general recommendations to avoid such defects and weaknesses have been established and specific recommendations for the ExoMars 2020 lander mission have also been established.

To read the full report — EXOMARS 2016 – Schiaparelli Anomaly Inquiry — go to:

http://exploration.esa.int/mars/59176-exomars-2016-schiaparelli-anomaly-inquiry/

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