Space

ESA confirms cause of Schiaparelli spacecraft's Mars crash

ESA confirms cause of Schiapar...
Schiaparelli with parachute deployed
Schiaparelli with parachute deployed
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Artist’s impression of the ExoMars 2020 rover (foreground), surface science platform (background) and the Trace Gas Orbiter (top)
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Artist’s impression of the ExoMars 2020 rover (foreground), surface science platform (background) and the Trace Gas Orbiter (top)
Heatshield sensors on the Schiaparelli module
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Heatshield sensors on the Schiaparelli module
Composite of the ExoMars Schiaparelli module elements seen by NASA’s Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) on 1 November 2016
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Composite of the ExoMars Schiaparelli module elements seen by NASA’s Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) on 1 November 2016
Schiaparelli with parachute deployed
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Schiaparelli with parachute deployed

After a seven-months investigation, ESA has released the results of its inquiry into the crash of its unmanned Schiaparelli lander on Mars last October. From telemetry data and orbital images, the investigators have confirmed that the accident was due to a sudden, violent rotation of the module that fooled the onboard computer into thinking that it had already landed and caused it to shut down its landing thrusters while still high above the planet's surface.

On October 16, 2016, Schiaparelli attempted to land on the Red Planet several days after it separated from its Trace Gas Orbiter (TGO) mothership. The six-minute hypersonic entry into the Martian atmosphere went as expected as the spacecraft collected data and beamed it back to the TGO.

Then Schiaparelli jettisoned its parachute 3.7 km (2.3 mi) above the surface and fired its thrusters for just three seconds instead of the planned 30. The end result was that the probe dropped 3,700 m (12,000 ft) before hitting the ground.

Heatshield sensors on the Schiaparelli module
Heatshield sensors on the Schiaparelli module

Analysis of the computer telemetry showed that the lander's onboard computer mistakenly believed that it was on the ground when it was still thousands of feet in the air. In fact, it had even initiated its ground program and was sending housekeeping data. Later images by NASA's Mars Reconnaissance Orbiter (MRO) confirmed that the spacecraft had crashed and was destroyed by the explosion of its fuel tanks on impact.

ESA set up an independent external inquiry chaired by ESA's Inspector General to determine the cause of the accident and to make recommendations as to how to avoid a repetition.

The newly released report identifies the circumstances and the root causes, stating that about three minutes after entering the atmosphere, Schiaparelli deployed its parachute. As it did so, the spacecraft oscillated on the tether and was subjected for about a second to a violent rotation that was outside of the design specifications of the Inertial Measurement Unit (IMU), which tracks the rotation rate of the lander as it descends.

Composite of the ExoMars Schiaparelli module elements seen by NASA’s Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) on 1 November 2016
Composite of the ExoMars Schiaparelli module elements seen by NASA’s Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) on 1 November 2016

Despite the fact that Schiaparelli had another system for measuring altitude, the saturation of the IMU caused a large attitude estimation error by the guidance, navigation and control system software. This, in turn, caused the computer to miscalculate data from the Doppler radar and it believed that it was not only landed, but was underground. As a result, the landing thrusters were shut down 27 seconds too early and ended up striking the Martian surface at a speed of 540 km/h (335 mph).

Ironically, ESA contends that the landing was successful – aside from the crash, explosion, and total loss of the spacecraft. However, the inquiry says that the data from the event will be valuable in planning the upcoming ExoMars 2020 landing.

Artist’s impression of the ExoMars 2020 rover (foreground), surface science platform (background) and the Trace Gas Orbiter (top)
Artist’s impression of the ExoMars 2020 rover (foreground), surface science platform (background) and the Trace Gas Orbiter (top)

"Interestingly, had the saturation not occurred and the final stages of landing had been successful, we probably would not have identified the other weak spots that contributed to the mishap," says Jan Woerner, ESA's Director General. "As a direct result of this inquiry we have discovered the areas that require particular attention that will benefit the 2020 mission."

Source: ESA

5 comments
Nik
''You learn by your mistakes'' is a well known saying, but a damned expensive one in this case. The trick is to make small mistakes.
Bob Flint
More like serval big mistakes, a simple count down over distance covered from the last known position before starting the violent spin. Better question is why did it spin out of control in the first place? Objects in motion not knowing if they are standing still seems so unbelievable given the fact it got this far in the first place.If we ever get a human near the planet, then this sort of final decent will likely still reside with human pilot
CharlieSeattle
Deploy a space elevator from orbit to the Martian surface. Less gravity so unreeling a carbon fiber nanotube yoyo will work there.
Gregg Eshelman
Easy way to avoid a repeat would be to use a physical contact probe like the Apollo missions.
Martin Winlow
"Interestingly, had the saturation not occurred and the final stages of landing had been successful, we probably would not have identified the other weak spots..." I think this is what is called 'spin'. it seems incomprehensible to me that Gregg Eshelman's suggestion is not standard equipment considering the tiny cost it would add. Next time, maybe. But not quite as incomprehensible as the Beagle debacle ('metric Vs imperial units').