The Schiaparelli probe was an ESA Mars probe which crashed 19 October 2016 while attempting to land. The ESA is working on understanding what went wrong:
Source: ESA
Good progress has been made in investigating the ExoMars Schiaparelli anomaly of 19 October. A large volume of data recovered from the Mars lander shows that the atmospheric entry and associated braking occurred exactly as expected.
The parachute deployed normally at an altitude of 12 km and a speed of 1730 km/h. The vehicle’s heatshield, having served its purpose, was released at an altitude of 7.8 km.
As Schiaparelli descended under its parachute, its radar Doppler altimeter functioned correctly and the measurements were included in the guidance, navigation and control system. However, saturation – maximum measurement – of the Inertial Measurement Unit (IMU) had occurred shortly after the parachute deployment. The IMU measures the rotation rates of the vehicle. Its output was generally as predicted except for this event, which persisted for about one second – longer than would be expected.
When merged into the navigation system, the erroneous information generated an estimated altitude that was negative – that is, below ground level. This in turn successively triggered a premature release of the parachute and the backshell, a brief firing of the braking thrusters and finally activation of the on-ground systems as if Schiaparelli had already landed. In reality, the vehicle was still at an altitude of around 3.7 km.
I wonder how they program these beasts – is this the result of engineers just writing code to handle envisionable scenarios, or are they built using neural networks and machine learning? They mention a computer simulation – I would have to think that one could cover most scenarios by varying the inputs to the simulator across entire ranges, evaluating the responses of the probe’s programs and modifying accordingly. At least that’s how I would have done it. This may lead to tens of thousands of scenarios, but computer cycles are generally cheap. And while atmospheric simulations are complex – even the thin Martian atmosphere is, no doubt, a bit of a challenge – actual orbital mechanics are mostly relatively simple math. (Beyond me, of course. Don’t ask me to solve the three body problem!)
Unless, of course, you inadvertently mix your measurement units. RIP1, Mars Climate Orbiter.
1That would be Rest In Pieces, of course.
