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ESA: European Mars Lander Crash Caused By 1-Second Glitch (space.com)
An anonymous reader quotes a report from Space.com: The European Space Agency (ESA) on Nov. 23 said its Schiaparelli lander's crash landing on Mars on Oct. 19 followed an unexplained saturation of its inertial measurement unit (IMU), which delivered bad data to the lander's computer and forced a premature release of its parachute. Polluted by the IMU data, the lander's computer apparently thought it had either already landed or was just about to land. The parachute system was released, the braking thrusters were fired only briefly and the on-ground systems were activated. Instead of being on the ground, Schiaparelli was still 2.3 miles (3.7 kilometers) above the Mars surface. It crashed, but not before delivering what ESA officials say is a wealth of data on entry into the Mars atmosphere, the functioning and release of the heat shield and the deployment of the parachute -- all of which went according to plan. In its Nov. 23 statement, ESA said the saturation reading from Schiaparelli's inertial measurement unit lasted only a second but was enough to play havoc with the navigation system. ESA said the sequence of events "has been clearly reproduced in computer simulations of the control system's response to the erroneous information." ESA's director of human spaceflight and robotic exploration, David Parker, said in a statement that ExoMars teams are still sifting through the voluminous data harvest from the Schiaparelli mission, and that an external, independent board of inquiry, now being created, would release a final report in early 2017.
Overflows and bad data problems happened to ESA before.
When the altitude stops changing for a whole second the filter is going to have to be a long one! And that ain't desirable for responsive control.
The real question is how could the sensory processor have overloaded in the first place? My money is on simple [b]code bloat[/b]. Ie: They used a bunch of generic libraries that use further libraries that use further libraries that use further libraries that use further libraries that use further libraries ...
So they didn't correlate the IMU data with ranging radar or even barometric altitude information so as to avoid this?
I know weight and volume are at a premium on such craft but a barometric sensor (even one capable of operating in Mars's rarefied atmosphere, is the size of a thumbnail and weighs just a fraction of a gram.
Sigh!
> ...control software spat an Ada stack trace over a line...
Eh, no. The failure of the INS's control software caused the INS to send diagnostic data (rather than sensor data) to the control systems, which then did what they _thought_ they were being commanded to do.
None of the code in the system was modified in flight.