3 ms·

> Better for safety to have conflicting inputs that require an arbiter, than a system that's confidently wrong on a single input and drives you at full speed in

> Better for safety to have conflicting inputs that require an arbiter, than a system that's confidently wrong on a single input and drives you at full speed into a 'Wile E. Coyote' wall painted to look like a tunnel. Reminded of the recent Japanese lunar probe that failed[1]. They relied on a radar ranging sensor to determine altitude, and when they flew over a large crater the sudden change in distance to ground caused the software to fail the radar sensor. This again meant it had to rely only the IMU, which has drift issues[2], causing it to believe it was just above ground when it was in fact way above. I'm thinking a camera looking down in combination with the radar would have been more resilient, as there would be less need to rely on hardcoded threshold values in order to determine when to fail the sensors. [1]: https://www.youtube.com/watch?v=2JlUnOAiMm4 https://www.youtube.com/watch?v=2JlUnOAiMm4 [2]: https://en.wikipedia.org/wiki/Inertial_navigation_system#Drift_rate https://en.wikipedia.org/wiki/Inertial_navigation_system#Dri...

lsaferite 3y ago
Not having read anything on the failure, I'm surprised they wouldn't have other range finding methods. Like LIDAR actually, just not the LIDAR everyone thinks of. They have them on commercial drone packages. It's like a single beam LIDAR setup. Does better at long distance range finding than the mmWave Radar units. The mmW unit handles water better though. The engineers that built the JP lander are likely far smarter than I am and probably thought things through much better than my simple armchair observations.
- magicalhippo 3y ago
  A single beam LIDAR would suffer the same problem. That is, the radar was accurate, the problem was the team hadn't foreseen the probe flying over such a deep crater, thus the threshold for failing the sensor in case of a sudden large change in apparent altitude was set too low. This is why I suggested a visual-based sensor, since it would be using a very different measuring scheme, and one which could also be used to cross-check the IMU data.

lsaferite 3y ago

Not having read anything on the failure, I'm surprised they wouldn't have other range finding methods. Like LIDAR actually, just not the LIDAR everyone thinks of. They have them on commercial drone packages. It's like a single beam LIDAR setup. Does better at long distance range finding than the mmWave Radar units. The mmW unit handles water better though. The engineers that built the JP lander are likely far smarter than I am and probably thought things through much better than my simple armchair observations.

magicalhippo 3y ago
A single beam LIDAR would suffer the same problem. That is, the radar was accurate, the problem was the team hadn't foreseen the probe flying over such a deep crater, thus the threshold for failing the sensor in case of a sudden large change in apparent altitude was set too low. This is why I suggested a visual-based sensor, since it would be using a very different measuring scheme, and one which could also be used to cross-check the IMU data.