3 ms·

> The trick is trying to figure out where to spend your limited resources as the project is going. In a situation such as this where you don't have the funds t

by redcalx 10y ago

> The trick is trying to figure out where to spend your limited resources as the project is going. In a situation such as this where you don't have the funds to test everything to the level you would like and the cost of a failure is large, I wonder if a reasonable compromise is to hire a smallish team of 'adversaries'. I.e. their full time job is to try and find issues with other people's work; and to ask what could go wrong, or, what is likely to to go wrong - let's go see if we can break that. I also find the idea of a risk register useful. I.e. during development you'll often have thoughts about whether particular edge cases are truly being handled properly, but often the day to day cost versus benefit decisions mean you can't explore all of these issues. If however you log them then this can serve as a source of ideas for an adversarial team, or indeed your own investigations if you happen to have bits of free time for testing.

plafl 10y ago
Engineering simulators are used for this purpose, I have worked on them, and seen them being used precisely for trying to find unexpected system behaviors under sensor or other subsystem failures (valves, computers, motors, power,...). This is quite costly. In commercial aviation there are teams for developing the simulations and separate teams just trying all kind of strange scenarios. In less critical projects, say for example drones, I have seen it done too although with smaller teams. As I see it with the limited information we have right now it seems that either the error was made when writing the requirements for the IMU or the IMU wasn't the correct one. Having worked writing navigation software I cannot help siding with the software developers. The IMU is usually the central piece of the navigation system, at best they could have flagged it as failed but that is usually way more improbable that the altimeter failing. And even if they discarded the IMU measures I don't know what other sensors could be used to get at least the vehicle attitude. I think that after the saturation they were doomed and a software solution is not realistic.
- redcalx 10y ago
  > software solution is not realistic. I would expect such a role to be holistic; to consider the entire system and ways it could fail. The boundaries between sub-systems would be high on the list of targets; software-software, software-hardware, hardware-hardware. It's not a matter of siding with anyone, it's about accepting that an error has been made at some level, and asking if there are general purpose strategies for increasing the probability of identifying errors without having to build a simulation. Simulations of course have all the same problems - they're complex and therefore expensive and will contain defects. Regarding the other point about probabilistic models compensating for sensor failures; it depends on which sensors fail and when. Parts of a descent are highly predictable, so e.g. if you know height and you're in free-fall then you can model pretty accurately where you're likely to be in +t seconds, and can use that as a prior for sensory input. OTOH if you're in the final landing stage using retro-thrusters then feedback sensors are paramount to doing landing correctly. I accept that a probabilistic model would be more expensive to develop; initially anyway, and therefore may be unrealistic with the resources available.

by redcalx 10y ago

plafl 10y ago

Engineering simulators are used for this purpose, I have worked on them, and seen them being used precisely for trying to find unexpected system behaviors under sensor or other subsystem failures (valves, computers, motors, power,...). This is quite costly. In commercial aviation there are teams for developing the simulations and separate teams just trying all kind of strange scenarios. In less critical projects, say for example drones, I have seen it done too although with smaller teams. As I see it with the limited information we have right now it seems that either the error was made when writing the requirements for the IMU or the IMU wasn't the correct one. Having worked writing navigation software I cannot help siding with the software developers. The IMU is usually the central piece of the navigation system, at best they could have flagged it as failed but that is usually way more improbable that the altimeter failing. And even if they discarded the IMU measures I don't know what other sensors could be used to get at least the vehicle attitude. I think that after the saturation they were doomed and a software solution is not realistic.

redcalx 10y ago
> software solution is not realistic. I would expect such a role to be holistic; to consider the entire system and ways it could fail. The boundaries between sub-systems would be high on the list of targets; software-software, software-hardware, hardware-hardware. It's not a matter of siding with anyone, it's about accepting that an error has been made at some level, and asking if there are general purpose strategies for increasing the probability of identifying errors without having to build a simulation. Simulations of course have all the same problems - they're complex and therefore expensive and will contain defects. Regarding the other point about probabilistic models compensating for sensor failures; it depends on which sensors fail and when. Parts of a descent are highly predictable, so e.g. if you know height and you're in free-fall then you can model pretty accurately where you're likely to be in +t seconds, and can use that as a prior for sensory input. OTOH if you're in the final landing stage using retro-thrusters then feedback sensors are paramount to doing landing correctly. I accept that a probabilistic model would be more expensive to develop; initially anyway, and therefore may be unrealistic with the resources available.