4 ms·

I wonder how the radiation affects things like ESC motor timing, communication protocols, the cou inside the drone flight computer etc.

teeray 3y ago
I once heard that things like NOP slides[0] are sometimes used in radioactive environments just in case jumps are off due to bit flips. [0] https://en.wikipedia.org/wiki/NOP_slide https://en.wikipedia.org/wiki/NOP_slide
- proaralyst 3y ago
  That only helps if your flips are in the low bits though right? And naively I'd expect bit flips to be uniformly distributed through the address bits
colechristensen 3y ago
It comes out as bit flips in memory and noise on communication lines. There are many mitigations. State machines that recover from "impossible" to reach paths, redundancies like calculating the same thing more than once, checksumming/error correcting codes, repeatedly setting a state that "should" not need to be changed. But also lots of things don't matter. Like if your ESC hiccups for a millisecond or gives a blip too much power no one cares because there are no long term consequences. Like the extra noise in the video feed, ok it's there but of no actual consequence. The important parts are long term stored variables and ensuring that state is maintained or can recover. The surface area of things that really matter which are vulnerable to radiation is really quite small, the rest has either 0 effect or manifests as very survivable noise. Source: ran the flight computer team on a student satellite competition long ago.
- bahmboo 3y ago
  Were there problems with CPU state that caused crashes? A bit flip on the stack could easily trigger a memory fault.
  - colechristensen 3y ago
    We never launched so it was all theoretical. We never got to the point of actual radiation testing, this is done but a very advanced kind of thing to do, for example we did go to a Lockheed Martin location a few times to, test our GPS receiver which had its restrictions removed and would work in orbit. (when configured with the right firmware this had ITAR restrictions, was considered munitions, students from certain countries couldn't participate) They also had facilities for environmental testing: heat, cold, vibration, vacuum, etc. The two hardest parts of designing a satellite are attaching to the rocket and surviving launch and managing your temperature in orbit. I don't remember all of the details of the OS level things we didn't have control of for the different OS options out there, we were just going to use Linux though, it was a viable option. One of the things you do is have a really simple hardware watchdog which will just reboot everything if it stops receiving the right health indications for exactly the case of difficult to recover faults.

teeray 3y ago

I once heard that things like NOP slides[0] are sometimes used in radioactive environments just in case jumps are off due to bit flips. [0] https://en.wikipedia.org/wiki/NOP_slide https://en.wikipedia.org/wiki/NOP_slide

proaralyst 3y ago
That only helps if your flips are in the low bits though right? And naively I'd expect bit flips to be uniformly distributed through the address bits

colechristensen 3y ago

It comes out as bit flips in memory and noise on communication lines. There are many mitigations. State machines that recover from "impossible" to reach paths, redundancies like calculating the same thing more than once, checksumming/error correcting codes, repeatedly setting a state that "should" not need to be changed. But also lots of things don't matter. Like if your ESC hiccups for a millisecond or gives a blip too much power no one cares because there are no long term consequences. Like the extra noise in the video feed, ok it's there but of no actual consequence. The important parts are long term stored variables and ensuring that state is maintained or can recover. The surface area of things that really matter which are vulnerable to radiation is really quite small, the rest has either 0 effect or manifests as very survivable noise. Source: ran the flight computer team on a student satellite competition long ago.

bahmboo 3y ago
Were there problems with CPU state that caused crashes? A bit flip on the stack could easily trigger a memory fault.
- colechristensen 3y ago
  We never launched so it was all theoretical. We never got to the point of actual radiation testing, this is done but a very advanced kind of thing to do, for example we did go to a Lockheed Martin location a few times to, test our GPS receiver which had its restrictions removed and would work in orbit. (when configured with the right firmware this had ITAR restrictions, was considered munitions, students from certain countries couldn't participate) They also had facilities for environmental testing: heat, cold, vibration, vacuum, etc. The two hardest parts of designing a satellite are attaching to the rocket and surviving launch and managing your temperature in orbit. I don't remember all of the details of the OS level things we didn't have control of for the different OS options out there, we were just going to use Linux though, it was a viable option. One of the things you do is have a really simple hardware watchdog which will just reboot everything if it stops receiving the right health indications for exactly the case of difficult to recover faults.