4 ms·

Pretty mind-blowing if true. That is an unbelievably basic mistake to make.

by visviva 4y ago

jackmott 4y ago
[dead]
wilg 4y ago
a basic mistake huh?
- iancmceachern 4y ago
  In a way, yes. Many of the systems on these satellites rely on math and physics we've only recently mastered, high speed radio telecommunications and all that goes with it is truly magic, a modern marvel. Inertial stuff however, that's all basic Newtonian physics, we've had that mastered for a bit longer. Side note/fun fact - many satellites use tape measures for this purpose, literally tape measures. They're called gravity gradient booms. So, I get your point, it's not a simple mistake compared to me forgetting my keys this morning, but it is a simple mistake in the context of a satellite.
  - wilg 4y ago
    my main point is that its silly to assume the satellite designers at SpaceX made some kind of remedial physics error as opposed to a more subtle error that is the result of engineering or design tradeoffs
    - iancmceachern 4y ago
      I dont know, I'm a designer like that and I make far more remedial errors than errors that were carefully weighed and considered.
      - wilg 4y ago
        That's fair enough, but in that light I feel like the parent commenter should be less incredulous.
        deleted 4y ago
        [deleted]
  - ilyagr 4y ago
    > many satellites use tape measures for this purpose, literally tape measures. They're called gravity gradient booms. Could you elaborate a bit? What part of a satellite is a tape measure useful for? How is it useful?
    - upofadown 4y ago
      An example: * https://tigersats.princeton.edu/cubesatkit https://tigersats.princeton.edu/cubesatkit An unrolled tape measure is stiff so that the satellite/weight system will align up and down. As skinny things tend to do in orbit.
    - peterfirefly 4y ago
      It's a bit like a keel for a (water) ship. You lower it and the gravitational pull on it will be slightly higher down where it is than up where the satellite is. Or you raise it up above where the satellite is -- same idea. The "tape measure" is a mass at the end of a tether (the "tape") and they are of course not "literally tape measures". https://en.wikipedia.org/wiki/Gravity-gradient_stabilization https://en.wikipedia.org/wiki/Gravity-gradient_stabilization
      - ilyagr 4y ago
        Fascinating, thanks!
      - iancmceachern 4y ago
        They are literally tape measures. Source: I know engineers at Lockheed martin.. Manufacing that tape is a highly specialized big factory scale production process. It doesn't make sense to build a special tape factory just for the 100 feet of it they need for satalites annually. The tape many of them use is sourced from the same suppliers as tape measures for these reasons.
  - hinkley 4y ago
    One of the qualities of aerospace is that we get less forgiving of people making the same mistake over time. If someone mixed up metric and imperial units on a mars lander again they’d be vilified.
- visviva 4y ago
  > a basic mistake huh? Yes, a basic mistake. I'm not sure what you're getting at with your comment, but this is literally the kind of thing that should be caught very early on, probably just by updating a few parameters (or even just one) in the attitude control sim and observing the outputs. If this claim is true (a big "if", admittedly), this is a breakdown in the kind of fundamental systems engineering that they teach to undergrads building cubesats.
perihelions 4y ago
Same type of mistake as Ariane 5. Upgraded the size of some parts (from Ariane 4), but failed to thoroughly check every other system component would be compatible with the up-scaling. Specifically: the real-time control software was carefully written for the small parts, but not adequate for the upgraded parts because the bigger numbers would overflow a fixed-width integer field. https://en.wikipedia.org/wiki/Ariane_flight_V88?useskin=vector https://en.wikipedia.org/wiki/Ariane_flight_V88?useskin=vect... - "The greater values of BH caused a data conversion from a 64-bit floating point number to a 16-bit signed integer value to overflow and cause a hardware exception.[5] The programmers had protected only four out of seven critical variables against overflow to keep within a required maximum workload target of 80% for the on-board Inertial Reference System computer, and relied on assumptions which were correct for the Ariane 4, but not Ariane 5, trajectory about the possible range of values for the three unprotected variables.[6]"

Pretty mind-blowing if true. That is an unbelievably basic mistake to make.

jackmott 4y ago

[dead]

wilg 4y ago

a basic mistake huh?

iancmceachern 4y ago
In a way, yes. Many of the systems on these satellites rely on math and physics we've only recently mastered, high speed radio telecommunications and all that goes with it is truly magic, a modern marvel. Inertial stuff however, that's all basic Newtonian physics, we've had that mastered for a bit longer. Side note/fun fact - many satellites use tape measures for this purpose, literally tape measures. They're called gravity gradient booms. So, I get your point, it's not a simple mistake compared to me forgetting my keys this morning, but it is a simple mistake in the context of a satellite.
- wilg 4y ago
  my main point is that its silly to assume the satellite designers at SpaceX made some kind of remedial physics error as opposed to a more subtle error that is the result of engineering or design tradeoffs
  - iancmceachern 4y ago
    I dont know, I'm a designer like that and I make far more remedial errors than errors that were carefully weighed and considered.
    - wilg 4y ago
      That's fair enough, but in that light I feel like the parent commenter should be less incredulous.
      - deleted 4y ago
        [deleted]
- ilyagr 4y ago
  > many satellites use tape measures for this purpose, literally tape measures. They're called gravity gradient booms. Could you elaborate a bit? What part of a satellite is a tape measure useful for? How is it useful?
  - upofadown 4y ago
    An example: * https://tigersats.princeton.edu/cubesatkit https://tigersats.princeton.edu/cubesatkit An unrolled tape measure is stiff so that the satellite/weight system will align up and down. As skinny things tend to do in orbit.
  - peterfirefly 4y ago
    It's a bit like a keel for a (water) ship. You lower it and the gravitational pull on it will be slightly higher down where it is than up where the satellite is. Or you raise it up above where the satellite is -- same idea. The "tape measure" is a mass at the end of a tether (the "tape") and they are of course not "literally tape measures". https://en.wikipedia.org/wiki/Gravity-gradient_stabilization https://en.wikipedia.org/wiki/Gravity-gradient_stabilization
    - ilyagr 4y ago
      Fascinating, thanks!
    - iancmceachern 4y ago
      They are literally tape measures. Source: I know engineers at Lockheed martin.. Manufacing that tape is a highly specialized big factory scale production process. It doesn't make sense to build a special tape factory just for the 100 feet of it they need for satalites annually. The tape many of them use is sourced from the same suppliers as tape measures for these reasons.
- hinkley 4y ago
  One of the qualities of aerospace is that we get less forgiving of people making the same mistake over time. If someone mixed up metric and imperial units on a mars lander again they’d be vilified.
visviva 4y ago
> a basic mistake huh? Yes, a basic mistake. I'm not sure what you're getting at with your comment, but this is literally the kind of thing that should be caught very early on, probably just by updating a few parameters (or even just one) in the attitude control sim and observing the outputs. If this claim is true (a big "if", admittedly), this is a breakdown in the kind of fundamental systems engineering that they teach to undergrads building cubesats.

perihelions 4y ago

Same type of mistake as Ariane 5. Upgraded the size of some parts (from Ariane 4), but failed to thoroughly check every other system component would be compatible with the up-scaling. Specifically: the real-time control software was carefully written for the small parts, but not adequate for the upgraded parts because the bigger numbers would overflow a fixed-width integer field. https://en.wikipedia.org/wiki/Ariane_flight_V88?useskin=vector https://en.wikipedia.org/wiki/Ariane_flight_V88?useskin=vect... - "The greater values of BH caused a data conversion from a 64-bit floating point number to a 16-bit signed integer value to overflow and cause a hardware exception.[5] The programmers had protected only four out of seven critical variables against overflow to keep within a required maximum workload target of 80% for the on-board Inertial Reference System computer, and relied on assumptions which were correct for the Ariane 4, but not Ariane 5, trajectory about the possible range of values for the three unprotected variables.[6]"