5 ms·

Amazing that someone thought up a solution to a hypothetical problem 46 years ago, then fired it 30 billion km away

• behnamoh 3y ago
  Sometimes we don’t give enough credit to previous generations.
  • detourdog 3y ago
    I only give credit to previous generations. Firm believer that we only understand in retrospect.
• bumby 3y ago
  Aerospace has a very high quality standard compared to other industries. Lots of formal processes capture what would otherwise be informal design decisions elsewhere. In this case, they probably have reams of pages detailing a failure mode effects analysis (FMEA). One mode is “oops, we sent the wrong command” and the document would define the specific design mitigation(s) for that outcome until it reaches an accepted risk threshold.
  • aetherspawn 3y ago
    FMEDA probably. And in recent times, fault tree analysis seems to be better for complex systems.
    • deleted 3y ago
      [deleted]
    • bumby 3y ago
      As far as I’m aware, no NASA standards call for FMEDA. It doesn’t mean a project manager couldn’t levy it, but it’s not often that a contractor adds additional requirements to a gov funded build.
      • aetherspawn 3y ago
        FMEA relies on a really smart person anticipating all the different combinations of failures worth exploring (NxM), not just N or M. Some failures are fairly common, and individual failures might be fairly inert but have more serious consequences if they are cascaded with another specific failure.. for example, cruise control enable + failure of steering wheel control pad _and_ previously undetected failure of brake sensor/brake light circuit = cruise control stuck ON. Actually, this failure is inert if the cruise control is OFF when it happens. Contrived example but you get the idea ... I have seen a lot of FMEDA (and other tool) use lately to combat concerns with cascading failure, but not sure what's currently standard at NASA or how they deal with this. I would think cascading failure would be their expected scenario on a 10+ year unmanned mission.
        • bumby 3y ago
          NASA STDs, handbooks, guidebooks, NPDs and NPRs are all open-source. They don’t mention FMEDA, and they don’t generally have a detectability column in their FMEA. IMO they are a little outdated
          • sheepshear 3y ago
            I've done for NASA what they were calling FMECA and FTA for a subsystem. They had a lot of freedom to tailor the analysis to the situation, and the end result didn't quite match anything established. We addressed detection in some of the FMECA columns which are not traditionally for detection; and events in some of the FTA. It was a contortion of terminology and format to modernize and maximize the value of the analysis given their limited resources and the bureaucracy of what they were allowed/required to do on paper. Here's how I would describe the possible analysis approaches in broad terms, avoiding terminology that NASA does not officially use. - Start from the hazard of being pointed in the wrong direction and work backwards to identify the causes, forming a tree. - Start from the event of commanding the wrong direction and work forwards to identify mitigations or the lack thereof, also forming a tree. - Start from looking at a component or subsystem, list all the ways it can fail without regard for the application. Then consider the application and work up towards the causes/events. - Close any gaps between the top-down and bottom-up approaches.
• rcxdude 3y ago
  It's not really hypothetical: losing communication with stuff in space is a very common failure mode and a huge amount of the system design is focused on making it as unlikely as possible (generally the radio system gets a huge priority in almost everything and there are a lot of failsafes built at every level to make it possible to reestablish communication if anything disrupts it).
  • JdeBP 3y ago
    Indeed. Voyager 2 has in fact been listening via its backup receiver since 1978.
  • dekhn 3y ago
    I was amused to learn that if modern satellites lose contact with earth, they go into "safe mode": pointing towards sun, solar panels fully deployed, everything else except telemetry, radio, and temperature management disabled, waiting for further instructions. https://en.wikipedia.org/wiki/Safe_mode_in_spacecraft https://en.wikipedia.org/wiki/Safe_mode_in_spacecraft Imagine deploying a billion dollar piece of hardware and hoping that it has enough intelligence to keep itself from burning up before you can reestablish contact!
• jjk166 3y ago
  It wasn't a solution for this specific problem. Spacecraft orientations are going to drift over time, periodically rehoming is the simplest way of dealing with it. That it doesn't care whether the orientation drift was natural or artificial is just a bonus.
• whartung 3y ago
  The Voyager that's flying now is not necessarily the Voyager that was launched. The hardware is the same, but they've updated, patched, and rewritten the software that's running in it throughout the years. I'm not suggesting that the failsafe mode wasn't originally considered, and implemented, but simply that it doesn't have to be the case. They could have made changes to it over time.
  • Shawnj2 3y ago
    It’s possible to update the Voyager FSW?
• kdinn 3y ago
  Actually there's a couple of work arounds for this problem as they anticipated it all along. My father was Director of Operations at Tidbinbilla deep space tracking station which ran most of the comms to Voyager 1. I am paraphrasing what he said as a non-technical person: Voyager has both a dish receiver, and a pole antenna. The dish is the usual mechanism for comms but in an emergency such as this they would send commands to the other antenna. To do this they would turn the main tracking station dish up to max, and send a "TURN AROUND!" signal out. But prior to that they had to alert the local electricity grid, and the local air traffic control to not have any planes flying over at the time! I guess the Voyagers are too far away for this manoeuvre now.