3 ms·

> The most recent mars rover uses, essentially, a half-speed imac processor from 1990s. Isn't this because they need to be specified, texted, and certified to

• jvanderbot 3y ago
  Well, the mars helicopter essentially uses a cell phone, so not really. And it's not that low power. But yeah, the mentality was: We know this works, it's too costly to guarantee a new one will work, and too risky to just try it. Same in the military. Imagine the military didn't have radiation, temperature, etc requirements
  • ch4s3 3y ago
    From what I understand the helicopter was a special case and sort of a side mission meant to test off the shelf parts.
    • jvanderbot 3y ago
      Sure, but those COTS parts still underwent lots and lots of rad/ vac testing. There's a design-for-resilience vs test-for-resilience tradeoff at play. I'm saying that not all systems require design-for-resilience.
      • godelski 3y ago
        Well to nitpick, that's because the two are kinda the same. Testing is part of design and vise versa in these types of systems. But otherwise I agree with the points you've made (seems we've been responding in parallel lol)
      • giantrobot 3y ago
        Ingenuity is also running a very customized software stack to go along with the highly tested hardware. IIRC the OS can reboot in a some relatively small number milliseconds. It's meant to be able to crash in mid-air and reboot and recover before the probe loses lift and crashes in most flight envelopes. The software is also set up to crash and reboot rather than try to recover or operate in a compromised state.
        • deleted 3y ago
          [deleted]
        • jvanderbot 3y ago
          Yeah, I suspect we were both in or close to 347 at the time this was getting made.
  • heavyset_go 3y ago
    AFAIK the helicopter wasn't mission critical, it was a nice-to-have demo project that piggybacked on Perseverance's mission.
• AlexandrB 3y ago
  Not sure if true, but I also recall reading that ICs made with larger processes are more resilient to cosmic ray strikes. So modern 7nm chips might have an inherent disadvantage in these applications.
  • godelski 3y ago
    This is true. You can think about this fairly simply as you just have to think about the amount of energy traveling within a transistor and what that energy's proportionate level is to a cosmic ray. Smaller IC's are more likely to be hit (cross-section is higher due to density AND that we operate in fields, no need for a direct physical interaction of the mass). But that's not why they cost so much. Rad hardened ICs are built differently. They are built on a sapphire base: Silicon on Sapphire (SoS). Process is more complicated and expensive. That said, there are more people looking at commercial off the shelf (COTS) and just building redundant systems because 2 COTS CPUs can be cheaper (and more powerful) and because ECC has gotten much better. But this is really only for LEO right now, but may be used in deeper space missions later on. Realistically it is just going to be dependent on how much your ride costs. LEO is cheap now, so risk of failure is dramatically reduced. Your ride is still most of your cost though.
• godelski 3y ago
  Not everything needs to meet those specific standards, but essentially yes. My sibling comment mentioned Ingenuity (Mars Helicopter), but let's mention Curiosity. It often gets cited as costing $2.5 billion dollars. So that alone says why you wouldn't want to risk anything (see my other comments, especially about TRL[note]). But that also took almost a decade![other note] Time is also very expensive, so how much would you risk? On a 10 year project, that is going to operate for another 12+ years (still going, landed in 2011) with no way to repair or fix the product, you probably want that thing to be reliable as shit. Worth an extra year or two to make that happen. [note] TRL 9 pretty much doesn't exist in these types of missions. We don't have decades of operation of specific devices on other planets. But you still use very robust and redundant systems. [other note] People often cite this as a waste of money, but when we consider the time it is pittance in the government budget. Costs could definitely come down, but in government money can only exchange hands through leaky buckets. NASA politically prides itself as having parts from every state, which from an engineering perspective should sound like a logistic nightmare, and it is. But this is the type of people you are voting for, people that love pageantry over pragmatism. (pageantry gets votes, pragmatism doesn't)