4 ms·

Presumably they've actually quantified these probabilities and think that the chance of that is relatively very low compared to the chance of something going wr

Presumably they've actually quantified these probabilities and think that the chance of that is relatively very low compared to the chance of something going wrong in the design. These things are not cheap, so it makes sense not to have to make three if the launch succeeds and design fails.

mikepurvis 5y ago
Oh yes, I totally agree— this is a very proven rocket, and the deployment sequence is very, very much not proven. So it absolutely makes sense to have gone this way.
- CamperBob2 5y ago
  That's assuming that anything that goes wrong in the deployment sequence necessitates a clean-sheet redesign of the whole thing. No reason to think that.
  - mikepurvis 5y ago
    But with so many things that could go wrong in such a tightly integrated system, it's impossible to predict which components or assemblies may be affected by a partial redesign.
    - CamperBob2 5y ago
      If you say so.
Kaibeezy 5y ago
Ariane 5 appears to have 96% mean reliability. Source: 2021 Space Launch Report – Launch Vehicle by Success Rate (spacelaunchreport.com) - https://www.spacelaunchreport.com/log2021.html#rate https://www.spacelaunchreport.com/log2021.html#rate https://news.ycombinator.com/item?id=29554274 https://news.ycombinator.com/item?id=29554274
- JumpCrisscross 5y ago
  The footnote about Lewis Point Estimates is super interesting. "Lewis Point Estimate Determined as Follows. Maximum Liklihood Estimate (MLE)= x/n where x=success, n=tries For MLE<=0.5, use Wilson Method = (x+2)/(n+4) For MLE Between 0.5 and 0.9, use MLE = x/n For MLE>=0.9, use Laplace Method = (x+1)/(n+2) Lewis, J. & Lauro, J., "Improving the Accuracy of Small-Sample Estimates of Completion Rates", Journal of Usability Studies, Issue 3, Vol. 1, May 2006, pp. 136-150."
  - Kaibeezy 5y ago
    Concur. You have to see this thread on it in the NASA Spaceflight forum - https://forum.nasaspaceflight.com/index.php?topic=39928.0 https://forum.nasaspaceflight.com/index.php?topic=39928.0

mikepurvis 5y ago

Oh yes, I totally agree— this is a very proven rocket, and the deployment sequence is very, very much not proven. So it absolutely makes sense to have gone this way.

CamperBob2 5y ago
That's assuming that anything that goes wrong in the deployment sequence necessitates a clean-sheet redesign of the whole thing. No reason to think that.
- mikepurvis 5y ago
  But with so many things that could go wrong in such a tightly integrated system, it's impossible to predict which components or assemblies may be affected by a partial redesign.
  - CamperBob2 5y ago
    If you say so.

Kaibeezy 5y ago

Ariane 5 appears to have 96% mean reliability. Source: 2021 Space Launch Report – Launch Vehicle by Success Rate (spacelaunchreport.com) - https://www.spacelaunchreport.com/log2021.html#rate https://www.spacelaunchreport.com/log2021.html#rate https://news.ycombinator.com/item?id=29554274 https://news.ycombinator.com/item?id=29554274

JumpCrisscross 5y ago
The footnote about Lewis Point Estimates is super interesting. "Lewis Point Estimate Determined as Follows. Maximum Liklihood Estimate (MLE)= x/n where x=success, n=tries For MLE<=0.5, use Wilson Method = (x+2)/(n+4) For MLE Between 0.5 and 0.9, use MLE = x/n For MLE>=0.9, use Laplace Method = (x+1)/(n+2) Lewis, J. & Lauro, J., "Improving the Accuracy of Small-Sample Estimates of Completion Rates", Journal of Usability Studies, Issue 3, Vol. 1, May 2006, pp. 136-150."
- Kaibeezy 5y ago
  Concur. You have to see this thread on it in the NASA Spaceflight forum - https://forum.nasaspaceflight.com/index.php?topic=39928.0 https://forum.nasaspaceflight.com/index.php?topic=39928.0