5 ms·

From Elon just now via Twitter: "There was an overpressure event in the upper stage liquid oxygen tank. Data suggests counterintuitive cause. That's all we ca

by 51Cards 11y ago

From Elon just now via Twitter: "There was an overpressure event in the upper stage liquid oxygen tank. Data suggests counterintuitive cause. That's all we can say with confidence right now. Will have more to say following a thorough fault tree analysis."

myth_buster 11y ago
Received telemetry from Dragon after the event - Gwynne (From Conference). Bit of positive news to take from this sad day.
- 51Cards 11y ago
  Yeah, it is too bad there wasn't some way to deploy the parachute system manually. It would be nice if the cargo could be saved.
  - myth_buster 11y ago
    I think Gerstenmaier was saying that may be a distant possibility.
    - will_hughes 11y ago
      While they might be able to recover the items, re-qualifying something that's been dunked in seawater after being dropped from 35km+ is probably a non-trivial task. That's assuming it wasn't exposed to explosion debris.
Havoc 11y ago
>Data suggests counterintuitive cause. What does this sentence mean?
- greglindahl 11y ago
  It means that the cause was surprising, not one that your intuition would think of.
- CamperBob2 11y ago
  It's sort of like "Prepare for unforeseen consequences."
- chillingeffect 11y ago
  I'm guessing if there was an overpressure event, that one would normally think that it was due to unanticipated heat, or a valve opening incorrectly (too early/late, far/little), etc. but that data from a measurement system on e.g. thermal or flow indicate the opposite, such as temperature doing down instead of up. I wonder what the specs are for the systems they're using for telemetry... must be a gazillion channels at a high rate...
TeMPOraL 11y ago
I wonder if "overpressure event" is a significant information, or is it just an euphemism for "explosion"?
- grinich 11y ago
  Usually they call those RUD, or "rapid unplanned disassembly." ;) I imagine this was literally an overpressure event, where perhaps something occurred with the 2nd stage tank mixers. (The explosion occurred close to MECO.)
phkahler 11y ago
>> "That's all we can say with confidence right now. Will have more to say following a thorough fault tree analysis." You're supposed to do the fault tree analysis before you build the rocket Elon. The safety critical systems on your car have these done. Or perhaps they never did one for over pressure because it seems implausible for the pressure to increase.
- deleted 11y ago
  [deleted]
- robzyb 11y ago
  > You're supposed to do the fault tree analysis before you build the rocket Elon. How can you do a fault tree analysis before things go wrong? Maybe fault tree analysis means something different to you. According to Wikipedia, it is "a top down, deductive failure analysis in which an undesired state of a system is analyzed using Boolean logic to combine a series of lower-level events." There needs to be an undesirable (and presumably unforeseen) state to be analysed before you do the fault tree analysis.
  - HeyLaughingBoy 11y ago
    I'm no Risk expert, but going from memory, you hypothesize potential failures based on experience and knowledge of the module. Then you use the FTA to understand what faults may result in the failures under examination. FTA can be used either pre- or post- event.
    - robzyb 11y ago
      > FTA can be used either pre- or post- event. Fair point. OP's objection to a post-event FTA still makes no sense, though.
      - fian 11y ago
        Generally you do a Root Cause Analysis post-event, not a Fault Tree Analysis. Fault Trees are typically used to determine the probability of a bad thing (fault) occurring. This probability is used to populate a Risk Matrix (Probability vs Consequence). The Risk Matrix is used to decide whether the risk is low enough vs the consequence within a design. It the risk is too high, then more redundancy or layers of protection are likely to be needed. Root Cause Analysis builds a tree of possible causes that will look much like the Fault Tree diagram but may include more human factors (was the part inspected before use, was the equipment maintained etc). There is a lot of overlap of techniques within the Risk Engineering discipline. Fault Trees can be mapped to Reliability Block Diagrams (AND gates are equivalent to Parallel pathways, OR gates are equivalent to Series pathways for example). The mention of Fault Tree Analysis being required post event seems a bit odd. It may just have been a confusion of terms in the heat of the moment.

by 51Cards 11y ago

myth_buster 11y ago

Received telemetry from Dragon after the event - Gwynne (From Conference). Bit of positive news to take from this sad day.

51Cards 11y ago
Yeah, it is too bad there wasn't some way to deploy the parachute system manually. It would be nice if the cargo could be saved.
- myth_buster 11y ago
  I think Gerstenmaier was saying that may be a distant possibility.
  - will_hughes 11y ago
    While they might be able to recover the items, re-qualifying something that's been dunked in seawater after being dropped from 35km+ is probably a non-trivial task. That's assuming it wasn't exposed to explosion debris.

Havoc 11y ago

>Data suggests counterintuitive cause. What does this sentence mean?

greglindahl 11y ago
It means that the cause was surprising, not one that your intuition would think of.
CamperBob2 11y ago
It's sort of like "Prepare for unforeseen consequences."
chillingeffect 11y ago
I'm guessing if there was an overpressure event, that one would normally think that it was due to unanticipated heat, or a valve opening incorrectly (too early/late, far/little), etc. but that data from a measurement system on e.g. thermal or flow indicate the opposite, such as temperature doing down instead of up. I wonder what the specs are for the systems they're using for telemetry... must be a gazillion channels at a high rate...

TeMPOraL 11y ago

I wonder if "overpressure event" is a significant information, or is it just an euphemism for "explosion"?

grinich 11y ago
Usually they call those RUD, or "rapid unplanned disassembly." ;) I imagine this was literally an overpressure event, where perhaps something occurred with the 2nd stage tank mixers. (The explosion occurred close to MECO.)

phkahler 11y ago

>> "That's all we can say with confidence right now. Will have more to say following a thorough fault tree analysis." You're supposed to do the fault tree analysis before you build the rocket Elon. The safety critical systems on your car have these done. Or perhaps they never did one for over pressure because it seems implausible for the pressure to increase.

deleted 11y ago
[deleted]
robzyb 11y ago
> You're supposed to do the fault tree analysis before you build the rocket Elon. How can you do a fault tree analysis before things go wrong? Maybe fault tree analysis means something different to you. According to Wikipedia, it is "a top down, deductive failure analysis in which an undesired state of a system is analyzed using Boolean logic to combine a series of lower-level events." There needs to be an undesirable (and presumably unforeseen) state to be analysed before you do the fault tree analysis.
- HeyLaughingBoy 11y ago
  I'm no Risk expert, but going from memory, you hypothesize potential failures based on experience and knowledge of the module. Then you use the FTA to understand what faults may result in the failures under examination. FTA can be used either pre- or post- event.
  - robzyb 11y ago
    > FTA can be used either pre- or post- event. Fair point. OP's objection to a post-event FTA still makes no sense, though.
    - fian 11y ago
      Generally you do a Root Cause Analysis post-event, not a Fault Tree Analysis. Fault Trees are typically used to determine the probability of a bad thing (fault) occurring. This probability is used to populate a Risk Matrix (Probability vs Consequence). The Risk Matrix is used to decide whether the risk is low enough vs the consequence within a design. It the risk is too high, then more redundancy or layers of protection are likely to be needed. Root Cause Analysis builds a tree of possible causes that will look much like the Fault Tree diagram but may include more human factors (was the part inspected before use, was the equipment maintained etc). There is a lot of overlap of techniques within the Risk Engineering discipline. Fault Trees can be mapped to Reliability Block Diagrams (AND gates are equivalent to Parallel pathways, OR gates are equivalent to Series pathways for example). The mention of Fault Tree Analysis being required post event seems a bit odd. It may just have been a confusion of terms in the heat of the moment.