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Crew Dragon only has a handful of missions. What the previous commenter is talking about is risks that may have been ignored/downplayed/unsuccessfully mitigated

Crew Dragon only has a handful of missions. What the previous commenter is talking about is risks that may have been ignored/downplayed/unsuccessfully mitigated but that Crew Dragon is simply lucky enough not to have faced. With time and more flights, more things will have a chance to go wrong, and in spaceflight, resting on your laurels is the best way to make sure that when it does go wrong it will be catastrophic.

chinathrow 5y ago
I agree regarding the handful of missions argument with Crew Dragon, but let's not forget all the successful Cargo Dragon missions here as I'm sure they play a role in (ongoing) safety assessments.
- InTheArena 5y ago
  Sure. It helps. One of the things NASA considered was Shuttle-C, a cargo varient of the space shuttle system, which would have given NASA a way to tinker on the engine /SRB stack without crew onboard. Of course, that would not have saved columbia (the orbiter itself was the problem). This stuff is called rocket science for a reason.
  - progre 5y ago
    Well, still... It's not exactly brain surgery is it?
bryanlarsen 5y ago
NASA calls it "normalizing of deviance", and it's why we lost both Shuttles. For example, the O-Rings were designed as a backup, the force generated by the solid rocket motors was supposed to seal the SRM sections together. But they knew after the first launch that the O-Rings were what was actually sealing the SRM's. But the O-Rings worked, so they didn't stop the program to fix the design. Later they found evidence of blow through the O-Rings, and again decided that since that didn't cause a crash, they were OK. Until they didn't. Tile strike damage was a similar normalization that killed 7 people. Does SpaceX normalize deviance? They fixed the toilet, so they didn't normalize that, but what about the delayed opening of the 4th parachute in the Crew 2 landing? It seems suspicious that they launched Crew 3 so quickly after an apparent anomaly. They do claim that the delayed opening is nominal behaviour seen and accepted in testing -- that this behaviour only happens when the other 3 parachutes are working fine. If one of the others had failed the 4th would have opened quicker due to increased air pressure. https://arstechnica.com/science/2021/11/double-dragon-nasa-plans-a-spacex-splashdown-on-monday-launch-wednesday/ https://arstechnica.com/science/2021/11/double-dragon-nasa-p...
- rbanffy 5y ago
  > that this behaviour only happens when the other 3 parachutes are working fine I'd love to see the causal relationship between both that makes it safe to land with 3 parachutes (I remember they added the 4th as an added precaution that reminds me of the O-ring issue)
- thaeli 5y ago
  NASA seems to normalize deviance when they're under political pressure to do so. I'm not sure they can be entirely trusted when it comes to their own launch systems, because of the politics involved - but so far they haven't shown similar hesitancy with commercial launch systems. It's a good separation of concerns; when NASA is "just the customer" and it's not "their rocket" they are in a better position to hold a firm line on safety issues. That NASA did not see the parachute as an issue speaks volumes. It looked bad visually, but having watched enough space launches and how mission control reacts to off-nominal data - clearly they were comfortable with the performance, because they didn't flinch at all. NASA just doesn't sign off on these commercial launches with NASA astronauts on board if they have any inkling that something won't go right - they aren't under the political pressure to "save the Shuttle program" or whatever. I have more concern about NASA getting politically-imposed "go fever" with SLS.
- jpgvm 5y ago
  SpaceX is on the other end of the scale, they continually change their vehicles to make small improvements all the time. It's highly unlikely the same paralysis could manifest at SpaceX with it's current culture. More likely is a failure of the other extreme where if changes are normalized and something that seems sufficiently simple actually has an outsized impact on the craft. I think such a thing is still relatively unlikely given how much testing and modelling goes into all their changes but it's much more likely than catastrophic failure occurring due to known design deficiencies that are left because they haven't yet caused failures.
  - 14 5y ago
    This made me think of a local pilot who didn’t load his load correctly and when he went to climb some of the load shifted back in the plane. The sudden weight caused the plane to nose up and the plane lost lift and fell to the pilot and passenger death. Something as simple as a missing strap can bring down a plane. I can only imagine the amount if potential disasters on a rocket.

chinathrow 5y ago

I agree regarding the handful of missions argument with Crew Dragon, but let's not forget all the successful Cargo Dragon missions here as I'm sure they play a role in (ongoing) safety assessments.

InTheArena 5y ago
Sure. It helps. One of the things NASA considered was Shuttle-C, a cargo varient of the space shuttle system, which would have given NASA a way to tinker on the engine /SRB stack without crew onboard. Of course, that would not have saved columbia (the orbiter itself was the problem). This stuff is called rocket science for a reason.
- progre 5y ago
  Well, still... It's not exactly brain surgery is it?

bryanlarsen 5y ago

NASA calls it "normalizing of deviance", and it's why we lost both Shuttles. For example, the O-Rings were designed as a backup, the force generated by the solid rocket motors was supposed to seal the SRM sections together. But they knew after the first launch that the O-Rings were what was actually sealing the SRM's. But the O-Rings worked, so they didn't stop the program to fix the design. Later they found evidence of blow through the O-Rings, and again decided that since that didn't cause a crash, they were OK. Until they didn't. Tile strike damage was a similar normalization that killed 7 people. Does SpaceX normalize deviance? They fixed the toilet, so they didn't normalize that, but what about the delayed opening of the 4th parachute in the Crew 2 landing? It seems suspicious that they launched Crew 3 so quickly after an apparent anomaly. They do claim that the delayed opening is nominal behaviour seen and accepted in testing -- that this behaviour only happens when the other 3 parachutes are working fine. If one of the others had failed the 4th would have opened quicker due to increased air pressure. https://arstechnica.com/science/2021/11/double-dragon-nasa-plans-a-spacex-splashdown-on-monday-launch-wednesday/ https://arstechnica.com/science/2021/11/double-dragon-nasa-p...

rbanffy 5y ago
> that this behaviour only happens when the other 3 parachutes are working fine I'd love to see the causal relationship between both that makes it safe to land with 3 parachutes (I remember they added the 4th as an added precaution that reminds me of the O-ring issue)
thaeli 5y ago
NASA seems to normalize deviance when they're under political pressure to do so. I'm not sure they can be entirely trusted when it comes to their own launch systems, because of the politics involved - but so far they haven't shown similar hesitancy with commercial launch systems. It's a good separation of concerns; when NASA is "just the customer" and it's not "their rocket" they are in a better position to hold a firm line on safety issues. That NASA did not see the parachute as an issue speaks volumes. It looked bad visually, but having watched enough space launches and how mission control reacts to off-nominal data - clearly they were comfortable with the performance, because they didn't flinch at all. NASA just doesn't sign off on these commercial launches with NASA astronauts on board if they have any inkling that something won't go right - they aren't under the political pressure to "save the Shuttle program" or whatever. I have more concern about NASA getting politically-imposed "go fever" with SLS.
jpgvm 5y ago
SpaceX is on the other end of the scale, they continually change their vehicles to make small improvements all the time. It's highly unlikely the same paralysis could manifest at SpaceX with it's current culture. More likely is a failure of the other extreme where if changes are normalized and something that seems sufficiently simple actually has an outsized impact on the craft. I think such a thing is still relatively unlikely given how much testing and modelling goes into all their changes but it's much more likely than catastrophic failure occurring due to known design deficiencies that are left because they haven't yet caused failures.
- 14 5y ago
  This made me think of a local pilot who didn’t load his load correctly and when he went to climb some of the load shifted back in the plane. The sudden weight caused the plane to nose up and the plane lost lift and fell to the pilot and passenger death. Something as simple as a missing strap can bring down a plane. I can only imagine the amount if potential disasters on a rocket.