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Was there mention of why they did not do a launch escape while the F5 was at full throttle? I understand this reduces the risk and was probably deemed to be goo

Was there mention of why they did not do a launch escape while the F5 was at full throttle? I understand this reduces the risk and was probably deemed to be good enough of a test, but I was expecting the test to be "worst case scenario" or in other words, F5 on full power at MaxQ.

Taniwha 7y ago
I think that "F5 on full power at MaxQ" is not a worst case scenario, it's more like "flying nominally" - doing it at maxQ is certainly the thing to do - but "on FS flameout" is more realistic
- saberdancer 7y ago
  FS flameout may be more realistic, but you need to test for worst case scenarios. Having F5 throttle down allows any kind of Dragon acceleration to pull it away from the Falcon. The critical design element of an crew ejection system is that it needs to out-accelerate the rocket so testing while the Falcon remained at full power seems logical. They probably have reasons not to do it.
gpm 7y ago
The Falcon 9 never goes through MaxQ at full throttle, throttling down before MaxQ and up after MaxQ is part of the normal flight path. This Falcon 9 followed the normal flight path right up to the point where the abort was artificially induced. I believe the abort did actually take place at full throttle though, it happened at the point of max drag which occurs shortly after Max Q, and is after the rocket has throttled back up. The intent was definitely to trigger the abort at the worst time during the normal flight path.
- foota 7y ago
  Wouldn't it be good to test whether the abort works in the face of an unexpected flight path, which could potentially be more stressful? Although there's probably not much of a difference if they full throttled shortly after MaxQ and then aborted.
  - brianwawok 7y ago
    This test seems more useful? Why put it through a path that can’t happen? If throttle is out of control and randomly going, that’s a good case to trigger an abort right then.
    - foota 7y ago
      Because if the throttle is out of control then that's exactly the case you'll be in? One where you're at MaxQ and have throttle at full. The test imo should be done at the worst possible scenario that the rocket could physically be in (i.e., no need to test at a speed/stress that is physically impossible to reach, but what if the rocket starts thrusting unexpectedly in a different direction or something?)
      - brianwawok 7y ago
        If your throttle is out of control, you presume that would trigger an abort. Instead of waiting until you are at max speed in the wrong part of the flight?
        saberdancer 7y ago
        It can happen at maximum speed. Before you say that Falcon is not at full throttle when at maximum speed, sure. Let's assume the worst case scenario, Falcon reaches max q and due to a glitch throttles up to full throttle and starts veering off course. This is a worst case scenario probably, and I was surprised that SpaceX did not test this extreme possibility. That's our point. Testing with the assumption that Falcon accepts throttle down command from the Dragon seems like a waste of test scenario.
- saberdancer 7y ago
  Good point about MaxQ, but it was not an important part of my question. What I was surprised is that the Dragon sent a command to the Falcon to shut down the engines. In a catastrophic scenario, it may be that the Falcon does not accept commands and is "stuck" at full throttle. I was expecting them to test ejection while the rocket is at full power without shutting down engines. I guess they do not need to test it that way, they can easily calculate or measure if the acceleration was high enough and by initiating throttle down the capsule minimizes the risk of being hit by rocket debris after it falls apart. In a real life emergency such risks are acceptable, but in a test probably unnecessary.
- iso1210 7y ago
  What if the "throttle down" part of the process doesn't engage for some reason? Is the fuel injection into the engine failsafe?
  - gpm 7y ago
    If the "throttle down" before MaxQ fails? I would assume that Dragon would detect the anomaly and abort immediately, before the extra acceleration had time to increase velocity enough to cause an issue. Dragon doesn't need Falcon 9 to throttle down to abort, the Falcon 9 needs to slow down a bit during MaxQ, but the instantaneous acceleration of the Falcon 9 during abort isn't supposed to matter.
    - iso1210 7y ago
      The immediate abort would then have to life the dragon away from a fully accelerating F9

Taniwha 7y ago

I think that "F5 on full power at MaxQ" is not a worst case scenario, it's more like "flying nominally" - doing it at maxQ is certainly the thing to do - but "on FS flameout" is more realistic

saberdancer 7y ago
FS flameout may be more realistic, but you need to test for worst case scenarios. Having F5 throttle down allows any kind of Dragon acceleration to pull it away from the Falcon. The critical design element of an crew ejection system is that it needs to out-accelerate the rocket so testing while the Falcon remained at full power seems logical. They probably have reasons not to do it.

gpm 7y ago

The Falcon 9 never goes through MaxQ at full throttle, throttling down before MaxQ and up after MaxQ is part of the normal flight path. This Falcon 9 followed the normal flight path right up to the point where the abort was artificially induced. I believe the abort did actually take place at full throttle though, it happened at the point of max drag which occurs shortly after Max Q, and is after the rocket has throttled back up. The intent was definitely to trigger the abort at the worst time during the normal flight path.

foota 7y ago
Wouldn't it be good to test whether the abort works in the face of an unexpected flight path, which could potentially be more stressful? Although there's probably not much of a difference if they full throttled shortly after MaxQ and then aborted.
- brianwawok 7y ago
  This test seems more useful? Why put it through a path that can’t happen? If throttle is out of control and randomly going, that’s a good case to trigger an abort right then.
  - foota 7y ago
    Because if the throttle is out of control then that's exactly the case you'll be in? One where you're at MaxQ and have throttle at full. The test imo should be done at the worst possible scenario that the rocket could physically be in (i.e., no need to test at a speed/stress that is physically impossible to reach, but what if the rocket starts thrusting unexpectedly in a different direction or something?)
    - brianwawok 7y ago
      If your throttle is out of control, you presume that would trigger an abort. Instead of waiting until you are at max speed in the wrong part of the flight?
      - saberdancer 7y ago
        It can happen at maximum speed. Before you say that Falcon is not at full throttle when at maximum speed, sure. Let's assume the worst case scenario, Falcon reaches max q and due to a glitch throttles up to full throttle and starts veering off course. This is a worst case scenario probably, and I was surprised that SpaceX did not test this extreme possibility. That's our point. Testing with the assumption that Falcon accepts throttle down command from the Dragon seems like a waste of test scenario.
saberdancer 7y ago
Good point about MaxQ, but it was not an important part of my question. What I was surprised is that the Dragon sent a command to the Falcon to shut down the engines. In a catastrophic scenario, it may be that the Falcon does not accept commands and is "stuck" at full throttle. I was expecting them to test ejection while the rocket is at full power without shutting down engines. I guess they do not need to test it that way, they can easily calculate or measure if the acceleration was high enough and by initiating throttle down the capsule minimizes the risk of being hit by rocket debris after it falls apart. In a real life emergency such risks are acceptable, but in a test probably unnecessary.
iso1210 7y ago
What if the "throttle down" part of the process doesn't engage for some reason? Is the fuel injection into the engine failsafe?
- gpm 7y ago
  If the "throttle down" before MaxQ fails? I would assume that Dragon would detect the anomaly and abort immediately, before the extra acceleration had time to increase velocity enough to cause an issue. Dragon doesn't need Falcon 9 to throttle down to abort, the Falcon 9 needs to slow down a bit during MaxQ, but the instantaneous acceleration of the Falcon 9 during abort isn't supposed to matter.
  - iso1210 7y ago
    The immediate abort would then have to life the dragon away from a fully accelerating F9