SpaceX F9 : Crew Dragon In-Flight Abort Test : Jan. 19, 2020 : Discussion

[pietro]

How is this conflicting? This "special configuration of min-acceleration" lines up with how Elon said it was specifically set up to be sensitive to loss of thrust (at a specific time) so that as soon as the engines started to shut down, the abort would start.

I understood that to mean that reaching the minimum speed would trigger an abort (which would trigger engine shutdown AND SD activation at the same time).

If it meant that at this speed it will trigger engine shutdown, which will then trigger the abort, I guess I misunderstood.

(and we do have the video which seems to show the SD's firing while the engines seem to still be running).

It happened most probably like this:

* SpaceX set up the abort system so that it would trigger if acceleration decreases to the number in the tweet which is way higher then the usual trigger and was seleted so that it would "naturally" happen during MaxQ throttle-back
* rocket was launched with increasing acceleration
* this activated the rule that any abnormally low acceleration should trigger abort (this would protect against the boosters failing rather gracefully with not a ka-boom, but a puff-no-fire)
* as usual just before MaxQ booster throttled back causing the acceleration to decrease
* since the trigger value was set to a high setting, the decreasing acceleration triggered the abort rule
* Crew Dragon in parallel (a) commanded the booster to shut down and (b) initiated its own abort sequence by (among other things) turning on the SuperDracos to plaid and triggering the disengagement from the interstage
* booster as a good behaving citizen shut down
* Crew Dragon successfully decoupled and started to get away from the booster on its merry way
* due to the sudden deceleration (air resistance) and initial inertia the LOX and or fuel hit the top wall of stage 1 with a force that caused discontinuity in the walls of tanks that led to a RUD and and that to the separation of the top of the first stage, the upper stage and interstage from the bulk of the first stage

[Comga]

“Most probably”?
 
Every reasonable position has been stated and posted.
Until we get more information directly from SpaceX or NASA we cannot convincingly distinguish between them.

edit: Also some unreasonable hypothesis.  Do we have to refute each one of them?

[Alexphysics]

* SpaceX set up the abort system so that it would trigger if acceleration decreases to the number in the tweet which is way higher then the usual trigger and was seleted so that it would "naturally" happen during MaxQ throttle-back
* rocket was launched with increasing acceleration
* this activated the rule that any abnormally low acceleration should trigger abort (this would protect against the boosters failing rather gracefully with not a ka-boom, but a puff-no-fire)
* as usual just before MaxQ booster throttled back causing the acceleration to decrease
* since the trigger value was set to a high setting, the decreasing acceleration triggered the abort rule
* Crew Dragon in parallel (a) commanded the booster to shut down and (b) initiated its own abort sequence by (among other things) turning on the SuperDracos to plaid and triggering the disengagement from the interstage
* booster as a good behaving citizen shut down
* Crew Dragon successfully decoupled and started to get away from the booster on its merry way
* due to the sudden deceleration (air resistance) and initial inertia the LOX and or fuel hit the top wall of stage 1 with a force that caused discontinuity in the walls of tanks that led to a RUD and and that to the separation of the top of the first stage, the upper stage and interstage from the bulk of the first stage

1. That number is not an acceleration it is a velocity.
2.
3. More
4. Sure, that's something that did happen
5. Mmmm nope, the booster throttled back up after Max-Q, as usual.
6. Crew Dragon triggered the abort more than a dozen seconds after the Falcon 9 throttled up after Max Q, I don't even know at this point if you watched the webcast at all.

And the rest is all the same discussion all over again. Did anyone hear pay attention to the webcast at any point? I mean, seriously. Because I've seen many comments with questions or stating "how things happened" that could have solved and/or corrected by paying attention to the webcast 🙄

[TheRadicalModerate]

6. Crew Dragon triggered the abort more than a dozen seconds after the Falcon 9 throttled up after Max Q, I don't even know at this point if you watched the webcast at all.

And the rest is all the same discussion all over again. Did anyone hear pay attention to the webcast at any point? I mean, seriously. Because I've seen many comments with questions or stating "how things happened" that could have solved and/or corrected by paying attention to the webcast 🙄

Can't resist giving the dead horse one more whack.

The goal of the test was likely to come up with the most challenging separation problem they could, short of actually blowing the rocket up with the D2 still attached.  That basically comes down to an optimization problem with the following variables:

1) Acceleration of the the F9 core (you want it as high as possible).
2) Dynamic pressure (˝𝜌v˛).
3) Supersonic wave drag.

What you're trying to verify is that the D2 can have an adequate relative separation acceleration, with the D2 at its nominal abort thrust, under conditions where the rocket is still chasing you, and your dynamic pressure- and wave-induced forces are at a maximum.  That's likely sometime after max-q, because you want to be throttled up, but before max thrust-induced acceleration, because by then the drag forces will be negligible.

This is also why I still think that the abort was likely triggered while the F9 was still at full thrust, because that's the condition under which the forces minimized the separation acceleration at the nominal D2 abort thrust.

[PM3]

Drogue chutes found :-D

https://twitter.com/BrockHooper2/status/1223025488089747456

[sferrin]

Drogue chutes found :-D

https://twitter.com/BrockHooper2/status/1223025488089747456

Probably fetch a few dollahs on ebay.     Any word on when they want to do a manned flight?

[Comga]

Any word on when they want to do a manned flight?

That’s in the DM-2 thread and over in L2.

[WannaWalnetto]

Maybe I’m visually impaired, but I couldn’t find a dedicated DM-2 thread in L2.  Found lots of other good stuff, just couldn’t find that forum. 

Would somebody guide me to the right place?

[DwightM]

It's in Tread 23 of the L2 SpaceX Discussion.

[WannaWalnetto]

It's in Tread 23 of the L2 SpaceX Discussion.

Sorry, still not seeing it.  Closest match I found was “
L2 Level SpaceX Discussion Section from L2 Update Thread Content THREAD 22.”

Edit:  Nevermind.  Found what I was looking for on the public side. I went to “ SpaceX Manifest Updates and Discussion Thread 5” and followed the link that was in the first post.  Took me to “ SpaceX Falcon 9 / Dragon 2 : SpX-DM2 : Q2-2020.” 

[Lars-J]

This discussion of where to find L2 content is OH SO fascinating in the non-L2 section. 

[Coastal Ron]

Any word on when they want to do a manned flight?

That’s in the DM-2 thread and over in L2.

For those that have L2 access, here is a relevant post:
https://forum.nasaspaceflight.com/index.php?topic=49778.msg2040885#msg2040885

[kdhilliard]

Another element of the IFA Test used as rehearsal for DM-2 but not previously mentioned here is the final countdown callout:

... three, two, one, zero.  Ignition.  Liftoff!  Semper Fi.  Aim High.  Go Falcon.  Go Dragon.

The two mottos being those of Doug Hurley's US Marine Corps and of Bob Behnken's US Air Force.

Link to T-10 in the full SpaceX webcast:
* https://youtube.com/watch?v=mhrkdHshb3E&t=1067s
Link to T-3 in the their recently released Recap video:
* https://youtube.com/watch?v=DJ70N5HahDU&t=15s

_{Come CFT, will ULA match with a "Semper Fortis. Aim High. Semper Fi."?}