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

[Paul_G]

It would be unlike Elon to not want to recover the core, if only for the showmanship.

The AFTS might think otherwise though.

I've read that the trajectory that Crew Dragon follows to minimise G-loads and to ensure that an abort can be survived at any point in the trajectory means that S-1 would be recovered on an ASDS rather than return to launch site, and the point that the abort will be triggered, it wasn't possible to work out a trajectory that allow the stage to be recovered even if it survived the event.

Paul

[niwax]

I need to find where, but I remember SpaceX (I think Elon) mentioning that they want to try to land the in-flight abort mission.

It would be unlike Elon to not want to recover the core, if only for the showmanship.

The AFTS might think otherwise though.

I'm not sure how that's supposed to work - the second stage engine will be a mass simulator, is the separation pusher alone strong enough to have enough space for the stage to turn around?

[CorvusCorax]

I need to find where, but I remember SpaceX (I think Elon) mentioning that they want to try to land the in-flight abort mission.

It would be unlike Elon to not want to recover the core, if only for the showmanship.

The AFTS might think otherwise though.

I'm not sure how that's supposed to work - the second stage engine will be a mass simulator, is the separation pusher alone strong enough to have enough space for the stage to turn around?

S2 doesn't usually ignite until several seconds after stage sep when S1 is already in its flip. There's many things that can go wrong here, but the lack of engine isn't one of them,

SpaceX doesn't do hot-staging.

[hopalong]

I'm not sure how that's supposed to work - the second stage engine will be a mass simulator, is the separation pusher alone strong enough to have enough space for the stage to turn around?

They do not separate, the forces involved with the MaxQ abort will destroy the 2nd stage and the self-distruct (if used) will destroy 1048, remember MaxQ happens long before staging.

[ugordan]

I'm not sure how that's supposed to work - the second stage engine will be a mass simulator, is the separation pusher alone strong enough to have enough space for the stage to turn around?

At the point of abort, the M1Ds will be turned off so there will be no sufficient (forget about cold gas ACS) control authority preventing subsequent tumbling of the stack during unpowered coast as the dynamic drag will still be significant at that point. In addition, separation pushers are too weak to combat that same aero-drag meaning that any successful S1-S2 separation is highly unlikely.

What is likely to happen is that the AFTS will just terminate the stack once the vehicle exceeds allowed angle of attack and/or angular rates post-abort or when it detects inadvertent S1-S2 separation (i.e. S2 being ripped off from the interstage during tumble, if it does not disintegrate before that). It may take several seconds for that condition to occur, but it's virtually guaranteed that it *will* occur.

Take a look at this Delta failure and imagine what will happen when the dynamic pressure environment is *much* more significant than on this flight:

[Helodriver]

The Delta GOES G failure is not a good example of a booster failure from overpressure or necessarily indicative of that will happen to the Inflight Abort Booster. 

GOES G had a premature main engine shutdown and tumbled out of control under power of the three airlit SRMs that were unable to steer the stack.  Once the stack began to tumble the payload and fairing were lost but booster itself remained intact despite rotating completely about its long axis twice and through its own plume with an open cylinder where its upper portions had been.  It only broke up when the FTS was triggered. If anything its an example of how well a booster structure can survive despite high off nominal angles of attack. 

IF the Inflight Abort booster can maintain its attitude after Dragon departs and IF the abort test occurs without shutting down S1 engines, it may be possible to continue under power to its normal burnout altitude, jettison the inert second stage, and descend for a normal landing either RTLS or on OCISLY.

Alternately, if S1's engines are shut down during the abort, it might be possible to jettison the inert S2 after coasting upward toward ballistic apogee, reorienting with the cold gas system thrusters. and doing a heavily modified landing sequence with the three air relightable engines on S1. This is admittedly unlikely as its never been test flown.

I'd love to see them attempt stage recovery but its most likely that it will not survive, if that's the case and that's what the engineers believe, then it will probably fly without fins and legs to avoid dumping useful and expensive parts into the sea, as the legs and fins are superfluous to the abort test itself.   

[space_snap828]

At the point of abort, the M1Ds will be turned off so there will be no sufficient (forget about cold gas ACS) control authority preventing subsequent tumbling of the stack during unpowered coast as the dynamic drag will still be significant at that point. In addition, separation pushers are too weak to combat that same aero-drag meaning that any successful S1-S2 separation is highly unlikely.

What is likely to happen is that the AFTS will just terminate the stack once the vehicle exceeds allowed angle of attack and/or angular rates post-abort or when it detects inadvertent S1-S2 separation (i.e. S2 being ripped off from the interstage during tumble, if it does not disintegrate before that). It may take several seconds for that condition to occur, but it's virtually guaranteed that it *will* occur.

Take a look at this Delta failure and imagine what will happen when the dynamic pressure environment is *much* more significant than on this flight:

That failure is one of the most interesting to me. The main engine shuts down, but the solid boosters continue to push forward. Aerodynamic forces are strong, overcoming any other way the rocket had to control itself. The fragility of the whole vehicle is painfully apparent, too. It only takes a few degrees off to cause breakup, so the poor Falcon rocket probably doesn't stand a chance. (On another note, that failure shows the results of a lack of engine redundancy. A failure in it's single engine doomed the flight).

[crandles57]

Would attempting an ocean landing with S2 still attached be

a) possible and
b) interesting and/or useful test of control systems with weird top heavy and high total weight and also likely weird weight distribution and
c) interesting and/or possibly useful to recover a S2 albeit damaged beyond repair and unused. Not sure if any launch wear would be distinguishable from abort damage and landing topple and sea water damage. Is launch wear of interest or would it only be of interest if the S2 had used engines?

Maybe unused fuel means it can't survive landing topple but perhaps fuel could be used up? (Edit: 'used up' presumably meaning vented or replaced with something inert or...)

Maybe top heavy weight means it can't survive landing topple?

Can't imagine trying to actually land with S2 attached - presumably far to much chance of damaging landing pad / ASDS to be worth risk.

[ugordan]

The Delta GOES G failure is not a good example of a booster failure from overpressure or necessarily indicative of that will happen to the Inflight Abort Booster. 

GOES G had a premature main engine shutdown and tumbled out of control under power of the three airlit SRMs that were unable to steer the stack.  Once the stack began to tumble the payload and fairing were lost but booster itself remained intact despite rotating completely about its long axis twice and through its own plume with an open cylinder where its upper portions had been.

I disagree, it's a pretty good illustration on what happens when you lose control and AoA starts to increase rapidly. IMHO, it's pretty indicative the booster was compromised as well as it's seen to be venting propellant vigorously from the top *and* mid section (2:08 into the video). While the top might be attributed to the 2nd stage, the mid-section cannot.

In any case, the reason I posted this video was to illustrate what happens to an uncontrollable booster as any deviation from a very small AoA will be quickly amplified by the aerodynamic forces and result in a fast tumble and, in case of a F9 max drag abort, likely vehicle breakup shortly thereafter.

It only broke up when the FTS was triggered. If anything its an example of how well a booster structure can survive despite high off nominal angles of attack. 

It was also some 30 seconds after max-Q. Granted, Delta reaches max Q faster and in lower atmosphere so I don't know how the Q environment quantitatively compares to what the F9 in-flight abort will be. My gut feeling tells me the Delta failure was at a lower Q, but I have zero data to back that up.

IF the Inflight Abort booster can maintain its attitude after Dragon departs and IF the abort test occurs without shutting down S1 engines, it may be possible to continue under power to its normal burnout altitude, jettison the inert second stage, and descend for a normal landing either RTLS or on OCISLY.

IIRC, the plan is to shut down the engines and then abort so the stage will be unpowered and uncontrollable.

Alternately, if S1's engines are shut down during the abort, it might be possible to jettison the inert S2 after coasting upward toward ballistic apogee, reorienting with the cold gas system thrusters. and doing a heavily modified landing sequence with the three air relightable engines on S1. This is admittedly unlikely as its never been test flown.

That's one of my points, it's unlikely to survive more than a few seconds of unpowered coast before the onset of tumble and breakup. Even if it did, I'm not convinced the apogee reachable by what, 400-500ish m/s velocity at abort would take it out high enough in the atmosphere that aeroloads would not prevent a clean S2 sep, especially when tumbling when the energy will be dissipated faster. Cold gas is is also woefully underpowered for atmospheric flight even for roll control purposes, let alone pitch and yaw.

[Norm38]

I wonder if B1050 is in the scrap heap.  Musk said he'd try to use it on an internal mission. This seemed like the best candidate use.  As any unexpected failure would only make the test more realistic.

[Alexphysics]

The Delta GOES G failure is not a good example of a booster failure from overpressure or necessarily indicative of that will happen to the Inflight Abort Booster. 

GOES G had a premature main engine shutdown and tumbled out of control under power of the three airlit SRMs that were unable to steer the stack.  Once the stack began to tumble the payload and fairing were lost but booster itself remained intact despite rotating completely about its long axis twice and through its own plume with an open cylinder where its upper portions had been.

I disagree, it's a pretty good illustration on what happens when you lose control and AoA starts to increase rapidly. IMHO, it's pretty indicative the booster was compromised as well as it's seen to be venting propellant vigorously from the top *and* mid section (2:08 into the video). While the top might be attributed to the 2nd stage, the mid-section cannot.

In any case, the reason I posted this video was to illustrate what happens to an uncontrollable booster as any deviation from a very small AoA will be quickly amplified by the aerodynamic forces and result in a fast tumble and, in case of a F9 max drag abort, likely vehicle breakup shortly thereafter.

It only broke up when the FTS was triggered. If anything its an example of how well a booster structure can survive despite high off nominal angles of attack. 

It was also some 30 seconds after max-Q. Granted, Delta reaches max Q faster and in lower atmosphere so I don't know how the Q environment quantitatively compares to what the F9 in-flight abort will be. My gut feeling tells me the Delta failure was at a lower Q, but I have zero data to back that up.

IF the Inflight Abort booster can maintain its attitude after Dragon departs and IF the abort test occurs without shutting down S1 engines, it may be possible to continue under power to its normal burnout altitude, jettison the inert second stage, and descend for a normal landing either RTLS or on OCISLY.

IIRC, the plan is to shut down the engines and then abort so the stage will be unpowered and uncontrollable.

Alternately, if S1's engines are shut down during the abort, it might be possible to jettison the inert S2 after coasting upward toward ballistic apogee, reorienting with the cold gas system thrusters. and doing a heavily modified landing sequence with the three air relightable engines on S1. This is admittedly unlikely as its never been test flown.

That's one of my points, it's unlikely to survive more than a few seconds of unpowered coast before the onset of tumble and breakup. Even if it did, I'm not convinced the apogee reachable by what, 400-500ish m/s velocity at abort would take it out high enough in the atmosphere that aeroloads would not prevent a clean S2 sep, especially when tumbling when the energy will be dissipated faster. Cold gas is is also woefully underpowered for atmospheric flight even for roll control purposes, let alone pitch and yaw.

Basically all of this plus that the EIS clearly stated that no grid fins or legs for this booster, that this one will be going totally expendable. IF they were planning any recovery, this would mean a complete revisit of the study and we would have seen changes to it or an update to it. But as far as I know there's not any change nor update on it.

People, admit it, it's going to be lost, just don't insist for the 1000000th time that they have to recover it because there is a very high chance of it not surviving and in the case it survives, it'll not be controllable and there are many ways to demonstrate that. Now just relax, enjoy the fireworks and hope for the best. 

[Tulse]

Is there a connection between the fact that this booster underwent the highest re-entry heating to date for boosters on the Nusantara Satu mission and its use in expendable mode for the abort test?  Did SpaceX figure they could test a high-energy re-entry, without risking a future full launch with a potentially stressed booster?

[niwax]

Is there a connection between the fact that this booster underwent the highest re-entry heating to date for boosters on the Nusantara Satu mission and its use in expendable mode for the abort test?  Did SpaceX figure they could test a high-energy re-entry, without risking a future full launch with a potentially stressed booster?

I don't think so, SpaceX hasn't been shy about trusting their rockets. The very first third reflight happened an a 2x GTO booster that also happened to be the first Block 5 ever made with no longer-than-usual refurbishment time.I'm sure they'd rather expend a used booster than a new one, but previous reports had the abort test on a new booster.

[Sesquipedalian]

Would attempting an ocean landing with S2 still attached be

a) possible and
b) interesting and/or useful test of control systems with weird top heavy and high total weight and also likely weird weight distribution and
c) interesting and/or possibly useful to recover a S2 albeit damaged beyond repair and unused. Not sure if any launch wear would be distinguishable from abort damage and landing topple and sea water damage. Is launch wear of interest or would it only be of interest if the S2 had used engines?

Whether or not it's possible, it would certainly be interesting.

[abaddon]

I wonder if B1050 is in the scrap heap.  Musk said he'd try to use it on an internal mission. This seemed like the best candidate use.  As any unexpected failure would only make the test more realistic.

It needs to get to max q first, that's pretty far into first stage flight.  When Musk mentioned an internal mission, i assumed a Starlink flight.  Even that seems really unlikely though.  Best guess is it will be harvested for parts.

[crandles57]

Would attempting an ocean landing with S2 still attached be

a) possible and
b) interesting and/or useful test of control systems with weird top heavy and high total weight and also likely weird weight distribution and
c) interesting and/or possibly useful to recover a S2 albeit damaged beyond repair and unused. Not sure if any launch wear would be distinguishable from abort damage and landing topple and sea water damage. Is launch wear of interest or would it only be of interest if the S2 had used engines?

Whether or not it's possible, it would certainly be interesting.

Is that interesting as in Chinese curse or usefully interesting?

I am not at all an expert so take my guess with ton of salt: Even if interesting/useful enough to want to test it, NASA is likely to refuse as different software from previous flights would be needed to add in options to start engines at higher altitude in order to allow sufficient deceleration if extra mass is believed to be attached. Lots of software changes like that is not what they want for safety of astronauts so unless such software is already built in and sufficiently tested on several flights, there is no chance of this actually being done.

[gongora]

We've seen a detailed document filed for environmental reviews that is unambiguous about how the test would take place.  I'm kinda feeling like maybe we should have a separate speculation thread for people who want to discuss alternate scenarios.

[joek]

We've seen a detailed document filed for environmental reviews that is unambiguous about how the test would take place.  I'm kinda feeling like maybe we should have a separate speculation thread for people who want to discuss alternate scenarios.

Agree.  In case anyone has not noticed from the thread title: this dates back to SpaceX CCiCap SAA (2012, aka CCDev-3), *not* CCtCap.

[Sesquipedalian]

Whether or not it's possible, it would certainly be interesting.

Is that interesting as in Chinese curse or usefully interesting?

The former.  I think a RUD is the most likely outcome.  If it managed to beat the odds, that would also be cool enough to be interesting.

[Nomadd]

I wonder if B1050 is in the scrap heap.  Musk said he'd try to use it on an internal mission. This seemed like the best candidate use.  As any unexpected failure would only make the test more realistic.

Any unexpected failure would only make the test useless. It's timed to abort at a certain point and if it didn't, they wouldn't be proving what they need to prove.