Author Topic: SpaceX F9 : Crew Dragon In-Flight Abort Test : Jan. 19, 2020 : Discussion  (Read 357573 times)

Offline Tomness

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Reusing a previously flown F9 Block IV & reusing DM-1 for in-flight abort co-align  with $30 million mile stone. They have no need to recover the stage, no need for the upperstage, just test all systems for Crew Dragon's ability to abort in-flight.

Offline envy887

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Just blow it all to heck at Max-Q and show that it works... period...  8)

If the IFA Test is to be a demonstration of D2 ability to prevent LOC at the conditions that would have the highest chance for a LOC event.  use a working S2  fill it with propellant and then use the S2 FTS to initiate a catastrophic event.   when Dragon and the simulated test humans inside are shown to have survived this worst case scenario so that there would be no LOC then you have set bar very high for safety and Risk reduction.

I doubt it's realistic to expect the escape system to save the capsule in the event of a no-notice upper-stage explosion.  Apollo's LES, for example, required 2-3 seconds' warning, depending on which stage was exploding.
That number assumes a detonation of a fairly large fraction of the fuel, which realistically isn't going to happen. And the overpressure limits are probably very different than Dragon, which has no forward heat shield to deploy in order to pop the chutes.

Offline WindyCity

Would it make sense, in simulating a genuine anomaly, to detonate the booster at MaxQ? Would firing the superdracos atop a healthy first stage yield the same confidence as testing the response of the sensors and capsule to an actual RUD?

Offline envy887

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Would it make sense, in simulating a genuine anomaly, to detonate the booster at MaxQ? Would firing the superdracos atop a healthy first stage yield the same confidence as testing the response of the sensors and capsule to an actual RUD?

What do you mean by "detonate"? The FTS system does not do anything like that, it just unzips the fuel tanks and aeroloads take care of the rest.

Offline jpo234

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Would it make sense, in simulating a genuine anomaly, to detonate the booster at MaxQ? Would firing the superdracos atop a healthy first stage yield the same confidence as testing the response of the sensors and capsule to an actual RUD?

What do you mean by "detonate"? The FTS system does not do anything like that, it just unzips the fuel tanks and aeroloads take care of the rest.
Blow up a COPV? Or rupture the common bulkhead? That would be spectacular!
« Last Edit: 06/18/2018 06:49 pm by jpo234 »
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Offline Nomadd

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Has MaxQ ever had anything to do with an actual failure?
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Offline whitelancer64

Has MaxQ ever had anything to do with an actual failure?

In the past, yes. One of the major issues that Von Braun had with the V2 was with the fuel and LOX tanks buckling in flight at Max Q. They lost a lot of rockets before they realized what was happening.

It's not so much an issue now, since we know about aerodynamic pressures and can design rockets to handle them, but it is still the point at which the rocket is most likely to structurally fail from exterior pressure.
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Offline mme

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Has MaxQ ever had anything to do with an actual failure?
I think the point of testing at Max-Q is that is that is the worst case scenario for the capsule to escape (it's under max aerodynamic load), not that it's the most likely time to fail.
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Offline Proponent

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>
I doubt it's realistic to expect the escape system to save the capsule in the event of a no-notice upper-stage explosion.  Apollo's LES, for example, required 2-3 seconds' warning, depending on which stage was exploding.

Except that CRS-7's Cargo Dragon survived the breakup of F9's upper stage without a LAS, surviving until it hit the drink. As a result, SpaceX changed their code to deploy the chutes in a similar incident.

The SuperDraco's achieve full thrust in about 100 milliseconds, and ISTR there are break wires on the stages to signal a breakup to the safety system.

That one Dragon, which was already falling away from the booster, survived activation of the first stage's FTS does not mean that a Dragon is likely to survey detonation of the second stage's propellant load.  The Apollo calculations I linked to above are pretty simple.  The detonation of a stage's propellant load causes an outward-radiating over-pressure front.  The escaping capsule must be able to outrun that front until it has weakened to the point that it is no longer capable of seriously damaging the capsule.
« Last Edit: 06/19/2018 12:22 pm by Proponent »

Offline Proponent

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I doubt it's realistic to expect the escape system to save the capsule in the event of a no-notice upper-stage explosion.  Apollo's LES, for example, required 2-3 seconds' warning, depending on which stage was exploding.
That number assumes a detonation of a fairly large fraction of the fuel, which realistically isn't going to happen. And the overpressure limits are probably very different than Dragon, which has no forward heat shield to deploy in order to pop the chutes.

The calculation was no doubt conservative, but unless demonstrated otherwise I don't think one can assume that the escape system is a highly reliable means of saving crew and capsule in the case of stage exploding without warning.

Offline docmordrid

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>
I doubt it's realistic to expect the escape system to save the capsule in the event of a no-notice upper-stage explosion.  Apollo's LES, for example, required 2-3 seconds' warning, depending on which stage was exploding.

Except that CRS-7's Cargo Dragon survived the breakup of F9's upper stage without a LAS, surviving until it hit the drink. As a result, SpaceX changed their code to deploy the chutes in a similar incident.

The SuperDraco's achieve full thrust in about 100 milliseconds, and ISTR there are break wires on the stages to signal a breakup to the safety system.

That one Dragon, which was already falling away from the booster, survived activation of the first stage's FTS does not mean that a Dragon is likely to survey detonation of the second stage's propellant load.  The Apollo calculations I linked to above are pretty simple.  The detonation of a stage's propellant load causes an outward-radiating over-pressure front.  The escaping capsule must be able to outrun that front until it has weakened to the point that it is no longer capable of seriously damaging the capsule.

>
I doubt it's realistic to expect the escape system to save the capsule in the event of a no-notice upper-stage explosion.  Apollo's LES, for example, required 2-3 seconds' warning, depending on which stage was exploding.

Except that CRS-7's Cargo Dragon survived the breakup of F9's upper stage without a LAS, surviving until it hit the drink. As a result, SpaceX changed their code to deploy the chutes in a similar incident.

The SuperDraco's achieve full thrust in about 100 milliseconds, and ISTR there are break wires on the stages to signal a breakup to the safety system.

That one Dragon, which was already falling away from the booster, survived activation of the first stage's FTS does not mean that a Dragon is likely to survey detonation of the second stage's propellant load.
>

When has an upper stage detonated which wasn't a solid  or hypergolic? Even the F9 AMOS-6 upper stage failure wasn't a detonation but a much slower conflagration Crew Dragon could easily outrun (as overlaid video of AMOS-6 & the pad abort test clearly demonstrated.) ISTM without a plugged nozzle or failed case on a solid booster true upper stage detonations are very unlikely.

DM

Offline envy887

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I doubt it's realistic to expect the escape system to save the capsule in the event of a no-notice upper-stage explosion.  Apollo's LES, for example, required 2-3 seconds' warning, depending on which stage was exploding.
That number assumes a detonation of a fairly large fraction of the fuel, which realistically isn't going to happen. And the overpressure limits are probably very different than Dragon, which has no forward heat shield to deploy in order to pop the chutes.

The calculation was no doubt conservative, but unless demonstrated otherwise I don't think one can assume that the escape system is a highly reliable means of saving crew and capsule in the case of stage exploding without warning.

Actual detonation of a significant fraction of a liquid stage's propellant load, especially in flight, is extremely unlikely.

Offline Pete

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...The detonation of a stage's propellant load causes an outward-radiating over-pressure front.  The escaping capsule must be able to outrun that front until it has weakened to the point that it is no longer capable of seriously damaging the capsule.

Detonation? Seriously? How are you going to manage that?
Any conceivable failure mode will result in at worst a rapid deflagration, not a detonation. Thus any/all phenomena accompanying the failure propagate at subsonic speeds.
If the vehicle is subsonic, the abort system needs to get it out of the fireball before the capsule's mechanical and thermal limits are exceeded.
If the vehicle is supersonic, the abort system just has to activate quickly enough and strongly enough to open up an aerodynamically significant gap between itself and the explosion. (and not get run over)
The Dragon's Draco are *quite* strong enough to do this, all that is in dispute/needs testing is whether the system activates quickly enough, at the right time, yet still gently enough to not turn its occupants into strawberry jam.
The pad abort test has done most of that, already.

Offline WindyCity

Any conceivable failure mode will result in at worst a rapid deflagration, not a detonation. Thus any/all phenomena accompanying the failure propagate at subsonic speeds.
If the vehicle is subsonic, the abort system needs to get it out of the fireball before the capsule's mechanical and thermal limits are exceeded.
If the vehicle is supersonic, the abort system just has to activate quickly enough and strongly enough to open up an aerodynamically significant gap between itself and the explosion. (and not get run over).

Was the failure of the Spx-7 mission on June 28th, 2015, occurring at supersonic speed, a deflagration? The explosion was triggered by the rupture of a carbon fiber-wrapped pressure vessel. Would a similar event, not a detonation, be the most likely scenario for an in-flight accident that triggered the launch escape system?
« Last Edit: 06/19/2018 10:08 pm by gongora »

Offline envy887

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Any conceivable failure mode will result in at worst a rapid deflagration, not a detonation. Thus any/all phenomena accompanying the failure propagate at subsonic speeds.
If the vehicle is subsonic, the abort system needs to get it out of the fireball before the capsule's mechanical and thermal limits are exceeded.
If the vehicle is supersonic, the abort system just has to activate quickly enough and strongly enough to open up an aerodynamically significant gap between itself and the explosion. (and not get run over).

Was the failure of the Spx-7 mission on June 28th, 2015, occurring at supersonic speed, a deflagration? The explosion was triggered by the rupture of a carbon fiber-wrapped pressure vessel. Would a similar event, not a detonation, be the most likely scenario for an in-flight accident that triggered the launch escape system?

There is no evidence that the COPV ruptured, AFAIK. Their was an unintended release of helium, likely from broken plumbing going to the tanks, which overpressured the LOX tank and caused it to fail.

A rupturing COPV would probably cause a small detonation, since it would likely release enough energy to ignite the carbon overwrap. The accompanying overpressure wave would be much less severe than a detonation of a significant fraction of the fuel if mixed with the LOX.

Offline woods170

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Any conceivable failure mode will result in at worst a rapid deflagration, not a detonation. Thus any/all phenomena accompanying the failure propagate at subsonic speeds.
If the vehicle is subsonic, the abort system needs to get it out of the fireball before the capsule's mechanical and thermal limits are exceeded.
If the vehicle is supersonic, the abort system just has to activate quickly enough and strongly enough to open up an aerodynamically significant gap between itself and the explosion. (and not get run over).

Was the failure of the Spx-7 mission on June 28th, 2015, occurring at supersonic speed, a deflagration? The explosion was triggered by the rupture of a carbon fiber-wrapped pressure vessel. Would a similar event, not a detonation, be the most likely scenario for an in-flight accident that triggered the launch escape system?

There is no evidence that the COPV ruptured, AFAIK. Their was an unintended release of helium, likely from broken plumbing going to the tanks, which overpressured the LOX tank and caused it to fail.

A rupturing COPV would probably cause a small detonation, since it would likely release enough energy to ignite the carbon overwrap. The accompanying overpressure wave would be much less severe than a detonation of a significant fraction of the fuel if mixed with the LOX.

According to the NASA report of the CRS-7 event a strut supporting a COPV failed, resulting in the COPV breaking lose from its remaing supports, in an upward motion, due to the positive buoyancy of the COPV in LOX. What happened next is that the high-pressure plumbing attached to the COPV snapped off. At that point the COPV pretty much became a rocket, due to high-pressure helium coming out of the COPV unregulated, and shot upwards towards the forward bulkhead of the LOX tank. The COPV contents (high-pressure helium) went into the LOX tank real quick, resulting in the over-pressurization of the LOX tank and ultimately failure of the forward bulkhead of the LOX tank (which had already been weakened by the impact of the broken lose COPV. The rest we know.

The LOX tank failure was not a detonation though. Impressive as the failure looked there was only localized combustion, much like what happened to Challenger. Everybody referred to that one as "an explosion". But it wasn't. And neither was CRS-7. A LOX tank rupturing upon over-pressurization does not equal detonation, nor does it equal an explosion.

Also: from page 5 from said NASA report:
Quote from: NASA
In other words, the vehicle went from flying fine to conflagration in less than a second
« Last Edit: 06/20/2018 08:59 am by woods170 »

Offline JamesH65

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I doubt it's realistic to expect the escape system to save the capsule in the event of a no-notice upper-stage explosion.  Apollo's LES, for example, required 2-3 seconds' warning, depending on which stage was exploding.
That number assumes a detonation of a fairly large fraction of the fuel, which realistically isn't going to happen. And the overpressure limits are probably very different than Dragon, which has no forward heat shield to deploy in order to pop the chutes.

The calculation was no doubt conservative, but unless demonstrated otherwise I don't think one can assume that the escape system is a highly reliable means of saving crew and capsule in the case of stage exploding without warning.

Actual detonation of a significant fraction of a liquid stage's propellant load, especially in flight, is extremely unlikely.

AIUI, it's impossible with RP-1 under these circumstances. (But am still reading through Ignition!, so still a few more chapters to learn)

Offline speedevil

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AIUI, it's impossible with RP-1 under these circumstances. (But am still reading through Ignition!, so still a few more chapters to learn)
I hesitate to say impossible - RP-1 can get to a really, really fine mist, if you dump it out into a mach 1 airstream, and mixed with oxygen it could plausibly detonate.
I think you're going to have contrived circumstances to get a meaningful fraction to detonate though.
If you look at the CRS failure frame-by-frame, and work out the speeds of the various flame-fronts involved, they pretty much all look subsonic IIRC.
Tiny parts detonating - sure. Global mixing without ignition followed by a detonation of all of it - not a hope in hell.

Offline envy887

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AIUI, it's impossible with RP-1 under these circumstances. (But am still reading through Ignition!, so still a few more chapters to learn)
I hesitate to say impossible - RP-1 can get to a really, really fine mist, if you dump it out into a mach 1 airstream, and mixed with oxygen it could plausibly detonate.
I think you're going to have contrived circumstances to get a meaningful fraction to detonate though.
If you look at the CRS failure frame-by-frame, and work out the speeds of the various flame-fronts involved, they pretty much all look subsonic IIRC.
Tiny parts detonating - sure. Global mixing without ignition followed by a detonation of all of it - not a hope in hell.

There are a few failures that would cause a large detonation, e.g. a LOX downpipe or common bulkhead bursting that dumps a significant amount of LOX into the RP-1 tank, followed by some ignition source like another pressure release. This type of failure was investigated and then ruled out as a cause of the AMOS-6 anomaly.

Offline RocketLover0119

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Per Chris B's pre launch article for CRS-15, looks like this will end up being a block v booster-

"Although SpaceX does have one remaining Block 4 first stage – Core 1042 which was used last October to deploy Koreasat 5A – this is not expected to fly again making the CRS-15 launch the last to use a Block 4 vehicle, or any version of Falcon 9 other than the Block 5."

https://www.nasaspaceflight.com/2018/06/final-block-4-falcon-9-crs-15-dragon-launch/
« Last Edit: 06/29/2018 01:47 am by RocketLover0119 »
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