Quote from: John Alan on 06/09/2018 09:58 pmJust blow it all to heck at Max-Q and show that it works... period... Quote from: kevindbaker2863 on 06/14/2018 05:46 pmIf 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.
Just blow it all to heck at Max-Q and show that it works... period...
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.
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?
Quote from: WindyCity on 06/18/2018 06:25 pmWould 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.
Has MaxQ ever had anything to do with an actual failure?
Quote from: Proponent on 06/17/2018 03:54 am>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.
>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.
Quote from: Proponent on 06/17/2018 03:54 amI 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.
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.
Quote from: docmordrid on 06/17/2018 04:35 amQuote from: Proponent on 06/17/2018 03:54 am>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.
Quote from: docmordrid on 06/17/2018 04:35 amQuote from: Proponent on 06/17/2018 03:54 am>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. >
Quote from: envy887 on 06/17/2018 08:21 pmQuote from: Proponent on 06/17/2018 03:54 amI 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.
...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.
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).
Quote from: Pete on 06/19/2018 03:35 pmAny 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?
Quote from: WindyCity on 06/19/2018 06:13 pmQuote from: Pete on 06/19/2018 03:35 pmAny 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.
In other words, the vehicle went from flying fine to conflagration in less than a second
Quote from: Proponent on 06/19/2018 12:26 pmQuote from: envy887 on 06/17/2018 08:21 pmQuote from: Proponent on 06/17/2018 03:54 amI 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)
Quote from: JamesH65 on 06/20/2018 10:34 amAIUI, 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.