Author Topic: SpaceX Falcon 9 v1.1 - SpX-7/CRS-7 DRAGON FAILURE - Discussion Thread 2  (Read 706556 times)

Offline miiser

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I remember that with the launch of the first Falcon v1.1 Elon Musk said that he was afraid of bending.
Could this have played a role  ?

Certainly, bending/torque would contribute to the buckling load on the wall.

I also notice that, right before failure, the ring of condensation vapor around the Dragon became asymmetric, with a sort of bump on top.  Possibly the vehicle is beginning to flex abnormally at this point in time with the wall starting to buckle on one side.  But this could be nothing/optical effects.

When Musk mentioned bending I think he was referring to the first stage due to fact that it was long and slender. The issue with this flight appeared to be in S2 and S1 displayed no signs of bending and in fact kept trying to fly even after S2 started to go away.

I think you are correct regarding the concern specifically involving S1.  Although I think the bending would be dimensionally small (though producing large stresses) and not be visible in the video.  And if the entire vehicle were slightly bowed, including S1, that would explose S2 to asymmetric loading which would promote buckling.
« Last Edit: 07/04/2015 11:53 am by miiser »

Offline Jim

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and speed increase as the atmosphere thins and the propellant weight decreases, so they tend to balance each other out, but the atmosphere would still be pretty thick at this point in the flight.  The load would still be pretty near MAXQ.

No, the loads drop off quickly and it was over a 100,000 ft.  So the term nowhere near max q is quite correct.  BTW, prop weight has nothing to do with q loads.
« Last Edit: 07/04/2015 12:15 pm by Jim »

Offline speedevil

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Max Q of F9 v1.1 happens something like 70 seconds into the flight. At the moment of failure, F9 is indeed nowhere near max Q. You can tell that via the bar at the bottom and announcer calling out max Q at 75 seconds or so. New informational displays of spacex show the event and info about it until a new event occurs which must be confusing for some people.

To put some numbers on this, at 43km, the atmosphere has a density of around 2 grams/m^3, compared with 1400g/m^3 at sea level.
The pressure is halving every 4 or so seconds.

The 'Q' - dynamic pressure is around 1400Pa - about 1/4 PSI.

Dynamic pressure at 'Max Q' is of the order of 14PSI.

Offline Pete

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...
 And if the entire vehicle were slightly bowed, including S1, that would explose S2 to asymmetric loading which would promote buckling.

And this would be *abundantly* clear from telemetry.

... but the atmosphere would still be pretty thick at this point in the flight.  The load would still be pretty near MAXQ.
The dynamic pressure at that time was under 2% of Max-Q, and dropping rapidly towards zero.

Offline Rocket Science

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So what does "KICK" stand for at SpaceX? Is this some modality of pitch change that is in some form unique?
« Last Edit: 07/04/2015 03:00 pm by Rocket Science »
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Offline Chris Bergin

When someone asks a question, the answer - on a place like this - will likely come from someone who knows what they are talking about. If that answer doesn't fit your view you don't then stamp your feet and have a fit about it or it'll be the last thing you do on here.

Thread trimmed.
« Last Edit: 07/04/2015 02:51 pm by Chris Bergin »
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Offline Prober

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A few friends who work at JSC have told me that Gerst has gone from his "everything will be fine" of Sunday to wanting a full-blown NASA-led investigation. That might be just to preempt a congressional investigation. But you're right; the silence is deafening.

Anyone else at NASA getting the same vibes?

No, that is just nonsense since NASA has no authority to lead the investigation.  The friends don't know how things work.  It was a commercial launch and hence  It is a Spacex led investigation with the FAA as the lead gov agency.  NASA also has a rep and it is from LSP vs the ISS program since they have the rocket expertise even though ISS has the contract. 

Congress also has no authority either.  The only thing it can investigate is NASA's contracting mechanism and management of the contract.

There is no need for any updates until there are updates to be given

NASA will be the one to approve SpaceX's resumption of CRS launches, manifesting of ISS cargo, and ISS rendezvous.

So if NASA wants to conduct its own mishap investigation, SoaceX will either cooperate or face the consequences.

think your putting too much focus on SX.

"wanting a full-blown NASA-led investigation."    can understand this statement
it the might be the whole ISS supply contract that's under review.   

My guess is that Gerst who goes before Congress next week, wishes to preempt questions from Congress.   He would say he "started a new investigation".    Just a tool (often used in politics) to keep the funding going and keep DC happy.


 Edit: poor wording, more coffee ;D
« Last Edit: 07/04/2015 03:12 pm by Prober »
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Offline the_other_Doug

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Spacecraft Tank Pressures-Typical
Hydrazine: 150 PSI at lift off
Oxidizde: 250 PSK at lift off
Helium used for repress of Hydrazine & Oxidizer at launch: 4500 PSI typ
Soon after SV separation Helium Tank is activated
Hydrazine and Oxidizer Pressure at 300 PSI

Tanks are required to be qualified to 50 x 0 to 450 PSI (for Hydrazine and Ox)
Then, after that, they are required to not burst at 600 PSI

Helium tank no-burst pressure: 9000 psi.

Plumbing and valves: similar design/qual regime.

Now just manufacture, test, install, operate  the flight units as good as the qual unit

For SpaceX, if a helium bottle is inside the LOX tank, what is its pressure:
Did this helium tank rupture, causing LOX tank to rupture.

Did SpaceX actually test the tanks as they were used in flight (i.e. test-like-you-fly)
We shall see.

No hydrazine in either stage.  Both stages use LOX and RP-1 (a highly refined version of kerosene).  The LOX is cryogenic (i.e., a liquified gas at extremely cold temperatures), unlike the room-temperature hydrazine (propellant)/nitrogen tetroxide (oxidizer) fuels used in hypergolic engines.  Only the Dragon itself uses hypergolic fuels, for the Draco (and, on Dragon v2, Super Draco) engines; none are used in the Falcon stages.  All of the hypergolic fuels in that stack popped off the stack when the Dragon came loose; none were involved in the failure or conflagration.

It's a little hard to take your numbers seriously when you're not even talking about the same kind of engines and propellants as were actually in use on the stages in question...
-Doug  (With my shield, not yet upon it)

Offline cleonard

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Spacecraft Tank Pressures-Typical
Hydrazine: 150 PSI at lift off
Oxidizde: 250 PSK at lift off
Helium used for repress of Hydrazine & Oxidizer at launch: 4500 PSI typ
Soon after SV separation Helium Tank is activated
Hydrazine and Oxidizer Pressure at 300 PSI

Tanks are required to be qualified to 50 x 0 to 450 PSI (for Hydrazine and Ox)
Then, after that, they are required to not burst at 600 PSI

Helium tank no-burst pressure: 9000 psi.

Plumbing and valves: similar design/qual regime.

Now just manufacture, test, install, operate  the flight units as good as the qual unit

For SpaceX, if a helium bottle is inside the LOX tank, what is its pressure:
Did this helium tank rupture, causing LOX tank to rupture.

Did SpaceX actually test the tanks as they were used in flight (i.e. test-like-you-fly)
We shall see.

No hydrazine in either stage.  Both stages use LOX and RP-1 (a highly refined version of kerosene).  The LOX is cryogenic (i.e., a liquified gas at extremely cold temperatures), unlike the room-temperature hydrazine (propellant)/nitrogen tetroxide (oxidizer) fuels used in hypergolic engines.  Only the Dragon itself uses hypergolic fuels, for the Draco (and, on Dragon v2, Super Draco) engines; none are used in the Falcon stages.  All of the hypergolic fuels in that stack popped off the stack when the Dragon came loose; none were involved in the failure or conflagration.

It's a little hard to take your numbers seriously when you're not even talking about the same kind of engines and propellants as were actually in use on the stages in question...

I believe that the numbers were pulled off of a web page of some spacecfaft like a comsat.  The pressure in the Falcon RP1 and LOX tanks is lower as the engines are pump fed and not pressure fed like those numbers indicate.  I have no idea of the exact pressures for the Falcon, but I'd wager that it is under 50psi.  More pressure means more metal for strength and that equals weight.  I also don't know the numbers for the Falcons Helium bottles, but I'd guess that it's at least 3000 psi and may well be 4500psi.  The Helium is in the LOX tank  because you can get 3x the amount of Helium in a given tank volume at LOX temperatures of around 100K vs 300 K room temperature.  Smaller Helium tanks equals less weight.

Helium at 4500 psi in a tank stores a lot of energy.  So much that a complete tank rupture would most likely be a more spectacular vehicle failure than was seen.


Offline the_other_Doug

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OK -- with the old thread shut down, I can't quote it, but Appable did a nice job on highlighting potential vapor plumes in the stabilized tracking video I have been discussing, and Demofsky pulled out a still that rather supports what I'm talking about.

Those images show that what I was looking at must be plumes of vapor being released -- as time goes on, they puff out from the body of the rocket and stream back away from it.  They're absolutely not reflections of sunlight off the rocket, and they're not the supersonic-transition compression vapor seen generated along the leading edges of the solar panel fairings at max-Q nearly a minute before these puffs of vapor began to form.

Again -- I've not been able to find anything from earlier flights that show this kind of obvious, visible  venting from the base of S2 during MVAC chilldown.  Can anyone out there find any good examples from tracking video of earlier flights showing this kind of S2 venting starting 20 to 30 second prior to MECO?  Because if we don't see it on any other flights, then this wasn't being caused by the chilldown venting, and we have to assume it was being caused by the LOX tank overpressurization event.  And that means that the overpressure condition began at least 10 to 15 seconds before S2 began to obviously fail.

Which begs the question as to why, with that much time during which the problem was developing, SpaceX can't as of yet find any reason why the tank was over-pressurizing.
-Doug  (With my shield, not yet upon it)

Offline the_other_Doug

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Spacecraft Tank Pressures-Typical
Hydrazine: 150 PSI at lift off
Oxidizde: 250 PSK at lift off
Helium used for repress of Hydrazine & Oxidizer at launch: 4500 PSI typ
Soon after SV separation Helium Tank is activated
Hydrazine and Oxidizer Pressure at 300 PSI

Tanks are required to be qualified to 50 x 0 to 450 PSI (for Hydrazine and Ox)
Then, after that, they are required to not burst at 600 PSI

Helium tank no-burst pressure: 9000 psi.

Plumbing and valves: similar design/qual regime.

Now just manufacture, test, install, operate  the flight units as good as the qual unit

For SpaceX, if a helium bottle is inside the LOX tank, what is its pressure:
Did this helium tank rupture, causing LOX tank to rupture.

Did SpaceX actually test the tanks as they were used in flight (i.e. test-like-you-fly)
We shall see.

No hydrazine in either stage.  Both stages use LOX and RP-1 (a highly refined version of kerosene).  The LOX is cryogenic (i.e., a liquified gas at extremely cold temperatures), unlike the room-temperature hydrazine (propellant)/nitrogen tetroxide (oxidizer) fuels used in hypergolic engines.  Only the Dragon itself uses hypergolic fuels, for the Draco (and, on Dragon v2, Super Draco) engines; none are used in the Falcon stages.  All of the hypergolic fuels in that stack popped off the stack when the Dragon came loose; none were involved in the failure or conflagration.

It's a little hard to take your numbers seriously when you're not even talking about the same kind of engines and propellants as were actually in use on the stages in question...

I believe that the numbers were pulled off of a web page of some spacecfaft like a comsat.  The pressure in the Falcon RP1 and LOX tanks is lower as the engines are pump fed and not pressure fed like those numbers indicate.  I have no idea of the exact pressures for the Falcon, but I'd wager that it is under 50psi.  More pressure means more metal for strength and that equals weight.  I also don't know the numbers for the Falcons Helium bottles, but I'd guess that it's at least 3000 psi and may well be 4500psi.  The Helium is in the LOX tank  because you can get 3x the amount of Helium in a given tank volume at LOX temperatures of around 100K vs 300 K room temperature.  Smaller Helium tanks equals less weight.

Helium at 4500 psi in a tank stores a lot of energy.  So much that a complete tank rupture would most likely be a more spectacular vehicle failure than was seen.

Okay, here's a thought --and keep in mind, I have no idea how the initial conditions could have happened -- but if you put three times the amount of helium in a tank at LOX temperatures than you would be able to at room temperatures, and then that helium tank rises to room temperature somehow, wouldn't that dramatically increase the pressure inside said helium tank?  Perhaps to the point where the tank or tank fittings would catastrophically fail?

I admit, I can't think of a scenario in which the helium tank temp could rise and cause the LOX overpressurization event without positing a failure farther up in the timeline, in the LOX tank itself, that would cause the helium tank temperature to rise.  But, still -- what happens to the pressure inside a helium tank pumped up to 4500 psi at LOX temperatures if the temperature in the tank then rises to room temperature again?
-Doug  (With my shield, not yet upon it)

Offline Bubbinski

Launch day was a beautiful day, obviously weather was "go" when they lifted off. Could a wind shear close to limits have developed right where the Falcon 9 was when the 2nd stage failed, or has that been ruled out?
I'll even excitedly look forward to "flags and footprints" and suborbital missions. Just fly...somewhere.

Offline Sohl

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... what happens to the pressure inside a helium tank pumped up to 4500 psi at LOX temperatures if the temperature in the tank then rises to room temperature again?

It goes up, a lot.  But most of my rooms are not 45km above ground level. 

More seriously, I think it's pretty hard to make a thermodynamic model that would heat up a He tank fast enough, even if a lot of the LOX spilled.

Offline vanoord

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Okay, here's a thought --and keep in mind, I have no idea how the initial conditions could have happened -- but if you put three times the amount of helium in a tank at LOX temperatures than you would be able to at room temperatures, and then that helium tank rises to room temperature somehow, wouldn't that dramatically increase the pressure inside said helium tank?  Perhaps to the point where the tank or tank fittings would catastrophically fail?

Yes. If the temperature of a gas increases, the volume increases - and if it can't expand because it's contained within a tank, the pressure would increase.

The trouble is, there's no easy way of bring the temperature of the Helium up as the tanks are immersed in LOX.


The simplest way of increasing the pressure in the LOX tank substantially would be to release all the helium into it.

I can't help but keep coming back to a failure of either one or more of the Helium tanks / or a value sticking open that would result in significant leak of Helium into the LOX tank, resulting in the LOX tank failing.

The bit that stops me is the question of whether the Helium COPVs have a sufficient volume of gas inside them that if they were vented into the LOX tank it would cause it to rupture?

Presumably there's sufficient Helium in the tanks to fill the LOX tank as the LOX is used up, but not much more. To work out whether open Helium venting into a full tank would cause failure, you'd need to know:
- LOX tank volume
- volume and pressure of LOX in the tank when full
- Volume of ullage (calculated from the above)
- Helium COPVs volume
- volume and pressure of Helium in the COPVs when full (presumably volume is as above)
- bursting pressure of the LOX tank (*at the external pressure applicable at that altitude)

Basically, is there enough Helium in the COPVs for an unintended venting into the LOX tank to push it beyond its rated pressure?

If that's not the case, a rapid failure of a COPV is left as the more likely candidate.
« Last Edit: 07/04/2015 04:30 pm by vanoord »

Offline OxCartMark

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The trouble is, there's no easy way of bring the temperature of the Helium up as the tanks are immersed in LOX.
I think the suggestion was that the He tank temperature rose because they were no longer immersed in LOX.  In that scenario the heat transfer rate wouldn't be enough to appreciably raise the temperature and / or pressure of the helium in such a short time frame, a minute or so.  ... Unless the scenario involves fire in the LOX tank which would more directly result in the demise of the LOX tank, as well as burning the composite off the COPV.

I can't help but keep coming back to a failure of either one or more of the Helium tanks / or a value sticking open that would result in significant leak of Helium into the LOX tank, resulting in the LOX tank failing.

The bit that stops me is the question of whether the Helium COPVs have a sufficient volume of gas inside them that if they were vented into the LOX tank it would cause it to rupture?

Presumably there's sufficient Helium in the tanks to fill the LOX tank as the LOX is used up, but not much more. To work out whether open Helium venting into a full tank would cause failure, you'd need to know:
- LOX tank volume
- volume and pressure of LOX in the tank when full
- Volume of ullage (calculated from the above)
- Helium COPVs volume
- volume and pressure of Helium in the COPVs when full (presumably volume is as above)
- bursting pressure of the LOX tank (*at the external pressure applicable at that altitude)
If it was a close case you'd need to know those factors, but the basics of that scenario lead you to know that there is enough helium to burst the LOX tank (***assumption, LOX tank relief valves inadequate for flow rate***).  Consider, a) there is enough helium in those tanks to pressurize the empty LOX tank to approximately 3 atm.  b) the gas space at the top of the tank is less than 10% of the whole tank volume, probably less than 5%  c) the safety factor of the tank with respect to the design pressure (assumed 3 atm.) is less than 2, probably closer to 1.4.  These three factors together in absence of relief valves which could relieve the helium release fast enough are so certain to burst the tank that no calculation is necessary.

I'm not saying this was the scenario, just trying to put more reality into the post above.
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Offline cleonard

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[
Basically, is there enough Helium in the COPVs for an unintended venting into the LOX tank to push it beyond its rated pressure?

If that's not the case, a rapid failure of a COPV is left as the more likely candidate.

Since stage 2 had not yet fired so the LOX tank was full.  I'm sure that it is not 100% filled, but for the sake of argument say it was 90% full.  There is enough Helium to fill both the LOX tank and the RP1 tank at perhaps a couple of atmospheres when they are empty. 

If the LOX tank is at 90% full then there is enough Helium to get the LOX tank to several hundred PSI.  I'm pretty sure that there is enough Helium in a single COPV to pop the LOX tank when it's full.
« Last Edit: 07/04/2015 05:00 pm by cleonard »

Offline kevin-rf

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Was thinking, the SD card failed in my phone causing it to get hot to the touch. I wonder, do any electronics exist inside the LOX tank that if they failed in a similar manner could generate enough heat to overwhelm the vent valve and cause the stage to burst. I have a hard time imaging anything being able to draw enough current without blowing a breaker, but thought I would ask.

Leaking He plumbing sounds more plausible.
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Offline R7

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So what does "KICK" stand for at SpaceX? Is this some modality of pitch change that is in some form unique?

The 'pitch kick' in the SpaceX feed progress bar after lift-off? I believe that's their name for the maneuver to initiate gravity turn. For a few seconds after T-0 the vehicle goes straight up. The kick starts the turning by pitching the vehicle couple degrees towards intended launch azimuth. Velocity vector begins to turn to follow it. If necessary (depends on kick pitch rates) the vehicle then holds the attitude until velocity vector runs parallel with it. Then the vehicle begins to pitch following the path resulting from gravity turning.

How much vertical ascend before the kick, what's proper initial kick angle etc are questions which depend on the mission and are answered by the hazy art of trajectory optimization.
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Offline robertross

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Was thinking, the SD card failed in my phone causing it to get hot to the touch. I wonder, do any electronics exist inside the LOX tank that if they failed in a similar manner could generate enough heat to overwhelm the vent valve and cause the stage to burst. I have a hard time imaging anything being able to draw enough current without blowing a breaker, but thought I would ask.

Leaking He plumbing sounds more plausible.

It's not good practice to put active electronic components into a hazardous area. Typically they use intrinsically safe barriers to bring voltages & currents into & out of these areas and house the active electronics in a less hazardous area (hence on top of the LOX dome).

(intrinsically safe meaning that even with a fault there is not enough energy to create a hazardous situation)

Offline Mike_1179

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What changes are needed from a "base model" F9 v1.1 to allow for use of densified LOX? Are any of these changes evaluated on a flight where they wouldn't be needed, like this one?

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