SpaceX Falcon 9 v1.1 - SES-8 - DISCUSSION THREAD

[ugordan]

Along with the significant venting along the 1st stage LOX tank, there was a lesser (but still notable) amount of venting from the 2nd stage LOX tank - there was a "crown" of vapor over the stack.

Some bit of vapor coming off the tanks is normal as water in the air condenses after wind sweeps along the tank. Not as much as on the 1st stage, though.

[Chris Bergin]

Do we have any other historical examples of something like this? I've honestly never seen a vehicle vent like that before, but I'm guessing it looks more dramatic than it is.

And I've not heard a scrub yet!

[mheney]

Do we have any other historical examples of something like this? I've honestly never seen a vehicle vent like that before, but I'm guessing it looks more dramatic than it is.

And I've not heard a scrub yet!

I'd think this was more of an "abort" than a "scrub" situation ....

[deltaV]

From the update thread:

FWIW, it seems pretty periodic, vent periods starting every 220-ish seconds and lasting about 35 seconds.

That periodicity could be explained by a pressure relief valve with hysteresis (either mechanical or in software). Overpressure is detected, it vents for a while, the venting relieves the overpressure, the valve closes again, overpressure builds up again, and it repeats.

[neoforce]

longer video posted: 

[mr. mark]

I was a little more than worried that the situation would spin out of control almost had to go pull out my lucky SpaceX employee coffee mug.

[edkyle99]

Do we have any other historical examples of something like this? I've honestly never seen a vehicle vent like that before, but I'm guessing it looks more dramatic than it is.

There was a big LOX leak at LC 39A during the early days of Saturn V.  SLC 37B was damaged by a big cryogen leak (LH2?) during a Delta 4 WDR several years ago.  I'm sure there are other examples. 

This one doesn't look like vehicle to me at first glance, but then again it was a long camera shot, interrupted.

 - Ed Kyle

[Lars_J]

longer video posted:  ...

It would be interesting if a much longer version could be posted - because there were some large episodes of venting (similar magnitude) that come and went, before this one.

[aero]

Isn't the first stage stabilized by pressurization of the tanks? If so, then is it only needed during launch when thrust forces are applied? I'm thinking that a balloon tank would collapse with reduced tank pressure and the loaded US on top? Lots of assumptions here.

[Joffan]

Isn't the first stage stabilized by pressurization of the tanks? If so, then is it only needed during launch when thrust forces are applied? I'm thinking that a balloon tank would collapse with reduced tank pressure and the loaded US on top? Lots of assumptions here.

Depends how far it is into "balloon" territory. My understanding is that the SpaceX tanks are only using the extra strength/rigidity of pressurization for the launch load; static and handling loads can be handled with the material strength of the tanks. Some tanks (Centaur?) needs to be continuously pressurized for handling.

[Space OurSoul]

I have followed a long sequence of guesses and backtracking to try and explain this to myself, the end of which I offer here hoping for correction from better-informed readers- thanks in advance.

My first reaction was that LOX had to be running down the side of the vehicle- it seems impossible that so much vapor could be caused by mere condensation, and a seam rupture would be far more dramatic and short-lived. But then how to explain the apparent coincidence that the vapor appears to cover the whole extent of the LOX tank but not any of the kero? Perhaps the skin temperature over the kero tank is high enough (and it's a big enough heat reservoir) that the falling LOX has no choice but to fully evaporate before it gets an appreciable distance down the outside of the kero tank.

So then what went wrong? If we assume only one point of failure (that being more likely), then I think it has to be an umbilical connection issue (assuming my guess about flowing LOX is right)- the umbilical has at least partially parted from the vehicle.

But then, valves on one side or other of the umbilical have to be opened in order to allow LOX to flow out. The fact that the venting is periodic implies that it's intentional, and perhaps even a pre-planned procedure for this eventuality: They can't get a crew in to fix the umbilical connection because they can't offload in order to safe the vehicle first. Their only option is to let the LOX tank vent like this.

[WHAP]

I have followed a long sequence of guesses and backtracking to try and explain this to myself, the end of which I offer here hoping for correction from better-informed readers- thanks in advance.

My first reaction was that LOX had to be running down the side of the vehicle- it seems impossible that so much vapor could be caused by mere condensation, and a seam rupture would be far more dramatic and short-lived. But then how to explain the apparent coincidence that the vapor appears to cover the whole extent of the LOX tank but not any of the kero? Perhaps the skin temperature over the kero tank is high enough (and it's a big enough heat reservoir) that the falling LOX has no choice but to fully evaporate before it gets an appreciable distance down the outside of the kero tank.

There are instances where the plume only appears to exist from about the upper 2/3 of the tank, and other times when it does appear to go below the interface with the RP1 tank.  That temperature difference that you mention is valid here.  I think that all supports the "lox running down the side of the vehicle" theory.

So then what went wrong? If we assume only one point of failure (that being more likely), then I think it has to be an umbilical connection issue (assuming my guess about flowing LOX is right)- the umbilical has at least partially parted from the vehicle.

Given that the tank fills from the bottom, and there's no external plumbing for the first stage that extends above the LOX/RP1 interface, an umbilical separation doesn't appear plausible.  There's no umbilical from the vent valve at the top of the tank (venting O2 into the air is OK), so nothing to fail there.

But then, valves on one side or other of the umbilical have to be opened in order to allow LOX to flow out. The fact that the venting is periodic implies that it's intentional, and perhaps even a pre-planned procedure for this eventuality: They can't get a crew in to fix the umbilical connection because they can't offload in order to safe the vehicle first. Their only option is to let the LOX tank vent like this.

Periodic venting does not indicate intention.  Even if they could not drain the vehicle, you would not expect to see a plume any larger than during a normal tanking.  In fact, if they stopped filling and were only venting, you might expect the plume to start decreasing.  This looks to me to be an overfill situation.  The question is how could the overfill last for so long?  This should require multiple failures on the ground side, but it could also be a control system issue.  A structural failure of the tank in some manner to permit LOX to run out is possible, but doesn't seem likely.  The margins on this tank, which needs to maintain pressure and all of the loads during lift off and ascent, should be more than enough to prevent a weld failure or something similar when just under tanking conditions.

[hrissan]

If this is intentional, may be SpaceX is experimenting with LOX chilled below boiling temperature? Then at the end of tanking you get lots of warmer LOX in the tank, fresh super-cold LOX flows from the bottom and pushes warmer LOX (it has low density, so it is at the top) up through vent...

Then if you know there are only so much warm LOX, the simplest method is set the flow so that overflowing LOX fully evaporates before reaching ground.

Too barbaric to be true!

[Robotbeat]

The reason why they don't release a ton of stuff anymore (such as an official live feed of the hot fire) is that people hyperventilate when they see anything they weren't expecting to.

The increase in humidity could be partly to blame for the huge clouds of water vapor. The other part could be over-filling of the LOx tank from the GSE. We'll find out. If they do a hot fire today, it's obviously not a huge problem with the rocket.

[Robotbeat]

Isn't the first stage stabilized by pressurization of the tanks? If so, then is it only needed during launch when thrust forces are applied? I'm thinking that a balloon tank would collapse with reduced tank pressure and the loaded US on top? Lots of assumptions here.

Depends how far it is into "balloon" territory. My understanding is that the SpaceX tanks are only using the extra strength/rigidity of pressurization for the launch load; static and handling loads can be handled with the material strength of the tanks. Some tanks (Centaur?) needs to be continuously pressurized for handling.

I'm pretty sure they need to be pressurized when full, though not when empty (unlike Centaur, which needs pressurization either way). Or at very least, needs pressurization during launch.

[rcoppola]

Well they did the Static Fire. It would seem I for one certainly overreacted. Lesson learned...again.

So then, what the heck was all that venting? Could it be as simple as fuel / tank / environmental temp variations?

[ugordan]

So then, what the heck was all that venting?

The GOX relief vent, anyone know if it's a binary, open/closed thing or is there something inbetween as well? If there is, could it have been intermittently stuck at full open?

[pippin]

Could this have been a 2nd stage engine flow test of some kind?
Does the interstate have enough venting space for that?

[Chris Bergin]

Well they did the Static Fire. It would seem I for one certainly overreacted. Lesson learned...again.

So then, what the heck was all that venting? Could it be as simple as fuel / tank / environmental temp variations?

Everyone's classing it as an issue, but not saying what. So I'm shrugging my shoulders!

I'd understand if it was just me saying "Blimey, that's a lot of venting" before someone experienced posted "Shut up Chris, stop comparing everything to Shuttle!"  But we had engineers on that thread saying "That's not good!" (by reaction). So I don't think it was the magic LOX fairies at work - clearly something was off nominal.

So I guess the correct reaction would be somewhere inbetween "Wooo, SpaceX RULES so much Falcon's even vent more than every other rocket!" and "OMG, it nearly exploded"

If I get to know, you'll get to know. I'll draft up the article, and see if someone will give me some info on the vent-a-thon between writing it and publishing it.

[QuantumG]

So... any pics or video of the static fire?