SpaceX Starship - Integrated Flight Test #2 - Starbase TX - Including Post Launch Dissection

[scaesare]

I botted this and it turns out that a 5 bar pressure differential will move liquid oxygen at about 30 m/s, which is 67 mph or 108 km/h. That's ignoring the additional velocity that would come from gravity or from the rocket accelerating. It also ignores complexities such as surface tension, turbulence, and so on.

To get a sense of 5 bar of pressure, two-liter soda bottles apparently sit at around 3.5 bar, and they burst at around 10 bar.

As another reference point: 5 bar is about 90 PSI.

Your home water pressure is typically around half of that. So, imagine double what garden hose can deliver for pressure (not volume, which is far greater for a rocket engine)

(and "botted"... great verbing)

 

[JB47394]

Out of curiosity, what pipe length and diameter was that based on?

None. It was a pure pressure differential calculation. I assume that pipe diameter only comes into play when considering those other factors.

 

[mongo]

None. It was a pure pressure differential calculation. I assume that pipe diameter only comes into play when considering those other factors.

Huh...
I'm no ME, but I don't get how it can give a terminal velocity based on a pressure differential without a given drag force to counter further acceleration.
Not that it matters.

 

[JB47394]

Huh...
I'm no ME, but I don't get how it can give a terminal velocity based on a pressure differential without a given drag force to counter further acceleration.
Not that it matters.

It is the exit velocity from the system. No pipe. The bot was using Torricelli's Law after converting the pressure differential to an equivalent column height of liquid oxygen.

Torricelli's law - Wikipedia

en.wikipedia.org

 

[mongo]

It is the exit velocity from the system. No pipe. The bot was using Torricelli's Law after converting the pressure differential to an equivalent column height of liquid oxygen.

Torricelli's law - Wikipedia

en.wikipedia.org

Ah, I don't think that applies in this case since p1 != p2 and the ullage gas (if maintained) imparts an unbounded amount of energy into the system versus only having the potential energy as a source. Plus gravity acting on all particles is different than pressure acting only on the crossection. A longer column accelerates slower due to pressure whereas a taller column has more force at the base due to gravity.

 

[JB47394]

Ah, I don't think that applies in this case

Hmmm. We know the mass flow rate for Raptor engines. According to Wikipedia It's 510-650 kg/s for LOX. Call it 600 kg/s.

600 kg/s / (30 m/s * 1141 kg/m3) = 0.0175 m2

So at that speed, the diameter of the pipe would be 15 cm, or about 6 inches.

I went to the recent CSI Starbase video and did some pixel measurements and, sure enough, the LOX pipes are about 6 inches in diameter.

 

[ICUDoc]

I teach Poiseuille-Hagen pretty much every week.
Lots of assumptions, but the maths check out

 

[scaesare]

CSI Starbase's 80 minute examination of the booster failure.

I found the chapter called "Fuel Slosh Intro" the most interesting. It includes a water simulation to show what might have happened to the LOX during staging. They also mention that the LOX baffles have been greatly reinforced on Booster 10, making me wonder if they were damaged from the aggressive sloshing. They draw no conclusions and are content to describe some possible failure modes.

One thing that annoyed me was talking about the autogenous pressurization system using 5 bar of pressure to help keep the liquids seated in the tanks.

Edit: I forgot to mention that they estimate the heat shield part of the hot staging ring is 6-12mm thick because although it is welded from below, no weld discoloration can be seen on the top. It's too thick for that.

Got a chance to watch this finally...

I also found that plate thickness estimates interesting... and the point about sparks being visible during the initial hot stage event... I had understood the coloration of the exhaust plume was likely do to the steel being ablated, but had not noticed sparks. I wonder how much of that dome material is removed...

I also found it interesting he largely dismissed water-hammer effects... feeling slosh was more likely the issue. The engines failing on one side first tend to support that.

Would be nice to see the fluid dynamics done gain with software that can model something other than H2O.

(on edit): Oh and we talked about grid fin interaction during hot staging a while back... they believe the grid fins were oriented to leverage the exhaust of the Ship to help the booster flip...

 

[mongo]

FAA is happy?
S25 engines shut down due to fire cutting communication lines (or loss of aft computer).

H/t Marcus House

February 26, 2024

Shana Diez

Director of Starship Reliability Space Exploration Technologies 1 Rocket Road Hawthorne, California 90250

Dear Ms. Diez,

On November 18, 2023, at 13:02:50 UTC, Space Exploration Technologies, Inc. (SpaceX) conducted Starship Super-Heavy Orbital Test Flight 2 (OTF-2) launch operations from its Boca Chica, Texas site under Federal Aviation Administration (FAA) launch license VOL 23-129 Rev. 1. After a successful ascent and stage separation, the Super-Heavy Booster 9 (B9) suffered a mishap during its boostback burn resulting in a mid-air explosion and vehicle loss.

Following a successful start-up of all engines and separation from B9, Starship Ship 25 (S25) had a nominal ascent until 13:09:55 UTC, when the planned pre-second engine cutoff Liquid Oxygen dump started. Over the next minute, several explosions and sustained fires were observed in onboard camera aft video streams, ultimately resulting in a loss of communication between the forward and aft flight computers. This resulted in a commanded shutdown of all six engines, and an Autonomous Flight Safety System flight termination triggering at 13:10:55 UTC per flight safety rules.

The FAA classified the Starship Super-Heavy OTF-2 launch as a mishap, as defined in Title 14 Code of Federal Regulations (14 CFR) § 401.7 paragraphs (7) and (9).¹

Following the launch, the FAA, consistent with its statutory authority under Title 51 of the U.S. Code and 14 CFR § 450.173(e), required SpaceX to conduct a mishap investigation following its approved mishap plan under FAA oversight. The FAA conducted a final review of the B9 and S25 mishap reports. The primary focus of these reviews was to ensure operator compliance with 14 CFR § 450.173. The FAA has been provided with sufficient information and accepts the root causes and corrective actions described in the mishap reports. Consequently, the FAA considers the mishap investigation that SpaceX was required to complete to be concluded.

"Prior to the next launch, SpaceX must implement all corrective actions and receive a license modification from the FAA that addresses all safety, environmental and other applicable regulatory requirements. The FAA is evaluating SpaceX’s license modification request and expects SpaceX to submit additional required information before a final determination can be made."

https://twitter.com/x/status/1762236963791454680

 

[JB47394]

The most important part:

Consequently, the FAA consider the mishap investigation that SpaceX was required to complete to be concluded.

Now we can get back to watching for TFRs and NOTAMs. Well, after the Ship 28 static fire and a successful wet dress rehearsal.

 

[mongo]

The most important part:


Now we can get back to watching for TFRs and NOTAMs. Well, after the Ship 28 static fire and a successful wet dress rehearsal.

Still need to address any corrective actions that came out of the investigation
More details on SpaceX's website.
Booster loss was likely due to energetic engine failure caused by LOX filter blockage.

SpaceX

 

[Star K1tty]

Things are moving forward!

SpaceX discloses cause of Starship anomalies as it clears an FAA hurdle

"Several engines began shutting down before one engine failed energetically."

arstechnica.com

 

[ecarfan]

"The most likely root cause for the booster RUD was determined to be filter blockage where liquid oxygen is supplied to the engines, leading to a loss of inlet pressure in engine oxidizer turbopumps that eventually resulted in one engine failing in a way that resulted in loss of the vehicle," the company stated. "SpaceX has since implemented hardware changes inside future booster oxidizer tanks to improve propellant filtration capabilities and refined operations to increase reliability."

The LOX goes through a filter before reaching the engines? I did not realize that.

 

[ecarfan]

"A leak in the aft section of the spacecraft that developed when the liquid oxygen vent was initiated resulted in a combustion event and subsequent fires that led to a loss of communication between the spacecraft’s flight computers," the company said. "This resulted in a commanded shut down of all six engines prior to completion of the ascent burn, followed by the Autonomous Flight Safety System detecting a mission rule violation and activating the flight termination system, leading to vehicle breakup."

“…in the aft section…” is pretty vague.

A “vent” is sort of a controlled leak. The LOX tank is “aft”. Did the vent mechanism fail such that too much LOX was vented too quickly. Or was the leak from somewhere else?

Not enough information…

 

[Grendal]

“…in the aft section…” is pretty vague.

A “vent” is sort of a controlled leak. The LOX tank is “aft”. Did the vent mechanism fail such that too much LOX was vented too quickly. Or was the leak from somewhere else?

Not enough information…

From the previous information provided by Elon, I think that means that SpaceX was trying to vent some LOX because they didn't have payload mass/weight. The vent ignited instead of just venting the fluid/gas and that started a fire which led to the damage which caused the loss of the vehicle.

So it probably would have gone just fine if they hadn't dumped LOX in a way that led to combustion.

 

[Grendal]

SpaceX's update on the 2nd launch:

SpaceX

SpaceX designs, manufactures and launches advanced rockets and spacecraft.

www.spacex.com

 

[ecarfan]

From the previous information provided by Elon, I think that means that SpaceX was trying to vent some LOX because they didn't have payload mass/weight. The vent ignited instead of just venting the fluid/gas and that started a fire which led to the damage which caused the loss of the vehicle.

Yes, I understand why the vent was planned, I’m just not clear on where the leak was. The phrasing of the statement does not imply that the vent location was the cause of the fire, only that “a leak” occurred “aft”. It would be odd to me to call a planned vent a “leak”. It was an intentional vent. To my reading, the implication is that there was a LOX leak somewhere other than the vent location. But maybe I’ve got it wrong.

 

[JB47394]

The LOX goes through a filter before reaching the engines? I did not realize that.

SpaceX seriously beefed-up the baffles in Booster 10. I assume that the understrength baffles were torn up and parts blocked the LOX intakes.

It would be odd to me to call a planned vent a “leak”.

The leak may actually have been a leak of the vented oxygen back into the ship. The rate of venting would probably have created, then maintained, a bubble of oxygen that hung around by the vent. When I say bubble, it may have been 200 meters in diameter. The gas in that bubble would try to enter every cubic cm of volume that didn't have any gas in it. So some oxygen may have gotten into electronics boxes and so on, found a source of ignition, and started a fire. The fire would only last while the oxygen vent was underway, but it was apparently enough to short out some wiring.

I'm speculating on the meaning of "leak", but the effect I described seems a plausible failure mode.

 

[Grendal]

Yes, I understand why the vent was planned, I’m just not clear on where the leak was. The phrasing of the statement does not imply that the vent location was the cause of the fire, only that “a leak” occurred “aft”. It would be odd to me to call a planned vent a “leak”. It was an intentional vent. To my reading, the implication is that there was a LOX leak somewhere other than the vent location. But maybe I’ve got it wrong.

Good point. Maybe the the venting action popped a line somewhere causing a "leak" in an unplanned area.

 

[scaesare]

Berger's take in his Ars article as well: SpaceX discloses cause of Starship anomalies as it clears an FAA hurdle

The LOX goes through a filter before reaching the engines? I did not realize that.

Yeah, I wonder what this looks like, and where it is... Is this a relatively coarse screen at the turbopump inlet or is it a much finer gauge filter somewhere in the plumbing before the turbopump inlet? The SpaceX article says "where liquid oxygen is supplied to the engines" so I wonder if a common location in the manifold feeding all engines, or one per engine...

SpaceX seriously beefed-up the baffles in Booster 10. I assume that the understrength baffles were torn up and parts blocked the LOX intakes.

It kinda feels like a blocked intake and a blocked filter are different enough things that they wouldn't have described it that way. (If a rag got lodged in my car's intake, I wouldn't describe it as a filter issue).

That having been said, your comment made me ask the question above... the disintegrated baffle idea is interesting, and makes me wonder if there's a screen in the LOX plumbing that the chunks of baffle got sucked up against... I guess that could be a "filter blockage". Probably comes down to debris size...

The leak may actually have been a leak of the vented oxygen back into the ship. The rate of venting would probably have created, then maintained, a bubble of oxygen that hung around by the vent. When I say bubble, it may have been 200 meters in diameter. The gas in that bubble would try to enter every cubic cm of volume that didn't have any gas in it. So some oxygen may have gotten into electronics boxes and so on, found a source of ignition, and started a fire. The fire would only last while the oxygen vent was underway, but it was apparently enough to short out some wiring.

I'm speculating on the meaning of "leak", but the effect I described seems a plausible failure mode.

So we've seen gas venting on rockets and ships before, and think that some of that is propellant in addition to inert gas. Do F9 or Heavy ever dump significant amounts of propellent during flight?

Good point. Maybe the the venting action popped a line somewhere causing a "leak" in an unplanned area.

Any ideas where the LOX vents are?