SpaceX Starship : Texas Prototype(s) Thread 20 : Discussion

[bfabry]

Hi guys, hope this hasn't already been asked, but does anyone know or have any guesses as to what is that white thing (in the red box in the pic) on SN15?

Photo by Jack Beyer for NSF, from twitter (sorry, don't know how to put the link without the preview being shown  )

Some wild speculation here but the centre white circle has a diameter of ~60cm.
Coincidentally, a Starlink user terminal is around the same diameter... 

Huh. It looks like at least part of it is a white plastic cover which does a little bit yell "radio!".

[aero]

SN 11 was the one that fell over in the high bay, wasn't it? You don't suppose it suffered undetected internal damage leading to the explosion do you?

[hartspace]

SN 11 was the one that fell over in the high bay, wasn't it? You don't suppose it suffered undetected internal damage leading to the explosion do you?

SN9 was the one that tipped over in the high bay

[Steve G]

Wouldn't I like to be the owner of the local scrap metal company.

[OTV Booster]

I have a question:
How do they manage ullage in f9, main tanks of SS, SH?
Is it because there is no violent flip and slosh?
Do they calculate how much ullage they should "waste" to keep propellant pressures in correct range?
After all they are subcooling to fit more propellant in and then they have to waste some of that for ullage.

Second question:
Is it better to store hot ullage gas in your tanks at 6 bar or in copv's at much more bar?
I guess the answer is no part is the best part.

Where to store ullage makeup gas? Both places IMO. When the launch burn starts ullage pressure can be on the low side as the pressure head is high. Ullage pressure need be only high enough to meet structural needs. As the fuel level drops along with the pressure head feeding the engines, the ullage pressure needs to rise to compensate.


Unfortunately, the autogen makeup gasses are warm and will shrink when contacting the densified propellants. Storing in a high pressure COPV gives at least a few moments to let it cool if the COPV's aren't in the engine bay. The gasses will further cool as they drop to ullage pressures but my unsupported WAG is they'll still be warm in comparison to the props. They will condense and the solution is to pile on more makeup gas.


As an ideal, makeup gasses would enter the COPV at a low temp so that full pressure is available later in the flight for other systems needing methane pressure. This would keep the COPV volume low. It would also minimize shrinkage as the gas contacts the chilled propellant in its ullage role. So much for ideals.


Temperature and pressure will be doing their codependent dance everywhere throughout every system. It's so complicated it makes my blood Boyle.

[OTV Booster]

I have a question:
How do they manage ullage in f9, main tanks of SS, SH?
Is it because there is no violent flip and slosh?
Do they calculate how much ullage they should "waste" to keep propellant pressures in correct range?
After all they are subcooling to fit more propellant in and then they have to waste some of that for ullage.

Second question:
Is it better to store hot ullage gas in your tanks at 6 bar or in copv's at much more bar?
I guess the answer is no part is the best part.

- The Falcon 9 uses helium to fill the ullage space in the tanks. The helium is stored at high pressure in COPVs immersed in the LOx tank to increase helium density.  I believe the helium is warmed (~250 F) through a heat exchanger before entering the tanks through a regulator and distribution system situated around the top of the tanks. Note the conflicting requirements for the ullage gas. It wants to be cold for high density storage, but needs to be warm for low density ullage filling.

- The SH uses warm gases, GOx and GCH4 (~500 F) tapped off of the Raptor engines to fill the ullage space in the tanks. The gases enter the tanks through a regulator and distribution system situated around the top the tanks. Note, this is similar to the Space Shuttle autogenous system.

- The SS is more complicated. It requires feeding engines from main and header tanks and after extensive time (minutes to months) between starts. To do this SS requires COPVs for both GOx and GCH4. Also, these COPVs probably have to be recharged from on board liquid propellants during extended missions. Ullage pressure of both sets of tanks need to be managed throughout the mission. COPVs will be part of the system which manages tank pressures whenever the Raptors are not firing. We again have a conflict between ullage gas COPV storage temperature and ullage filling temperature. Since there is no ready heat source with the Raptors off, a compromise temperature will probably be used (~100 F ?).

- Ullage pressure changes with changes in temperature. It has to be actively managed.

John

So for the SH there will not be a need for COPV's with propellant gas(fuel and oxidizer)?
How about the slight delay of maybe a second before autogen gas starts flowing?

Given that the SH tanks have significant head pressure when full and even when at flight levels still have a fair degree of ullage volume, that should not be an issue.

The Starship methane header tank pressure issues are a combination of both a small initial ullage volume and the high degree of mixing caused by the slosh, as well as a limited head pressure requiring gaseous pressurisation.

Where did this come from? If anything, initial SH ullage pressure will be low. IMO. The engines are picky about inlet pressure. That big tall SH will have a high head pressure at launch. Only enough ullage pressure to keep it from buckling.


Actually we're both working in a knowledge vacuum. The one and only SH in the whole world is not a flight article. Even Elon only knows what his plans are, not what he will actually end up doing.

[FinalFrontier]

Per a post in the update thread, SpaceX has posted an update.

SpaceX site has updated.

Click through to get to the actual post, and the attached update.

What caught my eye was they say SN11 experienced a Rapid Unscheduled Dissasembly (RUD). That seems to weigh against the theory that the FTS triggered, IMHO.

So, other than the FTS, what failure modes could cause the sudden wide dispersion of parts that we saw? It would have to be quite an energetic event IMHO. Common bulkhead failure?

Ignition of the CH4 inside the main tank or header tank.
Source would be either a fire in the repress AP line or a raptor exploding energetically enough to pop the aft bulkhead with heated shrapnel.

Still don't think this was it. Imho right now I still think it was FTS activation for vehicle off course due to failed engines/relight fail.But I rank the above scenerio as the "second most likely" candidate.

According to those who've seen the debris pics (I'm not one of 'em, so I'm just going on the opinions of others here) the main tanks were pretty shredded. So, I think you're right that there was ignition of the CH4 inside the tank. The problem IMHO is, that'd also require O2. Maybe the LOX downcomer for the LOX header let go inside the CH4 tank? Or. the CH4 downcomer (or manifold) did so inside the LOX tank? I think you may be right regarding energetic failure of a Raptor.

My guess on the FTS issue is that if it was the FTS, SpaceX would know, and if they knew, they wouldn't be saying a RUD. Just tea-leaf reading on my part though.

Took awhile for the folks on a certain infamous Titan IV failure to finally come to terms with the fact that their AFTS malfunctioned and to verify the telemetry and failure mode. Similar things on other rockets in the not so distant past as well. Sometimes it's very hard to tell if an FTS activated or not especially if it was a malfunction triggered activation and it can sometimes be even harder to accept that fact if so.

So I am still skeptical about this not being some form of FTS activation.

But with that said it's becoming more likely it was ignition in the methane tank. As far as O2 content you just need to get to LEL% LFL to have combustion. Not much O2 is needed. A very small leak in the LOX downcomer or O2 getting in through one of the cold gas thruster or tank vent through hulls would be enough.
So the question becomes what was the ignition source.
IMHO was either raptor engine 2 exploding or perhaps even worse, engine two exploding and sending a flash front up the AP pressurizer line into the tank. This could also have happened without any raptor issue and instead a simple fire occurring inside that line.
We had a fire in the vacinity of this line as well as the main fuel return valve from the chamber coolant visible in the video footage on the bad engine, which suggests a crack or failure of some kind.
Having looked at the video a few more times I think this was a contributing factor in some way but I don't know exactly how yet, that is something hopefully SpaceX figures out and tells us.

Regarding the LOX downcomer. Yes it is also possible that the pipe itself failed explosively during landing burn startup. This would have caused a rapid over pressurization of the CH4 tank as all of the LOX pressure in the LOX header tank was instantly dumped into the CH4 tank. This would likely also cause ignition and you'd get a big explosion and many small bits.
So this is also a possibility. Causes of this could include again, a fire in one of the AP pressurizer lines coming off the engines or a failure of raptor engine 2 that caused a a significant back pressure event and a pressure "kick" back up the LOX manifold into the line. Either of these would cause the downcomer pipe to rupture and the rest is as we saw.

All of these are possibilities and what is challenging is they all would happen extremely extremely fast. Perhaps not quite as fast as the COPV explosion and carbon fiber ignition on AMOS-6 but still very fast.
In tank over pressure and combustion events are very difficult to dissect afterwards because they happen extremely fast and the exact behavior inside when it's happening is difficult to model and often unique case by case.

We will see what they come up with. If it was a pressurizer line fire a check valve or flame arrestor is probably an easy fix here. If it was a pressure kick back up the line some kind of emergency relief valve or burst disk might be an easy fix for that.

[vaporcobra]

Hi guys, hope this hasn't already been asked, but does anyone know or have any guesses as to what is that white thing (in the red box in the pic) on SN15?

Photo by Jack Beyer for NSF, from twitter (sorry, don't know how to put the link without the preview being shown  )

My post fell through the cracks during the late FAA inspector furor 😅 I'm still very curious, too. Much better photos from Mary during SN15's high bay move today, thankfully!

Have to admit that my first thought was a Starlink dish, as the location makes no sense for a window test. If not Starlink, some other kind of flat-panel antenna, or possibly an EMR-transparent 'window' for some other kind of communications equipment.

[CamiloPasin]

The white plastic thing is a new telemetry antenna. The older little ones are missing anyway. But it is not Starlink, probably the same s-band encoded up/downlink for telemetry and video feed that they have been using and was picked up by hijackers not long ago. The similarity with a starlink dish may not be coincidence tho, it could be very well based on the phased array antenna technology they already have been mass producing.

I do hope that this new antenna will give a better video downlink.

[vaporcobra]

The white plastic thing is a new telemetry antenna. The older little ones are missing anyway. But it is not Starlink, probably the same s-band encoded up/downlink for telemetry and video feed that they have been using and was picked up by hijackers not long ago. The similarity with a starlink dish may not be coincidence tho, it could be very well based on the phased array antenna technology they already have been mass producing.

Hmmm, good call, as it turns out! Looks to be roughly the same size as what I believe is Falcon 9 S1's main antenna, minus the enclosure/box around Starship's. Booster pictured is B1061.

[CardBoardBoxProcessor]

The brief look inside of SS was the methane tank. Isn't liquid methane clear and colorless but we see it looking cloudy? What would it look like when mixed O2

[Alvian@IDN]

The brief look inside of SS was the methane tank. Isn't liquid methane clear and colorless but we see it looking cloudy? What would it look like when mixed O2

It's a great sign of autogenous pressurization, because helium wouldn't make such a visual effects because of much less saturation. Also a gaseous methane in this tank is still very close to liquid temperature, thus creating a fog when in contact with liquid methane

[meekGee]

Speaking of FTS, if it wasn't activated, wouldn't we be seeing the bomb squad and dogs searching the wetlands?

How DO they handle a missing explosive device?  This is obviously something that's been addressed before.

hmmm...

[KilroySmith]

If I were building a FTS system, I’d make sure that the explosive elements had a transmitter built into them, to make finding them after an accident a bit easier.

[CJ]

The brief look inside of SS was the methane tank. Isn't liquid methane clear and colorless but we see it looking cloudy? What would it look like when mixed O2

It's a great sign of autogenous pressurization, because helium wouldn't make such a visual effects because of much less saturation. Also a gaseous methane in this tank is still very close to liquid temperature, thus creating a fog when in contact with liquid methane

Hrmmm. If the vapor inside the CH4 tank is indeed close to liquid temp, then could it be possible that, during the start of the flip, there was liquid slosh, causing a recondensation of some of the vapor, resulting in a pressure drop and a common dome failure?

[laserguy]

So, I am now pretty sure, based on RGV's photos that the Methane header tank is in two halves, top half landed next to the pad, lower half landed across the road in the bay. We've never seen the tank fail like that on previous flights, in SN10 it was still spherical after being expelled out the bottom of the tank at high speed.
So, I'm thinking the explosion started inside there?

Where is that split, in relation to the location of the FTS?

I know some sources are swearing that the FTS was not triggered - but what if some fault caused the FTS to fire accidentally? Maybe even a defect in the FTS itself?

[matthewkantar]

Speaking of FTS, if it wasn't activated, wouldn't we be seeing the bomb squad and dogs searching the wetlands?

How DO they handle a missing explosive device?  This is obviously something that's been addressed before.

hmmm...

They do have a lot of personnel out recovering wreckage. They also warned that though the road was open, not to leave it. It is possible they have recovered, or are looking for UXBs.

[sanman]

What are the key improvements in SN15 over SN11 and other previous prototypes?

[Star One]

What are the key improvements in SN15 over SN11 and other previous prototypes?

I don’t think anything has been said about the specifics so far other than there is hundreds of them.

[Haur]

I have a question:
How do they manage ullage in f9, main tanks of SS, SH?
Is it because there is no violent flip and slosh?
Do they calculate how much ullage they should "waste" to keep propellant pressures in correct range?
After all they are subcooling to fit more propellant in and then they have to waste some of that for ullage.

Second question:
Is it better to store hot ullage gas in your tanks at 6 bar or in copv's at much more bar?
I guess the answer is no part is the best part.

- The Falcon 9 uses helium to fill the ullage space in the tanks. The helium is stored at high pressure in COPVs immersed in the LOx tank to increase helium density.  I believe the helium is warmed (~250 F) through a heat exchanger before entering the tanks through a regulator and distribution system situated around the top of the tanks. Note the conflicting requirements for the ullage gas. It wants to be cold for high density storage, but needs to be warm for low density ullage filling.

- The SH uses warm gases, GOx and GCH4 (~500 F) tapped off of the Raptor engines to fill the ullage space in the tanks. The gases enter the tanks through a regulator and distribution system situated around the top the tanks. Note, this is similar to the Space Shuttle autogenous system.

- The SS is more complicated. It requires feeding engines from main and header tanks and after extensive time (minutes to months) between starts. To do this SS requires COPVs for both GOx and GCH4. Also, these COPVs probably have to be recharged from on board liquid propellants during extended missions. Ullage pressure of both sets of tanks need to be managed throughout the mission. COPVs will be part of the system which manages tank pressures whenever the Raptors are not firing. We again have a conflict between ullage gas COPV storage temperature and ullage filling temperature. Since there is no ready heat source with the Raptors off, a compromise temperature will probably be used (~100 F ?).

- Ullage pressure changes with changes in temperature. It has to be actively managed.

John

So for the SH there will not be a need for COPV's with propellant gas(fuel and oxidizer)?
How about the slight delay of maybe a second before autogen gas starts flowing?

Given that the SH tanks have significant head pressure when full and even when at flight levels still have a fair degree of ullage volume, that should not be an issue.

The Starship methane header tank pressure issues are a combination of both a small initial ullage volume and the high degree of mixing caused by the slosh, as well as a limited head pressure requiring gaseous pressurisation.

Where did this come from? If anything, initial SH ullage pressure will be low. IMO. The engines are picky about inlet pressure. That big tall SH will have a high head pressure at launch. Only enough ullage pressure to keep it from buckling.


Actually we're both working in a knowledge vacuum. The one and only SH in the whole world is not a flight article. Even Elon only knows what his plans are, not what he will actually end up doing.

I believe that's what I said. SH has relatively high head pressure from 30/60m of propellants, so a lack of gas pressure when lighting at launch isn't as much of an issue - but even then there's a non-trivial quantity of ullage volume which will not significantly lose pressure due to expansion before the autogenous supply kicks in. And when they want to relight for the landing burn, you've now got a 90+% empty tank at a reasonable pressure so probably doesn't even need any make-up pressurant supply - although since it's there anyway, might as well use it.