totm nov 2023 SpaceX Discussion Thread

[magnemoe]

6 hours ago, Spaceception said:

https://x.com/SpaceX/status/1793998848584794574 

https://www.spacex.com/updates/#flight-3-report

Still jettisoning the hotstage ring. This has to be a temporary thing, right? Can't be fully reusable if you're intentionally discarding hardware.

https://www.spacex.com/launches/mission/?missionId=starship-flight-4

S29 will be attempting a flip and burn (mentioned in the flight timeline), not just a splashdown. Higher confidence in reentry?

Did flight 2 jettison the hot stage ring? Yes it add drag to the top, but any simulated landing would be useless without is as it will be present on later landings and catch attempt. 

[darthgently]

51 minutes ago, magnemoe said:

Still jettisoning the hotstage ring. This has to be a temporary thing, right? Can't be fully reusable if you're intentionally discarding hardware

Given the mechanical and thermal stresses such a relatively weak structure appears to go through and the tolerances it must meet to mate with SS,  I wonder how many cycles they could realistically get out of it.  Still, probably more than one and would seem better to bring it back and scrap it than to hurl it away

[mikegarrison]

7 hours ago, Meecrob said:

I've been out of the loop for a bit. So this failure mode is similar to the FOHE on the British 777 at Heathrow a decade or so back?

Vaguely? There is always going to be some water in solution with the  jet fuel, and it can freeze up.

The specific issue (I think) was the ice freezing onto the walls of the fuel lines at low fuel flows, and then being knocked loose when the fuel flows were increased when the engine was commanded to go to higher power. The soft, slushy ice then clogged the intake to the fuel/oil heat exchanger, which starved the engine of fuel. The plane had flown through unusually cold air.

The design had met all certification requirements, but this incident revealed that the certification requirements were not completely adequate, and so both the design and the certification requirements were changed. It only affected the RR Trent engines.

https://en.wikipedia.org/wiki/British_Airways_Flight_38

Edited May 25 by mikegarrison

[CBase]

Since they claimed it was too much ice clogging the filters, @Ultimate Steve is probably right that unlike the 777 RR Trent issue this is about having so much ice returned to the tank.

Either they need improved filters to better cope with the amount of ice or reduce the amount. Any heat exchanger at Raptors mean actually 39 more parts while inside tanks you have at most 8 of them, probably less as header tanks might not need them. I could even image that you could alter the flow in the pre burner to have a lower burned fuel ratio being fed back at the autogenous pressurization inlet.

I mean any remaining ice after landing would slow down reuse. They would have to drain the tanks, let them heat up enough for any ice to melt and then drain it as well until refuel could start. So reducing the amount of ice sounds more attractive.

[magnemoe]

22 hours ago, darthgently said:

Given the mechanical and thermal stresses such a relatively weak structure appears to go through and the tolerances it must meet to mate with SS,  I wonder how many cycles they could realistically get out of it.  Still, probably more than one and would seem better to bring it back and scrap it than to hurl it away

I would not call it weak, it has to support upper stage trough maxQ including bending forces. 
But it faces two thermal shocks, first is separation, after upper stage goes to full trust its not longer required to be structural, it then faces the heating during reentry from an suborbital trajectory. 
Yes the protective cover over the top of first stage take more of an pounding during separation is not structural, just to protect first stage an be an weather covering for the top systems at other times. 

But, down the line they will want to reuse it. My guess is that they will make it more of pipes like the Russian hot staging segment as easier to protect or cool but they will anyway have extra drag on the top, but it might be so different the current design does not matter?

[darthgently]

3 minutes ago, magnemoe said:

I would not call it weak, it has to support upper stage trough maxQ including bending forces. 
But it faces two thermal shocks, first is separation, after upper stage goes to full trust its not longer required to be structural, it then faces the heating during reentry from an suborbital trajectory. 
Yes the protective cover over the top of first stage take more of an pounding during separation is not structural, just to protect first stage an be an weather covering for the top systems at other times. 

But, down the line they will want to reuse it. My guess is that they will make it more of pipes like the Russian hot staging segment as easier to protect or cool but they will anyway have extra drag on the top, but it might be so different the current design does not matter?

Pipes for the coolant flow also for the excellent rigidity for same mass of hollow cylinders over what is there now.  Agree

[Exoscientist]

On 5/24/2024 at 12:34 PM, Meecrob said:

I see @Exoscientist is currently busy. No doubt running the numbers on other engines that had test stand mishaps and the later service lives of said engines.

I've been out of the loop for a bit. So this failure mode is similar to the FOHE on the British 777 at Heathrow a decade or so back?

 

 IF the fuel venting seen for both the booster and ship after their burns was real that suggests the problem is with the Raptor itself.

 It is also notable that in the recent test stand explosion there was a fuel leak after the engine start, the engine was shutdown, and then the RUD occurred.

 Then this is a highly important question for SpaceX to answer, and for the FAA to ask about, if whether the fuel or LOX venting seen on both stages after their burns was real or not.

  Bob Clark

 

 

 

 

 

[Meecrob]

24 minutes ago, Exoscientist said:

snip

Just off the top of my head, wasn't SpaceX testing out a flame suppression system in the skirt?

Since Elon demolishes launchpads with rocket engines, he might test fire suppression systems with makeshift flamethrowers?

A bit more possible (with regards to IFT-3 reentry) is the vent was on purpose to spin Starship up to see how it deals with the thermal load. Its all well and good to see how the tiles are dealing with the heat, but when things go sideways (no pun intended), you wanna know how the bare skin deals with the heat as well.

Also, I think the long term goal is to not have tiles on LEO Starships, but we will have to see.

Edited May 27 by Meecrob

[mikegarrison]

18 hours ago, Meecrob said:

A bit more possible (with regards to IFT-3 reentry) is the vent was on purpose to spin Starship up to see how it deals with the thermal load. Its all well and good to see how the tiles are dealing with the heat, but when things go sideways (no pun intended), you wanna know how the bare skin deals with the heat as well.

That's a wildly generous take on it. "No, we didn't lose directional control -- we WANTED our spacecraft to wildly tumble during re-entry." However, it is contradicted by what SpaceX themselves said during and after the flight, where they said they lost control of the vehicle.

[tater]

Another routine flight to space.

[Flavio hc16]

https://www.reddit.com/r/SpaceXLounge/s/ghD0FBEIi8

 

FAA determine no public safety issues from IFT-3, clearing final hurdle before launch licence 

[tater]

 

liftoff in 5 min

[mikegarrison]

Um. What was that? Japan is a very different place, I guess.

[tater]

24 minutes ago, mikegarrison said:

Um. What was that? Japan is a very different place, I guess.

Yeah, I included it because it was bizarre.

[Gargamel]

Anybody happen to see that spacex was streaming flight 4’s launch countdown?   And then the stream was locked down and the account locked also?    The stream was deleted from my history, and I can’t find spacex on the site right now. 

[Flavio hc16]

8 minutes ago, Gargamel said:

Anybody happen to see that spacex was streaming flight 4’s launch countdown?   And then the stream was locked down and the account locked also?    The stream was deleted from my history, and I can’t find spacex on the site right now. 

If it was on YouTube, you were watching a scam, it had 300k views and they were using ift-1 footage.

[Ultimate Steve]

47 minutes ago, Gargamel said:

Anybody happen to see that spacex was streaming flight 4’s launch countdown?   And then the stream was locked down and the account locked also?    The stream was deleted from my history, and I can’t find spacex on the site right now. 

Scam stream. Flight 4 isn't until the 5th at the earliest. SpaceX no longer streams on YouTube.

I'm beginning to see why Elon moved everything to X, he may just be tired of scammers using his likeness. Or at least that may be a part of it.

[NFUN]

1 hour ago, Ultimate Steve said:

Scam stream. Flight 4 isn't until the 5th at the earliest. SpaceX no longer streams on YouTube.

I'm beginning to see why Elon moved everything to X, he may just be tired of scammers using his likeness. Or at least that may be a part of it.

and plenty of generally informed people wouldn't have gotten the memo that it's not on youtube anymore, guaranteeing that many flock to the scam feeds masquerading as something official because there is no official feed to be found

[darthgently]

2 hours ago, NFUN said:

because there is no official feed to be found

Not on YouTube

[Codraroll]

5 hours ago, darthgently said:

Not on YouTube

Yeah, but YouTube is where a lot of people will be looking. That makes them prime targets for scammers. I'm gonna bet that the stream Gargamel watched included a lot of talk about cryptocurrency investment and not a whole lot about rockets.

[Meecrob]

23 hours ago, mikegarrison said:

That's a wildly generous take on it. "No, we didn't lose directional control -- we WANTED our spacecraft to wildly tumble during re-entry." However, it is contradicted by what SpaceX themselves said during and after the flight, where they said they lost control of the vehicle.

I believe that SpaceX does not tell the whole truth in press releases.

I did not believe for a second that they were serious about the "flip" maneuver for staging. Now, it seems fairly obvious that they were working on the hot staging ring the whole time, only it wasn't ready for IFT-1 and they weren't going to delay the launch to wait for it.

 

23 hours ago, mikegarrison said:

"No, we didn't lose directional control -- we WANTED our spacecraft to wildly tumble during re-entry."

Yes, exactly. This is flight test. There is a non-zero chance an anomaly might occur on an operational flight that causes a tumble during reentry. SpaceX is testing in case it happens. They don't want to learn when re-entering from Mars. CFD cannot model this accurately. CFD can't even model a Cessna without verifying the results in real life, so a program as hardware-rich as Starship is definitely doing as many real-life tests as they possibly can. 

Think of it this way, Elon wants to have his own "Little Joe" moment.

Also, have you seen the footage? Go call up a PR firm and ask how much it would cost to produce a video that captures as much attention as those shots of the plasma streaming off the aft flaps.

 

Edited May 29 by Meecrob

[darthgently]

38 minutes ago, Meecrob said:

I believe that SpaceX does not tell the whole truth in press releases.

I did not believe for a second that they were serious about the "flip" maneuver for staging. Now, it seems fairly obvious that they were working on the hot staging ring the whole time, only it wasn't ready for IFT-1 and they weren't going to delay the launch to wait for it.

 

Yes, exactly. This is flight test. There is a non-zero chance an anomaly might occur on an operational flight that causes a tumble during reentry. SpaceX is testing in case it happens. They don't want to learn when re-entering from Mars. CFD cannot model this accurately. CFD can't even model a Cessna without verifying the results in real life, so a program as hardware-rich as Starship is definitely doing as many real-life tests as they possibly can. 

Think of it this way, Elon wants to have his own "Little Joe" moment.

Also, have you seen the footage? Go call up a PR firm and ask how much it would cost to produce a video that captures as much attention as those shots of the plasma streaming off the aft flaps.

 

Agree. I would posit with the SpaceX fail faster philosophy it matters less whether they intended a failure and much more how prepared they were to gather rich data from the failure and spend resources mining that data to the fullest.  As long as the failures fit the time and financial budgets, that is.  There are those limiting factors.  But not taking risks, and learning from the results, incurs huge costs also that shouldn't be underestimated and also impact time and financial budgets.  Judge by results, right?  SpaceX seems to be surfing the risk-reward wave pipe pretty well so far 

[mikegarrison]

1 hour ago, Meecrob said:

I did not believe for a second that they were serious about the "flip" maneuver for staging. Now, it seems fairly obvious that they were working on the hot staging ring the whole time, only it wasn't ready for IFT-1 and they weren't going to delay the launch to wait for it.

Of course they were serious.

I'm sure they had trade studies and considered hot staging, ullage motors, and this flip thing.  They chose the crazy, risky one just in case it actually worked. The flip failed pretty spectacularly, so then they went with one of the safer options. It's a pattern with them.

Also, there is a huge difference between pushing the boundaries of the envelope in flight test with the cost of occasional failure versus intentionally failing the test. "Test to destruction" is of course a real thing, and commonly done, but when you do it, you state in the test plan that you are doing it. SpaceX didn't try to explain away their test failure after the test flight, so I don't really understand why their fans seem to now be trying to do so.

Edited May 29 by mikegarrison

[darthgently]

18 minutes ago, mikegarrison said:

versus intentionally failing the test.

If intentional, is it a failure though?  It seems to me they are simply prepared for "success" or "failure" and so it becomes a valid test either way.   

For these stepwise explorations I'm not sure they are as concerned so much in defining success and failure wrt to a specific outcome as they are as to whether learning occurs.  In other words, they aren't defining the result beforehand so much as spending attentional resources on what actually happens. 

Obviously the ultimate goal has clear success criteria, but in the shorter term, when venturing into the unknown, the flowing and analysis of data, aka learning, is what defines success

Edited May 29 by darthgently

[tater]

One feature (problem, lol?) with current Starship testing is that they are optimizing for both the vehicle, and the process of making the vehicle. As a result, they are truly hardware rich. The feature/issue with this is that the current build might be several vehicles newer than the next one to fly. They are not shy about scrapping deprecated designs, but some seem far enough along they feel it's best to dispose of them by flying them to gain data, even if some aspects of the design to fly are currently irrelevant.