totm nov 2023 SpaceX Discussion Thread

[RealKerbal3x]

A few pics from yesterday of SN8's nosecone (credit @Nomadd on the NSF forum)

[Spaceception]

Looking forward to seeing a fully stacked Starship again. They'll probably roll it out sometime today or tomorrow, right?

[StrandedonEarth]

29 minutes ago, RealKerbal3x said:

A few pics from yesterday of SN8's nosecone (credit @Nomadd on the NSF forum)

Now they just need to get someone up there with a Jiffy marker ( gotta have that xylene) to draw windows on it

[RealKerbal3x]

1 minute ago, Spaceception said:

Looking forward to seeing a fully stacked Starship again. They'll probably roll it out sometime today or tomorrow, right?

Most likely, unless something was amiss with the static fire and they need to do it again.

[sevenperforce]

34 minutes ago, RealKerbal3x said:

Most likely, unless something was amiss with the static fire and they need to do it again.

I wonder if they will do a partial detank and then do a header-tank static fire as well, feeding only from the header tanks to simulate the restart and landing.

[RealKerbal3x]

1 minute ago, sevenperforce said:

I wonder if they will do a partial detank and then do a header-tank static fire as well, feeding only from the header tanks to simulate the restart and landing.

I was wondering about that, they're going to need to be able to restart the engines mid-flight. Simulating it with a static fire would be a good idea.

[sevenperforce]

22 minutes ago, RealKerbal3x said:

I was wondering about that, they're going to need to be able to restart the engines mid-flight. Simulating it with a static fire would be a good idea.

I wonder A LOT about how the plumbing is set up there. Presumably there is a valve setup which can feed either from the header tanks or from the mains. If they did a partial detanking to empty the mains, however, the T/W for three Raptors firing at once would be pretty extreme...might stress the hold-down clamps.

If this static fire went off without a hitch, then I am guessing we see two more: the first to simulate the header-fed burn by itself, and then the second where all tanks are filled and they feed first from the mains for a split second, then cut the engines, then switch valves and fire from the headers a few minutes later without any recycle.

I would have thought it possible that for the CH4 tanks, the main simply feeds into the header, which in turn feeds the engines, and so they close a flow valve between the main and the header immediately after MECO in order to trap the header tank in the "full" state. This avoids needing an extra flow path near the engines. However they'd definitely need a separate flow path and valve near the engines for the header tank, obviously.

In that C-bass animation on the last page, it showed the feed line from the LOX header tank coming down through the main LOX tank, internal to the vehicle. Do we know if that's the design, or will the LOX downcomer from the header tank flow along an external raceway for SN8?

1 hour ago, RealKerbal3x said:

Looking more closely at how the angle on the squid-fins/canards works, I wonder if I was wrong to assume that the lateral edge of the new fins doesn't run parallel to the side of Starship.

This view, at least, suggests that the LOX downcomer is at least internal to the fairing. Whether it exits the fairing and runs along the outside of the lower section or whether it remains internal...well that remains to be seen.

[RealKerbal3x]

6 minutes ago, sevenperforce said:

In that C-bass animation on the last page, it showed the feed line from the LOX header tank coming down through the main LOX tank, internal to the vehicle. Do we know if that's the design, or will the LOX downcomer from the header tank flow along an external raceway for SN8?

I don't know. We've seen the stump of the LOX header's downcomer on the forward bulkhead, so we know it at least runs through the CH4 tank, but beyond that I don't know if that line runs through the LOX tank or just empties into it instead. Seeing as propellant needs to flow from the header tanks to the engines even if the main tanks are empty, I'd guess it's the former but since we don't have official schematics of that area we can't know for sure.

[Silavite]

While exact probabilities are impossible to nail down, do y'all think that the first 15 km hop is more likely to succeed or fail? (By fail, I mean a total loss of the vehicle.)

I feel pretty confident saying that it's more likely to fail. The first in-flight use of the aerodynamic controls, the first time that the vehicle will be subject to significant transverse loads (via the bellyflop fall), the first in-flight restart of the Raptors, and a much longer duration than previous hops greatly increases the risk of failure, in my opinion.

[sevenperforce]

7 minutes ago, RealKerbal3x said:

I don't know. We've seen the stump of the LOX header's downcomer on the forward bulkhead, so we know it at least runs through the CH4 tank, but beyond that I don't know if that line runs through the LOX tank or just empties into it instead. Seeing as propellant needs to flow from the header tanks to the engines even if the main tanks are empty, I'd guess it's the former but since we don't have official schematics of that area we can't know for sure.

Oh, I didn't realize we had seen the stump. If that is the case then yeah, it has to flow all the way to the engines. Which I suppose means a different valve design for LOX than for CH4.

I wonder how autogenous pressurization is handled for the LOX header tank. Gaseous CH4 can be piped into the CH4 main tank which in turn pressurizes the header; you only need to fire the engines for a split second before you have ullage and can open the valves to maintain head pressure. But you'd need a separate GOX press line running all the way up to the header tank. I wonder if they have a separate CH4 gas line for the CH4 header tank too, just as a failsafe.  

2 minutes ago, Silavite said:

While exact probabilities are impossible to nail down, do y'all think that the first 15 km hop is more likely to succeed or fail? (By fail, I mean a total loss of the vehicle.)

I feel pretty confident saying that it's more likely to fail. The first in-flight use of the aerodynamic controls, the first time that the vehicle will be subject to significant transverse loads (via the bellyflop fall), the first in-flight restart of the Raptors, and a much longer duration than previous hops greatly increases the risk of failure, in my opinion.

A loss seems more likely than not. The big question is where the loss will take place. I think there are a few particularly significant failure modes:

1. Structural/valve/engine failure from a longer-duration burn and associated heat, stress, and vibration (the engines can probably take it, since they've all gone through full-duration test fires, but I don't know about the thrust puck)
2. Aerodynamic control loss due to structural or systems failure for the flap drive mechanism
3. Aerodynamic control loss due to computational challenges
4. Restart failure
5. Thrust puck failure at restart
6. Hard/off-center landing with leg failure and tipover

I think the most likely failure modes, in descending order, are 5, 2, and 6.

I would give them a 35% chance of success.

[RealKerbal3x]

3 minutes ago, sevenperforce said:

Oh, I didn't realize we had seen the stump. If that is the case then yeah, it has to flow all the way to the engines. Which I suppose means a different valve design for LOX than for CH4.

There's definitely some complex plumbing going on around the thrust dome. Obviously there's the big CH₄ (I just realised you can do subscript/superscript ) downcomer coming through the centre of the LOX tank, but there's also the smaller downcomer from the LOX header, and it all has to feed into the engines. It'll get even more complex when we see Starships with RVacs. I have mad respect  for these engineers

Also:

 

[RCgothic]

The data is good:

The vibration is apparently nothing to worry about.

[sh1pman]

R-Boost variant is for Super Heavy, right?

[sevenperforce]

1 hour ago, sh1pman said:

R-Boost variant is for Super Heavy, right?

Right. Those will be the fixed, non-throttleable engines on the periphery of the Super Heavy once it is upgraded. Early Super Heavy boosters will likely use the regular Raptors.

[tater]

This is pretty cool to watch happening.

 

[tater]

Can't remember if it was mentioned, but they are painting SN5 and the nosecone that goes with it (no fins) white.

Dog and pony show soon, I guess.

[RealKerbal3x]

2 hours ago, tater said:

Can't remember if it was mentioned, but they are painting SN5 and the nosecone that goes with it (no fins) white.

Dog and pony show soon, I guess.

Yeah, you can see them painting the nosecone at the end of this video:

But where did you see that they're painting SN5 white as well? I don't see any sign of that.

[Codraroll]

10 hours ago, RCgothic said:

The data is good:

The vibration is apparently nothing to worry about.

"Proceeding with nosecone, mate". Any others who read this tweet again in an Australian accent?

[Nothalogh]

8 hours ago, sh1pman said:

R-Boost variant is for Super Heavy, right?

Spelled with two "R"s, for a double dose of...

[magnemoe]

16 hours ago, sevenperforce said:

Oh, I didn't realize we had seen the stump. If that is the case then yeah, it has to flow all the way to the engines. Which I suppose means a different valve design for LOX than for CH4.

I wonder how autogenous pressurization is handled for the LOX header tank. Gaseous CH4 can be piped into the CH4 main tank which in turn pressurizes the header; you only need to fire the engines for a split second before you have ullage and can open the valves to maintain head pressure. But you'd need a separate GOX press line running all the way up to the header tank. I wonder if they have a separate CH4 gas line for the CH4 header tank too, just as a failsafe.  

A loss seems more likely than not. The big question is where the loss will take place. I think there are a few particularly significant failure modes:

1. Structural/valve/engine failure from a longer-duration burn and associated heat, stress, and vibration (the engines can probably take it, since they've all gone through full-duration test fires, but I don't know about the thrust puck)
2. Aerodynamic control loss due to structural or systems failure for the flap drive mechanism
3. Aerodynamic control loss due to computational challenges
4. Restart failure
5. Thrust puck failure at restart
6. Hard/off-center landing with leg failure and tipover

I think the most likely failure modes, in descending order, are 5, 2, and 6.

I would give them a 35% chance of success.

If they saw 1,4,5 or 6 as failure points they would do far more static fires and smaller jumps. Kind of how the doubled down on pressure testing after some fails here. 
2 is most likely 3 less, some chance for the others, still say they are pretty confident so 75% chance for success. 

[RealKerbal3x]

B1051.6 is returning to Port Canaveral:

 

[sevenperforce]

2 hours ago, magnemoe said:

If they saw 1,4,5 or 6 as failure points they would do far more static fires and smaller jumps. Kind of how the doubled down on pressure testing after some fails here. 
2 is most likely 3 less, some chance for the others, still say they are pretty confident so 75% chance for success. 

5, thrust puck failure at restart, seems like the most likely failure mode to me because there’s really no way to test for it without a full-up launch. Transverse loading during gimbal is going to put some unique stresses on the thrust puck and the entire airframe. 

[Rakaydos]

5 hours ago, RealKerbal3x said:

Yeah, you can see them painting the nosecone at the end of this video:

But where did you see that they're painting SN5 white as well? I don't see any sign of that.

Speculation on NSF is that the white sections Will go to join the other lunar lander mock-ups.

[sevenperforce]

Just now, Rakaydos said:

Speculation on NSF is that the white sections Will go to join the other lunar lander mock-ups.

That’s a flex. 

[RealKerbal3x]

17 minutes ago, sevenperforce said:

That’s a flex. 

"Nice plastic mock-up! Here's our flight-proven vehicle!"