totm nov 2023 SpaceX Discussion Thread

[Brotoro]

How much of a gap is a problem?  Can't the bulges (that hinge outward to release the gear) be fit tight enough to the body to prevent gas entry? Perhaps if you pressurize the inside of the bulges? (Pressurize with what? Methane? They were thinking of using methane to cool the skin earlier. But it would make a disconcerting exciting fire ball upon deployment. Maybe pressurize the bulges with methane/LOX compunction products...have a small APU burner to make the gas?)

[sevenperforce]

1 minute ago, YNM said:

I've always assumed that it'd be a little like 'ye olde' Shuttle with thermal insulation on the other, non-heatshield side...

I am pretty sure I remember Elon specifically saying that going with stainless steel means you need no leeward shielding or insulation at all.

[Brotoro]

*combustion products

[sevenperforce]

1 minute ago, Brotoro said:

How much of a gap is a problem?  Can't the bulges (that hinge outward to release the gear) be fit tight enough to the body to prevent gas entry?

If they fit tight enough to prevent gas entry then you don't need any heat shield underneath.

I mean, I suppose that's the brute force solution. Use F9 legs covered in reinforced carbon-carbon instead of just the ablative black paint on the current F9 legs. They close flush to the stainless steel skin all the way around and you simply cut the tiles to wrap around them. Simple enough. You don't even need to bother with a bulge.

[YNM]

Just now, sevenperforce said:

I am pretty sure I remember Elon specifically saying that going with stainless steel means you need no leeward shielding or insulation at all.

What, they don't need to roll the tanks ? Or is it going to be stainless side to the Sun, heat shield side away all through interplanetary transit ? Honestly I don't think the tiles are that heavy, even if it is they can just run all the pipes etc. on the other side.

Also at the very least you need insulation up in the crew compartment, although this would cover all sides equally.

[sevenperforce]

1 minute ago, YNM said:

What, they don't need to roll the tanks ? Or is it going to be stainless side to the Sun, heat shield side away all through interplanetary transit ? Honestly I don't think the tiles are that heavy, even if it is they can just run all the pipes etc. on the other side.

This was back when they were exploring transpiration cooling rather than the heat shield tiles, but the same principle applies for the leeward side.

He's talking about re-entry, though. Not interplanetary transit.

I don't think the weight offset from the tiles is significant.

[YNM]

4 minutes ago, sevenperforce said:

He's talking about re-entry, though. Not interplanetary transit.

Well, they need to start thinking about that... Pretty sure Shuttle's insulation pads weren't designed with re-entry in mind really, but rather for keeping the craft warm or something. Apollo needs the roll program because of the stainless I suppose... Orion capsule is covered with Nomex on the non-heatshield side.

Edited March 10, 2021 by YNM

[Brotoro]

Maybe the offset center of mass with the tiles installed sits over one of the Raptors. Not as much tilt needed during landing.

[sevenperforce]

Just now, Brotoro said:

Maybe the offset center of mass with the tiles installed sits over one of the Raptors. Not as much tilt needed during landing.

Starship needs to be able to come down on any of the three Raptors; that's the whole engine-out idea (and the reason they went from the 2017 IAC design with 2 SL Raptors to the present design with 3).

Also, the offset center of mass with the tiles installed sits opposite the single dorsal engine, between the two ventral engines.

[tater]

17 minutes ago, sevenperforce said:

The mounting points for the leg (for the F9 style, the telescoping cylinder) would have to pass through the interior heat shield. 

You would need a flush fit during re-entry or you would have re-entry plume recirculation between the carbon-carbon aeroshell and the inner tile pattern, in precisely the place where the machinery of the legs is stored.

If you have a flush fit, you don't need the underlying tile pattern.

Yes, the struts, etc do join to the steel, with TPS all around them—that region would then be covered by TPS on the actual gear. Take an F9 type leg, with the outer part when folded against the tank being TPS. Underneath it, not steel—but tiles. Yeah, there's a missing tile where the struct attaches, but that is covered by the gear itself (TPS).

Edited March 10, 2021 by tater

[sevenperforce]

2 minutes ago, tater said:

Yes, the struts, etc do join to the steel, with TPS all around them—that region would then be covered by TPS on the actual gear. Take an F9 type leg, with the outer part when folded against the tank being TPS. Underneath it, not steel—but tiles. Yeah, there's a missing tile where the struct attaches, but that is covered by the gear itself (TPS).

But why would you need the tiles underneath? If the outer part can be folded flush against the tank then it provides all the TPS for that region.

[tater]

2 minutes ago, sevenperforce said:

But why would you need the tiles underneath? If the outer part can be folded flush against the tank then it provides all the TPS for that region.

There seems to be 2 elements to the TPS system. A blanket, that is delicate, and a tile system above. Run the blanket over the entire windward side. Tile it, and wher ethe gear fold against the outside, the concern is infiltration. You could either have the gear (I'm thinking F9 for simplicity and proof of concept, it could be different in shape/size) mount in flush (cutting the tiles so the gear folds into the gap), but that is a series of long gaps for infiltration. Instead, run the tiles UNDER the place where the TPS covered leg touches, so any infiltration hits tile, or tile gaps that change direction (hexes). If mass is that much of a concern, past the 1 partial tile the gear overlaps, just cover the TPS blanket with a sheet of something to protect it (it's cloth).

[sevenperforce]

2 minutes ago, tater said:

You could either have the gear (I'm thinking F9 for simplicity and proof of concept, it could be different in shape/size) mount in flush (cutting the tiles so the gear folds into the gap), but that is a series of long gaps for infiltration. Instead, run the tiles UNDER the place where the TPS covered leg touches, so any infiltration hits tile, or tile gaps that change direction (hexes). If mass is that much of a concern, past the 1 partial tile the gear overlaps, just cover the TPS blanket with a sheet of something to protect it (it's cloth).

Ah,  yes, I didn't think about the long gas flow path. 

But yeah if you do it that way you don't even have to cut the tiles. Just have them extend inward.

You would simply omit tiles that were completely shrouded by the leg.

[tater]

1 minute ago, sevenperforce said:

You would simply omit tiles that were completely shrouded by the leg.

You could, but seriously, compared to 100t of steel, how much mass is that? Sure, it all comes out of payload mass, but this is not a smallsat launcher.

It's a few square meters. Still you could throw a RCC sheet over the gear shaped hole (with hex edges to match the hexes) just to protect the blanket. Course maybe that mass is not hugely different than the tile mass.

 

[magnemoe]

5 hours ago, zolotiyeruki said:

Given that they're planning to land on 1-2 engines anyway (i.e. center of thrust is offset), plus the gimbal range, I'm not particularly concerned about the small shift in CoM due to the tiles.  Besides, if you double-hull the windward side, that would shift the fuel leeward, but you'd be adding a whole second layer of stainless steel on the windward side, too, therefore adding more weight where you don't want it.

This, you only have fuel in the header tank then landing. Now you could offset the header tank but this would change CoM more sideways during landing. 

[zolotiyeruki]

1 minute ago, magnemoe said:

This, you only have fuel in the header tank then landing. Now you could offset the header tank but this would change CoM more sideways during landing. 

And the LOX header tank in the nose shifts the CoM higher, away from the engines, making the gimballing even more effective

[tater]

 

 

[RCgothic]

 

 

[Brotoro]

Music!

Live at T minus 11 minutes

[Brotoro]

Falcon 9 is in Startup

And we have liftoff!

Is this tracking camera Infrared?

Stage sep good

Interesting ground view of stage 2 burning away from booster

Entry burn looked norminal. No excess nasty flaming.

Booster landed. Huzzah!

[Brotoro]

Good preliminary orbit.

[sevenperforce]

That was the shortest MVac burn I’ve ever seen. 

[magnemoe]

Just now, sevenperforce said:

That was the shortest MVac burn I’ve ever seen. 

The second burn or circulation? I missed it but they tend to be short and you want it to be as short as possible. Now as they run lots of starlink launches they probably optimize trajectory. 

[sevenperforce]

2 hours ago, magnemoe said:

The second burn or circulation? I missed it but they tend to be short and you want it to be as short as possible. Now as they run lots of starlink launches they probably optimize trajectory. 

The second burn. It was so short the bell didn't even glow.

EDIT: Here's the burn. The startup appears to be longer than the burn itself.

Incredibly precise. It's also really really cool to see that tiny chunk of ice suddenly break free under the acceleration, tumble down the engine bell, then get yeeted off into the cosmos by the exhaust plume.

[Serpens Solidus]

29 minutes ago, sevenperforce said:

Incredibly precise. It's also really really cool to see that tiny chunk of ice suddenly break free under the acceleration, tumble down the engine bell, then get yeeted off into the cosmos by the exhaust plume.

Looks like it got yeeted off into Earth instead