totm nov 2023 SpaceX Discussion Thread

[Flavio hc16]

10 minutes ago, KSK said:

That right there is why I like Elon's SpaceX persona.  The general openness about problems and fessing up when he made what now seems to be the wrong call.

Yes, and on the other hand, hindsight is 20/20

[tater]

So the question remains, how do/did they solve the pressure issue post SN10 in such a short time frame?

I would assume they still had autogenous pressurization, and then supplemented it with He? Maybe dump the He, and fix in terms of when, how much, and how long pressure is fed back to the headers?

[RCgothic]

I presume vestigial helium tanks are just a small mass penalty and they always planned to go back to autogenous pressurisation and so never removed the system.

[Spaceception]

4 hours ago, JIMMY_the_DOG said:

not until they get to orbit, and need the heat protection

I seem to remember that they were planning on having a full heatshield for supersonic high altitude tests. I'm sure someone else knows for sure if I need to be corrected, but that's supposed to be the step right before orbit.

[tater]

2 hours. Weather 90% go.

 

[Brotoro]

Clicking on that says Live in 34 hours, March 11, 4:10AM

[tater]

4 minutes ago, Brotoro said:

Clicking on that says Live in 34 hours, March 11, 4:10AM

Just saw that.

 

 

[tater]

 

Building a launch tower on Mars might be non-trivial  

[cubinator]

35 minutes ago, tater said:

Building a launch tower on Mars might be non-trivial  

Just grapple hook the landing spaceship on the side of Olympus Mons. Delightfully counterintuitive!

Better legs don't cut into the 100+ ton payload that much, do they?

[sevenperforce]

7 hours ago, RCgothic said:

As tater said, SN12, 13 and 14 were scrapped due to (as yet unknown) upgrades to SN15 and subsequent prototypes.

(Landings excepted) testing has gone pretty smoothly so far, so it wouldn't be worth delaying flight experience with SN15-type prototypes in order to get more flight experience with SN8-type ones. Totally worth the manufacturing practice though.

 

 

I mean I did say that the obvious fix was to use auxiliary gaseous methane tanks fed from the autogen press lines to supplement header tank pressure, used both for the header tank press and eventually for hot-gas thrusters.

If only he had listened.......

[kerbiloid]

9 hours ago, RCgothic said:

Helium ingestion caused low thrust.

The engine started speaking with funny thin voice.

[Elthy]

On the SpaceX reddit someone posted this link for an explanation of "ullage collapse": https://hydrogen.wsu.edu/2015/03/19/explaining-ullage-volume-collapse/

Its realy counterintuitive and propably a quite unique problem of Starship, as no other rocket does such a violent shake during an ordinary flight.

[Brotoro]

Mind blown.

[JoeSchmuckatelli]

how much more weight will SS have with all the tiles on it?

 

(also - if they're only on one side, doesn't that make landing a bit more... fraught?)

 

[cubinator]

11 minutes ago, JoeSchmuckatelli said:

(also - if they're only on one side, doesn't that make landing a bit more... fraught?)

Don't you see, they have lots of Mystery Goo canisters to offset the weight on the other side.

Spoiler

 

[GuessingEveryDay]

15 minutes ago, JoeSchmuckatelli said:

how much more weight will SS have with all the tiles on it?

 

(also - if they're only on one side, doesn't that make landing a bit more... fraught?)

 

They can also make the tanks slightly smaller, so the curve doesn't match the wall entirely, and is off enough to offset the weight of the tiles.

[GuessingEveryDay]

Like this:

The bold part of the line is the side with the tiles, and the blue circle is the fuel tank. They can move the tanks to offset the weight of the tiles.

[paul_c]

19 minutes ago, GuessingEveryDay said:

Like this:

The bold part of the line is the side with the tiles, and the blue circle is the fuel tank. They can move the tanks to offset the weight of the tiles.

How does that help with full/empty different CoM, etc?

[GuessingEveryDay]

Move it to the point where the two CoM are close as possible.

[zolotiyeruki]

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.

[tater]

Tiles are not terribly heavy, they can probably easily ballast the windward side if desirable since any such ballast will be outside a tank radius, whereas the CM of the tiles is inside the tanks.

[paul_c]

36 minutes ago, GuessingEveryDay said:

Move it to the point where the two CoM are close as possible.

You'll have to elaborate there - a full tank weighs much more than an empty tank. Thus, putting the tank anywhere other than centre, is not "as close as possible".

Putting something else - it could be anything, so long as its staying attached for the landing - would work fine though. I imagine there is a lot of plumbing, electrical wiring, computer modules, other rocketry stuff inside the fuselage, so it will be very easy to rebalance the CoM to the middle even with one side tiled.

[tater]

Thinking about legs, it occurs to me that we don't necessarily have to consider "external" legs (within a bulge, etc) as being under the heat shield, or perforating it.

Ie: a bulge is covered with tiles, and if the gear pop out, they must not break the tiles, or have a gap. Even a Shuttle like gear door is trouble in this reading of things.

What if the hull is in fact a perfect cylinder, covered with TPS. The legs are then outside the TPS, and themselves covered with TPS (or the gear cover made of something that functions as such)? Yes, twice the mass of TPS in those regions.

Imagine a F9 type leg where the aeroshell over it is reinforced carbon-carbon (like shuttle leading edges). This is mounted on top of a complete tile pattern. Perhaps there could be some vertical, leveling feet inside the skirt as the gear are now as well. The F9 style function as outriggers for rough ground (with crush cores), the vertical ones more like jacks.

[YNM]

2 hours ago, JoeSchmuckatelli said:

how much more weight will SS have with all the tiles on it?

(also - if they're only on one side, doesn't that make landing a bit more... fraught?)

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

[sevenperforce]

14 minutes ago, tater said:

Thinking about legs, it occurs to me that we don't necessarily have to consider "external" legs (within a bulge, etc) as being under the heat shield, or perforating it.

Ie: a bulge is covered with tiles, and if the gear pop out, they must not break the tiles, or have a gap. Even a Shuttle like gear door is trouble in this reading of things.

What if the hull is in fact a perfect cylinder, covered with TPS. The legs are then outside the TPS, and themselves covered with TPS (or the gear cover made of something that functions as such)? Yes, twice the mass of TPS in those regions.

Imagine a F9 type leg where the aeroshell over it is reinforced carbon-carbon (like shuttle leading edges). This is mounted on top of a complete tile pattern. Perhaps there could be some vertical, leveling feet inside the skirt as the gear are now as well. The F9 style function as outriggers for rough ground (with crush cores), the vertical ones more like jacks.

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.