totm nov 2023 SpaceX Discussion Thread

[Hotel26]

6 hours ago, Exoscientist said:

nytimes.com

There's your major malfunction...

Edited Monday at 10:36 PM by Hotel26

[tater]

Double header tonight, wonder if I will be able to see the VSFB one from here?

[tater]

VSFB NASA launch scrubbed.

[FleshJeb]

10 hours ago, Nuke said:

id also not rule out sabotage either

"Never attribute to malice that which is adequately explained by incompetence." --Hanlon's Razor

[Nuke]

2 hours ago, FleshJeb said:

"Never attribute to malice that which is adequately explained by incompetence." --Hanlon's Razor

i said i wouldnt rule it out, i didnt say it was likely. i can imagine that security at spacex is rather high.

[Meecrob]

On 3/9/2025 at 10:53 PM, darthgently said:

We mostly just watch him pwn himself these days

Good to know! Awesome launch the other day, can't wait to see what fixes are in store

15 hours ago, Exoscientist said:

p. SpaceX needs a true Chief Engineer making the engineering decisions

Sorry, I'm taken designing my cargo pods

[Hotel26]

5 hours ago, FleshJeb said:

"Never attribute to malice that which is adequately explained by incompetence."

I don't want to be "methodical" or anything, but once you've ruled out incompetence (or, at least, "failed to attribute it"), it is clear that Hanlon's Razor does not rule out other possibilities, yes?

You could, for example, apply a maxim from an investigative field, alternatively, and look for "means, Motive and opportunity".  But I think we are far from that yet...

Let's wait and see what facts and determinations are made, why don't we?

Edited yesterday at 09:30 AM by Hotel26

[Lisias]

6 hours ago, FleshJeb said:

"Never attribute to malice that which is adequately explained by incompetence." --Hanlon's Razor

Once is an accident; twice, a coincidence; thrice is a conspiracy!

[darthgently]

SpaceX seems very certain it is a resonance issue in the new plumbing.  I’m thinking they probably have simulation or sensor data reasons for zeroing in on this.   [snip]

Edited 20 hours ago by Vanamonde
Avoid politics, please.

[darthgently]

Well played

 

[tater]

 

[Minmus Taster]

1 hour ago, darthgently said:

Well played

 

To be fair Saturn V wasn't reusable and was designed almost 60 years ago but they raise a good point, what exactly is the benefit of those downcomers though? They seem like they take up space and can easily fracture under strain.

[darthgently]

3 minutes ago, Minmus Taster said:

To be fair Saturn V wasn't reusable and was designed almost 60 years ago but they raise a good point, what exactly is the benefit of those downcomers though? They seem like they take up space and can easily fracture under strain.

I think they are supposed to better guarantee props flow under strange inertial conditions.  

I’m thinking that if they are going this route they need to have less symmetry in the plumbing so that none of the pipes has the same resonant frequency as any other so any resonance in isn’t amplified  back to it by the others.

This could perhaps be done by welding on various weights at various points along the pipes without much added weight.

 I’m just having armchair fun and am not being critical nor think I have any real answers

[zolotiyeruki]

If you're looking to shift the resonant frequencies of the downcomers, it'd probably be lighter to change the stiffness rather than the weight.

[tater]

 

[darthgently]

18 minutes ago, zolotiyeruki said:

If you're looking to shift the resonant frequencies of the downcomers, it'd probably be lighter to change the stiffness rather than the weight.

Sure, like tightening and loosening guitar strings. Makes sense.

 Tune them such that none of the resonant freqs has a common factor with any other perhaps

Edited yesterday at 02:57 PM by darthgently

[tater]

Testing this will of course be difficult, has to be simulated because the problem is at a low propellant state (mass), hence at high g.

I guess they should build  test rig/vehicle that somehow mimics 4 g—that's the only way! Even if such a rig requires 10 years and 10s of billions of $, that would clearly make more sense than throwing away a few tens of millions of $ on a Starship over the Gulf!

Edited yesterday at 03:06 PM by tater

[Exoscientist]

 The suggestion that a Moon landing can be mounted with a launcher at ca. 60 ton payload capacity is derived from a proposal from the early 1990's  for a low cost follow-up to Apollo called Early Lunar Access(ELA):

Moon denied: the 1993 Early Lunar Access proposal.
by Dwayne A. Day
Monday, January 9, 2023

https://www.thespacereview.com/article/4511/1

 It would use a Gemini-sized capsule for a 2-person crew lunar mission at ca. 3 tons dry mass for the capsule. Studies had shown the Gemini capsule could be adapted to carry a crew of two for a lunar mission. Unlike, Apollo there would be only this one crew module that would go all the way to the surface of the Moon and back to Earth, in contrast to the Apollo architecture that had a second smaller, crew module for the lunar lander.

 Interestingly, the hydrolox lunar lander stage would have about the same gross mass as the fully fueled Blue Moon MK1 lander with a 3 ton dry mass crew capsule added, i.e., ca. 25 tons.

The plan was to use only one other additional in-space stage, a Centaur-like stage to perform the translunar injection(TLI) burn. This stage and the lander stage would be launched separately and link up in low Earth orbit. A spaceflight rule-of-thumb is a hydrolox Centaur-like stage can get a payload mass of equal size to its prop load mass to TLI. So a hydrolox stage would be needed at 25 tons or more prop mass. Centaur itself did exist at ca. 20 tons but a slightly larger one would be needed. The ELA plan was proposed in 1993, perhaps they were thinking of an extended Centaur. In any case, a hydrolox stage of the needed size did come into play with the Delta IV Heavy's upper stage, first launched in 2004.

 Besides that problem, the plan was to have the 25 ton hydrolox lander launched on the Space Shuttle. The shuttle then would need its payload capability expanded slightly to 25 tons. Another issue is NASA for safety reasons did not want a hydrolox stage in the shuttle payload bay.

 For these reasons the plan did not progress beyond just the proposal stage. But now we do have a hydrolox upper stage in the DIVH upper stage of the needed size to do the TLI burn. And we do have a launcher at 60+ ton capacity in the Falcon Heavy. The Falcon Heavy would need to be man-rated or Falcon 9 would need to be launched separately to get the crew to orbit.

 The New Glenn at 45 ton payload capability as partially reusable likely could also get ca. 60 tons to orbit expendable.

Edited 22 hours ago by Exoscientist
Clarity

[darthgently]

2 hours ago, tater said:

Testing this will of course be difficult, has to be simulated because the problem is at a low propellant state (mass), hence at high g.

I guess they should build  test rig/vehicle that somehow mimics 4 g—that's the only way! Even if such a rig requires 10 years and 10s of billions of $, that would clearly make more sense than throwing away a few tens of millions of $ on a Starship over the Gulf!

Yep.  Sometimes the cheapest simulation is the real world.  Very often actually

[Vanamonde]

Avoid politics, please. Some commented removed. 

[tater]

 

[tater]

 

[darthgently]

22 hours ago, darthgently said:

Avoid politics, please

It wasn’t, but okay

[Minmus Taster]

I found this theory in the comments of TheSpaceEngineers's S34 failure animation, personally I think it's promising, thoughts anyone? If the issue does in fact lie in the downcomers can they been reenforced? Or would changing the design in exchange for lower Raptor 3 performance actually be beneficial for the engines survival.

Spoiler

Very long writeup....So theory is....
1 - High levels of LOX in the tank dampened the effects of the harmonic frequencies/vibrations since the new RVac methane downcomers are mostly submerged at that point. 
1.1 - The new downcomers are likely susceptible to vibrations because they are long and thin...just think of a Guitar String..
2 -  As LOX starts depleting, more of the RVac downcomers gets exposed and with no LOX to dampen their vibrations, it starts causing damage.
3 -  E4 RVac methane downcomers eventually rupture. This reduces the amount of Methane thats is being fed to RVac No. E4 which leads to 2 possible effects.
3.1 - Methane is needed for Regenerative cooling of the raptor engines. If not enough methane is being fed, these engines might overheat, its likely what we saw on the engine camera view of RVac E4 with its burnthorugh on the engine bell.
3.2 -  Not enough methane also means the engine suffers a reduction in thrust, as highlighted by SpaceEngineer at T+7.43 so the ship starts pitching over to the side of the failing RVac E4.
3.3 -  Not enough methane also means the engine is running at oxygen-rich combustion, which is very destructive (Look at SN8)
4 -  Both Oxygen-rich combustion and severe overheating combined caused a catastrophic and energetic failure of RVac no. E4. This blast instantly knocks out 2 of the Sea Level raptors and heavily damages the 3rd one. The 3rd Sea level Raptor with its heavy damage eventually fails as well catastrophically.
5 - S34 starts tumbling due to asymmetric thrust from the 2 remaining RVacs that cant gimbal.......and the rest is history.

Key Points:

## S34's Fix - It likely didnt work because the conditions they tested S34 is inaccurate and doesn't replicate S33's conditions at failure. 
- As I highlighted, the problem starts as LOX levels starts to get low. 
- However, S34 conducted a 1min static fire test with FULL LoX tanks. So the data they gathered is already incorrect leading to improper fixes.
- The fact that S34 failed in the same manner and within the same time-frame as S33 leads credence to the idea that the root cause of the failure wasn't addressed properly or at all.
- Thus, they need to redo the test with S35 static firing with a low level of LOX. They either need to anchor it down or add heavy ballast in the payload or fully fuel the methane tanks.

## Bandaid solution?? - If SpaceX desires to keep both S35 and S36 both of which are too advanced in their production for major revisions. They could sacrifice mass and HEAVILY reinforce the new V2 RVac downcomers with numerous stringers, supporting frames, and other reinforcements to atleast minimize the damage caused by the vibrations.

## Major revision?...A Block 1.75 Starship - If SpaceX engineers thinks that the V2 design is way too flawed. They could revert the entire downcomer and its associated plumbing in the engine section back to V1 spec. This seems only applicable to Ship 37 onwards, which are still not stacked and incomplete and thus can take in major revisions in designs. So you are left with V2 Flaps, V2 thermal protection system, V2 Tank size, V2 hull, V2 payload section with a V1 downcomer and engine plumbing, basically a Block 1.75 Starship

- The V2 plumbing are likely designed for higher fuel flow needed by Raptor 3. Reverting to V1 plumbing might result on a reduction thrust to Raptors-3. However, it might be beneficial for for reliability as Raptor 3 running below its designed/specified thrust output might actually lessen the stress and wear on the engine.

- At this point of the above decision...that basically means relegating S35 and S36 to testing articles to further learn more about the harmonic frequency problem for a permanent and effective fix if SpaceX still desires to keep the V2 design eventually.

[Nuke]

the bandaid soluton, or the 1.75 downgrade might at least allow the other v2 features to be tested (still havent seen the new flaps or tps in action yet). then take what you learn for v3. you cant do that if you cant get the v2 features to orbit. we do know the v1's reentry system is probibly non viable for reusability (probibly fine for ships that never come home, like tankers and lunar lander vehicle, or disposable configs). a starship 2.25 is probibly the better option since we know what happens when you fix the wrong thing. seems they addressed the attic fires instead of trying to figure out what was leaking.

Edited 4 hours ago by Nuke