totm nov 2023 SpaceX Discussion Thread

[NSEP]

I looked around on @ruimtevaart's twitter page and i found this:

And what is this, huh?

[sh1pman]

4 minutes ago, NSEP said:

I looked around on @ruimtevaart's twitter page and i found this:

And what is this, huh?

Dragon 2?

[sevenperforce]

46 minutes ago, NSEP said:

I looked around on @ruimtevaart's twitter page and i found this:

And what is this, huh?

THAT looks like a flight test article.

[tater]

Yes, yes it does.

[Ultimate Steve]

Aww yeah!

[CatastrophicFailure]

 

C’mon down to CrAzy ElOnS used rocket lot! Prices so low, we’re practically givin’ ‘em away! Starting this month, save even more on our huge INVENTORY BLOWOUT SALE! We’re overstocked and need to clear out space for next year’s model!

 

[PB666]

4 hours ago, tater said:

It's Sheila Jackson Lee. Not the sharpest knife in a drawer full of pretty dull knives (Congress).

On topic:

 

(I'll admit that in the small pic on the right, I assumed that the hair covers were clear, and they were all gingers with dorky haircuts)

Ooompa, loompa, doopity do, we've a climate observatory for you...

They just might be getting ready to do a beer run for the ISS. Better yet champagne, that would go over well in Zero-g.

[_Augustus_]

3 hours ago, sevenperforce said:

THAT looks like a flight test article.

It's the pad abort vehicle AKA DragonFly.

[CatastrophicFailure]

 

[DAL59]

[1101]

26 minutes ago, DAL59 said:

I think, technically, they can both win.... and the structural integrity of FH loses...

[magnemoe]

9 minutes ago, 1101 said:

I think, technically, they can both win.... and the structural integrity of FH loses...

Old KSP players know this as telescoping. However its was mostly because of high g load on weak joints. 
Structural fail caused engine and perhaps lower segment crash into the higher ones, this tended to cause an cascade fail.
Another reason why never launch kerbals in hitchhiker modules. 

[tater]

https://www.teslarati.com/spacex-bfr-mars-spaceship-launch-orbit-2020/

Quote

Speaking on a launch industry round-table at the Satellite 2018 conference, SpaceX President and COO Gwynne Shotwell revealed that the company intends to conduct the first orbital launches of BFR as early as 2020, with suborbital spaceship tests beginning in the first half of 2019.

 

[PB666]

19 hours ago, CatastrophicFailure said:

 

If I am taking the report right, NASA is blaming the usage of substandard parts and not an unforeseen material defect. Whereas Space X thinks its a material defect.
Secondarily NASA thinks SpaceX should stick only with Aerospace qualified parts in their complex constructs (i.e. tanks, fuel lines, engine mounts, etc). Even getting nitpicky to the point of specifying the type of stainless steel used. ?

[cubinator]

7 minutes ago, PB666 said:

If I am taking the report right, NASA is blaming the usage of substandard parts and not an unforeseen material defect. Whereas Space X thinks its a material defect.
Secondarily NASA thinks SpaceX should stick only with Aerospace qualified parts in their complex constructs (i.e. tanks, fuel lines, engine mounts, etc). Even getting nitpicky to the point of specifying the type of stainless steel used. ?

What's NASA got against Jeb's Junkyard?

[PB666]

19 hours ago, 1101 said:

I think, technically, they can both win.... and the structural integrity of FH loses...

MaxQ if my numbers are close is around 470,000 N per meter at 65 seconds of flight, this is divided by the forward facing area of the 2.6m diameter PL fairing nose piece and 2 @ 1.85 meter Booster nosecone ~43 meters. Although most of pressure is on the nose cone we can guess that  minimum pressure is above 10930 pa/sq. meter. Still a long way to go before hitting 50,000. BTW, drag on the falcon only counts  a little portion of lost acceleration, the major consideration I think in rocket maneuverability and structural integrity. The rockets thrust relative to sea-level performance reaches a max at around 25 seconds at 93% maximum and is below 30% as is approaches booster separation. It is in most of its flight nowhere near maximum acceleration. Because of the increased thrust to mass ratio of Falcon heavy it goes off the pad slowly, but then quickly surpasses the F9 Hepasat launch in velocity but then decelerates more rapidly approaching Mach and the F9 surpasses it velocity per unit time, The FH passes maxQ around 66 seconds into the flight (really 64 given the slow power up at launch) were as the Latest F9 hit max Q at 77 seconds. It was already pushing pressure on the nose cone harder than the most recent F9 launch. BTW gravity at MaxQ accounts for 70% of the thrust, drag 2.6% and the remaining 27.4% is acceleration, given that its was around 93% before maxQ it could have mechanically dealt with a drag force almost 4 times as much without suffering a loss of speed. However in order for it to reach that drag it would have to accelerated more quickly and hit max Q earlier and at a lower altitude with more pressure.

I wish Space X would provide their launch data to the enthusiast. I hate guessing what the COD is and their Mach drag is.
 

[tater]

 

Edited March 13, 2018 by tater

[DerekL1963]

1 hour ago, PB666 said:

Secondarily NASA thinks SpaceX should stick only with Aerospace qualified parts in their complex constructs (i.e. tanks, fuel lines, engine mounts, etc). Even getting nitpicky to the point of specifying the type of stainless steel used. ?

Referencing TR-1:  Specifying the material based on a thorough understanding of the material's properties and recommended usages isn't "nitpicking".  It's bog standard engineering practice.  It's so standard it was taught in high school metal working classes (back when high schools had metal working classes).

If SpaceX wasn't doing that, and/or if SpaceX was specifying a material contrary to the manufacturers recommendations - that's a pretty serious error.   And looking at TF-1 and -2, it looks like it might possibly be an endemic problem, not a one-off.

[Green Baron]

There are hundreds if not thousands of different alloys for combinations of temperature, pressure, brittleness, flexibility and all have their specified uses, in case of critical applications like in refineries or power plants certifications on site are made to prove that the material withstands the predicted conditions. Material science invents new alloys with stated specifications if necessary and checks the suitability in lab or under real circumstances. Protocols come with a part if regulations say so, like for instance a valve in the cooling circuit of a power plant or a reactor inlet or connector. Even screws and nuts have to fulfill requirements if used in critical applications.

Good SpaceX doesn't make airliners, they'd be in big steaming trouble had a plane crashed because of such a failure. And good that NASA hit them on the fingers to use the right stuff if they want a certification.

We aren't yet so far that high performance rockets are made from diy stuff :-)

 

[PB666]

4 minutes ago, DerekL1963 said:

Referencing TR-1:  Specifying the material based on a thorough understanding of the material's properties and recommended usages isn't "nitpicking".  It's bog standard engineering practice.  It's so standard it was taught in high school metal working classes (back when high schools had metal working classes).

If SpaceX wasn't doing that, and/or if SpaceX was specifying a material contrary to the manufacturers recommendations - that's a pretty serious error.   And looking at TF-1 and -2, it looks like it might possibly be an endemic problem, not a one-off.

That's the point of what they are doing, using the lowest cost structural unit that can withstand the task and then improving it if it fails. What NASA is essentially saying is that they expect upper stage LOX tank to fail again, whereas as SpaceX is more along the line if we just inspect more closely it wont happen again. I did notice one change, in the last 2 flight (FH and F9 Hepstat) which I have deconvoluted the acceleration data from both flights, During the Earlier flights they did they were pressing 4 to 5 g's close to stage 1/2 separation, In the last two flights its been 30.77 m/s (including the force of gravity) for falcon heavy at 145 seconds and 36.8 m/sec² for for Hispasat at 147 sec. So basically they have solved the problem by lowering A_max
The higher g-forces of the early flight aren't warranted and if you have a crew on board you will never even approach 4 gs. This I believe was the solution to their problem. It offered them no real benefit by accelerating faster past 2.5 g forces, and all they had to do was change the timing of their late stage throttle down, rather than a few seconds before meco, 10s of seconds before Meco.

I don't have the telemetry data from the flight that failed, but I think that they believe they have solved the problem by lowering the force on the part during launch. This is not a problem later in the flight because as the S2 is used (initially 2nd stage acceleration is around 1g) by the time that the g-forces increase much of the oxygen (causing the bouyancy) is gone and also much of the pressurization helium is gone.

I am not justifying their cost analysis, because if push came to shove they could make the part in-house, but I can justify the stance that if it failed because of high g-loading, then they feel that they solved the problem by inspecting the parts more carefully for defects and by lowering the g-Max . . despite your engineering background . . .that is nonetheless a valid solution.

Why does accelerating past 2.5 g not an issue. if vertical velocity is to remain constant 25^2  = 9.15^2 + X^2 Where X is the change of horizontal velocity  X = 23.26 or 93% of thrust ends up as horizontal velocity. If on the other hand your g-force is 45 

45^ = 9.15^ + X^2 = 44.05 and 98% of thrust that amounts roughly to a loss of 5% of dV over a 10 second period of a segment that lasts 155 seconds or so essentially 0.003% loss of dV on the stage.  Note 9.15 include circular velocity gravity depression. Where g losses really matter is when TWR is close to 1, then you want all the thrust that can be delivered, but even at that they are not generally close to max thrust even when they are past MaxQ, they always have room for at least one engine to fail and continue the flight as normal.

I have made this recommendation so many time here, if your first stage is bulky or you have g-sensitive parts, just slow down your ascent, passing Mach higher does wonders for alleviating dynamic pressure and also aids in relieve those g-loaded parts of stress.

 

8 minutes ago, Green Baron said:

There are hundreds if not thousands of different alloys for combinations of temperature, pressure, brittleness, flexibility and all have their specified uses, in case of critical applications like in refineries or power plants certifications on site are made to prove that the material withstands the predicted conditions. Material science invents new alloys with stated specifications if necessary and checks the suitability in lab or under real circumstances. Protocols come with a part if regulations say so, like for instance a valve in the cooling circuit of a power plant or a reactor inlet or connector. Even screws and nuts have to fulfill requirements if used in critical applications.

Good SpaceX doesn't make airliners, they'd be in big steaming trouble had a plane crashed because of such a failure. And good that NASA hit them on the fingers to use the right stuff if they want a certification.

We aren't yet so far that high performance rockets are made from diy stuff :-)

 

You mean like the jack screws on the DC-9 Md-88 to MD-90. Airlines don't subject their craft to g-loads of 50 m/sec. See other post, I think Space Xs solution is appropriate. I don't think half their flights would have made it to orbit if it was inappropriate. Airlines made alot of structural error that us oldtimers lived through, how about those pod mounts on the Airbus 380 for the rolls engines. They get corrected. Sometimes you don't want the craft to fly a certain way, like through a downburst. 

 

[DerekL1963]

8 minutes ago, PB666 said:

That's the point of what they are doing, using the lowest cost structural unit that can withstand the task and then improving it if it fails.

 

9 minutes ago, PB666 said:

I am not justifying their cost analysis, because if push came to shove they could make the part in-house, but I can justify the stance that if it failed because of high g-loading, then they feel that they solved the problem by inspecting the parts more carefully for defects and by lowering the g-Max . . despite your engineering background . . .that is nonetheless a valid solution.

No, that is not a valid solution for real world hardware.  There's a reason why it's not standard engineering practice.  There's a reason why even back alley grease monkey machine shops specify their materials.  Because SpaceX's "solution" is how you lose payloads and vehicles worth a fair fraction of a billion dollars.  If there's any remaining hardware that's not up to snuff in Falcon, or any such hardware in Dragon 2 - that's how people end up dead.

[Green Baron]

59 minutes ago, PB666 said:

You mean like the jack screws on the DC-9 Md-88 to MD-90. Airlines don't subject their craft to g-loads of 50 m/sec. See other post, I think Space Xs solution is appropriate. I don't think half their flights would have made it to orbit if it was inappropriate. Airlines made alot of structural error that us oldtimers lived through, how about those pod mounts on the Airbus 380 for the rolls engines. They get corrected. Sometimes you don't want the craft to fly a certain way, like through a downburst.

No, i mean knowingly using inappropriate materials because its cheaper. This is simply carelessness or maybe worse.

If you mean Quantas 32 with the Airbus A380 thing, fatigue cracking is very difficult to predict and find out and maintenance errors can (but should of course not) happen. It is a totally different thing if things happen in course of a complex flow or are made wilfully.

 

Edited March 13, 2018 by Green Baron

[DerekL1963]

1 hour ago, PB666 said:

I think Space Xs solution is appropriate. I don't think half their flights would have made it to orbit if it was inappropriate. Airlines made alot of structural error that us oldtimers lived through

So long as it's less than 1/2 flights inappropriate.  If it's 1/100 inappropriate, they may not have seen it yet (or if they've seen it they may not have realized the seriousness).  Or, to put it another way, it was fine to fly with leaky o-rings - until suddenly one day it wasn't.  In the same way, it was safe to fly with substandard and misspecified parts...  until one day it wasn't. 

And while airframe manufacturers made some errors that some people lived through - they also made errors that people died from.  It's disingenuous at best to leave out that half of the story.

[IncongruousGoat]

Regardless of how we feel about the cause of the failure, what'll be interesting is how SpaceX reacts to this new report. Either they decide the conclusions they came to in 2015 were correct, implying that they trust their own judgement more than NASA's, or they heed NASA's conclusions, implying that they trust NASA more than their own engineers. Either way, it has serious implications for how SpaceX are going to present themselves in the coming months and/or years.

[PB666]

1 hour ago, DerekL1963 said:

 

No, that is not a valid solution for real world hardware.  There's a reason why it's not standard engineering practice.  There's a reason why even back alley grease monkey machine shops specify their materials.  Because SpaceX's "solution" is how you lose payloads and vehicles worth a fair fraction of a billion dollars.  If there's any remaining hardware that's not up to snuff in Falcon, or any such hardware in Dragon 2 - that's how people end up dead.

Your exaggerating.