totm nov 2023 SpaceX Discussion Thread

[mikegarrison]

8 hours ago, Nuke said:

they were using a tougher material than any previous rocket. as i understand it the fts was more or less an off the shelf model that was designed to rupture aluminum tanks. solving the problem seems just a matter of using a bigger explosive device. 

I certainly hope that's not true, because it would be pretty careless of them if so.

[Codraroll]

2 hours ago, mikegarrison said:

I certainly hope that's not true, because it would be pretty careless of them if so.

Can you even get an FTS "off the shelf"? Aren't those custom made to the rocket, always?

[Nuke]

were talking maybe less than a few grams of explosives, as little as necessary, its just that starship needed a little bit more. steel just doesn't propagate cracks the way aluminum does.

as for off the shelf, that seems to be the way things go for safety equipment. you want a tried and true design, and features more than a standard demo charge (telemetry and long range remote detonation are the big ones). whether they were left over from falcon testing or obtained by a supplyer of space hardware, idk.  scott manly did a video on that not to long ago. 

[RCgothic]

 

 

[sevenperforce]

8 hours ago, mikegarrison said:

16 hours ago, Nuke said:

they were using a tougher material than any previous rocket. as i understand it the fts was more or less an off the shelf model that was designed to rupture aluminum tanks. solving the problem seems just a matter of using a bigger explosive device. 

I certainly hope that's not true, because it would be pretty careless of them if so.

The Shuttle and STS booster segments are steel, so using a similar FTS charge would make sense.

It wouldn't necessarily be careless if they ran the numbers and they looked appropriate.

3 hours ago, Nuke said:

were talking maybe less than a few grams of explosives, as little as necessary, its just that starship needed a little bit more. steel just doesn't propagate cracks the way aluminum does.

Shocking how much my prior experience comes into play here, LOL.

Crack propagation in steel is a well-studied phenomenon in the field of transportation pipelines, although it primarily focuses on stress corrosion cracking (SCC) and other fatigue-based crack propagation. That's what you end up with in thick steels at ordinarily temperatures which are subjected to large internal pressure gradients. Rapid crack propagation in rupture scenarios can follow existing crack structures, but it is much more likely to burst at one point and then have a directional propagation through the steel at the local speed of sound. I remember one instance (I won't name the provider) where fatigue-based cracking weakened a particular bend in a pipeline, and then one day they had to abruptly shut down flow in an offshoot line several miles downstream. The spike in oil pressure from that shutdown propagated backward along the pipeline through the flow and intersected the existing standing-wave pressure gradient at that joint, causing a constructively-additive pressure excursion at the precise point of the SCC fatigue. The resulting rupture released all that energy in a beautiful sinusoidal wave for about 8' along the length of the pipeline. You could actually see where the crack propagation dropped below the speed of sound and stopped.

Of course we only figured all of this out AFTER an entire LAKE of crude oil got dumped into someone's farmland, but I digress.

All that to say: the relationship between rapid crack propagation, ductility, and tensile strength is a complex one, made all the more challenging by temperature. They may have been expecting crack propagation that happened in ground tests but didn't happen under cryo conditions, or they may have simply been relying on the rupture to cause tank implosion.

4 hours ago, Nuke said:

as for off the shelf, that seems to be the way things go for safety equipment. you want a tried and true design, and features more than a standard demo charge (telemetry and long range remote detonation are the big ones). whether they were left over from falcon testing or obtained by a supplyer of space hardware, idk.  scott manly did a video on that not to long ago. 

SpaceX uses the same FTS explosive initiator, detonator, and linear shaped charges used by NASA on the Shuttle and STS main tank and boosters. Although the shaped charges are linear, they do not run the full length of the tanks.

[Exoscientist]

23 hours ago, sevenperforce said:

If there's an actual problem, then we should identify the problem, characterize the problem, and determine whether it was a lapse in oversight or an unknown unknown...not create an independent commission to tie things up endlessly with no actual goal or objective.

 So you’re saying the FAA should investigate itself?

  Bob Clark

[sevenperforce]

5 minutes ago, Exoscientist said:

23 hours ago, sevenperforce said:

If there's an actual problem, then we should identify the problem, characterize the problem, and determine whether it was a lapse in oversight or an unknown unknown...not create an independent commission to tie things up endlessly with no actual goal or objective.

 So you’re saying the FAA should investigate itself?

I'm saying the FAA should investigate the incident.

Because that is its job.

There is no indication or suggestion (other than wild unsourced and unevidenced speculation) that that FAA ought to be investigated as an institution.

Failure investigations and process lapse evaluations happen all the time across industry and regulators.

[JoeSchmuckatelli]

13 minutes ago, sevenperforce said:

the FAA should investigate the incident.

They probably are / already have.

Strong suspicion that FAA simply asked SX what happened (beyond what everyone could see) and SX gave them open access.

No need to shut SX down for months for some hyped up Congressional Inquiry like dog-and-pony show.

Smart folks from the FAA look at what happened and what SX plans to do about it, write a report... done.

[mikegarrison]

By the way, the US *does* have an independent agency to investigate mishaps and accidents involving vehicles of all types: the NTSB.

I don't know, however, if rockets are part of their remit.

Edited May 24, 2023 by mikegarrison

[sevenperforce]

38 minutes ago, JoeSchmuckatelli said:

54 minutes ago, sevenperforce said:

FAA should investigate the incident.

They probably are / already have.

Strong suspicion that FAA simply asked SX what happened (beyond what everyone could see) and SX gave them open access.

No need to shut SX down for months for some hyped up Congressional Inquiry like dog-and-pony show.

Smart folks from the FAA look at what happened and what SX plans to do about it, write a report... done.

Yes, they are absolutely already investigating.

The suggestion by Bob seems to be that because there was something he thinks was a failure, that means we can infer a failure in the FAA's oversight process, and that means we can infer a fundamental flaw in the FAA oversight process, and that means we can infer that FAA is incapable of rectifying the fundamental flaws in its oversight process, and that means we can infer an independent commission is necessary to fix the inferred problems in the FAA.

[tater]

4 minutes ago, sevenperforce said:

Yes, they are absolutely already investigating.

 

"The NTSB will be the lead investigative agency for commercial space launch or reentry mishaps that result in: 

• A fatality or serious injury to any person, regardless of whether the person was on board the commercial space launch or reentry vehicle, or
• Damage to property not associated with the commercial space launch or reentry activities or the launch site, from debris that could reasonably be expected to cause death or serious injury.

The FAA will be the lead investigative agency for all other commercial space mishaps."

This from https://www.ntsb.gov/news/press-releases/Pages/nr20220909.aspx

Agreement between FAA/NTSB on sharing some duties WRT commercial space. Not sure if this particular incident qualifies under the second bullet. As you have said above, had the FTS been initiated lower, where the possible debris field might actually be "expected to cause death or serious injury", there's a chance it might have actually unzipped the vehicle promptly because the aero forces would have been far higher than they were at 30-whatever km. If that's in doubt enough, then seems like NTSB participates for sure.

[tater]

Arabsat moving to Friday.

[tater]

 

6 hours:

 

[Spaceception]

SN25/B9 are next for flight testing. 

 

[tater]

 

[JoeSchmuckatelli]

Let's hope those are real time estimates! 

[Minmus Taster]

49 minutes ago, tater said:

 

Adjusting for Elon time were at a brisk 6 months + the lawsuits! So another year at least unless elon can get miracle max out of retirement  : P

[tater]

 

9 minutes ago, Minmus Taster said:

Adjusting for Elon time were at a brisk 6 months + the lawsuits! So another year at least unless elon can get miracle max out of retirement  : P

I don;t get the continued "elon time" nonsense. As dates are closer to immediate, the slop decreases. Those estimates he gave are entirely reasonable.

[Meecrob]

2 hours ago, Minmus Taster said:

Adjusting for Elon time were at a brisk 6 months + the lawsuits! So another year at least unless elon can get miracle max out of retirement  : P

I get Elon always presents the most optimistic timeline possible with zero errors whatsoever, but compared to lots of other companies/organizations, his timelines aren't all that far off. Especially considering this is spaceflight. Starliner, SLS, Virgin Galactic, etc.. It seems more accurate to say that most space companies have no clue when their stuff will be ready.

 

Edit: How could I forget the whole "Where are my engines, Jeff" thing?

Edited May 27, 2023 by Meecrob

[Royalswissarmyknife]

14 minutes ago, Meecrob said:

Edit: How could i forget the whole "Where are my engines, Jeff" thing?

Where's my launch license, FAA?

[tater]

Live

[tater]

T-4 min

 

Also, missed this:

 

Liftoff

Max q

 

MECO

Sep

SES-1

 

[tater]

Entry burn

SECO-1

Landing. Another boring trip to space and back

[tater]

 

 

 

Edited May 27, 2023 by tater

[tater]