totm nov 2023 SpaceX Discussion Thread

[magnemoe]

11 minutes ago, mikegarrison said:

I think you underestimate the amount of energy released if a disk fails. It's usually treated for survivability design purposes as an infinite energy event.

No an infinite energy event is an high megaton nuke going off inside your structure. 
An catastrophic fail of an turbo pump is simply an large split bomb who is much easier than spin stabilized tungsten slugs from an 20mm gun. 
Apache gunships and A10 close in attack planes are very resistant to this from most relevant angles so they will fail in an dogfight who is outside their scope. 

More extreme for an falcon 9, you don't care about the outside only the other engines and the piping including the shut of valve. Your trust chamber is part of the armor as its now junk anyway. 
One benefit is that most of the force and sharpnels will come radial from the turbo pump. 

if you have one engine this is obviously irrelevant as if it fail mission fail, but if you have lots of engines its very relevant. 
Not sure how you test this realistic, saw an large vacuum pump at university there some blades had failed, not the ring itself but it was an cascade among the blades so we had an pile of small leafs in the bottom of it. Yes this was smaller and much heavier build so it would contained ring fails but still weird. 

 

[mikegarrison]

I think you misunderstand "infinite energy" in this context. It's obviously not physical reality, but an assumption for the purpose of risk mitigation. No practical amount of containment can be assumed to always withstand a disk failure, so you assume it *is* going to be uncontained. I'm not talking about a blade-out here, I'm talking about a whole disk failure.

The failure analysis then is focused on whether that one event will doom the vehicle completely or whether it can be survived. An example of this in airplane design was when United Airlines Flight 232 had a disk failure that took out all three supposedly redundant hydraulic systems and led to the semi-controlled crash at Sioux City. It's also a limiting factor for airplane altitudes, because if the engine is in line with the pressurized part of the cabin it must be assumed that a disk failure could lead to rapid depressurization. (This is why most airliners are limited to ceilings just above 40,000 feet. Bizjets that fly higher typically have the engines mounted where a disk failure won't immediately depressurize the cabin.)

Anyway, having so many engines together carries a strong risk of fratricide. If they are relying on armor to keep that from happening, that would lead to a very heavy structure, which is typically the opposite of what you want in a flight vehicle. I'm curious how they are addressing this risk in a human-rated vehicle.

Edited July 24, 2019 by mikegarrison

[mikegarrison]

See also https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/22187

AC20-128A "Design Considerations for Minimizing Hazards caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor Failure"

It's AC25-20 that says "Failures or a combination of failures which expose the occupants to: (1) cabin altitudes in excess of either 25,000 feet for more than 2 minutes, or (2) cabin altitudes that exceed 40,000 feet for any duration, shall be shown to be extremely improbable."

That's why airplanes that fly above 40,000 feet have to show that they can get below 40,000 feet quickly enough to prevent the cabin altitude from ever rising above 40,000 feet. That's a function of the size of the cabin, the amount of air being pumped in, and the assumed size of the hole that is letting the air out. Uncontained engine failures are part of the assumptions that play into the size of the hole you have to assume.

Edited July 24, 2019 by mikegarrison

[kerbiloid]

They can give it a name: "Jingle Bells effect".
One failed rocket bell makes others follow.

[Guest]

3 minutes ago, kerbiloid said:

They can give it a name: "Jingle Bells effect".
One failed rocket bell makes others follow.

The bells aren’t the point of failure tho o_o?

[kerbiloid]

1 minute ago, Dale Christopher said:

The bells aren’t the point of failure tho o_o?

Any bell doesn't jingle itself. Its mechanics does. Here it's a turbopump or so.

[Guest]

Spoiler

A bell with a blewn up turbo pump is a relatively quiet one tho since it’s no longer producing a permanent explosion >_<

mebe call it a runaway silent night reaction since all the engines will probably shut down from cascading fault detection >=]

 

Edited July 24, 2019 by Guest

[kerbiloid]

Spoiler

4 hours ago, Dale Christopher said:

since all the engines will probably shut down from cascading fault detection

In flight? Great.

 

Edited July 24, 2019 by kerbiloid

[Guest]

Spoiler

Fall out of the sky syndrome? effect >_<

 

Edited July 24, 2019 by Guest

[kerbiloid]

Spoiler

4 hours ago, Dale Christopher said:

Fall out of the sky syndrome? effect >_<

After the "jingle bells" the things "falling out of the sky" are very expectable.
Santa does this every year.

 

Edited July 24, 2019 by kerbiloid

[Geonovast]

Having to click on spoilers to see replies is getting pretty tedious, guys.

[tater]

23 minutes ago, Geonovast said:

Having to click on spoilers to see replies is getting pretty tedious, guys.

It's to hide stuff that is pretty off topic.

On topic:

Look at stage 2.

https://www.nasaspaceflight.com/2019/07/falcon-9-launch-dragon-third-crs-18/

It's for thermal control between LOX and RP-1.

[tater]

Pre-CRS-18 presser:

 

 

[Geonovast]

I'm confused... won't them changing anything on the F9 affect their human certification?  Or are they hoping to get another 7 flights in beforehand?

[tater]

Just now, Geonovast said:

I'm confused... won't them changing anything on the F9 affect their human certification?  Or are they hoping to get another 7 flights in beforehand?

They have their cert flights done, the changes were to the booster. CRS missions are not crew missions, so they can still experiment, and NASA still signs off I bet.

[tater]

 

They have the launch abort system removed, among a few other more minor changes (likely mass reduction).

 

(I doubt that paint color (or lack of paint) changes certification, anyway)

[tater]

 

[Nightside]

12 minutes ago, tater said:

I doubt that paint color (or lack of paint) changes certification, anyway

That thing is looking pretty rough at this point. 

[tater]

 

[Flying dutchman]

How about the expected hop?

[tater]

6 minutes ago, Flying dutchman said:

How about the expected hop?

Still looks to be on schedule. Road closure is such that I think it's after the CRS-18 launch.

[tater]

 

[RealKerbal3x]

5 hours ago, tater said:

 

They have the launch abort system removed, among a few other more minor changes (likely mass reduction).

So...what does this mean for the reusability of crewed Dragon V2s now? Will they not be reused at all, or are they planning to fly them with crew multiple times? I’m confused now

Edited July 24, 2019 by RealKerbal3x

[tater]

11 minutes ago, RealKerbal3x said:

So...what does this mean for the reusability of crewed Dragon V2s now? Will they not be reused at all, or are they planning to fly them with crew multiple times? I’m confused now

The NASA contract pays for a new Crew Dragon each time. They decided to alter Crew Dragon slightly for a dedicated cargo version (small changes, mostly), presumably just to run the production line and bang them out. Cargo versions will be nominally assumed to fly 5 times each, but more if that works out. Used Crew Dragons will be SpaceX property to do with as they please, I suppose.

[RealKerbal3x]

4 minutes ago, tater said:

The NASA contract pays for a new Crew Dragon each time. They decided to alter Crew Dragon slightly for a dedicated cargo version (small changes, mostly), presumably just to run the production line and bang them out. Cargo versions will be nominally assumed to fly 5 times each, but more if that works out. Used Crew Dragons will be SpaceX property to do with as they please, I suppose.

Does the contract allow reusing spacecraft on crewed flights, or does it specifically state that a newly built spacecraft must be used on every flight?