F9 Block 5 Updates and Discussion

[OnWithTheShow]

Think it might just be warm air ducted out off the TE that keeps the frost off of the SpaceX logo?

[zhangmdev]

The inside of legs is painted white. That is new.

[biosehnsucht]

I assumed the semi-active water cooling would just be having a resevoir of coolant and pumping it around the hot spots and less hot spots to spread the heat load out. I doubt they're spraying water out... seems unlikely to be effective. The fins themselves clearly don't need it.

edit: might not even need pumping if you essentially used giant heat pipes ... though I'm not sure if the physics holds up at scale for that to work, and if they'd be overly problematic in a rocket launch noise/vibration environment ...

[ZachS09]

The inside of legs is painted white. That is new.

Several Block 3/4 boosters had their landing leg interiors painted white.

[Kabloona]

40% margin is not a requirement

Jim, I thought 1.4 structure margins were a requirement for manned rating.

You are showing requirements for pressurized vessels and not structures.

Also, I don't think CCP is under contract for that document.

FS = 1.4 is definitely required for structure in that same document, JSC-65828 para 3.3.1.2.

How could CCP not be requiring structural margins of 1.4 for their own astros? It was definitely a requirement for Shuttle. When we had a payload on Shuttle, all our ASE structure was required to have FS = 1.4, and the safety reviews at JSC were brutal. I wasn't even a structural engineer, and that requirement got burned into my brain from seeing the grilling the structures guys got.

Also, Elon just cited the 1.4 requirement in his latest telecon. I can't imagine he was talking only about pressure vessels. And F9 was designed from the get-go to be human-rated. I'd be astonished if they weren't already at 1.4 for structure.



Update: Here's Elon's direct quote from his recent telecon. He's definitely talking about FS = 1.4 on structure:

Elon Musk: Man. There are 1000s and 1000s and 1000s of requirements. [] for even advanced rocket people to know what I'm talking about. So think of, so a human-rated rocket has to have high-end margins of safety in the structural -- [audio cut for 4s] -- vehicle, like a typical rule of thumb would be, for launching a satellite, you need to design the rocket to 25% margins, like essentially, take your worst-case flight load, worst possible scenario that the rocket would encounter, and then add 25% to that, the rocket has to be designed 25% above the worst-case load, for the case of a satellite launcher. For a human-rated launcher, it has to be designed to 40% of the worst-case load.

(bolding mine)

https://gist.github.com/theinternetftw/5ba82bd5f4099934fa0556b9d09c123e

(thanks to user theinternetFTW for the transcript)

[su27k]

I believe the FS=1.4 was in an old standard back in 2006 or so, the requirement was removed later because Ares I couldn't meet it. You can find tons of discussion in old Constellation threads, for example this one: https://forum.nasaspaceflight.com/index.php?topic=14408.msg317674#msg317674

Also:

https://forum.nasaspaceflight.com/index.php?topic=9460.660

https://forum.nasaspaceflight.com/index.php?topic=21269.520

https://forum.nasaspaceflight.com/index.php?topic=18311.msg499472#msg499472

https://forum.nasaspaceflight.com/index.php?topic=13959.msg306503#msg306503

It looks like FS=1.4 was used to exclude EELV from Constellation, this was happening when F9 was first designed, so it's not surprising that the requirement was included in F9's initial design. But it would be interesting if Block 5 still adhere to this standard, since it's no longer strictly required, and it must have no-small amount of performance penalty.

[AncientU]

I believe the FS=1.4 was in an old standard back in 2006 or so, the requirement was removed later because Ares I couldn't meet it. You can find tons of discussion in old Constellation threads, for example this one: https://forum.nasaspaceflight.com/index.php?topic=14408.msg317674#msg317674

Also:

https://forum.nasaspaceflight.com/index.php?topic=9460.660

https://forum.nasaspaceflight.com/index.php?topic=21269.520

https://forum.nasaspaceflight.com/index.php?topic=18311.msg499472#msg499472

https://forum.nasaspaceflight.com/index.php?topic=13959.msg306503#msg306503

It looks like FS=1.4 was used to exclude EELV from Constellation, this was happening when F9 was first designed, so it's not surprising that the requirement was included in F9's initial design. But it would be interesting if Block 5 still adhere to this standard, since it's no longer strictly required, and it must have no-small amount of performance penalty.

Are you sure it isn't being 'imposed' on SpaceX by NASA -- that is the functional equivalent of 'strictly required' for commercial crew.

Thanks for the above set of references... sheds much light on the question of NASA HSF taking a bye on imposing the same requirements on themselves as they impose on others.

From first reference:

So what happened?  The 1.4 Factor of Safety Requirement was originally included in 8705.2A when NASA wanted a reason to exclude EELVs from the ESAS Trade.  The requirement was removed in 8705.2B because Ares couldn't meet it.

And

So what happened?  Once again, NASA originally included a dual-fault tolerant requirement (8705.2A) for ESAS to exclude EELVs.  When it was clear that Ares/Orion could not meet the original dual fault tolerance requirement, NASA changed it (8705.2B)

[Kabloona]

Su27k, thanks for digging up those historical links about safety factor requirements.

IIRC, Elon has said from the beginning of F9 that it would have  a factor of safety of 1.4 for human rating. There's no way he changed his mind mid-program and said, oh, let's forget about that now and de-rate to 1.25. And he just talked on the phone call about how the vehicle is required to meet 1.4 for human rating.

Also, Garrett Reisman testified to Congress in 2015 about CCP and explicitly said F9 will have FS = 1.4 for human rating.

So I don't know how CCP is tailoring safety requirements, but SpaceX is clearly adhering to FS = 1.4.

[Rocket Science]

Over 45 years back when I first started in engineering 1.4 was considered the standard... Now this was in the age of "slide-rules" I might add...

[joek]

The 1.4 safety factor is, as far as I can tell, still a requirement for some systems based on CCT REQ 1130 (2015), which specifically references JSC 65828 (2011).

NB: The 1.4 safety factor stipulation is dependent on the scope and application of systems-subsystems-components.  That gets into a level of specificity difficult to authoritatively opine on without detailed knowledge.  (Knowledge unlikely to be available to most forum members without violating confidentiality agreements or NDA's.)

See also related documents here.

[Kabloona]

The 1.4 safety factor is, as far as I can tell, still a requirement for some systems based on CCT REQ 1130 (2015), which specifically references JSC 65828 (2011).

NB: The 1.4 safety factor stipulation is dependent on the scope and application of systems-subsystems-components.  That gets into a level of specificity difficult to authoritatively opine on without detailed knowledge.  (Knowledge unlikely to be available to most forum members without violating confidentiality agreements or NDA's.)

See also related documents here.

Thanks for that link, joe. Here's the paragraph from CCT-REQ-1130 that imposes FS = 1.4 on all primary structure via JSC 65828:

3.9.8.1.1 Structural Design Requirements
All flight hardware structures of the integrated space vehicle, except for glass or ceramic
windows, shall meet the intent of JSC 65828, Structural Design Requirements and Factors of
Safety for Spaceflight Hardware. [R.CTS.295]

I know it's easy to get lost in the weeds here. To clarify for those reading this thread, the question is whether Commercial Crew still requires FS = 1.4 on primary structure, as Elon implied in his recent phone call. (Primary structure = the big things, like tanks, interstages, adapters, etc, as well as pressure vessels)

So as far as I can tell, the above excerpt says yes, FS = 1.4 is still required on primary structure for Commercial Crew.

(FS = factor of safety)

Ayway, let's not get off-topic for this thread, which is Block 5. It's pretty clear from Elon's recent comments, not to mention SpaceX's entire history of touting FS = 1.4 for F9 human rating, that the vehicle does have FS = 1.4 on primary structure.

[Jim]

So as far as I can tell, the above excerpt says yes, FS = 1.4 is still required on primary structure for Commercial Crew.

It isn't.

[matthewkantar]

So as far as I can tell, the above excerpt says yes, FS = 1.4 is still required on primary structure for Commercial Crew.

It isn't.

-citation needed-

[envy887]

So as far as I can tell, the above excerpt says yes, FS = 1.4 is still required on primary structure for Commercial Crew.

It isn't.

Can you provide some examples of structures where it's not required?

[Kabloona]

So as far as I can tell, the above excerpt says yes, FS = 1.4 is still required on primary structure for Commercial Crew.

It isn't.

Then please explain. Because the top-level CCP documents quoted above do imply FS = 1.4 is required on primary structure. Are there lower-level "tailoring" documents for, say , ULA that lets Atlas V off the hook?

Or are they using that weasel phrase, "meet the intent of" to say well, OK, Atlas V "meets the intent of" JSC 65868 even though it doesn't have 1.4 on primary structure?

I understand Atlas V wasn't designed to that standard, so ULA must be getting a pass somehow. But evidently F9 *was* designed to that standard, as Elon keeps quoting it.

[zhangmdev]

https://forum.nasaspaceflight.com/index.php?topic=39766.msg1821863#new

The new leg is fascinating. It almost looks like the leg itself is white, and the black stuff is some kind of coating. And those rows of bumps disappeared?

[Kabloona]

https://forum.nasaspaceflight.com/index.php?topic=39766.msg1821863#new

The new leg is fascinating. It almost looks like the leg itself is white, and the black stuff is some kind of coating. And those rows of bumps disappeared?

No, the photo in that link is from an earlier version of F9 for comparison, to show that the umbilical connection design has remained unchanged. But at that time they painted/coated the legs white. The leg structure itself is carbon fiber composite, which is black when it comes out of the autoclave.

Probably for Block 5 they're coating the black composite legs with their new thermal protection material, which is also black, or painted black.

[livingjw]

I assumed the semi-active water cooling would just be having a resevoir of coolant and pumping it around the hot spots and less hot spots to spread the heat load out. I doubt they're spraying water out... seems unlikely to be effective. The fins themselves clearly don't need it.

edit: might not even need pumping if you essentially used giant heat pipes ... though I'm not sure if the physics holds up at scale for that to work, and if they'd be overly problematic in a rocket launch noise/vibration environment ...

Could be as simple as water soaked material backing the area needing cooled. I think I remember Lockheed had a water wick TPS design, but I can't find any info on it. Does anyone remember this?

John

[wannamoonbase]

I assumed the semi-active water cooling would just be having a resevoir of coolant and pumping it around the hot spots and less hot spots to spread the heat load out. I doubt they're spraying water out... seems unlikely to be effective. The fins themselves clearly don't need it.

edit: might not even need pumping if you essentially used giant heat pipes ... though I'm not sure if the physics holds up at scale for that to work, and if they'd be overly problematic in a rocket launch noise/vibration environment ...

Could be as simple as water soaked material backing the area needing cooled. I think I remember Lockheed had a water wick TPS design, but I can't find any info on it. Does anyone remember this?

John

After hearing they were using a water cooling system I assumed that the water is a consumable and not a closed look system.

water wicking TPS would be a very interesting and handy system.

[luinil]

https://forum.nasaspaceflight.com/index.php?topic=39766.msg1821863#new

The new leg is fascinating. It almost looks like the leg itself is white, and the black stuff is some kind of coating. And those rows of bumps disappeared?

No, the photo in that link is from an earlier version of F9 for comparison, to show that the umbilical connection design has remained unchanged. But at that time they painted/coated the legs white. The leg structure itself is carbon fiber composite, which is black when it comes out of the autoclave.

Probably for Block 5 they're coating the black composite legs with their new thermal protection material, which is also black, or painted black.

The interior of the leg is still white with the block 5 leg, only the exterior side gets black thermal protection.