ULA Vulcan Launch Vehicle (as announced/built) - General Discussion Thread 3

[PahTo]

Cross-posting from the cert2 thread since this is really the better one for discussions about the LV:

SRM/SRB characteristics/facts:
-length defines thrust (longer equals more thrust).
-diameter defines burn time (larger diameter equals longer burn time).

For the GEM63XL:
Given the longer motor casing (read thrust chamber) and shorter burn time while having the same OUTER diameter, this implies thicker casing to help contain that higher thrust (chamber pressure).*
Thus, the only things the 63 and 63XL have in common are outer casing diameter and HTPB prop.  I'd be surprised if the nozzles are the same.*
To ugordon's point later about 1/4 failure and manufacturing:  now we get to the root of the question.  Was it the actual fabrication of the nozzle/throat itself, or the assembly of said part(s) on to the motor itself (both are elements of "manufacturing").  If fabrication, was it a materials issue, or is the design too close to margin (the material too "thin" at the throat/top of nozzle?).

*it may be the prop casting is narrower inside the casing, but given physics, I believe it is thicker casing wall/thinner inner diameter.

As my dad likes to say:  More to be revealed.

[deltaV]

SRM/SRB characteristics/facts:
-length defines thrust (longer equals more thrust).
-diameter defines burn time (larger diameter equals longer burn time).

Throat area presumably also affects thrust and burn time.

[PahTo]

SRM/SRB characteristics/facts:
-length defines thrust (longer equals more thrust).
-diameter defines burn time (larger diameter equals longer burn time).

Throat area presumably also affects thrust and burn time.

Concur--of course the throat area (throat volume?) is defined/informed by motor length and diameter, along with desired performance optimization (in this case to maximize sea level thrust/getting up and out of the thickest part of the atm).

[lrk]

Higher chamber pressure means a faster burn rate, and (all else held equal) a longer motor would have a higher chamber pressure.  Since the GEM-63XL has a slightly shorter burn time than the GEM-63, it wouldn't surprise me if the nozzles were the same diameter.

It would seem reasonable to save costs by specing the case and nozzle design to be the same for both motors, and just eat a little bit of extra mass/less performance on the GEM-63. 

Hopefully the root cause is just a manufacturing/handling issue, and not a fundamental design problem.  If that is the case, and existing motors can't be easily fixed, then it might be a while before the next Vulcan flight. 

[TrevorMonty]

SRM/SRB characteristics/facts:
-length defines thrust (longer equals more thrust).
-diameter defines burn time (larger diameter equals longer burn time).

Throat area presumably also affects thrust and burn time.

These SRM don't burn fuel upward like sky rocket but outward from centre core, longer that core more surface area is being burnt.

https://www.researchgate.net/figure/Cross-section-of-a-solid-rocket-motor-AEROJET_fig1_4082762

[clongton]

The GEM-63 solid rocket booster, features a star-shaped central core. Specifically, the core has a 17-point star cross-section. This star-shaped design maximizes the surface area of the propellant at ignition, allowing for a high thrust at the start of the burn. As the propellant burns from the inside out, the changing shape of the core controls the thrust profile, providing sustained power throughout the rocket's ascent.

The GEM-63XL solid rocket booster, like the GEM-63, also features a star-shaped central core. Specifically, the core has an 11-point star cross-section, which maximizes the surface area at ignition to produce a higher initial thrust. As the propellant burns, the shape of the core evolves, controlling the rate of burn and the thrust profile over time.

The 11-point vs. the 17-point star cross-section produce different thrust curves by providing different surface areas for propellant burn. The changing thrust levels are controlled by the evolving core shape as the propellant is consumed. The anomaly occurred early in the burn, suggesting a significant delta in the evolving star-profile. IMO, this could have contributed to a higher than expected thrust level that could have overpowered the physical connection of the nozzle to the casing.

 The manufacturer of the GEM 63 series of solid boosters have been providing these for a very long time, so ISTM that it is unlikely to be a mechanical connection failure in and of itself, but rather an over-thrust condition that overpowered the connection and broke it loose, destroying the ablative lower nozzle and blowing off the upper nozzle at the connection point. After the booster lost its nozzle, the continuing exhaust plume is clearly burning off-nominal, which to me indicates an off-nominal central core shape in the propellant. That’s just an opinion that I have based on the limited evidence we have at the moment. Time (and data) will tell.

Scott Manley’s recent episode captured the nozzle (sans ablative section) spinning away from the ascending Vulcan, apparently still intact. You can watch it at the timestamp 6:30 to 6:40.

[PahTo]

The GEM-63 solid rocket booster, features a star-shaped central core. Specifically, the core has a 17-point star cross-section. This star-shaped design maximizes the surface area of the propellant at ignition, allowing for a high thrust at the start of the burn. As the propellant burns from the inside out, the changing shape of the core controls the thrust profile, providing sustained power throughout the rocket's ascent.

The GEM-63XL solid rocket booster, like the GEM-63, also features a star-shaped central core. Specifically, the core has an 11-point star cross-section, which maximizes the surface area at ignition to produce a higher initial thrust. As the propellant burns, the shape of the core evolves, controlling the rate of burn and the thrust profile over time.

The 11-point vs. the 17-point star cross-section produce different thrust curves by providing different surface areas for propellant burn. The changing thrust levels are controlled by the evolving core shape as the propellant is consumed. The anomaly occurred early in the burn, suggesting a significant delta in the evolving star-profile. IMO, this could have contributed to a higher than expected thrust level that could have overpowered the physical connection of the nozzle to the casing.

 The manufacturer of the GEM 63 series of solid boosters have been providing these for a very long time, so ISTM that it is unlikely to be a mechanical connection failure in and of itself, but rather an over-thrust condition that overpowered the connection and broke it loose, destroying the ablative lower nozzle and blowing off the upper nozzle at the connection point. After the booster lost its nozzle, the continuing exhaust plume is clearly burning off-nominal, which to me indicates an off-nominal central core shape in the propellant. That’s just an opinion that I have based on the limited evidence we have at the moment. Time (and data) will tell.

Thanks clongton--I wondered about the casting geometry.  Your supposition is certainly more informed than mine (as obviously so is Jim's).  Questions:
-if the casting was at issue (geometry, not prop), wouldn't inspections (visual and/or xray) catch such a deviation?
-is there a vrs of GEM63 with gimbal capability?  istr that is the case, and would think the assembly for a gimbal vrs is significantly different from the XL.

[DanClemmensen]

The thrust graph for the GEM 63XL has three curves, one for each of three temperatures. These are the initial temperature of the SRB propellant before T-0. Basically, the thrust is considerably higher on a hot day than it is on a cold day. How hot was at launch time time?

[mn]

....

. The anomaly occurred early in the burn, suggesting a significant delta in the evolving star-profile. IMO, this could have contributed to a higher than expected thrust level that could have overpowered the physical connection of the nozzle to the casing.

 The manufacturer of the GEM 63 series of solid boosters have been providing these for a very long time, so ISTM that it is unlikely to be a mechanical connection failure in and of itself, but rather an over-thrust condition that overpowered the connection
......

which to me indicates an off-nominal central core shape in the propellant. That’s just an opinion that I have based on the limited evidence we have at the moment. Time (and data) will tell.

Seems like an awful lot of assumptions based on so little information.

Just because they have been doing it for a long time doesn't mean there wouldn't be a manufacturing defect in the nozzle connection. (But somehow even though they have been doing it for a long time, a flaw in the star shape is more likely than a physical flaw in the nozzle/connection)? Like why is one more likely than the other if they have been doing both for the same time?

The star profile of all things is easy to see, if it was flawed it should have been caught?

Of course the burn would be 'off nominal' after losing the nozzle, please tell me how you see an off nominal star pattern in the burn and not just being off nominal because there's no nozzle?

[clongton]

Remember the last line in my post said:

That’s just an opinion that I have based on the limited evidence we have at the moment. Time (and data) will tell.

It's a reasoned opinion (not a statement of fact) based on not enough data and subject to change as more data becomes available. Don't read more into it than I actually said.

[FutureSpaceTourist]

https://twitter.com/ulalaunch/status/1845877852324925590

Today at @IAC2024 @ToryBruno shared #VulcanRocket engineering development innovations with #IAC2024  attendees. A key challenge in developing Vulcan was selecting a system architecture and leveraging the latest technologies to support a wide range of missions with a single launch vehicle configuration.

[FutureSpaceTourist]

Hey @torybruno , quick question. Is the Vulcan Pathfinder Tanking Test Booster still being rebuilt into a flight booster? And if so where is it in terms of production flow for flight?

https://twitter.com/torybruno/status/1848661925913080011

Yes. Next year

[FutureSpaceTourist]

https://twitter.com/torybruno/status/1851281939006709820

Another BE4...
#VulcanRocket

[FutureSpaceTourist]

https://twitter.com/torybruno/status/1852728403994005763

Several of you have said you’re interested in pad progress on the West Coast. This is for you. A brand new, gigantic CH4 tank has set out for California to support the #VulcanRocket ‘s SLC3 at VSFB

[FutureSpaceTourist]

https://twitter.com/torybruno/status/1861445206744142043

Becoming a routine sight. But never boring. BE4s. #VulcanRocket

[FutureSpaceTourist]

https://twitter.com/derekdotspace/status/1861446630639108481

The BE4 delivery rate is picking up. ULA now has confirmed engines in house for flights 3, 4, 5, and 6 of Vulcan Centaur.

[greybeardengineer]

Becoming a routine sight. But never boring. BE4s. #VulcanRocket

The recurring nature of these type of tweets seems to me to be like a form of overcompensation. I guess the years of questioning, memes, and derision over the lack of BE4s left a lasting impression on Tory.

[TrevorMonty]

Becoming a routine sight. But never boring. BE4s. #VulcanRocket

The recurring nature of these type of tweets seems to me to be like a form of overcompensation. I guess the years of questioning, memes, and derision over the lack of BE4s left a lasting impression on Tory.

I'd like see more of them in flight than on factory floor.

[Lee Jay]

Becoming a routine sight. But never boring. BE4s. #VulcanRocket

The recurring nature of these type of tweets seems to me to be like a form of overcompensation. I guess the years of questioning, memes, and derision over the lack of BE4s left a lasting impression on Tory.

I'd like see more of them in flight than on factory floor.

I'd like to see fewer purchases and more re-use of them.

[FutureSpaceTourist]

In response to claim ULA has 4 BE-4s:

https://twitter.com/torybruno/status/1861739330802168176

You are off by a factor of around 3x, not counting the BE4s currently assembled into NG