The Empire Strikes Back: ULA's Vulcan Rocket

Excelsior · 2015-04-14 14:04:50

ULA Unveils Next Generation Launch System with a Little Showmanship

'Behold Vulcan': Next-Generation Rocket Unveiled by United Launch Alliance

United Launch Alliance, the U.S. company behind the Atlas and Delta family of rockets, has unveiled Vulcan, its next generation launch system.
The new Vulcan rocket, which got its name through a poll that attracted more than a million votes, incorporates new engines, a reuse approach that features a mid-air recovery and a new upper stage aimed at enabling complex on-orbit operations.
"[Vulcan is] going to take the best parts of Delta and Atlas and combine them with new and advanced technology to provide a rocket that is not just as reliable and certain as Atlas has been, but also much more powerful, with higher performance, greater flexibility and [is] significantly more affordable," Tory Bruno, United Launch Alliance CEO, said in a press conference held Monday (April 13) at the Space Symposium in Colorado.
In March, the United Launch Alliance (ULA) announced that it plans to phase out use of all but the heavy-lift version of its Delta rocket by 2018. The Vulcan is ultimately intended to replace both the Delta and Atlas, initially as a medium-class launch vehicle to fly in 2019, and then in a heavy-lift configuration by 2024.
...
Step 1, first stage
"The first step is this much more powerful booster," Bruno described. "It will sit atop a pair of advanced technology Blue Origin BE-4 rocket engines. They will burn clean and inherently reusable liquid oxygen and methane fuel."
Last year, ULA announced that it had partnered with Blue Origin, the privately-funded aerospace company owned by Amazon.com founder Jeff Bezos, to create a replacement for the RD-180 engines that power the Atlas today. Under pressure by Congress to phase out all use of the Russian-made RD-180s, ULA selected the BE-4 for the Vulcan.
"They will replace the venerable RD-180s, which generate 930,000 pounds of thrust. This pair of BE-4s will kick that up to well over 1.1 million pounds of thrust, a significant improvement in performance," Bruno said.
"They will sit underneath a stretched set of tanks that will contain significantly more propellant so that we can take advantage of the increased power to provide more impulse as we go to space," he added.
The new booster will also increase the number of possible side-mounted solid rocket motors by one more than Atlas, for a total of six, providing up to 20 percent more power.
...
Step 2, second stage
"We are going to take a giant leap forward in our upper stage," Bruno said. "Burning liquid oxygen and hydrogen, it'll start with these very large high-capacity balloon tanks [that are] so thin, so lightweight, that on Earth they cannot even support their own mass. They would collapse without propellant or pressure to hold their shape. They are truly designed to fly in space."
The ACES will be powered by one to four rocket engines, which Bruno said will be chosen from the existing Aerojet Rocketdyne RL-10 that is used with the Centaur, the Blue Origin's BE-3, or a new engine based on technology being developed by XCOR Aerospace.
The ACES will also incorporate a new integrated vehicle fluids system.
"This is the ultimate in reuse," Bruno explained. "The thing that limits the performance of the upper stage systems in launch vehicles is time — time in space. Eventually our propellants boil off and we're out of usable propellant. This system changes all of that."
Using an advanced internal combustion engine developed by race car manufacturer Roush, the waste propellants will be recycled to re-pressurize the stage's tanks, to generate electrical power and to provide control and attitude thrust.
"This completely changes everything," stated Bruno. "This provides a tremendous extension to our ability to operate on orbit."
"We're going to go from hours to weeks with this system," he continued. "We can take multiple satellites into orbit, we can put them in different planes and when we are done with that we can fly back to space station for operations."
...
Steps 3 and 4: reuse and many uses
The third step of ULA's development plan is to introduce reusability. Instead of recovering the entire first stage, like its competitor SpaceX has been attempting to do using an ocean-based landing platform, ULA's "Sensible, Modular, Autonomous Return Technology," or SMART, initiative will seek to recover only the first stage engines.
"In this approach, when the booster is done and you are finished with the rocket engines, we will cut them off, we will return them to the Earth using an advanced inflatable hypersonic heat shield and then with a very low, simplified logistics footprint, we'll recover them in mid-air and return them to the factory to quickly recertify them and then plop them under the next booster to fly," Bruno described.
"This will take up to 90 percent of the propulsion cost out of the booster," he stated, adding that SMART is only the beginning of the company's plans for how to reuse other components of its launch system, with more details to be announced later. [The World's Tallest Rockets: How They Stack Up]
Finally, combining the three earlier steps, Bruno said the Vulcan rocket would be in position to offer distributed lift, enabling the launch of multiple spacecraft components on multiple launches that could then meet up in orbit by using the new ACES upper stage.
"Now this is the real game changer," he stated. "We could take on our first launch big fuel tanks, supplies, food [and] water, if it is manned mission. Then on the next flight, we bring up the spacecraft, the astronauts in their capsule, and with this advanced upper stage that can fly around for weeks, we can put these pieces together."
"We can go out and tap the resources that are in space," Bruno remarked. "We can asteroid mine and then build the infrastructure for a real and permanent human presence."

Bruno said the cost per launch would be under $100 million without giving specifics including the development costs which ULA says will come from their current profits. But should the government choose to invest the system, they wouldn't be opposed.
It's clear Bruno is trying to respond to the SpaceX threat and is playing catch up. Having finally seen the SpaceX threat for what it is, real as opposed to hype, it was either step-up and compete or eventually lose their lucrative military launch contracts to SpaceX.

https://youtu.be/emmeil-0u5k

It's probably too soon make a judgement in all but one thing, competition is good.

Last edited by Excelsior (2015-04-14 14:05:42)

SpaceNut · 2015-04-14 19:53:20

Would be cost competing with Space X but are they targeting Man rating at all is not indicated for what is basically a clean slate design.

Terraformer · 2015-04-15 10:05:21

ACES? As in, the Lunar architecture program? Good, good.

GW Johnson · 2015-04-15 16:17:22

BTW, the "new engine from XCOR" mentioned in some news releases for ACES is not turbo-pumped! It is LH2-LOX, yes, but it is piston-pumped with their proprietary heat engine, run off rocket engine waste heat!

This is actually a more reliable pumping technology with some years' demonstration behind it in small sizes, and in real manned rocket-powered airplanes. So far, their tests are running great at about 1/10 the thrust needed for ACES application. It is unique to XCOR so far.

GW

SpaceNut · 2022-10-10 18:37:32

Like all projects these days United Launch Alliance's debut Vulcan mission slips to 2023 -CEO

Atlas replacement due to Russian engine use but with development delays with the rocket's engines that are being built by Amazon.com billionaire Jeff Bezos' space company, Blue Origin.

Vulcan, priced at roughly $110 million per launch, already has some 80 contracted missions lined up. It will compete with SpaceX's Falcon 9, priced roughly $62 million per launch, and Blue Origin's forthcoming New Glenn rocket, which uses the same engines as Vulcan.

Seems any further delay may mean cancellation of those future contracts...

SpaceNut · 2022-10-12 21:16:36

The first two satellites of Amazon’s space-based internet constellation will be launched early next year on the maiden flight of a new rocket being developed by one of the U.S. Space Force’s biggest contractors.

SpaceNut · 2023-01-22 17:03:02

Well, it's about time Vulcan Rocket unloaded at Port Canaveral

United Launch Alliance s first Vulcan rocket is transported past the Navaho guided missile display at the entrance to Cape Canaveral Space Force Station Sunday, January 22, 2023

AA16D3NJ.img?w=800&h=415&q=60&m=2&f=jpg

Mars_B4_Moon · 2023-03-01 13:19:46

Sources say prominent US rocket maker United Launch Alliance is up for sale

https://arstechnica.com/science/2023/03 … -for-sale/

tahanson43206 · 2024-01-08 08:13:11

Per Google:

Liftoff of Vulcan, powered by two BE-4 methane engines and two GEM 63XL solid rocket boosters!
Twitter • 4 hours ago
NASA ✓
Twitter › NASA
The first U.S. commercial robotic launch to the Moon successfully lifted off Jan. 8 on the first flight of @ULALaunch’s #VulcanRocket. @Astrobotic’s Peregrine Mission 1 lander is expected to reach the lunar surface in February: go.nasa.gov/3NVw46S
Twitter • 5 hours ago
ULA
Twitter › ulalaunch
MISSION SUCCESS! ULA's #VulcanRocket successfully performed its #Cert1 flight test today! Thank you to the engineers, technicians and teammates across the nation who designed, built and launched this versatile new rocket. ULA success #159. newsroom.ulalaunch.com/re…
Twitter • 5 hours ago
Astrobotic
Twitter › astrobotic
The Peregrine lander #PM1 has already completed Phase One of its lunar journey: assembly of the spacecraft flight model, a rigorous acceptance testing campaign, and encapsulation within the @ulalaunch Vulcan rocket at Cape Canaveral. Phase Two of this mission begins tonight!
Twitter • 7 hours ago
Blue Origin
Twitter › blueorigin
Congratulations @ULALaunch! Team Blue celebrates Vulcan’s first launch! #PoweredByBE4
Twitter • 6 hours ago
Freeman Air and Space Institute
Twitter › freeman_air
?United Launch Alliance has successfully launched their Vulcan rocket. If the rocket's primary payload, Peregrine, lands successfully, it will become the first American spacecraft to reach the moon's surface since Apollo 17 in 1972. More here? ow.ly/p12e50QoGHr
Twitter • 7 minutes ago
News4JAX
Twitter › wjxt4
Astrobotic Technology's lander caught a ride on a brand new rocket, United Launch Alliance’s Vulcan, which streaked through the Florida predawn sky, on a route that should finish in an attempted landing on Feb. 23. www.news4jax.com/business…
Twitter • 9 minutes ago
waaytv
Twitter › WAAYTV
The launch of ULA's next generation Vulcan rocket today marked the beginning of a new era of space capabilities. www.waaytv.com/news/first…
Twitter • 9 minutes ago
News5
Twitter › News5PH
A robotic lander built by a private company was bound for the moon on Monday in an attempt to make the first U.S. lunar soft landing in more than half a century, after launching into space aboard a new Vulcan rocket. #News5 | via Reuters READ: news.tv5.com.ph/breaking/… pic.twitter.com/l105HJDs2…
Twitter • 23 minutes ago
KyivPost ✓
Twitter › KyivPost
?The United States launched a rocket to the Moon with a Ukrainian flag and map on board. The Vulcan Centaur rocket by United Launch Alliance (ULA) made its maiden flight on January 8 from the Space Force Station at Cape Canaveral in Florida, as reported by Space. About 50…
Twitter • 31 minutes ago
Michael Sheetz
Twitter › thesheetztweetz
ULA's Vulcan rocket roared off the launchpad early this morning, succeeding on its first attempt. Vulcan's debut is significant to the space industry for a host of stakeholders – Astrobotic, Blue Origin, Space Force, NASA and more: www.cnbc.com/2024/01/08/u…
Twitter • 33 minutes ago
Northrop Grumman ✓
Twitter › NGCNews
Providing nearly one million pounds of thrust at lift-off, two of our GEM 63XL solid rocket boosters helped power the inaugural flight of @ulalaunch’s #VulcanRocket and the Peregrine mission today. Learn more: news.northropgrumman.com/…
Twitter • 1 hour ago
Josh Wolfe ✓
Twitter › wolfejosh
HISTORY this AM! 1st ?? mission to ? since Apollo >50yrs ago! United Launch Alliance’ 198ft tall, 1.5M lb Vulcan rocket (2 methane Blue Origin BE-4 engines + twin solid-propellant boosters) carries Peregrine commercial moon lander @ Cape Canaveral Space Force Station ?
Twitter • 2 hours ago
Oliver Steinbock
Twitter › SteinbockGroup
Our group alumna, Keeley Hernesman, in front of the #Vulcan rocket which is now on its way to the Moon delivering the #Peregrine lander. Keeley worked at United Launch Alliance and is now at Lockheed Martin. The rocket launched successfully this morning; anticipated landing 2/23.
Twitter • 2 hours ago
Supercluster ✓
Twitter › SuperclusterHQ
Liftoff! The first flight of the @ulalaunch Vulcan Centaur rocket was a success, launching the Peregrine Lunar Lander to the moon from Cape Canaveral at 2:18 AM EST Captured by @erikkuna for Supercluster.
Twitter • 2 hours ago
The Mirror ✓
Twitter › DailyMirror
Lift off! ? The Vulcan rocket carrying the Peregrine lunar lander in its debut flight and marking the first US lunar landing attempt in over 50 years, has successfully launched from Cape Canaveral. Credit: @NASA
Twitter • 2 hours ago

View on Twitter
See amazing photos of ULA's 1st Vulcan Centaur rocket launch
www.space.com › ula-vulcan-centaur-rocket-launch-debut-photos
3 hours ago · United Launch Alliance's Vulcan Centaur rocket lifted off from Florida's Cape Canaveral Space Force Station early Monday morning (Jan. 8).
Top stories
ULA's Vulcan rocket launches as the newest challenger to SpaceX
CNBC 42 mins ago
First Vulcan rocket launch sends American Moon lander on journey to lunar surface
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ULA Vulcan launch: Watch liftoff of Peregrine Mission One to moon
USA Today 1 hour ago
First US moon landing mission in decades launches with NASA science, humans remains on board
CNN 3 hours ago
Vulcan Rocket Lifts Off, First U.S. Moon Launch in Decades
The New York Times 5 hours ago
Vulcan Centaur rocket launches private lander to the moon on 1st mission
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BBC 18 hours ago
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ULA says its Vulcan rocket is finally ready to fly – Spaceflight Now
Spaceflight Now 1 day ago
Nasa Peregrine 1: Vulcan rocket carrying Nasa moon lander lifts off in Florida
The Guardian 6 hours ago
ULA Launches the First Vulcan Centaur with the Peregrine Moon ...
www.youtube.com › watch
6 hours ago · United Launch Alliance is launching their first Vulcan Centaur rocket for it´s inaugural flight ...
Duration: 2:39:02
Posted: 6 hours ago
First US moon landing mission in decades launches with NASA ...
www.cnn.com › world › ula-vulcan-centaur-rocket-peregrine-launch-scn
4 hours ago · United Launch Alliance's next-generation Vulcan rocket launches on its debut flight from Cape Canaveral Space Force Station in Florida on ...
US launches its first moon-bound lander since the Apollo 17 mission
www.theverge.com › nasa-peregrine-mission-one-moon-lander-vulcan-cen...
1 hour ago · The United Launch Alliance (ULA) successfully launched its new Vulcan Centaur rocket from Cape Canaveral on Monday at 2:18AM ET, carrying a ...
New Vulcan rocket sends privately-built Moon lander to space
www.reuters.com › technology › space › vulcan-rocket-set-debut-launch-w...
2 hours ago · Space robotics firm Astrobotic's Peregrine lunar lander launched at 2:18 a.m. EST from Cape Canaveral, Florida on the first flight of Vulcan, a ...
Vulcan Cert-1 - United Launch Alliance
www.ulalaunch.com › missions › next-launch › vulcan-cert-1
5 hours ago · A United Launch Alliance (ULA) Vulcan VC2S rocket will launch the first certification mission from Space Launch Complex-41 at Cape Canaveral Space Force Station ...
Vulcan Centaur - Wikipedia
en.wikipedia.org › wiki › Vulcan_Centaur
27 minutes ago · Vulcan Centaur launched for the first time on January 8, 2024, successfully carrying Astrobotic Technology's Peregrine lunar lander, the first mission on NASA's ...
Vulcan - United Launch Alliance
www.ulalaunch.com › rockets › vulcan-centaur
The spacecraft is encapsulated in a 5.4-m- (17.7-ft-) diameter payload fairing (PLF), a sandwich composite structure made with a vented aluminum-honeycomb core ...

(th)

GW Johnson · 2024-01-08 15:12:54

Looks like the 2-SRB Vulcan/Centaur flight went off just about as planned. I can find nothing on-line to indicate the future upgrade to recoverable and reusable BE-4 engines has actually been funded. Right now, the thing is all-expendable. It will stay expendable until the engine recovery thing gets funded and developed.

Latest news stories indicate the Peregrine lunar lander is in "deep kimchee": loss of attitude control leading to loss of electricity, and a loss of propellant. Nobody has given up on it yet, so far as I can tell, but it does NOT look good, to say the least. It's in a highly elliptical orbit about the Earth, where the Vulcan/Centaur put it.

GW

update 1-11-24: latest reports seem to indicate it won't go to the moon, much less land. Too much propellant lost.

Last edited by GW Johnson (2024-01-11 13:10:20)

SpaceNut · 2024-01-26 17:26:43

Vulcan rocket's debut brings long-awaited challenge to SpaceX dominance

Vulcan's launch debut lets ULA start fulfilling a multibillion dollar backlog of some 70 missions, roughly split between government and commercial missions. Amazon's Kuiper satellite project occupies a majority of its commercial bookings.
The starting price for a Vulcan launch is roughly $110 million, half that of its predecessor Atlas V, which anchored ULA's dominance for U.S. national security satellite launches since ULA's 2006 formation. SpaceX's reusable Falcon 9 is pegged at roughly $62 million per launch, but sometimes more for Pentagon missions.
ULA and SpaceX vie head to head for national security missions. The Pentagon in 2020 picked ULA to launch 60% of its national security missions through 2027 and SpaceX to launch the rest. The Pentagon's next launch procurement will pick three core launchers, giving SpaceX and ULA a greater challenge.
Vulcan can use up to six solid rocket motors for extra boost, allowing it to loft up to 60,000 pounds (27,000 kg) of satellites in a low orbit, or 32,000 pounds (14,500 kg) to further orbits. SpaceX's Falcon 9 and Falcon Heavy - three Falcon boosters strapped together - can put up to 140,000 pounds (63,500 kg) to low Earth orbit, or 58,860 pounds (26,700 kg) to further orbits.
ULA used the Russian-made RD-180 engines for its workhorse Atlas V, and that became a security concern in 2014 after Russia invaded Crimea. That, and the rise of SpaceX's cheaper Falcon 9, prompted Vulcan's development.
Atlas V has 17 more booked missions left before retiring. ULA had bulk-ordered its RD-180 engines before American-Russian relations collapsed following Russia's large-scale February 2022 invasion of Ukraine.
Jeff Bezos' space firm Blue Origin has effectively replaced Russia's RD-180, now supplying Vulcan's twin BE-4 engines, which roared to life on Monday and marked Blue Origin's first step into Earth's orbit. Blue Origin is building its own launcher - New Glenn - a more powerful rival to Vulcan that uses 7 BE-4 engines.
ULA plans to increase production to 25 booster rockets annually by late 2025, Bruno said. And it has roughly 100 engineers designing future upgrades to cut production costs.
Those upgrades include a plan to recover and reuse Vulcan's BE-4 engines - about 65 percent of the booster cost - using a heat shield, parachutes and a helicopter to catch them out of the air. Smaller launcher Rocket Lab has adopted a similar strategy.
Bruno said Vulcan upgrades will begin in 2025, and occur every two to three years after that. ULA will test and implement its reuse strategy for Vulcan in the midst of its Amazon Kuiper missions.

SpaceNut · 2024-10-03 19:08:14

Successful Vulcan launch early Friday would unlock lucrative future for ULA

Vulcan takes two BE-4 engines, which along with up to six solid rocket boosters provided by Northrop Grumman, give Vulcan more power than either Atlas V or the now retired Delta IV Heavy, with 3.6 million pounds of thrust on liftoff.

Oldfart1939 · 2024-10-04 12:45:15

There was a "nominally successful" launch of the Vulcan rocket--in spite of an anomaly with one of the SRBs--which lost a nozzle before burnout.

GW Johnson · 2024-10-04 15:27:47

From AIAA’s “Daily Launch” email newsletter for October 4, 2024

Space
ULA’s new Vulcan Centaur rocket aces 2nd test launch

United Launch Alliance's (ULA) powerful new Vulcan Centaur rocket is two for two. Vulcan Centaur, the successor to ULA's workhorse Atlas V, launched today (Oct. 4) at 7:25 a.m. EDT (1125 GMT) after a series of holds, from Florida's Cape Canaveral Space Force Station, kicking off a key test flight called Cert-2. The rocket could soon be certified for U.S. national security missions.

My take on it:

If you follow the link to the article from Space, there is mention and a video showing a serious anomaly with one of the two solid boosters. The article says there was some sort of problem with the rocket nozzle, seen as an event creating a shower of glowing pieces. As near as I can tell, the exit expansion bell shattered (meaning it suddenly burst from its internal pressure and heating loads) downstream of the throat somewhere.

Because this failure took place downstream of the throat, it reduced the thrust from its nominal value to something nearer that of a sonic-only nozzle, without very much of a “P-A-kick load”. The sudden loss of thrust on that side was not enough to upset the vehicle’s attitude control, nor was it enough to prevent the vehicle from flying its intended trajectory anyway.

Had this bursting taken place ahead of the throat, the sudden change in thrust would have been much larger (loss of essentially all of the thrust), aggravated even further by a “P-A-kick” load of very significant size. That would likely have thrown the vehicle out of control. Even if it stayed in control, the vehicle would likely have been unable to fly its mission on thrust from only one of the boosters.

Somebody at Northrup-Grumman’s big solid motor operation (the monopoly that supplied these boosters) screwed up this nozzle design. That much is for sure! It is unclear whether that problem is a fundamental design error, or an undetected material quality defect. Neither is acceptable.

If I were making decisions for the Air Force, I would NOT certify this vehicle for launching spy satellites until I knew what actually caused the solid booster nozzle anomaly, and what must be done to see that it does not recur! Those payloads are expensive, and time-critical.

I would insist that the fix be demonstrated in flight, before even beginning to contemplate man-rating this vehicle! Why? Because I do not trust monopolies to behave ethically and responsibly. They never did before, in history. And big solid motors are now a monopoly in this country.

GW

Last edited by GW Johnson (2024-10-04 15:31:32)

tahanson43206 · 2024-10-04 15:47:03

For GW Johnson....

re Vulcan launch and solid failure....

Is there an argument to be made to eliminate the solids altogether, and replace them with Blue Origin rockets designed to return to Earth like Falcon 9 first stages?
(th)

GW Johnson · 2024-10-04 18:39:02

TH:

I honestly do not know. But I would assume that Blue Origin looked into that, while designing Vulcan.

Unlike some on these forums, I have no prejudice against solids. Those are just another tool to use, offering some very specific advantages, particularly during pre-launch checkout. But you do have to design them correctly, and you do have to verify your design is "right" with enough of the right kinds of testing to meet statistical standards.

Bear in mind that back in 1974 I worked on the Vought "Scout", which was a 4-stage solid satellite launcher. It flew 4 times experimentally, failing once, then operationally for over 30 years, without another single failure of the solids.

Just goes to show what can be done.

GW

Oldfart1939 · 2024-10-04 20:16:25

For all to verify that the nozzle of one of the SRBs failed, check at 06:39 minutes of this video by Scott Manley:
https://www.youtube.com/watch?v=xIHg-PPUZnk

Last edited by Oldfart1939 (2024-10-04 20:16:44)

GW Johnson · 2024-10-05 10:50:55

Interesting film and photos, including some detailed photos of how the nozzle assembly is made.

You can see the metal closure and contraction assembly to just past the throat, which pins into the aft end of the case. The inside of that has the ablative that actually forms the flow path surface, likely mostly silica phenolic. There would be a graphite throat insert piece, or insert pieces, likely backed to the outside and perhaps downstream with some sort of lower density graphite or maybe a carbon phenolic. All of this is bonded together and to the ablative substrate, in turn bonded to the metal shell. The metal shell is the pressure vessel, not the silica phenolic. You do not use ablative materials as pressure shells. Never!

The majority of the expansion bell shows an "ablative" construction, again likely silica phenolic, with evident glue joint seams. I would hazard the guess that there is a metal shell buried inside this piece into which there is a silica phenolic ablative liner bonded in place, that forms the flow path surface. In this particular big motor design, there are also silica phenolic pieces bonded to the outside, to protect the nozzle structure from the hot spreading liquid engine plumes at very high altitudes. (The edge streamlines bend around the nozzle lip to just a tad more than 90 degrees off-axis, as the air pressure drops to vacuum levels.)

This bell piece's metal core is what rivets into the metal-shelled aft closure-and-throat piece. You could see the rivets holding the two metal shell pieces together in one of the photos in Manley's video. I did not see anything that I recognized as pertaining to thrust-vectoring the nozzle; it appears to be a fixed geometry. That's good, because vectoring nozzles on solids have long been infamous as failure points.

If I had to guess a suspect to investigate, I'd guess the failure point is one of the adhesive bond lines between adjacent silica phenolic pieces, on the inside of the bell. In small motors, these ablative liners are monolithic pieces bonded to the metal shell. In really big motors. they cannot be monolithic, as no one make silica phenolic stock of that large a size. It is cured in a giant heated press. The adhesive bonds are less structurally strong than the silica phenolic material itself, inherently. All adhesives are stronger in shear than they are in tension. (Compression is strongest.)

That suspect fits the behaviors Manley described: a nozzle anomaly in a ground test, and now this same kind of nozzle anomaly in flight. But only a couple of failures out of many firings. If one of those longitudinal glue seams splits open, it lets the supersonic hot gas inside the split to contact the metal shell, burning a hole through it (and any ablative on the outside, which just takes a bit longer). Once the metal shell substructure has been weakened enough as the burn-through hole enlarges, the exit bell suddenly bursts due to the pressure inside of it, which while a small fraction of chamber pressure, is still much higher than the near vacuum outside.

The silica phenolic is a stiff material, but not infinitely so, it has a Young's modulus less than steel or aluminum, and it has some elongation-to-failure capability. The typical epoxies used to bond the ablative to the metal (and to adjacent ablative pieces) have very little elongation capability, rendering them quite brittle! If the metal bell shell is not quite stiff enough, it will swell under pressure by some amount, and the silica bonded to it will follow it, but circumferentially there might be too-high a tensile stress across the longitudinal bond seams between adjacent ablative pieces. That fractures the bond and allows it to part open slightly, letting the hot gas in.

Small motors with monolithic ablative liner pieces simply do not see this failure mode. It is peculiar to large motor nozzles, too big for the ablative liners to be monolithic parts. It'll be statistical: some will fail and others won't, with some erratically occurring occasional (statistical) failure rate. The "fix" is a stiffer metal shell that swells less under pressure and thus avoids tensile stress across longitudinal bond seams. That is either a thicker part, or a material with higher Young's modulus. Both offer a stiffer assembly at the cost of a heavier assembly. But if the occasional failure is unacceptable, that's just the price you have to pay!

Having built those solids for 2 decades, I did end up knowing a lot of real-world stuff about their designs. The 3-D computer models sometimes lie to you (GIGO), usually because the model in the code doesn't truly match what you are doing in the real world. Seeing that design analysis error takes experience and judgement not yet possessed by newbies out of school, trained to run those codes. If there is corporate ageism (and there nearly always is), there are few-to-none old hands there to pass on the experience. This is part of the art that was never written down, because nobody wanted to pay for writing it down.

This problem can be fixed and prevented, plain and simple. But it cannot be done easily and quickly and cheaply! It is a redesigned nozzle assembly that must be validated in multiple tests. A small redesign, but it still has to be properly tested! And THAT is the expensive, but utterly essential, part! Plus, they already have built a lot of motors with the vulnerable nozzle assemblies. Those will need replacement nozzle assemblies. Recalls are expensive, in any industry.

GW

Last edited by GW Johnson (2024-10-05 11:10:48)

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#1 2015-04-14 14:04:50

The Empire Strikes Back: ULA's Vulcan Rocket

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