Starship is Go...

tahanson43206 · 2025-03-05 08:32:31

It appears test flight 8 may happen today Wednesday 2025/03/05...

SpaceX Starship Flight 8 Tomorrow and New GigaBay Work
March 4, 2025 by Brian Wang
As flight testing and development of Starship continues at Starbase in Texas, SpaceX is building a new integration facility, called Gigabay, next to its HangarX location at NASA’s Kennedy Space Center. Additionally, SpaceX plans to complete the Starship launch pad at Launch Complex 39A (LC-39A) at Kennedy Space Center this year while the Environmental Impact Statements continue for potential Starship flight operations from both LC-39A and Space Launch Complex 37 (SLC-37) at Cape Canaveral Space Force Station (CCSFS).

(th)

Oldfart1939 · 2025-03-05 17:36:41

I've ben keeping up with the evolving story about IFT 7 the latest engineering info I've seen has pointed the finger at a massive vibrations problem--some 5X greater than the test stand results. Vibrations --> metal fatigue and cracking, which apparently caused the fuel leaks, leading to the RUD.

The Thursday flight on 3/6/2025 was earlier announced, but there was a damaged part during the stacking which may result in another day or 2 delay. WAS!!

GW Johnson · 2025-03-06 15:49:33

I rather suspect that the source of the leaks may be the stage itself, not the plumbing on the engine. But that's just a suspicion.

When they test engines in McGregor, it's just the one engine at a time. Usually the burns are around 23-4 minutes long. Sometimes shorter. There is no stage.

The first time there is a stage and more than 1 engine is the static fires at Boca Chica. Even that may not reveal excessive vibration, which for the first stage may stem from thrust interacting with supersonic aerodynamics.

Not where excessive vibration might be coming from on the second stage out in vacuum. I suspect SpaceX doesn't yet know, either.

GW

GW Johnson · 2025-03-06 19:01:15

According to what little I have seen, Flight Test 8 ended with a successful booster catch, but a second loss of the Starship upper stage.

I think it might now be clear that there are engine problems in both stages, and some sort of stage-related excessive vibration problem in the Starship upper stage. I think it is also clear that SpaceX has no clue what the vibration problem really is.

I will have to find the SpaceX video and go see it, before I can be specific about anything. The news reports vary too much.

GW

Last edited by GW Johnson (2025-03-06 19:02:05)

GW Johnson · 2025-03-07 09:01:58

The video on the SpaceX website is disabled to black. I cannot watch it.

As for the two failures, bear in mind that most flight vehicle failures in flight are due to multiple things acting together. Having only a single cause is unlikely in the extreme.

That being said, after flight 7, they made alleviating changes to the vehicle for flight 8. Those did not work, apparently. Which lends strong support to the suggestion that the real causes (plural!) were not what they assumed after flight 7, which was about leaks in engine plumbing.

There was a vehicle design change after flight 6. The vehicles for flights 7 and 8 were longer, with larger propellant tanks. Which raises the specter of some sort of slosh or other unstable-surface mode in the propellant tanks causing the vibration instead, and perhaps causing the fatal leaks to be in weld joints of the lower tank aft bulkhead instead of the feed plumbing. The larger propellant masses involved would likely amplify any such effect. It's only speculation, but a real possibility that they need to explore.

If it were me, I'd re-fly the older Starship upper stage design on flight 9, with the smaller tank volumes and shorter length, but with the improvements they made to the flaps, hinges, and heat shield. If that makes the ascent successfully, when the larger design did not twice in a row, that would pretty well nail it to the dynamics of the larger tanks vs smaller tanks.

If it's some sort of liquid-sloshing in the tanks that is the source, then a change to the baffles is indicated. And the tank structures in and adjacent to the aft bulkheads may need reinforcement to better resist the unanticipated loads. They need to instrument for these possible effects, probably to include in-tank camera views, and some strain gages and suitably-located pressure sensors.

That's not to say there might not also be failures in the engine plumbing too. But whatever is going on there, is apparently being overwhelmed by something else they have not identified yet.

This sort of thing happens often in experimental flight test. It shows up more often when you make too many changes to the vehicle design between tests, too early in the flight test program. In this particular case, it may also trace to believing too strongly in computer code outputs, by engineers who cannot detect a garbage-in/garbage-out problem because they have not done enough pencil-and-paper design analysis. Or cannot, because they were only taught how to use software packages.

That problem has existed for some long time now. I saw it during the Rogers Commission hearings after the Challenger loss. The thermal-structural model they had for the O-ring joint said it was OK to fly cold. But their model did NOT match what they built! And THAT is where the garbage got into the computer, making the output garbage, too!

GW

Last edited by GW Johnson (2025-03-07 09:07:16)

RobertDyck · 2025-03-08 13:04:50

GW Johnson,
I can watch video on the SpaceX website. When you click the REWATCH button it goes to a new black page, then after a second or two opens a video window. I use Firefox for my browser on Windows 10. Fully updated, version 136.0 (64-bit).

RobertDyck · 2025-03-08 13:08:15

One friend asked if NASA will stop using SpaceX for their mission to the Moon. With everything Elon Musk has done with DOGE, many people are dumping Tesla stock. But I pointed out NASA is not focused on making money, they're focused on results. And SpaceX has delivered. However, developing Starship is taking a long time. Is it time to consider an alternative?

I thread that I posted in 2016: Moon mission today - Dragon & Mars hab

RobertDyck · 2025-03-08 16:44:13

This YouaTube channel is not SpaceX, but the video is the feed from SpaceX with no commentary, no additions, no deletions, the entire SpaceX fees from introduction to SpaceX terminating their video.
YouTube: Replay! SpaceX Starship launches on flight 8, catches booster but loses ship again

RGClark · 2025-03-10 09:34:12

Finally, people are starting to ask the tough questions about the SpaceX development of Starship:

Twin Test Flight Explosions Show SpaceX Is No Longer Defying Gravity.
Consecutive losses of the Starship rocket suggest that the company’s engineers are not as infallible as its fans may think.
…
But these two Starship explosions were a step backward in SpaceX’s development process, as the flights could not even repeat the successes of earlier test flights, and they perhaps show that the company’s engineers are not as infallible as fans of the company sometimes like to think.
“There’s this persona that has built up around SpaceX, but you’re starting to see that they’re human, too,” said Daniel Dumbacher, a former NASA official who is now a professor of engineering practice at Purdue University and chief innovation and strategy officer for Special Aerospace Services, an engineering and manufacturing company whose customers include NASA, the United States Space Force and some of SpaceX’s competitors.
https://www.nytimes.com/2025/03/08/scie … -musk.html

Repeated engineering failures stem from the top. SpaceX needs a true Chief Engineer making the engineering decisions.

Bob Clark

Last edited by RGClark (2025-03-10 09:34:32)

tahanson43206 · 2025-03-10 09:59:40

In light of GW Johnson's analysis, as published here in the forum and elsewhere, I thought it might be possible for Google to survey the Internet to see what others might think about the recent Starship failures. Blaming Elon Musk seems to me to be amusing, because Elon Musk clearly has NO time to spend on SpaceX or Tesla or any of his other enterprises.

Conversation with Gemini
Hi Gemini! Thanks again for your help with previous questions. This one is a bit on the subtle side, because so little information is available. I'll understand if you have to make do with what little information you can find. The question is about the recent failures of the SpaceX engineering team with Starship tests 7 and 8. There is a school of thought that the problems SpaceX is seeing now are directly related to their decision to lengthen the Starship. Changes to the Heavy do not appear to have led to failure, but it seems clear that changes made to Starship caused (led to) the recent failures. Please see if you can find any informed speculation about the causes of the recent failure. Please note that vibration is reported to have occurred, but the video feed from Starship from separation to failure does not show any vibration. I understand the cameras are bolted to the frame so they might now show vibration, but nothing in the video of the aft section of the Starship shows anything out of order before failure.
It's true that analyzing SpaceX's Starship test flights involves navigating a complex web of technical details and evolving information. Here's a breakdown of what we know, with a focus on potential contributing factors to the recent Starship failures:
Key Points:
Recurring Issues:
Both Starship Flight 7 and Flight 8 experienced upper-stage failures during ascent. This suggests a persistent issue within the Starship vehicle itself.
Propellant leakage has been a recurring theme, though the origin points of these leaks have varied between flights.
Focus on Starship Changes:
While the Super Heavy booster has seen significant progress, including successful catch attempts, the Starship upper stage is where the primary challenges lie. This directs focus to the design and operational changes implemented in the Starship vehicle.
The changes to the Starship vehicle, including the lengthening, and internal plumbing changes could be contributing factors to the failures.
Vibration and Harmonic Response:
SpaceX has acknowledged issues with harmonic responses and vibrations in the propulsion system. These can lead to increased stress on hardware, potentially causing fatigue, leaks, and fires.
While visual confirmation of vibration can be challenging, the effects of such vibrations, like propellant sloshing and structural stress, can lead to observable failures.
Propellant Management:
Precise propellant management is crucial during ascent. Issues with fuel feed lines, tank pressures, and venting can lead to engine instability and failures.
The changes to the internal tankage and plumbing of the Starship vehicle could be contributing to the problems with propellant management.
Ongoing Investigations:
The FAA is conducting investigations into these incidents, which will provide more detailed insights into the root causes.
SpaceX is also actively analyzing data from each flight to identify and address problem areas.
Informed Speculation:
It's reasonable to speculate that the lengthening of the Starship and associated changes to its internal systems have introduced new challenges related to structural dynamics and propellant behavior.
The complexity of the Raptor engine system, combined with the extreme conditions of spaceflight, makes it susceptible to unforeseen issues.
The harmonics that are being found in the vehicle, could very easily be being exascerbated by the lengthening of the vehicle. Lengthening the vehicle would change the vehicles natural resonant frequencys.
The changes to the internal plumbing could be leading to new and unpredicted fluid dynamics within the fuel and oxidizer tanks.
Important Considerations:
SpaceX's iterative development approach involves learning from failures. Each test flight provides valuable data that informs future design improvements.
The Starship program is pushing the boundaries of space technology, and setbacks are to be expected.
In conclusion, while pinpointing the exact cause of the Starship failures requires further investigation, it's clear that a combination of factors, including structural dynamics, propellant management, and engine performance, are contributing to the challenges.
Thank you! I think your summary is as close as we can get until official reports are published.
You're very welcome! I'm glad I could provide a helpful overview. Space exploration is inherently complex, and SpaceX's approach of rapid iteration means we're often witnessing the engineering process in real-time. It's a fascinating journey, and I'm sure the official reports will offer even more clarity.

(th)

GW Johnson · 2025-03-12 09:07:36

Oscillations causing propellant leaks, fires, and explosions? GWJ 3-12-2025

I found a good Wikipedia article on “Pogo Oscillations” which explains (1) what happened on multiple Saturn-5 flights, (2) how longitudinal mode oscillations occur due to feedback, and (3) that this has been an issue with many rockets. Text from that article is appended below.

Bear in mind that there other oscillation modes in any flight structure besides longitudinal (usually down in the few to several Hertz range), but that lateral modes are generally going to be higher frequencies. I am familiar with combustion noise in ramjets and solid rockets, as being a few hundred Hertz, but usually only 1-5% of the average pressure level. If it exceeded 10%, we usually considered that “combustion instability” needing elimination, especially in solid rockets.

You don’t measure that sort of thing with digital data acquisition! The digitization (pixelation) totally obscures the real physics displayed in the pressure-tine trace! What was required was an analog tape recorder using FM data processing, and with at least 1 Megahertz response, because sometimes the instability oscillation frequencies could be several thousand to around a hundred thousand Hertz.

You play it back from the tape and plot it by analog means in different formats, until you can see that which you need to see in order to understand what happened. Usually you can pick out the frequency of the mode that is oscillating with feedback, as it will have the largest amplitude of all the other noise. This ain’t easy to do! And few do it that way anymore! Most of the young newbies out there would have no clue how to do it, and no experience at all with the antique analog equipment that is absolutely required to do this!

This phenomenon is flying-vehicle-related, something you would NEVER see in an engine-only ground test because none of the affected hardware is even there! And, you likely would NOT see it in a vehicle-mounted static test on the launch pad! That is because with the vehicle fixed to the pad, most all the flight-related oscillation modes are suppressed by the fixity, including any dynamic slosh effects inside the tanks that cause their own pressure fluctuations in the propellant feed lines. Basic message: what happens fixed to a launch pad is simply quite different from what happens flying free!

With it only showing up in a flying vehicle, plus having only youngsters on their staff who are oriented only to digital data acquisition (they hire no engineers over 40-45 years of age), I am entirely unsurprised that SpaceX has blown up two “Starships” during ascent without really understanding the cause yet! I hope they read this on the forums. They need it to work through this issue.

The longer upgraded “Starship” has a lower fundamental longitudinal structural vibration mode than the original shorter version, sort of like a longer organ pipe. But as the propellant load burns off, any propellant slosh mode frequencies can come to interact with rising longitudinal mode frequencies as the vehicle mass reduces. Same sort of thing affects all the modes, actually. Oscillation frequency is sort of a stiffness-divided-by-mass thing. And mass is dropping rapidly with time.

That time variation in natural frequencies also helps explain why the explosions occurred later in the ascent burn, by the way! That’s when the excitation better matched some natural mode frequency, allowing positive unstable feedback of energy. The oscillation amplitude then increases dramatically and quickly to dangerous levels.

GW

Quoted text:

From Wikipedia, the free encyclopedia
(Redirected from Pogo oscillations)

Pogo oscillation is a self-excited vibration in liquid-propellant rocket engines caused by combustion instability.[1] The unstable combustion results in variations of engine thrust, causing variations of acceleration on the vehicle's flexible structure, which in turn cause variations in propellant pressure and flow rate, closing the self-excitation cycle. The name is a metaphor comparing the longitudinal vibration to the bouncing of a pogo stick. Pogo oscillation places stress on the frame of the vehicle, which in severe cases can be dangerous.[1]

NASA Associate Administrator for Manned Space Flight George Mueller explained Apollo 6's pogo oscillation to a congressional hearing:

Pogo arises fundamentally because you have thrust fluctuations in the engines. Those are normal characteristics of engines. All engines have what you might call noise in their output because the combustion is not quite uniform, so you have this fluctuation in thrust of the first stage as a normal characteristic of all engine burning.

Now, in turn, the engine is fed through a pipe that takes the fuel out of the tanks and feeds it into the engine. That pipe's length is something like an organ pipe so it has a certain resonance frequency of its own and it really turns out that it will oscillate just like an organ pipe does.

The structure of the vehicle is much like a tuning fork, so if you strike it right, it will oscillate up and down longitudinally. In a gross sense it is the interaction between the various frequencies that causes the vehicle to oscillate.[2]

In general, pogo oscillation occurs when a surge in combustion chamber pressure increases back pressure against the fuel coming into the engine. This reduces fuel flow and thus chamber pressure. The reduced chamber pressure in turn reduces back pressure at the pump, causing more fuel to come in and repeating the cycle. In this way, a rocket engine experiencing pogo oscillations is conceptually operating somewhat like a pulsejet or pulse detonation engine. If the pulse cycle happens to match a resonance frequency of the rocket then dangerous oscillations can occur through positive feedback, which can, in extreme cases, tear the vehicle apart. Other situations that can induce fuel pressure fluctuations include flexing of fuel pipes.[3][4]

Pogo oscillation plagued the Titan II first stage during its development, which delayed man-rating the rocket for the Gemini program. The Saturn V first stage (S-IC) experienced severe pogo oscillation on the flight of Apollo 6, which damaged the S-II and S-IVB stages above and likely would have triggered an abort if the flight had carried a crew. The second stage (S-II) had less intense pogo on other flights. The oscillations during Apollo 13's ascent caused the center engine to shut down about two minutes earlier than planned. The loss in thrust was compensated by longer burns from the second and third stages.

Hazard
[edit]

If the oscillation is left unchecked, failures can result. One case occurred in the middle J-2 engine of the second stage, S-II, of the Apollo 13 lunar mission in 1970. In this case, the engine shut down before the oscillations could cause damage to the vehicle.[1] Later events in this mission (an oxygen tank exploded two days later) overshadowed the pogo problem. Pogo also had been experienced in the S-IC first stage of the uncrewed Apollo 6 test flight in 1968.[5] One of the Soviet Union's N1-L3 rocket test flights suffered pogo oscillations in the first stage on February 21, 1969. The launch vehicle reached initial engine cutoff, but exploded 107 seconds after liftoff and disintegrated.[6] There are other cases during uncrewed launches in the 1950s and 1960s where the pogo effect caused catastrophic launch failures, such as the first Soviet spacecraft to the moon Luna E-1 No.1 and Luna E-1 No.2 in September and October 1958.[7]: 440–446

Modern vibration analysis methods can account for the pogo oscillation to ensure that it is far away from the vehicle's resonant frequencies. Suppression methods include damping mechanisms or bellows in propellant lines. The Space Shuttle main engines each had a damper in the LOX line,[4] but not in the hydrogen fuel line.

End quote

Calliban · 2025-03-12 09:59:14

GW, that is an informative description. The problem would appear to be worse for large propellant tanks with a higher static pressure at the bottom of the tank. The bellow type throttle valves are an interesting solution. I would imagine that the time constant of those valves would need to be carefully tuned to avoid shocking the turbopump blades. Increasing chamber pressure would help as well, but SpaceX have already pushed chamber pressure to extreme levels from the specs that I have seen.

Last edited by Calliban (2025-03-12 10:01:48)

tahanson43206 · 2025-03-12 11:17:35

There may be helpful information in these links found by Google:

I think everyone has seen this from February 27:
https://www.fox7austin.com/news/spacex- … day-launch

This report contained nothing new about Test 8.
https://www.cbsnews.com/news/spacex-starship-launch-breakup-second-failure/#:~:text=Telemetry%20indicated%20the%20fire%20broke,due%20to%20unexpected%20harmonic%20vibrations.''

There was nothing new in this report either:
https://www.theregister.com/2025/02/26/ … _starship/

Based upon today's request to Google, nothing new has been published about the failure in Test 8.

Coverage of Test 7 seemed fairly similar in the three links.

The links above describe a number of changes made to try to reduce leaks and other risks.

Google did not find POGO in any of the searches it ran.

(th)

RGClark · 2025-03-13 06:54:57

NSF - NASASpaceflight.com
@NASASpaceflight
Interesting: SpaceX is looking to hire a Propulsion Systems Engineer, responsible for designing, analyzing, and building feedline system to feed Raptor engines on Starship.
https://boards.greenhouse.io/spacex/job … 607806002…
GlzFCVNXcAEgohI?format=jpg&name=medium
https://x.com/NASASpaceflight/status/18 … 5587286458

Repeated engineering failures stem from the top. First, hire a true Chief Engineer. Then follow standard industry practice of doing full-up(all engines), full mission duration, full thrust static tests.

Bob Clark

Last edited by RGClark (2025-03-13 06:56:00)

GW Johnson · 2025-03-13 19:24:46

You won't see POGO in a static test of stage on a stand. It is necessarily fixed to the stand, and that fixity precludes many of the vibration modes available in flight. That was precisely why they didn't see POGO until they flew, decades ago. It afflicted a lot of rockets. Titan-2 and Saturn-5 being only 2 examples.

I agree with you that SpaceX needs a true Chief Engineer who is a real engineer. Musk does not qualify, never did. He earned a bachelor of arts (not science!) in physics, and a bachelor level degree in economics. All his other "qualifications" and "certifications" are only honorary. Go look him up in Wikipedia. It's all there.

At one point, he was going to move SpaceX headquarters to Texas, but he never did. I think I might know why. Under Texas law (the engineering practice act), it is seriously illegal to publicly call yourself an "engineer" in Texas, unless you really are one. He calls himself SpaceX's "Chief Engineer". His ego would not let him relinquish that title.

Engineers who build public works in Texas must be board-certified and registered as professional engineers; it is illegal to practice public works engineering otherwise. For companies building things that are not public works, the engineers to not have to be registered professional engineers, but the top dog who signs the drawings needs to be. Some outfits get away with violating that, and apparently SpaceX is one.

GW

Last edited by GW Johnson (2025-03-13 19:30:29)

RGClark · 2025-03-18 08:00:42

“Angry Astronaut” discusses a critical review article of the Starship that claims it can’t be made to work:

Engineer claims that SpaceX Starship can't be fixed! Is he right?
https://www.youtube.com/live/CxEcTXTgiM … sl-0yQVCmi
(There is an audio glitch at the beginning of the video. Fast forward to the 7 minute point.)

In the video, Angry disagrees with the authors conclusions, the article being here:

Starship Was Doomed From The Beginning.
The fatal flaw SpaceX can’t overcome.
Will Lockett
Published in
Predict
8 min read
https://medium.com/predict/starship-was … 3bf809539c

The authors primary argument is the desire to make the upper stage reusable is making it too heavy. Angry Astronaut critiques this argument by saying the Space Shuttle was 100% reusable. This is not correct for the entire Space Shuttle system since the external tank was expendable. But it is true that the upper stage, the orbiter itself, was reusable.

Still, it has long been discussed in the field a criticism of the space shuttle system was how heavy that upper stage was compared to the payload. The dry mass of the shuttle orbiter was about 80 tons. But the payload was about 24 tons. The reusable upper stage was nearly 4 times heavier than the payload.

This is backwards in accordance to how normal rockets work. Normally you want to make that dry mass for the upper stage as low as possible since every extra kilo added to an upper stage dry mass subtracts directly from the payload possible.

Normally, the payload would be multiple times more than the dry mass of the upper stage. For instance for the F9 the payload is ca. 20 tons, but the upper stage dry mass is only ca. 4 tons. And for the Saturn V the payload to LEO was 100+ tons, while the dry mass of the upper stage, the 3rd stage, was only ca. 15 tons.

Quite interestingly, in regards to the Starship the payload for V1 according to Elon is only in the range of 40 to 50 tons, despite the original plan of 150 ton capacity. And indeed the dry mass of the Starship V1 is in the range of 160+ tons, quite analogous to the ratio for the reusable Space Shuttle orbiter of the dry mass of the upper stage being ca. 4 times more than the payload.

SpaceX recognized this is too low a payload for a rocket of the Superheavy/Starship size and wants to make the rocket larger to get to its desired payload capacity. Both attempts of flying the larger V2 upper stage resulted in the stage exploding in flight. The author of this critical review article argues its because of the need to lighten the dry mass of the vehicle to get the desired payload.

I don’t know if that is the case, but it should give SpaceX pause that in the V1 version, the one we know so far that can get to orbit, the payload had the same small proportion of the dry mass of the upper stage as did the Space Shuttle of only one fourth.

Bob Clark

GW Johnson · 2025-03-18 17:54:49

Comparisons to Shuttle are totally invalid, because it was NOT a "classic" two-stage vehicle! While none of the main engine propellants were in the orbiter, its main engines fired from launch all the way through the initial ascent. Their propellants were in the external tank. The only engines with propellant aboard the orbiter were the OMS engines and their storable hypergolics. These were used for orbit insertion at the end of the ascent, for on-orbit maneuvering, and for the de-orbit burn. The thing could not thrust greater than weight for launch without the solids. It was a sort of complicated stage-and-a-half. Unique is what it really was.

Myself, I think talking about Starship inert masses under 120 metric tons is utter rank nonsense! Are you listening, Musk?

But very substantially higher is also nonsense! Higher, maybe, but not dramatically so.

Growing the length makes that inert mass higher, yes, but it also makes propellant mass higher, at a faster rate. It is simply too early in the development flight test program to reliably predict what the final inert mass of a Starship (whichever version) is going to be. Mass ratio goes up when you do that, not down. And mass ratio determines the propellant mass fraction. For which if inert fraction remains the same percentage, gives you a higher payload fraction.

That being said, it is really easy to increase the inert fraction, which increase comes directly out of payload fraction.

Let's see if they can solve the POGO oscillation problem. There's a very significant thrust oscillation exciting longitudinal structural resonances in the longer updated Starship structure, and in the propellant feed plumbing. They really need to smooth out that thrust oscillation. Methane leaks easier than kerosene. It's almost as bad as hydrogen.

The new Raptor-3's are being tested at McGregor, and they have a rather substantial oscillation at 5-10 Hz, which rattles the ever-loving hell out of my doors and windows, but is too low a frequency to hear with the ears (the low-end cutoff for humans being about 20-25 Hz). The Raptor-2's had a similar oscillation, but at less amplitude. I heard/observed nothing like that with Raptor-1, or any of the Merlins.

This thrust oscillation in the Raptor-3's is large enough that I consider it "combustion instability". At the old rocket plant, we never allowed a design out the door with oscillations that large.

GW

kbd512 · 2025-03-19 13:11:58

If there's a mere kernel of truth to what Will Lockett is asserting about Starship's design being highly mass-constrained because it's already over its target inert weight, then there are alternative steels that will perform better than 304L. Stainless does a lot of things fairly well, but austenitic stainless yield strength and ultimate corrosion resistance are very pedestrian when compared to alternative options. I've stated this before, in this very thread, I think, but austenitic stainless steel is a poor structural steel when compared to other now-viable alternative cryogenic-capable steels, such as Mangalloy (high-Manganese steel alloys). Mangalloys have minimum yield strengths ranging between 58ksi and 78ksi. 304L stainless steels have minimum yield strength of 25ksi, and ultimate tensile strength of 70ksi. That means a Mangalloy is 2X as strong as 304L, at a minimum, and could be over 3X stronger than 304L.

Mangalloys don't do quite as well as austenitic stainless steels in V-notch tests at cryogenic temperatures, but they're still a very strong runner-up to stainless. As far as strength at elevated temperatures goes, Mangalloy is stronger until you reach temperatures where both steels become silly putty. There are trade-offs associated with every type of steel, which is why we have so many varieties to choose from.

If you require optimal corrosion protection, either from LOX or elevated temperatures associated with atmospheric reentry, there is no stainless steel I'm aware of that performs nearly as well as a Silicon-based CVD coating. It's not even close. There's a mountain of testing and real world use case evidence behind these coatings, which is why they're used in high temperature corrosive chemical processing plants where stainless fails, the oil and gas industry which exposes their piping and instruments to elevated temperatures and corrosive chemicals, and marine applications.

When your base steel structure is 3X stronger than 304L, as well as significantly cheaper than any grade of stainless, you can afford to build a lot more rockets without spending a lot of money. More importantly, you can achieve significant mass reduction on top of the base structural material cost reduction, which then leads to even more cost reduction. Making the vehicle 25% to 35% lighter is realistic, while still being significantly stronger than a vehicle made from 304L. What would a 35% mass reduction do for a Starship? Quite a lot. The engines don't need any more performance than they already have. If pushing the engines to their limits is part of the issue, then a significantly lighter vehicle will help.

Maximum allowable stress for a 304L welded tube / pipe (like a propellant feed line) is 14.9ksi, at least if you're following ASME BPVC. Well... That's very low compared to something "exotic" like A36 (one of the most common and cheapest types of structural steels, generally considered inadequate for any aerospace uses), which would still be 24ksi. While A36 won't survive cryogenic exposure, Mangalloy will. So... If we're running up against weight and strength issues, a cheaper steel with good mechanical properties at low and high temperatures, as well as a much greater strength reserve, is going to serve SpaceX better than 304L. Nobody with any sense attempts to fabricate buildings or ship hulls from stainless- the strength is too low, the cost too high, the corrosion resistance is not as great as cheaper alternatives, and the weight increase associated with using a weaker steel is too significant to merit its use outside of highly specialized use cases where more than one factor warrants its use.

I can't know if this Will Lockett fellow is "over-the-target", so-to-speak, or not, but if he's merely somewhere near the target, then perhaps someone at SpaceX ought to consider alternative fabrication materials. "The Angry Astronaut" makes a good point about Bill Gerstenmeier knowing a thing or two about aerospace engineering. If Bill thought this wouldn't work, he would've said something or left the company.

RGClark · 2025-03-20 08:33:13

Another article discusses this critical review of Will Locket and also the opinion of Robert Zubrin that SpaceX is taking the wrong approach in wanting to land the entire Starship on the Moon or Mars:

Mini-Starship or bust? Experts clash over SpaceX’s future.
https://floridamedianow.com/2025/03/spacexs-future/

As Zubrin notes, standard spaceflight engineeering says you add an additional, smaller upper stage to do high delta-v destinations. Zubrin has made this point numerous, numerous times:

https://x.com/robert_zubrin/status/1374 … 00896?s=61

https://x.com/robert_zubrin/status/1725 … 79000?s=61

https://x.com/robert_zubrin/status/1278 … 20833?s=61

https://x.com/robert_zubrin/status/1256 … 45728?s=61

https://x.com/robert_zubrin/status/1256 … 18819?s=61

https://x.com/robert_zubrin/status/1256 … 25249?s=61

https://x.com/robert_zubrin/status/1192 … 85987?s=61

https://x.com/robert_zubrin/status/1192 … 15552?s=61

https://x.com/robert_zubrin/status/1192 … 24192?s=61

https://x.com/robert_zubrin/status/1178 … 41184?s=61

https://x.com/robert_zubrin/status/1127 … 78464?s=61

https://x.com/robert_zubrin/status/1127 … 68961?s=61

And finally,

Robert Zubrin @robert_zubrin
Starship can revolutionize Earth to orbit. But for landing on the Moon or Mars we need to stage off it. Using Starship as a lunar lander is like using an aircraft carrier for white water rafting.
https://x.com/robert_zubrin/status/1178724273025933312?

Zubrin has also argued this directly to Musk and Musk has always stubbornly refused it. Stunning when you think about it, but the development problems with the Starship could be solved with one simple, and I say obvious, move: hire a true Chief Engineer to lead the development. But Musk is too close to it to see that he is the problem.

Bob Clark

Last edited by RGClark (2025-03-20 08:35:39)

RGClark · 2025-03-20 08:38:31

GW Johnson wrote:

…
This thrust oscillation in the Raptor-3's is large enough that I consider it "combustion instability". At the old rocket plant, we never allowed a design out the door with oscillations that large.
GW

There’s no telling if this will ever be solved with Musk serving as Chief Engineer. Look up ‘hubris’.

Bob Clark

kbd512 · 2025-03-20 11:38:43

Dr Clark,

All the personal attacks against Elon Musk, for whatever your personal motivations happen to be, won't solve a thing.

RGClark · 2025-03-20 14:27:41

kbd512 wrote:

Dr Clark,
All the personal attacks against Elon Musk, for whatever your personal motivations happen to be, won't solve a thing.

It’s not personal. It’s purely engineering. It’s literally basic spaceflight engineering that Elon is ignoring. No true Chief Engineer would ignore such principles. Basic principles in engineering are being repeatedly ignored by Elon. SpaceX has many very good engineers. But Elon repeatedly ignores their recommendations.

That is literally the only reason why Starship is not already delivering high payload mass to orbit.
If you read any of the biographies of Elon a common feature that emerges is Elon is brutal in firing those who he feels their engineering is not up to the job. He can’t see that he is that person now.

Bob Clark

kbd512 · 2025-03-20 18:31:38

Dr Clark,

That is literally the only reason why Starship is not already delivering high payload mass to orbit.

Unless you're privy to quite a bit more of the inner workings of the Starship program than everyone else here, that assertion is backed by nothing but a personal belief. You've convinced yourself that you know something on the basis of tidbits of information online with little greater context.

This reminds me of the time you told me about an Aluminum alloy "stronger than Carbon Fiber"? The way you came to that conclusion, which was also based upon something posted online, is remarkably similar to what I see here. You simply would not let go of that belief, despite the engineering data I provided.

If you've now convinced yourself that "just one man" is somehow preventing Starship from completing a successful orbital test flight, then I think you're making yet another logical leap, on the basis of what someone else posted online.

How is that an acceptable substitute for knowing something about what the engineers at SpaceX are actually doing?

Elon Musk clearly isn't the only person there who is doing things and making decisions at SpaceX. You may have convinced yourself that he is, but I can promise you that SpaceX would never have made Falcon I fly if that was actually true.

RGClark · 2025-03-21 01:57:45

Actually, I have given examples where Elon ignored basic principles of spaceflight engineering. The flame trench fiasco is one of many:

Read over those comments by Robert Zubrin I linked in post #2019. That he makes this point so vociferously suggests it’s because it’s basic spaceflight engineering being ignored: to get to high delta-v destinations use staging.

Bob Clark

GW Johnson · 2025-03-21 11:39:39

I've already voiced my opinions in other threads of Elon Musk as "Chief Engineer" of SpaceX. He has a BA in physics and a bachelor's in economics. All his other credentials are honorary. Look him up in Wikipedia.

The real engineer's at SpaceX are Glynn Shotwell and her team. They usually do pretty good, when Musk doesn't over-rule them, or piss off the FAA. But there are exceptions, as with any outfit.

But with the Musk legacy of hiring no one over 40-45 years of age, in order to be able to demand chronic 70-80 hour weeks, and the high turnover rate that causes, there are no oldsters at SpaceX who know much of anything about POGO instabilities! I think that's probably what they've bumped into.

And don't forget, the "science" in rocket science, being the stuff that was written down, is only about 40% or less of what you need to know, especially if you bump into a difficult, relatively-intractable problem. That is EXACTLY where the strategy of "build it, break it, build another" will let you down.

You need some oldsters who know the art, which was never written down because nobody wanted to pay for writing it all down. There would be few to none oldsters who would know the art of treating POGO, as the last time that was a big concern was 6 decades ago. I'm not one who knows that art myself. Solids and missiles are different from liquid-engine launchers.

GW

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