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I as well glad to see you are back visiting, I hope all is well.
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I was out of the country for 5 weeks, traveling in Europe with my family. All is well!
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Back to the topic at hand, loss of the Starship, and failure of Superheavy to return to the Gulf of Mexico near Starbase.
There isn't enough information on Starship for anything other than some guesses.
Focus on Superheavy, I really think this is the first time that a "flip maneuver" has been attempted with anything this large and containing significant mass of CH4 and LOX. I am in agreement with GW's thoughts of voids caused by sloshing around, subsequently interrupting flow through the turbopumps, leading to loss of the engines and their failure to relight. I have no idea whether SpaceX has done much baffling in the tanks?
Has anyone seen the inflight video from the NASA WB-57 from near 60,000 feet? Nothing that I have seen so far.
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I did a bit of Internet snooping today and found some WB-57 footage from the 14 April 2023 launch. Hoping for something similar from the Saturday flight, but so far nothing has been released (that I could find).
https://www.google.com/search?q=wb-57+n … A2TY0,st:0
Last edited by Oldfart1939 (2023-11-23 22:26:28)
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This was just aired on YouTube, and incudes some interesting speculation regarding the failure of Super Heavy to successfully complete the boost back burn and reasons for the destruction of Starship 25. They link heating from hot staging as the reason, and concluded that some changes to the heat protection on subsequent flights would be needed.
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The voice sounds like a real human, but pronounced several words wrong. I suspect an AI voice synthesizer, trained to sound like a specific human narrator.
Hot staging does raise the concern that flame within the engine compartment could damage Starship engines. Could it cook electronics? Melt wire insulation? Damage electric gimbal actuators? Although there is a concern of hot rocket exhaust causing damage to the first stage, the hot staging adapter has a flame redictor to prevent direct contact of rocket exhaust with the top of the liquid methane tank. If you look at the video, it appears the first stage lost control due to several engines failing to re-ignite. Or failing to maintain thrust. The flip maneouvre caused sloshing, and without a specific ullage thruster, main engines had to maintain acceleration to ensure propellant stayed settled on the bottom of the tanks. Very large propellant tanks require anti-slosh baffles, but the only rocket before that has had to deal with a flip is Falcon 9/Heavy. And it isn't as large. I'm not convinced baffles are sufficient to keep propellant settled. Well, at least some engines did continue to thrust, so perhaps anti-slosh baffles are the answer. In any case, RUD of the first stage appeared to be self-destruct. So I don't think the first stage issue was caused by hot staging.
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Here's a better analysis and without the annoying AI voice.
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The consensus here seems to be that something went wrong with settling the propellant in the booster during its flip. I cannot argue with that, it would be quite fatal to engine restarts.
There is a way besides baffles to "fix" the problem. Baffles are significant added inert mass, and can be "iffy" in their effectiveness. The simple lightweight solution was applied to the Saturn-5 second stage for starting after staging, which was utterly reliable in operational use. Each stage had 3 small solid "pancake" motors (for redundancy and summed thrust). These burned only several seconds, enough for the propellants to settle.
On a reusable stage, they are a small item you replace for the next flight, just like reloading bullets in your gun. They were about twice the size of an old-time spring-powered alarm clock, and less than 5 lbm each. 15 lbm of solid ullage motors on a stage massing many tons is a trivial inert penalty, wouldn't you say?
And the cases could be easily cleaned, re-insulated, and re-cast with propellant, being very small, unsegmented, and easily accessed in a stage landed on land, with no exposure to saltwater submergence. Being so small, there are many solids makers who could supply them, so competition precludes monopoly price-gouging.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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The real question to be resolved here is what happened to the Starship upper stage? Contact was lost just before engine cutoff. Nobody seems to know why, or what really happened.
Which points toward a serious instrumentation and telemetry shortfall for an experimental flight test. Almost any outfit experienced in flight tests of any kind knows better than that.
I agree that the test flight was largely successful, because (1) the vehicle rose undamaged from a pad that was not blasted to bits, and (2) the hot staging seems to have worked. Between the video and the telemetry, they should be able to figure out why the first stage failed after staging.
However, I am concerned about them identifying what went wrong with the second stage, because of the apparent paucity of data. The deafening silence about that is quite alarming.
GW
Last edited by GW Johnson (2023-11-26 11:18:57)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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For GW Johnson re #35...
I don't think there is a "deafening silence" ... I read a short item almost immediately that the Starlink system failed. The only mistake would appear to have been depending upon Starlink to provide reliable Internet. Starlink is good as a primary system, but there should have been a backup. My guess is that there ** will ** be a backup for the next flight.
(th)
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See my second sentence in post #24, in which I commented on loss of signal from Starlink.
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This just popped up on YouTube, and is a simulated "tank slosh" done by an engineer.
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GW Johnson,
I suspected Starship had a similar engine restart problem after flip. Similar to SuperHeavy. If engines completely shut off, as they would after orbital insertion, then how do they restart? Falcon 9 upper stage has cold nitrogen thrusters for attitude, and uses those same thrusters for ullage. However, Starship just uses autogenous gas for ullage thrust. How to separate gas from liquid in zero-G? And if heating in the vacuum of space is not sufficient, then there may not be enough gas for ullage thrust.
One commenter on YouTube said cold liquid mixed with gas may cause that gas to condense. That could cause the tank to crush due to lack of pressure. It wouldn't collapse like a can in air pressure, because space is vacuum, but could lack of pressure cause loss of strength under thrust? And lack of pressure could result in lack of ullage thrust. But all this is guessing. We have no video, no data.
Someone mentioned bright spots on Starship. Possibly hot spots where heat shield tiles fell off. But I don't know how they could have seen that. Video I saw ended with Starship thrusting away from SuperHeavy. It cut out before atmospheric entry.
If Starship did fail at atmospheric entry, I would call that a success. Last test didn't get nearly that far. Success of the rocket that far would mean the rocket worked.
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I saw multiple tiles falling off at launch, right off the pad, in close-up video camera angles. This was just bright spots appearing, the tiles themselves are too small to resolve, despite what some observers claim.
There's no public information about whether Starship had shut down and was trying to restart, or was still burning, when contact was lost. That's part of the "deafening silence" I commented about. All they said was it was "nearing" orbit altitude. The only figure I heard was about 100 miles up, with "orbit altitude" claimed to be 150 miles. I'm unsure how reliable any of that is.
Based on the 1 partial orbit flight plan, I don't think they intended to make an orbit insertion burn, they were already on a near-surface-grazing ellipse with its apogee at the intended orbit altitude. Any orbit insertion burn would have been at that apogee, halfway around the planet, and that's NOT where contact was lost! It was lost much earlier, way out over the Gulf or the Caribbean.
That being said, I have to doubt whether any restart was involved at all, for the Starship upper stage. There should have been no ullage effects for the upper stage during staging, because 3 engines were burning when they lit the 6 engines in Starship just fine. Starship left the vicinity of staging under its own thrust.
Now, if there was a failure of gas pressure in the propellant tanks aboard Starship, that could cause a loss of structural integrity, especially if they are counting upon the pressurization effect for part of their structural strength. I'm not sure they do, because the forward portion ahead of the tanks is not so pressurized, to the best of my knowledge. If it is, they have not said so in public.
If they are counting on pressurization for strength, the entry risk is elevated. Any lost tile on the windward side is a burn-through, and any burn-through is a depressurization. No way around that! None at all!
GW
Last edited by GW Johnson (2023-11-28 11:54:59)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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SpaceX narrators explicit stated they would not perform an orbital insertion. It would be almost orbit. That was for safety. However, I still believe that would require a deorbit burn. If it doesn't enter orbit, I guess you can't call it "deorbit". What would you call it? Atmospheric entry burn? Considering splash-down would be just outside Hawaii, that means more than 3/4 around the Earth. Boca Chica is 97°W, Hawaii is 155°W. Plus minutes. So about 58° short of circumference. Engines would turn off and coast before atmospheric entry.
I'm just guessing. I saw what you saw. It thrusted successful until loss of signal. Then nothing. After a certain time, they gave up waiting. Automation would have triggered the flight termination system after loss of signal for a certain time, so once that time elapsed there was no point in waiting longer.
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Assuming an intact and capable heat shield (something not yet demonstrated with Starship), there's no need for an entry burn. The trajectory, being a near-surface-grazing ellipse, will inherently take you into the atmosphere for hypersonic aerobraking. Speed at entry interface will be pretty close to 7.9 km/s.
The "entry burn" performed with Falcon cores being landed, is simply control of speed for an object hitting sensibly-dense air without any heat shield. With exposed lithium-aluminum alloy structure, service temperatures are limited to under about 350-400 F.
The only way to do that is to slow speeds back to something well under the 1.8-2 km/s staging speed. Falling back like that after the "boost-back burn", it would otherwise hit the denser air going way too fast. 1.8-2 km/s is about Mach 6 here on Earth. Boundary layer recovery temperatures will be near 2700 F, and that's way too hot. To reduce that to about 350-400 F, they have slow entry speeds to about 2-2.5 Mach, which is around only 0.8 km/s speed. So the "entry burn" dV is something just over 1 km/s. It's not trivial. That's driven by the choice of aluminum structure.
They have to do that substantial slowdown for entry because re-radiation cooling is rather weak at only 400 F, even with a dull black surface finish. It is much weaker still with those shiny light-colored surfaces on Falcon cores. There is a bit of convection into the propellant vapors inside the tanks, but not anywhere near enough to act as an entry coolant! So the skin will "soak out" very close to boundary layer recovery temperature, and rather quickly, because that skin is necessarily thin. No heat sink mass available.
You can go only a bit faster with titanium (about Mach 3 to 3.2), which has service temperatures (depending on which alloy) in the 600-800 F range. (Despite widespread belief otherwise, titanium is not a high-temperature material. It is no better than ordinary mild carbon steel at resisting heat.)
304L stainless has a service limit near 1200 F, determined more by scaling than strength, which is already somewhat weak at that temperature. Re-radiation cooling becomes feasible at surface temperatures in the 1000-1200 F range, but it only works good if the surface is dull and dark (which the exposed metal on Starship is not). SS316L is more expensive, but resists scaling to about 1600 F. All the stainlesses have about the same modest hot strengths. The hotter you take them, the weaker they get. They'll get you into the Mach 4-5 range, if surface finish is dull and dark. Slower if shiny.
The X-15 had structural skins made of "Inconel-X", now known as Inconel X-750 in Mil Handbook 5, which has a service temperature limit in the 1600-1700 F range, and is still substantially strong at that temperature. That's good as a lateral skin to about Mach 5.5-6.5, but it is rather heavy.
There are some exotic alloys used in turbine blades and afterburner parts that can go to the 1800-2000 F range as service temperatures. But they have fairly low hot strengths (which means turbine blades must be thick parts near their roots, and will likely also need internal liquid cooling with a sacrificial coolant).
Stagnation zones are more limited than lateral skins, because stagnation heating is higher than that on lateral skins. If cooled by re-radiation, the surface equilibriates hotter. To hold the temperatures to feasible levels, your speed limits are slower.
GW
Last edited by GW Johnson (2023-11-29 10:49:44)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Ok, so either mixing residual gas with remnant cryogenic propellant caused condensation of gas which reduced tank pressure too much, or they lost too many heat shield tiles. Shuttle lost heat shield tiles on its first launch. I could go into detail what Shuttle experienced, but if that's what happened to Starship, I consider this a successful test.
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Ps. Re post #42: Wonderful details! I bow at the feet of the master.
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