Starship is Go...

RobertDyck · 2025-03-21 13:09:11

The F1 engine of the first stage of Saturn V had a POGO problem. That was the largest rocket engine ever built. The top of the combustion chamber was injector holes alternating fuel/oxidizer. Combustion would oscillate. Just as an explosion be used to put out an oil fire, the explosion pushes the combustion away from the fuel source long enough to extinguish the fire. The same happened inside the engine. The F1 engine had a "burst" or "explosion" in one area of the combustion chamber, which put out the fire/combustion. But the engine was large enough that it didn't extinguish the entire engine. Compression caused a "burst" in another part of the combustion chamber. This caused cyclical bursts moving around the combustion chamber. Amplitude of the bursts increased with each one, until force ruptured the combustion chamber. This caused the engine to literally explode. I believe that's how POGO works. Engineers at Rocketdyne solved that by installing baffles in the combustion chamber. This contained the burst, and the engine basically acted as if it were several separate smaller rocket engines. The baffles didn't have to extend far past the injector plate; just ensure combustion expanded toward the throat, not sideways.

A view up the F1 engine:

GW Johnson · 2025-03-21 13:22:33

Rob:

The process you describe in the F1 is what causes serious thrust oscillations, which can build up and destroy the engine, or might not (just run very rough).

When that thrust oscillation interacts resonantly with either (or both) vehicle structural oscillation modes or organ-pipe fluid oscillation modes in tanks or plumbing, the entire vehicle is at risk of breaking up. The feedback is feed pressure changes feeding back into the rough-burning thrust oscillations. The term "POGO" encompasses all of those.

The Apollo-6 problem had thrust oscillations in the first stage kerosene-LOX F1's that shook the vehicle so violently as to damage the LH2-LOX J-2's in both the second and third stages. The Apollo-13 problem was J-2 engines shaking so violently in the second stage as to cause 1 engine to shut down lest it explode. Different, and yet many of the same things.

The Titan-II man-rating for Gemini was delayed by thrust oscillations that broke up test vehicles in flight. Those were NTO hydrazine storables. I'm not sure, but I think Atlas might have suffered from some of this, too.

GW

RGClark · 2025-03-21 17:58:20

Another expert engineer criticizes the multi-refueling approach SpaceX is taking to get to the Moon and Mars as a bad approach, former high ranking NASA official Daniel Dumbacher:

SpaceX Needs A New Mini-Starship To Land Humans On The Moon And Mars.
By Kevin Holden Platt, Contributor. Kevin Holden Platt writes on space defense…
Mar 17, 2025 at 11:33pm EDT
…
“Our approach today has a very low probability to match the ‘before 2030’ milestone for landing humans on the Moon,” Daniel Dumbacher, who formerly served as Deputy Associate Administrator of NASA’s Human Exploration and Operations Mission Directorate, in charge of the Artemis lunar landings, testified at the hearing.

While he didn’t mention the fiery breakup of SpaceX’s Starship during its January flight demo, Dumbacher, now a professor in aeronautical engineering at Purdue University, said that the ship’s need to be refueled with super-cooled liquid oxygen and methane in low Earth orbit via multiple dockings with still-to-be-developed tankers - a complicated operation that has never been tested - before each flight to the Moon involves an assemblage of complex technologies that might not be perfected within the next five years.

“We might have to build a lander - we might have to scale down the current lander,” Dumbacher told the House, “so that we get to that 2030 landing.”

To avert potentially spiraling problems with testing the colossal Starships during the countdown to this new Moon quest, he said, “I’d get myself a simplified lander - so that I can get to the Moon - that does not require multiple launches.”
…
https://www.forbes.com/sites/kevinholde … -and-mars/

Bob Clark

RobertDyck · 2025-03-21 18:22:33

Gary, that's scary because resonant frequency of the propellant tanks will change continuously has they are drained. Think slide whistle. Or music on water glasses.

GW Johnson · 2025-03-23 09:58:15

Rob:

That's exactly right: the susceptibilities shift dramatically as you burn off propellant. We saw the same things in solids: as the propellant burned back, the internal cavity drastically changed is size and shape, bringing different resonant frequencies into play. You should find it scary. It really is!

With the solids, we had to analyze the shit out of it, with our best shot at instability computer models (which were imperfect at best), and then test the shit out of it, with the right analog instrumentation, all done by people already experienced using that analog instrumentation for instability detection, before we ever let a solid design out the door! Nonmetallized reduced/min smoke required much greater care and attention in this area, because there were no metal oxide particles or droplets to provide any damping action, just the soot. Absolutely NONE of that was a single simple calculation. Test data ALWAYS trumped any analyses, too!

Actually, the same thing is true of liquids, just the details differ.

I suspect the "new space" outfits will be seeing a lot of POGO-type troubles as time goes by, because none of the youngsters at those outfits know anything substantive about instability (since that remained about 80-90% art, never written down). And none of those youngsters knows anything about the analog instrumentation required to diagnose it, or anything about how to go about doing this kind of work with that analog instrumentation.

Myself, I think SpaceX accidentally dodged the instability bullet with their kerosene-fueled Merlins, because of the damping effect of the soot cloud in the chamber flame. A soot cloud is inherent when burning long-chain carbon things like kerosene. Vaporizing droplets can assist with that damping effect. But with the methane-burning Raptors, there is no soot on the flame, and the droplets evaporate far quicker.

Since SpaceX hires no one past age 40 to 45, how would any of their engineers who design these things know anything at all about such instabilities? Or even recognize them? Much less how to deal with them when they crop up? And they DO crop up!

"Build it, break it, build another" is a strategy that will always fail, if you cannot recognize the problem to be corrected.

GW

Last edited by GW Johnson (2025-03-23 10:04:47)

RobertDyck · 2025-03-23 11:06:37

You could offer your services. Elon would probably consider 40 hours/week "part time". Even 20 hours/week could help them. You just need to identify the problems, let the youngsters learn from your experience, and do the hard work to work out the details.
SpaceX Careers

Last edited by RobertDyck (2025-03-23 17:30:54)

tahanson43206 · 2025-03-23 11:50:20

For RobertDyck re #2031

A casual reader of your post might assume from your wording that GW had NOT offered his services.

This post is intended to correct that misunderstanding.

Please do not continue this in public.

(th)

GW Johnson · 2025-03-23 15:40:39

Rob:

I tried but could not make the link you provided work. Since I come from the slide rule days, that should be entirely understandable, and yet totally outside anything SpaceX is familiar with. I will try some other way.

Tom:

I never applied at SpaceX in any of the last several years, after finding out some years ago that they hire no one over age 40 to 45, because they demand chronic 70-80-hour weeks. Oldsters cannot do that. So they do not want them.

Both:

The problem is now that SpaceX is in deep kimchee with what looks like POGO troubles with Starship. No one there in California or any other site would have the slightest idea how to recognize this as a problem, much less have any idea how to approach solving it. That is because (1) no one has faced this trouble in some decades, and (2) this is 80-90% art never written down decades ago. All the people who knew are long dead or retired, like me. Even even what I know is only tangentially useful, as it deals with solids, not liquids. The real expert in solid instabilities was my friend and mentor W. Ted Brooks, who died many years ago.

The real experts in liquid instabilities would have been those who designed the J-2's and F-1's for Saturn-5. They are all long dead. Period. 10% or at most 20% of what they knew was ever actually written down anywhere at all. It was development stuff, not production stuff, back then.

Production: 50% art, 40% science, 10% blind dumb luck. Only the science was ever written down.

Development: art and luck factors very much higher.

GW

Last edited by GW Johnson (2025-03-23 15:43:31)

GW Johnson · 2025-03-23 16:50:59

Today I finally did make the video work of Flight Test 8 on the SpaceX website. I DO NOT do X or any of that other social media BS. I never will.

I saw no surprises, except that the Starship upper stage loss occurred right before the end of the ascent burn, with little propellant left aboard. I did see first stage engine losses on both ascent and descent, excepting the 3 gimballed engines dead center. That makes me wonder if we didn't see POGO in both stages.

If the control software is formulated correctly, ascent oscillations risking engine damage might cause shutdowns that do not recur during descent. Except that there were 2 engines that failed to restart during the 13-engine initial boost-back burn. 11 were enough to slow it so that the "design 3" could recover it on the tower.

The upper stage Starship did not seem to suffer problems until right before the end of its ascent burn onto the ascent ellipse. Then it lost 1 vac engine, then all 3 SL engines (with the thrust vector gimbal capability), then another vac engine, then it obviously tumbled totally out of control until self-destruct ended this.

Bear in mind that this ascent ellipse has apogee at LEO altitude, but a perigee at, or very near, the surface. THAT is what ensures automatic de-orbit, if you do not do a circularization burn at apogee. The ascent ellipse perigee is well down in the atmosphere.

GW

Last edited by GW Johnson (2025-03-23 16:52:37)

RobertDyck · 2025-03-23 17:45:55

Gary, how does the Starship siphon work? When I see engines not restart, but they do restart later, I suspect a propellant feed problem. Do they have a slosh problem?

RGClark · 2025-03-27 14:38:40

New high temperature ceramic heat shield material promoted to SpaceX to solve their heat shield problems:

AN OPEN LETTER TO ELON MUSK.
Dr. Ed Pope
https://www.linkedin.com/feed/update/ur … 4910300160

Published 3/14/2025
MATECH, Cal Nano aim to commercialize UHT composites.
The partnership’s combined technological advances and manufacturing prowess will target the scale-up and industrialization of FAST SPS for high-temp and UHT composites serving aviation, defense.
https://www.compositesworld.com/news/ma … composites

GW, perhaps you should pitch your high temperature ceramic directly to SpaceX.

Bob Clark

GW Johnson · 2025-03-27 21:00:46

Rob:

I don't know what "Starship siphon" refers to. But I think your suggestion of propellant slosh may be right. That surface is variably sloshing around, which may transiently uncover the suction intakes for the turbopumps when the propellant level is low enough. That would be a separate problem from the possible POGO structural instability driven by thrust oscillations.

Bob:

My old silicate composite material has a limited temperature range and while stronger than NASA's shuttle tiles, limited strength. It was something that worked by chance for me 4 decades ago, but was never developed since.

Ed Pope has several modern unique materials for very harsh temperature and structural environments, all of which are better than my old stuff. His zirconium carbide oxide material in particular caught my eye.

GW

Last edited by GW Johnson (2025-03-28 11:01:36)

RGClark · 2025-04-03 08:44:00

Robert Zubrin again presents the argument a Starship Mars mission would be better implemented by using smaller lander stage to do the actual landing rather than the Starship itself:

The flaws in Musk’s Mars mission
Our future lies on the Red Planet.
Robert Zubrin
April 1, 2025 6 mins
Furthermore, it needs to be done correctly. SpaceX’s Starship, which claims to be the world’s most powerful reusable launch vehicle, promises to be a terrific asset. But Musk insists that it should be the only vehicle used for the mission. While a Starship upper stage could be refuelled on orbit by tanker Starships, enabling it in theory to fly from Earth orbit to Mars, its 100-tonne mass makes it suboptimal for use as an ascent vehicle. It would make far more sense to develop and use a similar but much smaller vehicle — a “Starboat” if you will — to travel between the surface of Mars and its orbit. Starship plus Starboat could enable highly efficient missions to Mars. But this will require a programme leadership capable of speaking truth to power.
https://unherd.com/2025/04/the-flaws-in … s-mission/

Bob Clark

Void · 2025-04-03 09:39:36

Dr. Zubrin is not wrong, and SpaceX is not wrong in my opinion.

But SpaceX may be looking at financials more. I believe SpaceX-Elon Musk, were concerned that the upstarts would eventually do better than Falcon 9, so they wanted to try to leapfrog to an upsize which would be harder for subsequent rivals to break into.

Among the non-China new upstarts are:
Terran-R
Neutron
Nova

If a smaller rocket company could evolve to have a "Starboat" sized, ship, then as Dr. Zubrin has suggested, it could be refilled by just one or two Starship tankers.

Dr. Zubrin is an "All-In" Mars guy so he will not like Stoke Space NOVA, but I think the two, that is Starship and an upgraded NOVA could be very good. But we still have to find out if NOVA can work, and if Starship Tankers can work for that matter.

https://www.bing.com/search?q=stoke+spa … 1&hsmssg=0

A Starship Tanker could refill a NOVA, so that it could land on Earth. (Hydrogen) This would then not require it to bring Hydrogen for landing to orbit.

If ice were to be found in quantity on the Moon, then the NOVA might make a good lander, which could be refilled from a Moon orbiting Starship, and from the surface of the Moon.

Dr. Johnson has already said that the NOVA most likely could not handle air braking from the Moon to Earth, with its active cooling method.

But otherwise, that setup looks good to me.

And I would wonder if a one-time ablative heat shield could be strapped onto NOVA, to facilitate, a Moon>>>Earth airbrake.

Perhaps that method would only air brake to Earth orbit, or maybe the one-time heat shield could be dropped after atmospheric entry.

Perhaps it may prove possible to manufacture such a one-time heat shield on the Moon.

But Terran-R, might eventually be adapted to become a Starboat.

I will apologize for the intrusion; in case this has annoyed you.

Ending Pending

Last edited by Void (2025-04-03 09:55:01)

RGClark · 2025-04-06 17:30:55

Video interview of Zubrin discussing his recent article in Unherd:

Robert Zubrin: How humans will live on Mars.
https://youtu.be/BCX9YPAZa5A?si=2Q8Hnxj1U_aTyqkY

He thinks SpaceX could succeed at a manned Mars mission, but Elon’s recent statement of a manned mission by 2028 is overly optimistic.

Interestingly, he says if Elons fails it would be for the reason I suggested: hubris.

Bob Clark

Last edited by RGClark (2025-04-06 17:56:52)

RGClark · 2025-04-10 12:57:17

SpaceX is having difficulty finding an effective thermal protection system for Starship. I had earlier speculated that if it were giving sufficiently large wings, it could go completely without TPS. The possibility was occasioned by this article:

Wings in space.
by James C. McLane III
Monday, July 11, 2011
Wing loading (the vehicle’s weight divided by its wing surface area) is a prime parameter affecting flight. The antique aluminum Douglas DC-3 airliner had a big wing with a low loading of about 25 psf (pounds per square foot of wing surface). At the other end of the spectrum, the Space Shuttle orbiter has a high wing loading of about 120 psf. This loading, combined with an inefficient delta-shaped wing, makes the orbiter glide like a brick. A little Cessna 152 private plane features a wing loading of about 11 psf and modern gliders operate down around 7 psf. A space plane with huge lifting surfaces and a very low wing loading might not require any external thermal insulation at all. Building a space plane with a wing loading of, say, 10 psf should not be an impossible proposition. Perhaps some day it will be done.
http://www.thespacereview.com/article/1880/1

I found a further article that allows this possibility to be further constrained:

SpaceOps 2010 Conference
25-30 April 2010, Huntsville, Alabama AIAA 2010-1928
Applications of Ultra-Low Ballistic Coefficient Entry Vehicles to Existing and Future Space Missions
David L. Akin∗
Space Systems Laboratory, University of Maryland, College Park, MD 20742
https://spacecraft.ssl.umd.edu/publicat … hieldx.pdf

As discussed there the relevant parameter is actually ‘ballistic coefficient’, (mass)/(drag coefficient*drag area), β = m/CD*A, given in metric units kg/m^2, where the drag area is by cross-section.

The author uses a slightly variant definition given in units of pascals where up in the numerator is given the weight in Newtons. But it’s easy to convert to the more commonly used version by dividing by g, 9.81 m/s^2, i.e., about 10. He estimates when ballistic coeffcient is below 200 Pa, or about 20 kg/m^2 in the more common units, the max temperature during reentry would be ca. 800°C. This should be a temperature stainless-steel is able to withstand.

I estimated an additional wing area of 36m*50m = 1,800m^2 would allow the max temperature to stay below the 800°C point:

Reentry of orbital stages without thermal protection, Page 2.
https://exoscientist.blogspot.com/2025/ … thout.html

Bob Clark

Last edited by RGClark (2025-04-13 14:36:05)

kbd512 · 2025-04-11 10:06:20

Dr Clark,

Antonov AN-225's wing area was 905m^2 and wing tank fuel capacity was 375m^3.

Concorde's wing area was 358m^2 and internal fuel capacity was 119.5m^3.

For Starship to have 1,800m^2 of wing area, the wing's fuel capacity would be at least 600m^3, which is a third of Starship's present propellant capacity. Since 304L stainless is such a weak structural metal relative to its mass, the wing would need to carry propellant and be shaped to resist both internal pressurization loads and aero loads lower in the atmosphere. This proposal would increase the weight of Starship to impractical levels, which is why it won't be done. A lifting body Starship, which may or may not remain within tolerable mass limits, would require a complete redesign to provide 1,800m^2 of lifting surface area.

GW Johnson · 2025-04-11 16:23:38

Bear in mind that lifting bodies have a substantially-lower lift curve slope that delta wings, in turn less than swept wings, and that in turn less than straight wings. There is more to available lift than just wing area! By around a factor of 2 to 3! Planform shape is a big influence, as is wing section shape (lifting body vs airfoil). Especially considering the differences between subsonic and supersonic/hypersonic designs!

That being said, I have been looking closely at Bob's suggestion that low ballistic coefficient might eliminate the need for heat shielding. I am running a generic study across a very wide range of ballistic coefficients, to see what the peak stagnation heating rates and peak deceleration gees look like, as well as end-of-hypersonics altitudes, for fixed entry speed and entry angle below horizontal, in Earth's atmosphere. These are at fixed mass and hypersonic drag coefficient, with a fixed "nose radius"/diameter ratio. I vary diameter. Just generic, but well within the ballpark.

I will not take this through any realistic vehicle designs, but it will provide design constraints in terms of surface stagnation zone temperatures, and average pressures across the heat shield at peak deceleration. Both are crucial heat shield parameters.

GW

RGClark · 2025-04-11 18:02:18

GW Johnson wrote:

Bear in mind that lifting bodies have a substantially-lower lift curve slope that delta wings, in turn less than swept wings, and that in turn less than straight wings. There is more to available lift than just wing area! By around a factor of 2 to 3! Planform shape is a big influence, as is wing section shape (lifting body vs airfoil). Especially considering the differences between subsonic and supersonic/hypersonic designs!
That being said, I have been looking closely at Bob's suggestion that low ballistic coefficient might eliminate the need for heat shielding. I am running a generic study across a very wide range of ballistic coefficients, to see what the peak stagnation heating rates and peak deceleration gees look like, as well as end-of-hypersonics altitudes, for fixed entry speed and entry angle below horizontal, in Earth's atmosphere. These are at fixed mass and hypersonic drag coefficient, with a fixed "nose radius"/diameter ratio. I vary diameter. Just generic, but well within the ballpark.
I will not take this through any realistic vehicle designs, but it will provide design constraints in terms of surface stagnation zone temperatures, and average pressures across the heat shield at peak deceleration. Both are crucial heat shield parameters.
GW

Thanks. I would be interested in seeing your conclusions.

Bob Clark

RGClark · 2025-04-11 18:22:24

kbd512 wrote:

Dr Clark,
Antonov AN-225's wing area was 905m^2 and wing tank fuel capacity was 375m^3.
Concorde's wing area was 358m^2 and internal fuel capacity was 119.5m^3.
For Starship to have 1,800m^2 of wing area, the wing's fuel capacity would be at least 600m^3, which is a third of Starship's present propellant capacity. Since 304L stainless is such a weak structural metal relative to its mass, the wing would need to carry propellant and be shaped to resist both internal pressurization loads and aero loads lower in the atmosphere. This proposal would increase the weight of Starship to impractical levels, which is why it won't be done. A lifting body Starship, which may or may not remain within tolerable mass limits, would require a complete redesign to provide 1,800m^2 of lifting surface area.

Keep in mind how huge Starship is. Jet fuel, kerosene, is a bit less than water’s density of a ton per cubic meter. Then the Antonov’s wing fuel load would be about 300 tons and the Concorde’s about 100 tons. The Starship carries 1,200 tons of propellant.

But it’s a bit like comparing apples to oranges. In this scenario the “wing” would not be carrying fuel. It would only be acting as a drag decelerator, a la the ‘parashield’.

Still, I’d like to see what could done with true wings using high lift/drag aerodynamics at hypersonic speed. This would undoubtedly make the wings smaller.

Optimum Mach 25 waverider [from Bowcutt, Anderson and Capriotti, 1987

Bob Clark

Last edited by RGClark (2025-04-11 18:31:32)

GW Johnson · 2025-04-11 21:55:26

The question of whether any given material can survive entry without adding extra heat protection is what I am trying to get to, with the entry study I am doing. The usual criteria for heat shield (or other) material selection are (1) the equilibrium surface temperature, and (2) the applied pressure, both of which it must withstand.

The question of whether a super-large lifting (or drag) surface can survive entry is a question of aerodynamic loads vs material strengths, as much as it is surviving temperatures and pressures. I am NOT addressing those issues! I leave that to others. Be aware that any given design must survive in both scenarios.

Also be aware that anything riding unprotected in the wake zone behind a heat shield of any kind, is exposed to plasma at the same effective temperature as that seen by the stagnation zone (numerically the speed in m/s equals the effective temperature in degrees K, to about 10% accuracy). The difference is a far lower heat transfer coefficient leading to far lower heating rates because the scrubbing action is far less away from the stagnation point.

This effect allowed Mercury and Gemini to have bare metal afterbodies of high-temperature exotic alloys, separated from the pressure shell by mineral wool insulation, coming back at roughly 7.74 km/s. Apollo returning from the moon at about 10.9 km/s could not; its afterbody was coated with cell-gunned Avcoat insulating ablative, same material as the windward-side heat shield, just thinner.

I will post my entry study on my "exrocketman" blog site once it is done. That will be soon. It will have a handful of figures in it, which makes it impossible to post directly here on the forums. Without those figures, the words will seem meaningless.

And by the way, the entry spreadsheet I am using to do this is the same one supplied with the "orbits+" course materials offered through these forums. That spreadsheet and its user's manual are supplied as course materials for lesson 7/7B. Using that tool, anyone one of you can do what I am doing! There's enough information in the user's manual to enable you to do that!

GW

Last edited by GW Johnson (2025-04-12 13:40:54)

tahanson43206 · 2025-04-12 08:19:35

For RGClark...

Here is a link to the report GW created about your idea/inquiry:
https://exrocketman.blogspot.com/

The article is at the top. I have offered to post the material here.

In the mean time, please visit the site and see if you can find an answer to the question you posed.

I saw a lot of images of plots and lots of text about re-entry, but i did not see a "bottom line" conclusion.

Please see if you can find the end result of all that work.

Update: I went back and reread more carefully. There is a reason I did not find a "bottom line". There is none!

Whether the inflatable or extendible heat shield concepts are survivable, I leave to others.

For RGClark.... please see if you can find any evidence of actual Real Universe data that can answer your question.

My expectation is that it doesn't matter how large the surface of the oncoming object may be. That surface is going to melt.

I offer as evidence the many asteroids that have entered the Earth's atmosphere. Some have been studied after landfall, and some have been observed in flight. I think the evidence you are going to find is always going to turn out the same way. I believe that whatever material you place in front of an object arriving at 11 Km/s will melt.

Update: GW Johnson has provided all the images for the heat shield study. I've saved them and plan to upload them this weekend.

In the mean time, they are all available now at the exRocketman blog.

Update: Void has been talking about heat shields made from Lunar and other non-Earth material. That might provide a solution for shipments that you or your competitors want delivered to Earth from space. You need to plan your flight so the heat shield ends up in the ocean rather than on top of a city or other inhabited location.

(th)

GW Johnson · 2025-04-12 14:01:06

I looked up the Stoke Space "Nova" design. It's more-or-less clear how the first stage is to work, rather similar to the Falcon cores and Superheavy, just using landing legs of some sort, unlike Superheavy, but like the Falcon cores.

It's the design of the "Andromeda" second stage that still seems to be in flux as testing proceeds. It would have some sort of metal base that is the heat shield, cooled by the hydrogen that fuels the circumference-mounted second stage thruster engines. I cannot really tell if it is simply to be cooled by backside hydrogen flow, or if it is transpiration-cooled by leaking hydrogen through the heat shield surface. I'm not sure Stoke knows yet, either.

The numbers as best we know them say that either regenerative cooling or transpiration cooling should work, but neither concept has ever actually flown and been tested in a real entry. Those and some other ideas were supposed to have been tested on the old X-20 "Dyna-Soar" spaceplane, but it was cancelled in 1963 before it could ever fly. X-20 had bare-metal exotic-alloy wings fuselage, and tail fins at the wingtips. It had leading edges and a nosetip made of graphite ablative, modified with rods (metal, ceramic, not sure) to conduct heat inward better. Graphite is both a poor insulator and a poor conductor of heat. It starts burning in air at about 5000 F, though. We got away with it as a slow-eroding throat insert in one-use solid rocket nozzles up to 6000 F gas temperatures, though.

GW

Last edited by GW Johnson (2025-04-12 14:10:20)

tahanson43206 · 2025-04-12 16:39:54

This post is reserved for a set of 7 images prepared by GW Johnson in an attempt to answer a question posed by RGClark regarding heat shields, and specifically what benefit there might be to stretching the heat shield to gigantic proportions.

Image 1

Image 2

Image 3

Image 4

Image 5

Image 6

Image 7

Image 8

Note: the labels for these images are probably in need of correction.
(th)

kbd512 · 2025-04-12 19:50:02

If you create a deployable fabric heat shield considerably larger than the vehicle being protected, how do you either jettison the heat shield or stow it in order to land?

We have a wealth of experience with improved lightweight heat shielding materials. The fastening methods, rather than the tiles themselves, seem to be failing. The tile losses appears to occur near discontinuous surfaces (the "step" or "lip" between protected areas that have tiles and nearby areas that don't any) to the oncoming flow around those complex hinged joints. I see what looks like gas cutting from the wake coming off the leading edges. As the AoA is varied to steer the vehicle during reentry, some of the flow appears to wash over parts of the vehicle that may not have that crazy-hot flow impinging upon it at reduced AoA. Maybe I'm wrong about that, but from the videos that's what it looks like to me.

The Space Shuttle Program developed Advanced Carbon-Carbon (ACC- an advanced RCC derivative) aileron, body flap, and rudder structures that both resisted mechanical / aero loads and acted as "hot structures" which had no thermal insulation. This is to say, the materials were not a more complex sandwich of HRSI, backing insulating felt, and Aluminum alloy primary structure. This was projected to save 700lbs of weight for the large body flap, and up to 7,000lbs of weight if the ailerons, rudder, and body flap were all made purely from ACC vs a mix of different TPS and structural materials.

Here's the NTRS Report:
RECENT ADVANCES IN CARBON-CARBON MATERIALS SYSTEMS

They were also contemplating replacing FRSI tiles on the orbiter's belly with ACC and switching to a hot structure that required little to no insulation. Starship's 304L primary structure could have a very thin layer of ACC with a very light aerogel insulation layer underneath. The body flaps could be replaced with monolithic ACC structures. This seems like a better way to solve the peak heating problem than fragile tiles near hinge lines. Monolithic ACC "fins", like the ACC orbiter body flap from that NTRS Report, doesn't have any tiles to lose. It's intrinsically capable of withstanding the temperatures FRSI tiles are subjected to, plus a little more, in addition to resisting the aero loads so no structure steel reinforcement is required. NASA also developed metal fasteners that wouldn't crack the ACC as they expanded at different rates.

This is less involved change proposal than completely redesigning the upper stage into a lifting body that lands on a runway.

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#2026 2025-03-21 13:09:11

Re: Starship is Go...

#2027 2025-03-21 13:22:33

Re: Starship is Go...

#2028 2025-03-21 17:58:20

Re: Starship is Go...

#2029 2025-03-21 18:22:33

Re: Starship is Go...

#2030 2025-03-23 09:58:15

Re: Starship is Go...

#2031 2025-03-23 11:06:37

Re: Starship is Go...

#2032 2025-03-23 11:50:20

Re: Starship is Go...

#2033 2025-03-23 15:40:39

Re: Starship is Go...

#2034 2025-03-23 16:50:59

Re: Starship is Go...

#2035 2025-03-23 17:45:55

Re: Starship is Go...

#2036 2025-03-27 14:38:40

Re: Starship is Go...

#2037 2025-03-27 21:00:46

Re: Starship is Go...

#2038 2025-04-03 08:44:00

Re: Starship is Go...

#2039 2025-04-03 09:39:36

Re: Starship is Go...

#2040 2025-04-06 17:30:55

Re: Starship is Go...

#2041 2025-04-10 12:57:17

Re: Starship is Go...

#2042 2025-04-11 10:06:20

Re: Starship is Go...

#2043 2025-04-11 16:23:38

Re: Starship is Go...

#2044 2025-04-11 18:02:18

Re: Starship is Go...

#2045 2025-04-11 18:22:24

Re: Starship is Go...

#2046 2025-04-11 21:55:26

Re: Starship is Go...

#2047 2025-04-12 08:19:35

Re: Starship is Go...

#2048 2025-04-12 14:01:06

Re: Starship is Go...

#2049 2025-04-12 16:39:54

Re: Starship is Go...

#2050 2025-04-12 19:50:02

Re: Starship is Go...

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