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#2251 2026-02-24 11:35:28
- GW Johnson
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Re: Starship is Go...
The "standard" Block 2 (about to become Block 3) Starship does its deorbit burn and its flip-and-landing burn on the propellant in the header tanks, so SpaceX says. They also said that those were transferred to the main tanks in the Block 2 design to make the landing burn. (Note that there is really nothing "standard" about Starship until all the experimental flight testing is successfully done.)
That transfer from headers to main tanks may or may not still be true in Block 3, as I saw in some illustrations plumbing direct to the engines from the header tanks. Those header tanks hold something like 20-25 tons at most, not anything like 100 tons! The ship explodes upon toppling over in the Indian Ocean, because not all of that 20-25 tons was used to make the landing. There are still fuel and oxidizer aboard when it falls over and breaks open.
I do not know of any variants yet being seriously considered except the HLS and some sort of propellant tanker. And that will likely be true until after the next round of Block 3 flight tests are done! Then it gets bigger yet again in the Block 4 design, which must again be proven in test before it can be considered as a viable prototype for any sort of real mission work. Excepting maybe HLS and the tanker, any other variants must wait until everything through Block 4 has been tested and found adequate.
As for the ballistic coefficient of a Block 2 or Block 3 Starship, the hypersonic drag coefficient of a round cylinder dead broadside to the wind is about 1.20 based on the cylinder blockage area, coming from my old Hoerner "drag bible". The drag coefficient of a flat plate normal to the wind in hypersonic flow is about 1.84, based on its blockage area. Same data source. I took a good guess for the effects of the pointed nose, and for the relative blockage areas of body and flaps, and determined a CD = 1.22 on a blockage area of just about 462 sq.m normal to the wind.
Starship does NOT enter normal to the wind, it enters at a nominal angle of attack of 60 degrees, although that varies some about that nominal angle. Thus the normal blockage area is not actually normal (90 deg) to the wind, it is about 30 deg off. That's no big impact on CD, but the effective blockage area is 462 sq.m times a cosine factor of 0.866 for that angled entry.
I used Bob's numbers of 120, 160, and 40 metric tons for the inert mass of Starship, even though I thought (and still think) the 40 ton figure is ridiculously unrealistic. To that I added 20 tons landing propellant, and 100 tons payload at Mars, and I added the same 20 tons of propellant and 0 tons of payload at Earth. That puts mass-at-entry 240, 280, and 160 metric tons at Mars, and 140, 180, and 60 metric tons at Earth.
I did entries at Mars at 7.5 km/s off a fast trajectory, and 2 deg below horizontal. I did entries at Earth at 7.9 km/s out of low circular LEO and 2 degrees below horizontal.
That's where my numbers came from! They should be pretty good, as good as the masses at entry are. The whole thing turned into a sensitivity study with ballistic coefficient the independent variable. The low inerts are ballistic coefficient roughly half those of the heavier values.
GW
Last edited by GW Johnson (2026-02-24 11:44:45)
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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#2252 2026-02-24 15:17:47
- SpaceNut
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Re: Starship is Go...
Moving fuels from the compressed tanks to the near empty tanks creates boiling due to a much lower pressure. It would be better to use a tank in a tank and a control valve.
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#2253 2026-02-26 15:13:33
- GW Johnson
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Re: Starship is Go...
Spacenut:
I quite agree that nested headers inside main tanks is better. For one thing, the main tank around the header can become almost-a-thermos-bottle, limiting evaporation losses.
But, SpaceX had to put the headers in the nose to get acceptable cg position for entry and descent, especially if no payload was aboard far forward.
GW
GW Johnson
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#2254 2026-02-26 15:49:11
- SpaceNut
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Re: Starship is Go...
Even a load of bricks would be able to prove performance of its thrust path as well as return as we will not be coming back empty from any destination.
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#2255 2026-03-01 13:02:01
- SpaceNut
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Re: Starship is Go...
So far besides the landing legs for moon or mars is the tiles do not seem to be strong enough for mars use as the crewed ships will need them to be beefed up or we will fail.
Future earth landing may be in the Motzilla but what about mars?
Maybe an added inspection and other replacement tiles might make it possible but at this point is a gamble.
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#2256 2026-03-03 15:26:39
- GW Johnson
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Re: Starship is Go...
What I think I see for an object of the size and shape as Starship, is quite a difference in peak heating during 7.5 km/s entry at Mars (off a fast interplanetary trajectory), versus 7.9 km/s entry at Earth (from low circular Earth orbit). At Earth, convective heating is modest due to the large radius of the vehicle, while plasma radiation heating is virtually nil. At Mars, convective is comparable to Earth, but plasma radiation heating is an order of magnitude larger, again due to the large radius of the vehicle.
Now, you can resist such heating either by ablation, or by refractive thermal re-radiation, or some of both. You want to minimize conduction into the interior, in either case. Things that can resist the mechanical forces tend to be dense. That opens up the path for conduction inward. It puts you to looking at metallic or hard ceramic tiles, but with some sort of lower-thermal-conduction layer underneath, to re-limit the conduction inward. High density ALWAYS correlates with high thermal conductivity.
SpaceX attempted some metallic tiles (not all of them) on Flight 10. They did not like the fast oxidation rates that they saw, which stained that heat shield orange. They went back to ceramic tiles in Flight 11, which worked. I do not know what that ceramic was. But it is dense and hard, and requires a low-conductivity ablative layer underneath. The low conductivity stops the inward conduction. The ablation capability provides the backup burn-through protection for a lost tile.
I see nothing at all from SpaceX that would address what is needed to make rough-field landings on soft ground. Moon, Mars, both are dominated by both softness and roughness.
GW
Last edited by GW Johnson (2026-03-03 15:27:22)
GW Johnson
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#2257 2026-03-03 15:43:03
- SpaceNut
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Re: Starship is Go...
I see flight 10 had the white from the nose plus the coloring, while 11 had just the staining colors and evidence of burning still.
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#2258 2026-03-03 15:45:34
- GW Johnson
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Re: Starship is Go...
There was no orange staining on 11. It was flight 10 that had both the white near the nose, and the orange staining all over the heat shield.
GW
GW Johnson
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#2259 2026-03-03 15:48:40
- SpaceNut
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Re: Starship is Go...
here is the still for 11
here is the still for 10
SpaceX's Flight 11 (Oct 2025) demonstrated improved structural integrity and less heat shield distress compared to Flight 10, despite both successfully achieving controlled ocean splashdowns. Flight 11 featured, for the second time, a V2 Starship that handled intense, intentional stress testing—including missing tiles in key areas—with less visible damage than Flight 10.
Flight 11 vs. Flight 10 Landing Breakdown:
Heat Shield/Damage: Flight 11 showed less, yet still significant, heat damage compared to Flight 10. Flight 11 lacked the metallic test tiles that caused excessive oxidation and orange coloring on Flight 10, though it still experienced high-heating, resulting in small flames and venting.Stress Testing: Both flights tested thermal protection, but Flight 11 intentionally left gaps in the heat shield without backup protection to test endurance, proving superior durability.
Performance: Both vehicles successfully executed the landing flip maneuver and soft splashdown. Flight 10 achieved a near-bullseye landing, and Flight 11 continued this precision.
Insights: Flight 10 was described as "charred" and "battered" due to its tests, while Flight 11 was in better condition, indicating progress toward full reusability
Both flights provided critical data, with Flight 11 demonstrating that the Starship could survive and maintain control despite severe, intentional damage to its thermal protection system.
here is the other view from space x
If you open the image in its own tab and zoom in on the image you will see the rust and holes still
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#2260 2026-03-04 16:04:09
- GW Johnson
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Re: Starship is Go...
I had not seen your Flight 11 photo with the reddish oxide stain before. I only ever saw the other one.
But there was a lot less of it than Flight 10. On both, it seemed to come from some locations on the belly, not so close to the nose. Where they deliberately left off tiles, perhaps?
GW
GW Johnson
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#2261 Today 19:55:13
- SpaceNut
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Re: Starship is Go...
The thickness of your jettisonable HIAD (Hypersonic Inflatable Aerodynamic Decelerator) shield is determined by the "thermal soak"—how much heat penetrates the layers before the ship slows down—rather than just the surface temperature.
On a Starship-scale Earth entry, you aren't just looking at a single layer; you’re looking at a layup (a multi-material sandwich). Based on NASA's LOFTID (Low-Earth Orbit Flight Test of an Inflatable Decelerator) data and current PICA-Flex performance, here is the "Turkey" on the thickness requirements:
The Total Layup Thickness: ~50mm to 75mm (2 to 3 inches)
To protect the ship's steel during a Mach 25 entry, the total stack height of the flexible shield would need to be roughly 50mm to 75mm. This is remarkably thin considering it replaces a 25–50mm rigid tile plus its mounting hardware.The Layer Breakdown:
Outer Ablative Layer (PICA-Flex): 15mm – 25mm
This is the "sacrificial" part. It is a 3D-woven carbon fabric impregnated with phenolic resin. During the peak 1500°C+ heat flux, this layer chars and "outgasses," creating a protective boundary layer of cool gas that pushes the plasma away.Insulation Mid-Layers (Carbon/Ceramic Felt): 30mm – 40mm
Beneath the PICA-Flex, you need several layers of "felt" (like Sigratherm or Pyrogel). This does the heavy lifting of stopping the heat from reaching the inflatable structure and the ship.Gas Barrier (Teflon/Zylon Laminate): ~2mm
A thin, gas-tight membrane that ensures the inflation gases don't leak out and the 10,000°C external plasma doesn't leak in.
Why so thin? (The Surface Area Advantage)
The reason this can be thinner than you'd expect is the Ballistic Coefficient.Starship (Standard): Falls like a heavy dart. It hits thick air while moving very fast, causing a "spike" in heat flux.
Starship (HIAD): If the centerline bag expands the width to 15 meters, the ship behaves like a "giant shuttlecock." It begins slowing down at 80km–90km altitude instead of 60km.
Because you are braking in thinner air, the peak heat flux (W/cm²) is lower. You are trading a "short, hot spike" for a "long, warm soak."
Mass Comparison: The "Turkey" on the Scale
Component — Hex-Tile System (Static) vs HIAD-PICA System (Jettisonable)
Areal Density: ∼15–20 kg/m² vs ∼8–12 kg/m²
Total Shield Mass: ∼8,000 kg vs ∼4,500 kg
Jettisonable Mass: 0 kg (Dead weight) vs ∼4,000 kg
By jettisoning the charred 4-ton shield before the landing flip, the Starship becomes significantly "lighter on its feet" for the final suicide burn.
The Centerline Airbag "Stand-off"
The airbag itself (the tori) would be inflated to a thickness of roughly 1 to 2 meters.This creates a literal dead-air space between the 1500°C heat shield and the 800°C structural steel.
This air gap is your "safety margin." If the PICA-Flex develops a small tear, the plasma has to travel through 2 meters of pressurized nitrogen before it can touch the ship's hull, giving the RCS (Reaction Control System) time to compensate or the ship to slow down.
The Bottom Line
You are looking at a 3-inch thick "blanket" supported by a 6-foot thick "air cushion." This is a much more resilient solution than a 1-inch thick "glass cracker" (the current tiles) glued directly to a flexing steel plate.Would you like to detail the "Trench Seal"—how the edges of this 15-meter wide blanket stay tucked into the ship's 9-meter body during the high-speed ascent?
For the monolithic PICA skin—the thin, rigid "shroud" that protects the ship before the HIAD/Airbag inflation—the thickness is optimized to survive only the first 300–400 seconds of peak reentry heating.
Because this shroud is jettisoned, we don't need the massive 50mm–80mm thickness of a permanent shield. Instead, we can use a "High-Flux, Low-Soak" strategy.
The Monolithic PICA Skin: 12mm to 18mm (0.5 – 0.7 inches)
This layer is essentially a "sacrificial veneer." Its job is to ablate and maintain the aerodynamic shape of the belly until the ship slows down to the deployment velocity (~Mach 10).Recession (Ablation): During Earth entry, PICA-X typically loses about 5mm to 8mm of material due to surface charring and recession.
Insulation Margin: You need an additional 7mm to 10mm of "virgin" material behind the char layer to ensure the heat doesn't melt the structural adhesive or the stowed HIAD fabric before the jettison event.
The "Clean Break" Attachment
Since this skin is monolithic (or made of 4–5 massive longitudinal panels), it doesn't use the thousands of individual studs like the current tiles.Linear Explosive Bolts ("Zip-Cord"): The skin is held in place by a perimeter of frangible joints.
Aerodynamic Overlap: The edges of the "fixed" tiles on the sides of the ship overlap the "jettisonable" shroud, forming a natural shingle that prevents high-pressure plasma from sneaking underneath.
Internal Standoffs: The skin is held 10mm–20mm away from the steel by ceramic spacers. This air gap provides a final layer of protection against heat soak before jettison.
The Sequence: From Shroud to Airbag
Entry Interface: 15mm Monolithic PICA — Hull Temp ~20°C (Ambient)
Peak Heating: 9mm PICA Remaining — Hull Temp ~150°C (Soaking)
Mach 10: JETTISONED — Hull Temp ~200°C
Mach 8: HIAD Airbag Inflated — COOLING (Radiative)
Why This Works
By using a thin monolithic skin first:You eliminate the Gap Heating failure point entirely during the most dangerous part of reentry.
You protect the HIAD fabric from the "initial punch" of Mach 25 plasma, which would be too hot for even the best carbon weaves to endure for long.
The total mass of a 15mm PICA skin over the windward belly is roughly 2,000 kg—less than half the weight of the current tile system.
The "Aero-Dynamic Push":
When the pneumatic latches fire, the high-pressure gas trapped in the stowage trench (and the beginning of the HIAD inflation) physically "kicks" the PICA skin away from the ship. This prevents debris from hovering near the hull and damaging the flaps.
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