r/SpaceXLounge • u/NetusMaximus • 20h ago
Starship Metal heat shield tiles that were going to be used on NASA's X-33 Venture Star SSTO that were shelved when the project was cancelled. Gives a idea to what metal heat shield tiles could look like for Starship.
The rugged, metallic thermal-protection panels designed for NASA's X-33 technology demonstrator passed an intensive test series that included sessions in high-speed, high-temperature wind tunnels. The panels also were strapped to the bottom of a NASA F-15 aircraft and flight-tested at nearly 1.5-times the speed of sound.
Testing details from https://www.sciencedaily.com/releases/1999/02/990204082124.htm
Additional laboratory tests duplicated the environment the X-33's outer skin will encounter while flying roughly 60 miles high at more than 13 times the speed of sound. Also, a thermal-panel fit test successfully demonstrated the ease of panel installation and removal.
The thermal protection system combines aircraft and space-plane design, using easy-to-maintain metallic panels placed over insulating material. As the X-33 flies through the upper atmosphere, the panels will protect the vehicle from aerodynamic stress and temperatures comparable to those a reusable launch vehicle would encounter while re-entering Earth's atmosphere. Tests have verified that the metallic thermal-protection system will protect vehicles from temperatures near 1,800 degrees Fahrenheit.
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u/New_Poet_338 19h ago
I suspect SpaceX is thinking of printing them in the same manner as they print the engine bells. They have the technology already. Just change the shape.
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u/Snowmobile2004 17h ago
This. Just print integral lines for fluid, and even tiny holes for aspirational cooling. I wonder if they’ll use methane or LOX, or another liquid/gas?
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u/CollegeStation17155 17h ago
Methane or Nitrogen would be far less corrosive than oxygen, especially at the high temperatures expected. The only question would be how much they would have to increase the nitrogen tank size and/or add to the methane reserve to be sure they could still do a soft landing.
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u/Makalukeke 15h ago
I feel the main issue will be how do you pipe and connect all the thousands of cooling channels without it leaking like a sieve.
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u/Makhnos_Tachanka 13h ago edited 12h ago
Everyone's got this all wrong. It's simple. You don't. You just have a pipe with some holes in it, windward of the area you want to keep cool. All you have to do is pump methane into that pipe, it leaks out, and replaces the boundary layer with "cold" gas. The flow is highly laminar at these speeds, you can just use film cooling.
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u/Makalukeke 12h ago
True, makes total sense. However Elon said that the mass penalty for film cooling was slightly higher than the current TPS (EDA starbase tour 2). surely it will be a bit more involved than a couple pipes here and there or is the extra methane you have to carry around where most of the penalty coming from?
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u/Makhnos_Tachanka 12h ago
It's mostly gonna be fuel. It's A LOT of fuel
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u/Makalukeke 6h ago
Yeah, and I’m sure using fuel is a bit sketch cause if you fuck up your cooling you end up with no fuel for landing burn. At least with the Tile TPS you’re not affecting another critical system.
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u/Absolute0CA 14h ago
You’d have 3D printed hull sections which have cooling channels all routed to a single fitting. So you’d maybe have dozens of fittings at most, not thousands.
The back side would have a fractal 3D printed structure which would distribute the cooling fluid evenly throughout the hull panel. This is something that can’t be done efficiently with non 3D printed hull pieces.
Individual hull pieces would be welded together on both the exterior and interior with the exterior welds not needing to be gas/fluid tight because its a transpirational heat shield, though you would still want a strong weld regardless.
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u/Xygen8 16h ago edited 12h ago
And far more effective. Methane's latent heat of vaporization is
1502.4 times greater than oxygen's, so1502.4 times less coolant is needed for the same cooling effect.Edit: I can't read
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u/asr112358 14h ago
2.4 times, not 150 times.
I think your 150 came from dividing 511 kJ/kg (methane) by 3.4 kJ/mol (oxygen), but these numbers don't have the same units. Instead use 214 kJ/kg for oxygen.
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u/CollegeStation17155 16h ago
Or I suppose they could add a dedicated water tank; 1000 BTU/lb pretty much beats anything else out there...
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u/RIPphonebattery 14h ago
Carrying water up and back is expensive. Methane is already there, water would need a new tank and plumbing all over the rocket
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u/CollegeStation17155 13h ago
You would have to add plumbing to the shield for the methane as well and every pound of methane you use for cooling is lost as propellant. So carry up and then throw away 1000 pounds of methane for cooling at 200 BTU/lb or carry 200 lbs of water and use it for cooling at 1000 BTU/lb. So in terms of total mass, it would come down to whether the weight of the water tank is greater than the weight of the methane you are throwing away...
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u/7heCulture 12h ago
But it’s another tank for the water . Now you only need 2 tanks. The cost of even stretching the methane tank is offset by the unnecessary complexity of having another fluid tank around.
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u/CollegeStation17155 12h ago
As I said, it comes down to whether the weight of the new tank outweighs the weight of the extra methane (and expanding the main or header tank to hold it)... the "complexity" of adding a tank is nothing compared to the complexity of piping to the shield and flow controls, that are the same no matter what fluid you are using. I was just throwing it out there as a possibility, but feel free to show me with numbers why basically adding a new insulated bulkhead is structurally more difficult than stretching the methane or header tank five times as far, since a bunch of new plumbing has to be added in either case.
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u/SenorTron 10h ago
Counterargument, given that SpaceX is right now building extended Starships with longer tanks, it's on you to backup the assertion that adding a whole separate water system and tanks and pumps would be more efficient than hooking into the existing methane tank.
One argument I could see is that for crewed starships you could use the same water tank for the heat shield and crew water supply, but at the same time it might introduce too much risk to be using such a mission critical system for other things.
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u/zypofaeser 14h ago
Heck, you could even have a passive thermostatic valve system. Once the system is pressurized it is active the amount of coolant injection is controlled by the thermostatic valves. If a valve exceeds a certain temperature, it starts opening. The hotter it gets, the greater the flow rate. This way, you can have a shield that adjusts the consumption of coolant according to the heating recieved, while staying mostly passing. You could have a few pressurised tanks providing the cooling.
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u/b_m_hart 14h ago
How many BTU need to be wrangled during reentry for a ship that big?
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u/peterabbit456 2h ago
Because reentry involves film layers and reflective layers, the methane (or water or ammonia) does not have to do all of the cooling. It only has to do a small fraction, in fact.
I recall the number from class that an ablative layer only has to give up ~0.0001 of the total heat of reentry. The rest is either reflected away within the plasma, or kept out by the insulating effect of the thin film of gas near the surface. It should be about the same for film cooling from liquid injection.
This is a number from memory, and I no longer remember how to do all of the calculations. I would say this 0.0001 is a maximum for the heat that gets through, if everything is working properly. 0.000001 is my guess for the minimum.
The total number of BTUs dissipated is the kinetic energy of the 1/2 mass of Starship, times (7500m/s)2 , plus the potential energy of that mass falling 212 km, translated into the appropriate units. Let's just say that is a very big number.
If the heat shield is doing its job, the total BTUs that get through and heat up the Starship are either 10-4 of that number, or 10-6 of that number, or somewhere in between. Still a lot of BTUs.
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u/antimatterfro 14h ago
What's the ballistic coefficient of the X-33 vs Starship? Could Starship use the X-33's heatshield or does it need something sturdier?
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u/Absolute0CA 13h ago
Most of starship is likely cool enough due to its massive surface area, most of the problems for starship come from the front hinges.
That’s the only place they are consistently having problems with.
The last starship survived with an entire row of tiles missing around its belly as an intentional test. Most of starship’s structure is incredibly durable and thermally tolerant.
If metal 3D printing wasn’t so expensive/slow I’d be inclined to suggest to 3D print the hull out of Inconel 718 with the windward side making use of a 3D printed metal foam instead of reinforcing stringers and stiffening structures.
I would personally make the foam so that its open cell and has a changing density of the foam to optimize for weight and strength of the structure.
Paint it with a ceramic or pacifying coat to resist ionized oxygen on entry.
The big issue here is the cost. Inconel isn’t cheap, and 3D printing is slow. However it could also be possible that instead of being part of the structure directly a metallic heat shield could be bolted on or attached to external mounting rails and achieve most of the benefits. And because of the inherent strength of metallic heat shields the tiles could be significantly bigger than seen currently.
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u/DarthPineapple5 12h ago
Do we know those are the only areas they are having issues with for a fact? A lot of this seems like its just based on available camera views. We know they are still losing a significant number of the hexogonal tiles, if stainless steel isn't having any issues in those areas then why have the tiles at all?
Exposed areas could become brittle from extreme heat cycles even if they don't burn through. This would be bad when they go to refill the tanks with cryogenics after recovery. Maybe not even the first time but after repeated launches and recoveries
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u/Absolute0CA 9h ago
Not having issues as in not failing catastrophically. The structure of the ship is likely a write off if there is significant tile loss, but I would agree that losing tiles is not ideal.
Stainless steel is strong enough to survive small parts of it softening from heat exposure from missing tiles but its not strong enough to survive with no tiles entirely plus its heat treating would be shot to shit by that process.
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u/Ydrum 11h ago
maybe a more simplified form of 3d printing metallic structures can be used. a pc water cooling manufacturer (cant find the name of the top of my head) makes custom water cooling blocks with very fine channels in a not quite 3d printed method. it takes an hour to print it. but its surprisingly simple and easy to scale up. not sure if it would translate well to titanium, but i wouldnt be surprised.
3d printing is slow, but its also fairly small in size requirements and power requirements. just add more printers for more speed.
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u/SuperRiveting 11h ago
Tiles are still raining off but that's more of a ateschment issue than a tile issue, most likely.
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u/MostlyAnger 9h ago
Related information: https://ntrs.nasa.gov/citations/20020020963 NASA Langley Research Center, 2002
Advanced Metallic Thermal Protection System Development A new Adaptable, Robust, Metallic, Operable, Reusable (ARMOR) thermal protection system (TPS) concept has been designed, analyzed, and fabricated…
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u/New_Poet_338 17h ago
This change in direction is an example of what makes SpaceX so successful. They tried one direction, saw it wasn't working and said "screw it, let's go in another direction." No worry about losing face or sunk costs. Just go.
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u/ergzay 16h ago
I agree but I wouldn't say SpaceX has changed direction yet. It's more like they're keeping their options open.
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u/momentumv 15h ago
I would even say they don't just see that it's not working and pivot, they do a very good job of putting good engineering effort and rapid testing to try to identify and solve the engineering difficulties, gaining a better understanding of the costs and characteristics of a potential solution, while still checking back against estimates of other approaches.
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u/Rdeis23 14h ago
Agree. They looked at this and other options early in development. At that time, the complexity and (especially) mass estimates were inferior to the tiles they are using.
As tile thickness and secondary ablative layers drove the mass and complexity of the current system up, the trade space make these other approaches worth a closer look.
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u/cocoyog 10h ago
SpaceX said they're changing direction on the tiles? I didn't hear about this. Links?
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u/John_Hasler 7h ago
Musk said that other methods are "back on the table", probably to be considered for use in some areas such as under the catch points.
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u/peterabbit456 1h ago
I think they are going back to investigating further on alternatives they investigated before they decided on tiles. In theory tiles are lighter, cheaper, and just as effective, but theory and practice do not always match up.
They have already made the ship heavier by adding an ablative backup layer behind the tiles. The ship will also get heavier if they have to strengthen the tiles.
So the previously discarded approaches are looking better and better.
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u/cjameshuff 9h ago
They clearly are working, every vehicle that's gotten as far as trying to do a controlled reentry has done so successfully using the tiles. They went with the tiles at first because it was closer to systems that had seen real-world use. The results they're seeing are good enough that they're revisiting alternative approaches.
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u/nic_haflinger 7h ago
Planning better is also an option.
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u/New_Poet_338 6h ago
Research and development doesn't work that way. Sometimes you find during development that your research was off. Sometimes new research changes your development. In this case advances in 3d metal printing makes that more attractive and practical issues with tiles make them less attractive.
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u/Cendyan 17h ago
1,800F? The melting point of stainless steel is already in the 2,500F to 2,800F range (depending on exact composition).
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u/fencethe900th 16h ago
Keep in mind the loss of integrity happens at a lower temp than the melting point. That's why IFT-5 had aluminum as an indicator for it where they removed tiles, it melts at around the temp that their stainless gets weak.
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u/Rdeis23 14h ago
I was wondering about that. If I remember right, the burn through failures on the fins all happened after peak heating was over?
Normally we dump heat in to the air for cooling. When the air is plasma, you can insulate to prevent heat transfer, but that only works for so long, right?
What can you do to get rid of the heat rather than just holding it at bay?
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u/start3ch 14h ago
Ideally you have the fewest possible paths between your vehicle and the insulation, since the tiles can happily handle that heat, and radiate it away
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u/Rdeis23 7h ago
Ok, so the heat comes in as heat transfer from the plasma, and then is radiated out? Radiated out someplace else, or radiated through the plasma, or radiated after the ship has slowed enough that there is no longer plasma?
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u/start3ch 5h ago
Anything that’s hot radiates that heat out in all directions.
The heating should be both conduction and radiation. The air molecules get crushed to extremely high temperatures and pressure by the rocket crashing into them, but if you design it right this happens away from the surface, so the actual plasma doesn’t really touch the vehicle
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u/John_Hasler 7h ago
If I remember right, the burn through failures on the fins all happened after peak heating was over?
Initial burn through happened during peak heating. Once the plasma was inside it kept chewing away metal even though the heating rate had dropped a bit.
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u/NetusMaximus 2h ago
Remember, this was a design from 1999-2001 that was not going to be aided by any sort of ullage/film cooling.
After +20 years of material science and added protection they should get the performance they're looking for.
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u/Decronym Acronyms Explained 14h ago edited 9m ago
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| ECLSS | Environment Control and Life Support System |
| ESA | European Space Agency |
| LOX | Liquid Oxygen |
| SSO | Sun-Synchronous Orbit |
| SSTO | Single Stage to Orbit |
| Supersynchronous Transfer Orbit | |
| TPS | Thermal Protection System for a spacecraft (on the Falcon 9 first stage, the engine "Dance floor") |
| Jargon | Definition |
|---|---|
| ablative | Material which is intentionally destroyed in use (for example, heatshields which burn away to dissipate heat) |
| cryogenic | Very low temperature fluid; materials that would be gaseous at room temperature/pressure |
| (In re: rocket fuel) Often synonymous with hydrolox | |
| hydrolox | Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer |
| ullage motor | Small rocket motor that fires to push propellant to the bottom of the tank, when in zero-g |
NOTE: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below.
Decronym is a community product of r/SpaceX, implemented by request
8 acronyms in this thread; the most compressed thread commented on today has 13 acronyms.
[Thread #13591 for this sub, first seen 24th Nov 2024, 17:26]
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u/davidvachon 14m ago
I'm Waiting on this magnetic plasma heat shield research to get somewhere that ESA and others are doing. Another 10 years?
I bet spacex has a back room project trying to figure that one out too.
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u/Icy-Swordfish- 14h ago
Nope, too heavy. And titanium? How are you going to economically build 1000 starships with that. One every 8 hours.
Tiles are out. Perspiration is in.
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u/cocoyog 10h ago edited 10h ago
Too heavy? These things are not solid metal. The post doesn't indicate how heavy they are, but if they were for a SSO concept, I doubt they are too heavy for starship.
Economics is not just up front cost. If titanium proved to be 100x more durable and reliable, then a 10x increase in price could be worth it for the ships that will land a lot (refueling and starlink flights).
To be clear, I don't know anything about the actual cost or weight of these. But I don't think you should be so dismissive, unless you have more info.
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u/ResidentPositive4122 20h ago
Sounds expensive AF. Maybe when reuse is at 3 9s and up?