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SpaceX CEO Elon Musk explains Starship’s ‘transpiring’ steel heat shield in Q&A
Speaking in a late-December 2018 interview with Popular Mechanics’ editor-in-chief, SpaceX CEO Elon Musk shared considerable insight into the thought processes that ultimately led him to – in his own words – “convince” his team that the company’s BFR rocket (now Starship and Super Heavy) should pivot from an advanced composite structure to a relatively common form of stainless steel.
Aside from steel’s relative ease of manipulation and affordability, Musk delved into the technical solution he arrived at for an advanced, ultra-reusable heat shield for Starship – build it out of steel and use water (or liquid methane) to wick reentry heat away.
When going to ~1750 Kelvin, specific heat is more important than latent heat of vaporization, which is why cryogenic fuel is a slightly better choice than water
— Elon Musk (@elonmusk) January 22, 2019
Although there has been some successful experimental research done on “transpirational” heat shields (relying on the heat capacity of vaporizing liquids or gases to soak up thermal energy during orbital rocket reentries), Musk is by no means wrong when he says that a stainless steel sandwich-hulled spaceship regeneratively cooled by microscopic holes and liquid water or propellant “has never been proposed before”. While the basic concept probably arose somewhere over the last 50-100 years, it does not appear that any serious theoretical or experimental research has been conducted to explore transpiration-cooled metallic heat shields, where metallic thermal protection systems (TPS) are already fairly exotic and unproven in the realm of modern aerospace.
“Very easy to work with steel. Oh, and I forgot to mention: [SpaceX’s high-quality] carbon fiber is $135 a kilogram, 35 percent scrap, so you’re starting to approach almost $200 a kilogram. [301] steel is $3 a kilogram.” – Elon Musk
While Musk’s solution could dramatically simplify what is needed for Starship’s high-performance heat shield, a stainless steel sandwich on half of Starship offers another huge benefit: the spacecraft can still gain many of the mass ratio benefits of stainless steel balloon tanks (metal tanks so thin that they collapse without positive pressure) while retaining structural rigidity even when depressurized. At the end of the day, Musk very well might be correct when he states that a stainless steel Starship can ultimately be more mass-efficient (“lighter”) than a Starship built out of advanced carbon composites, a characteristic he rightly describes as “counterintuitive”.
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- Starhopper and SpaceX’s spartan assembly facilities are pictured here, showing the inside of the aft section and a completed tank dome. (Austin Barnard)
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- Starship has been shown with actuating fins and canard wings since SpaceX’s September 2018 update. (SpaceX)
What does Science™ have to say?
Based on research done in the 2010s by German space agency (DLR), a porous thermal protection material called Procelit 170 (P170) – 91% aluminum oxide and 9% silicon oxide – was cooled from a peak heat of ~1750 C (3200 F) to ~25 C (75 F) during wind tunnel testing, demonstrating that an average of 0.065 kg (~2.3 oz) of water per second would be needed to cool a square meter of P170 to the same degree, assuming a heating rate of around 200 kW/m^2. Given that 300-series stainless steels have a comparatively huge capacity for radiating heat at high temperatures, will be dramatically thinner than Procelit in any given Starship use-case, and will not need to be cooled all the way to 25C/75F during hot operations, the DLR-derived number is barely relevant without another round of wind tunnel tests focused on metallic thermal protection systems. Still, it allows for the creation of a sort of worst-case scenario for BFS/Starship’s water-cooled shield.
Assuming that the windward side of Starship’s regeneratively cooled heat shield has roughly the same surface area as half of a cylinder, 800 m^2 (8600 ft^2) will have to be actively cooled with water, translating to a water consumption rate of approximately 52 kg/s (115 lb/s) if the entire surface is being subjected to temperatures around ~1750 C. That is, of course, a grossly inaccurate generalization, as aerodynamic surfaces dramatically shape, dissipate, and concentrate airflows (and thus heat from friction) in complex and highly specific ways. Much like NASA’s Space Shuttle or DLR’s theoretical SpaceLiner, the reality of reentry heating is that that heat typically ends up being focused at leading edges and control surfaces, which thus require uniquely capable versions of thermal protection (TPS). Shuttle used fragile reinforced carbon-carbon tiles at those hotspots, while DLR was exploring water cooling as a viable and safer alternative for SpaceLiner.
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- Starship’s first full-scale prototype is being rapidly assembled in South Texas. (NASASpaceflight – bocachicagal)
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- Starship’s first full-scale prototype is being rapidly assembled in South Texas. (NASASpaceflight – bocachicagal)
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- Meanwhile, giant 9m-diameter tank domes are being assembled and welded together a few hundred feet away from Starhopper. (NSF – bocachicagal)
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- SpaceX’s Starhopper seen in a January render and a January photo. (SpaceX/Elon Musk)
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- BFS seen standing vertically on the pads of its tripod fins. (SpaceX)
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- A NASA team—via a US Navy aircraft—captured high-resolution, calibrated infrared imagery of Space Shuttle Discovery’s lower surface in addition to discrete instrumentation on the wing, downstream, and on the Boundary Layer Transition Flight Experiment protuberance. In the image, the red regions represent higher surface temperatures. (NASA)
Aside from heat flux, it’s also unclear when or how long the cooling system will need to be supplied with water during potential Starship reentries. At worst, the spacecraft would need to supply a constant 50+ kg/s throughout a 5+ minute (600+ second) regime of high-velocity, high-drag reentry conditions. Assuming that Starship will need to rely heavily on aerobraking to maintain efficient interplanetary operations, it might have to perform 2+ active-cooling cycles per reentry, potentially requiring a minimum of 15 tons of water per reentry. Given that SpaceX intends (at least as of September 2018) for Starship to be able to land more than 100 tons on the surface of Mars, 15t of water would cut drastically into payload margins and is thus likely an unfeasibly large mass reserve or any given interplanetary mission.
“You just need, essentially, [a stainless-steel sandwich]. You flow either fuel or water in between the sandwich layer, and then you have [very tiny] perforations on the outside and you essentially bleed water [or fuel] through them … to cool the windward side of the rocket.” – SpaceX CEO Elon Musk (Popular Mechanics, December 2018)
The assumptions needed for the above calculations do mean that 30T is an absolute worst-case scenario for a regeneratively-cooled Starship reentry, given that SpaceX may only have to vigorously cool a small fraction of its windward surface and will likely be able to cut more than half of the water needed by allowing Starship’s steel skin to heat quite a lot while still staying well below its melting point (likely around 800C/1500F or higher). This also fails to account for the fact that a regeneratively-cooled stainless steel heat shield would effectively let SpaceX do away with what would otherwise be a massive and heavy ablative heat shield and mounting mechanism. Perhaps the benefits of stainless steel might ultimately mean that carrying around 10-30T of coolant is actually performance-neutral or a minimal burden when all costs and benefits are properly accounted for.
Probability at 60% & rising rapidly due to new architecture
— Elon Musk (@elonmusk) December 27, 2018
Musk clearly believes with almost zero doubt that a stainless steel Starship and booster (Super Heavy) is the way forward for the company’s BFR program, and he has now twice indicated that the switch away from advanced carbon composites will actually “accelerate” the rocket’s development schedule. For now, all we can do is watch as the first Starship prototype – meant to perform short hop tests ASAP – gradually comes into being in South Texas.
News
Tesla hits FSD hackers with surprise move
In recent weeks, the company has begun remotely disabling FSD capabilities on affected vehicles, and in some instances, permanently revoking access even for owners who paid thousands of dollars for the feature.
Tesla is cracking down on hackers who have figured out a way to utilize third-party programs to activate Full Self-Driving (FSD) in their vehicles — despite the suite not being approved for use in their country.
Tesla has launched a sweeping enforcement campaign against owners using third-party hardware hacks to activate FSD software in countries where the advanced driver-assistance system remains unregulated or unapproved.
In recent weeks, the company has begun remotely disabling FSD capabilities on affected vehicles, and in some instances, permanently revoking access even for owners who paid thousands of dollars for the feature.
Tesla has started remotely disabling Full Self-Driving on cars fitted with third-party CAN bus hacks in countries where the software is not yet approved.
This crackdown began after the hacks started spreading widely last month. 👇 pic.twitter.com/wL8VqZuTlK
— PiunikaWeb – helpful, and breaking tech news (@PiunikaWeb) April 9, 2026
Reports of the crackdown have surfaced across Europe, China, Japan, South Korea, and the UK, marking a significant escalation in Tesla’s efforts to enforce regional software restrictions.
FSD is Tesla’s flagship supervised autonomy package, which is available in several countries across the world. Currently limited by regulatory hurdles, it has not received full approval in most markets outside of the United States due to various things, such as safety standards, data privacy, and local traffic laws.
However, the company is working to expand its availability globally. Nevertheless, Tesla has installed the necessary hardware on vehicles globally, but locks the features based on geographic location.
Some owners have taken accessing FSD into their own hands, using jailbreak or bypass devices.
These “jailbreak” tools, typically €500 USB-style modules that plug into the vehicle’s Controller Area Network (CAN) bus, intercept signals to spoof approvals and unlock FSD, including advanced navigation, Autopark, and Summon features.
Hackers in Poland, Ukraine, and elsewhere have distributed the devices, with some claiming they work on HW3 and HW4 vehicles and can be unplugged to restore stock settings. In China alone, over 100,000 owners reportedly installed such modifications.
Tesla’s response has been swift and uncompromising. Recently, the company began sending in-car notifications and emails warning owners that unauthorized modifications violate terms of service, compromise vehicle safety systems, and expose cars to cybersecurity risks.
The email communication read:
“Your vehicle has detected an unauthorized third-party device. As a precaution, some driver assistance functions have been disabled for safety reasons. A software update will be available soon. Once you install the update, some features may be enabled again.”
Vehicles detected using the hacks have had FSD capabilities remotely disabled without refund. In some cases, owners report permanent bans, even if they had legitimately purchased the software package.
Tesla’s hardline stance underscores its commitment to regulatory compliance and safety.
Tesla has long argued that unsupervised FSD requires rigorous validation, and premature activation could endanger drivers and bystanders.
The crackdown sends a clear-cut message to those who are bypassing the FSD safeguards, but there are greater implications for Tesla if something were to go wrong. This is an understandable way to protect the company’s reputation for its FSD suite.
News
Tesla developing small, affordable SUV, report claims
This latest rumor deserves heavy scrutiny. Tesla has already walked away from a mass-market $25,000 EV once before.
Tesla is developing a small, affordable SUV, a new report claims, speculating that the automaker is planning to add yet another vehicle to its lineup at a price point similar to the Model 3 and Model Y, but smaller and more compact.
But it does not make a whole lot of sense, especially considering a handful of things CEO Elon Musk said and the overall plan for Tesla’s future.
Reuters reported that Tesla is in the early stages of developing an all-new, smaller, cheaper electric SUV. Citing four sources familiar with the matter, the story claims the vehicle would be shorter than the Model Y, built in China, and represent a fresh platform rather than a variant of the Model 3 or Y.
Suppliers have reportedly been contacted to discuss details, though Tesla has not commented. The move appears aimed at broadening affordability amid slowing EV demand and intensifying competition, particularly from Chinese rivals.
This latest rumor deserves heavy scrutiny. Tesla has already walked away from a mass-market $25,000 EV once before.
In 2024, the company scrapped its long-teased “Redwood” project for a budget-friendly car. Elon Musk explained the decision bluntly during an earnings call: a conventional low-cost model would be “pointless” and “completely at odds with what we believe.”
It’s sort of hard to believe this report: 3/Y are already relatively affordable, Elon said a $25k wouldn’t make sense, consumers want something larger than the Y with X going away, and Musk said what’s coming is “cooler than a minivan.”
Have to think the car is at least an SUV. https://t.co/4CQUV9ZNA5
— TESLARATI (@Teslarati) April 9, 2026
In other words, chasing a bare-bones cheap EV runs counter to Tesla’s core mission of accelerating sustainable energy through cutting-edge technology and autonomy rather than volume-driven price wars.
Musk’s own recent statements reinforce skepticism about a compact SUV pivot. Just two weeks ago, on March 25, he responded to fan requests for a minivan by posting on X: “Something way cooler than a minivan is coming.”
Elon Musk says Tesla is developing a new vehicle: ‘Way cooler than a minivan’
The remark came in the context of family-hauling needs, with Musk highlighting the Cybertruck’s ability to seat multiple child seats. It signals Tesla’s focus is shifting toward more spacious, innovative people-movers—not shrinking its lineup.
U.S. demand data echoes this logic.
The long-wheelbase Model Y L—a six-seat, stretched variant offering extra room for families—has generated massive interest wherever offered. Fans in the U.S. have basically begged for the Model Y L to make its way to the States, or for the company to develop a full-size SUV.
The Model Y L is selling well in China, where it is manufactured.
Delivery wait times for the Model Y L stretched into February 2026 as orders poured in. Tesla recently expanded the trim to eight new Asian markets, yet it remains unavailable in the United States, where consumer appetite for a larger, more practical SUV is reportedly strong.
American buyers have consistently favored bigger vehicles; the Model Y already outsells most competitors precisely because it delivers crossover utility without compromise. A compact model shorter than today’s bestseller would likely miss this mark entirely.
Tesla’s product strategy has long emphasized differentiation through autonomy, range, and desirability rather than racing to the bottom on price. Stripped-down variants of the Model 3 and Y have already struggled to ignite broad demand.
A new compact SUV built in China might sound logical on paper for cost-sensitive buyers, but it risks repeating past missteps—diluting brand cachet while ignoring clear signals from Musk and the market.
History suggests Tesla talks about affordable cars more often than it delivers them. Whether this Reuters scoop evolves into metal or joins the $25k project on the scrap heap remains to be seen.
For now, the smart money is on Tesla doubling down on “way cooler” vehicles that actually fit American families—and Tesla’s ambitious vision—rather than a smaller SUV that feels like yesterday’s news.
News
Tesla CEO Elon Musk says next FSD release is the one we’ve been waiting for
On Thursday, Musk teased the capabilities and next steps for Tesla’s Full Self-Driving software, focusing squarely on the incremental improvements of the current v14.3 suite, as well as the looming arrival of v15.
Tesla CEO Elon Musk teased the capabilities of a future Full Self-Driving release, but it seems like we are getting what Yogi Berra once called “DĂ©jĂ vu all over again.”
On Thursday, Musk teased the capabilities and next steps for Tesla’s Full Self-Driving software, focusing squarely on the incremental improvements of the current v14.3 suite, as well as the looming arrival of v15.
He confirmed that upcoming point releases of v14.3 will deliver additional polish to the current build, smoothing out remaining edges in an already capable system. These iterative updates, Musk noted, are designed to refine performance without requiring a full version overhaul.
Yet the real headline was Musk’s forecast for v15.
“V15 will far exceed human levels of safety, even in completely unsupervised and complex situations,” he wrote.
Tesla V14.3 self-driving review. The point releases will bring polish.
V15 will far exceed human levels of safety, even in completely unsupervised and complex situations. https://t.co/s4UK9RWw9f
— Elon Musk (@elonmusk) April 9, 2026
He clarified that v15 will be powered by Tesla’s long-awaited large model, an AI architecture with roughly 10x the parameters of the smaller model currently in widespread use. The leap, Musk explained, stems from the unusually rapid progress of the compact model, which has advanced so quickly that the larger counterpart has yet to catch up in real-world deployment.
However, it is becoming a pattern that is, by now, familiar to anyone following Tesla’s autonomous driving roadmap.
There’s no debating you on that 🤷
— TESLARATI (@Teslarati) April 9, 2026
Musk has consistently and repeatedly framed each successive major release as the one poised to deliver game-changing autonomy. Earlier versions were similarly positioned as a movement toward the final piece of the puzzle, only for attention to pivot to the next milestone once they arrived.
The refrain has become a recurring feature of FSD communication: current software is impressive, the point releases will sharpen it further, but the true breakthrough lies one major iteration ahead.
Musk’s latest comments fit squarely into that cadence. While v14.3 point releases are expected to tighten supervised driving behaviors in the coming weeks, v15 is cast as the version that finally crosses the threshold into unsupervised operation at human-or-better safety levels across demanding scenarios.
Our rate of advancement with the small model has been so fast that the large model has not yet caught up.
V15 will be the large model.
— Elon Musk (@elonmusk) April 9, 2026
The 10x parameter scale of the underlying large model is presented as the key technical enabler, promising richer reasoning and more robust decision-making than anything deployed to date.
Whether v15 ultimately fulfills that promise remains to be seen. Tesla’s history shows that each new target generates fresh excitement—and occasional skepticism—about timelines.
Fans realize Musk’s timelines for FSD are exciting, but rarely met:
You can see a rift happening in the Tesla bull community between a large group of reasonable people who aren’t afraid to acknowledge the elephants in the room, and those who are essentially bull bots whose entire identities are destroyed if they have to acknowledge any bump in…
— Mike P (@mikepat711) April 9, 2026
For now, Musk’s message is familiar: the immediate focus is polishing v14.3 through targeted point releases, while the 10x-parameter large model in v15 represents the next decisive step toward fully unsupervised, superhuman safety.
Hopefully, Tesla can come through, but we can only believe that once v15 gets here, v16 will be the next big step toward autonomy.
Drivers can expect continued refinement in the short term and a significantly more ambitious leap once the large model is ready. The cycle continues, but the stakes, Musk insists, keep rising.
Tesla hits FSD hackers with surprise move
Tesla developing small, affordable SUV, report claims
