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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.
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Elon Musk drops a bomb regarding Tesla Model S, X inventory
After more than a decade on the road, the original flagship sedan and SUV platforms are effectively at the end of the line. Production of new Model S and Model X vehicles has ceased, and custom orders were quietly halted in early April. What remains are roughly a few hundred factory inventory units scattered across the globe, mostly Plaid variants, and they are disappearing fast.
Elon Musk just dropped a bomb regarding Tesla Model S and X inventory, and as the company is phasing out the flagship vehicles, it sounds like the time to purchase one brand new is almost over.
Musk confirmed on Wednesday that there are “only a few hundred Tesla Model S & X cars left in inventory. Order now if you want one.”
Tesla is running out of units rather quickly.
The message from Musk reads like a final call for two of the company’s most storied vehicles.
Only a few hundred Tesla Model S & X cars left in inventory. Order now if you want one.
— Elon Musk (@elonmusk) April 8, 2026
After more than a decade on the road, the original flagship sedan and SUV platforms are effectively at the end of the line. Production of new Model S and Model X vehicles has ceased, and custom orders were quietly halted in early April. What remains are roughly a few hundred factory inventory units scattered across the globe, mostly Plaid variants, and they are disappearing fast.
The news marks the close of a remarkable 14-year chapter. Launched in 2012, the Model S redefined the electric vehicle with blistering acceleration, over-the-air updates, and a luxury interior that embarrassed traditional sedans.
The Model X followed in 2015, turning heads with its Falcon-wing doors and seating for seven.
Together, the Model S and Model X proved EVs could be desirable halo cars, not just eco-friendly commuters. Their departure clears factory space at Tesla’s Fremont plant for something the mass production of the Optimus humanoid robot, which Musk believes will be the greatest contributor to the company’s value.
Musk has repeatedly signaled that Tesla’s future lies beyond passenger cars. Resources once devoted to low-volume flagships are shifting toward autonomy, Robotaxis, and AI hardware. Optimus, the company’s general-purpose robot, is expected to handle manufacturing, household chores, and eventually complex labor.
In the short term, the scarcity has already driven prices on remaining inventory up by about $15,000, turning the last Model S and X into instant collector’s items.
Tesla uses Model S and X ‘sentimental’ value to enforce massive pricing move
The announcement underscores Tesla’s relentless pivot. While the Model Y continues to hold strong sales, the legacy S and X represented an earlier era of pure performance luxury.
The future has been paved by Tesla and Musk’s focus on autonomy, at least in the United States. Customers continue to call for a large SUV, which might be on the way after a recent nudge from Musk on X.
However, whatever the future holds, it has been forged by Tesla’s two flagship vehicles.
Once these final cars are gone, the Model S and Model X will live on only in driveways, forums, and the rear-view mirror of automotive history.
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Tesla Cybercab production ignites with 60 units spotted at Giga Texas
Designed exclusively for unsupervised Full Self-Driving, the Cybercab promises to deliver safe, affordable, on-demand mobility without human drivers. Early units with temporary controls allow engineers to refine hardware and software in controlled settings before full autonomous fleets hit the roads.
Tesla Cybercab production at Giga Texas seems to have ignited, as 60 units were spotted outside of the production facility on Wednesday, with speculation hinting the all-electric ride-hailing vehicle could be headed to the lineup sooner rather than later.
Interestingly, they were also spotted with steering wheels, which Tesla said the car would be void of.
Giga Texas observer and drone operator Joe Tegtmeyer shared on X a new post that revealed approximately 60 Cybercabs parked in two organized groups in the factory’s outbound lot—the largest concentration observed to date.
Happy 8 April (Wednesday) at Giga Texas, especially for those wanting an update on Cybercabs … I saw about 60 of them in two groups in the outbound lot today … the largest grouping yet!
Also, looks like at least some of these have white seats and most still have clearly… pic.twitter.com/mZbKH96bA7
— Joe Tegtmeyer 🚀 🤠🛸😎 (@JoeTegtmeyer) April 8, 2026
Tegtmeyer noted white seats inside several vehicles and clearly visible steering wheels on most. These are not yet the final steering-wheel-free production versions unveiled in 2024, but early units are likely undergoing validation testing for new features and real-world robotaxi operations across the country.
The timing could not be more symbolic. Tesla has consistently affirmed that mass manufacturing of the Cybercab would begin this month.
CEO Elon Musk has reiterated the April 2026 target multiple times, emphasizing that while initial output will be slow, following the classic S-curve of new-vehicle ramps, the Giga Texas line is being prepared to produce hundreds of units per week.
Tesla CEO Elon Musk outlines expectations for Cybercab production
The first Cybercab already rolled off the line in February, but April marks the official shift to volume production of this purpose-built, pedal- and steering-wheel-free autonomous vehicle.
These 60 Cybercabs signal far more than parked prototypes. They represent tangible proof that Tesla is executing on its ambitious robotaxi roadmap.
Designed exclusively for unsupervised Full Self-Driving, the Cybercab promises to deliver safe, affordable, on-demand mobility without human drivers. Early units with temporary controls allow engineers to refine hardware and software in controlled settings before full autonomous fleets hit the roads.
As production scales, Giga Texas, already home to Cybertruck production, will become the epicenter of Tesla’s autonomous revolution, targeting millions of vehicles annually in the years ahead.
For Tesla and its investors, this sighting underscores manufacturing excellence and timeline discipline. It counters skepticism about the company’s ability to deliver on next-generation vehicles amid a competitive autonomous landscape.
Broader implications are profound: lower transportation costs, reduced emissions, and safer roads as robotaxis proliferate. Musk’s vision of a future where Cybercabs operate 24/7, generating revenue for owners and riders alike, is now visibly underway.
With mass production officially ramping in April, today’s images are not just a snapshot of parked vehicles; they are the first frames of a mobility transformation. Tesla is not only meeting its commitments; it is accelerating toward an era where autonomy reshapes daily life. The Cybercab era has begun.
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Tesla makes major rebound in European market with 4x in registrations
Tesla delivered a striking performance in Germany’s automotive market in March 2026, with new vehicle registrations more than quadrupling year-over-year, according to official data from the German Federal Motor Transport Authority (KBA).
Tesla headlines will have you believe the company is dead to rights in Germany, selling nearly no cars, and stating consumers are more interested in other brands not run by CEO Elon Musk.
However, the latest data from Germany proves this might be a dying narrative.
Tesla delivered a striking performance in Germany’s automotive market in March 2026, with new vehicle registrations more than quadrupling year-over-year, according to official data from the German Federal Motor Transport Authority (KBA).
Newly registered Tesla vehicles jumped 315.1 percent to 9,252 units, marking the company’s strongest March on record in the country and signaling a sharp rebound after earlier challenges in the European market.
A big 4x from Tesla in Germany in March in vehicle registrations
Don’t let anyone tell you Tesla is dead in Europe https://t.co/24hyus1xTF pic.twitter.com/205yPwncRv
— TESLARATI (@Teslarati) April 7, 2026
The March surge accounted for roughly 72 percent of Tesla’s first-quarter total in Germany. Q1 registrations reached 12,829 vehicles, a 160 percent increase from the same period a year earlier. For context, the implied March 2025 figure was approximately 2,229 units—one of the brand’s weaker months in recent years.
These numbers underscore Tesla’s ability to capitalize on renewed demand in Europe’s largest car market, where the company had faced softening sales throughout much of 2025 amid heightened competition and broader economic pressures.
Germany’s overall new passenger car market also expanded in March, with 294,161 registrations—a 16 percent rise from the prior year. Battery-electric vehicles (BEVs) performed even more robustly, climbing 66.2 percent to 70,663 units and representing about 24 percent of all new car registrations.
Tesla’s 9,252 deliveries captured approximately 13.1 percent of the BEV segment for the month and roughly 3.1 percent of the total new car market, highlighting its continued leadership among pure-play electric brands despite growing competition from both domestic German manufacturers and Chinese entrants like BYD, which saw its own registrations surge 327.1 percent to 3,438 units.
The strong showing comes as Germany’s EV incentives and infrastructure investments continue to support adoption. Tesla’s lineup, anchored by the Model Y and Model 3, appears to have resonated with buyers seeking premium electric options.
Industry observers note that the concentrated March registrations, accounting for the bulk of the quarter, may reflect strategic inventory management, competitive pricing adjustments, or pent-up demand following a slower start to 2026.
This performance provides a much-needed bright spot for Tesla in Europe, where the brand had seen market share erosion in prior periods.
Tesla Model Y outsells all EV rivals in Europe in 2025 despite headwinds
With Q1 2026 registrations up significantly, Tesla has demonstrated resilience in a market that registered 699,404 new passenger cars for the quarter, up 5.2 percent overall. As the year progresses, sustained momentum in Germany could bolster Tesla’s European outlook, particularly if broader BEV growth persists amid evolving policy support and technological advancements.
The March 2026 data from the KBA paints a picture of Tesla’s renewed strength in Germany: a fourfold monthly leap, record quarterly gains, and a solid foothold in an expanding EV segment.
Whether this marks the beginning of a sustained recovery or a seasonal peak remains to be seen, but the numbers affirm Tesla’s enduring appeal in one of the world’s most competitive automotive landscapes.
Elon Musk drops a bomb regarding Tesla Model S, X inventory
Tesla Cybercab production ignites with 60 units spotted at Giga Texas
