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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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Tesla Giga Texas buzzing as new Cybertruck appears to enter production
Additionally, the Cybercab manufacturing ramp-up is continuing amidst Tesla’s busy May, which includes a handful of things from an automotive perspective.
Tesla Giga Texas is buzzing with a lot of action, as it appears the new Cybertruck trim that was offered a few months back has entered production. Additionally, the Cybercab manufacturing ramp-up is continuing amidst Tesla’s busy May, which includes a handful of things from an automotive perspective.
Drone operator Joe Tegtmeyer captured striking footage over Giga Texas on the morning of May 11, 2026, revealing fresh batches of Cybertrucks that may mark the start of series production for the long-awaited $59,990 Dual Motor AWD variant.
Tesla launches new Cybertruck trim with more features than ever for a low price
The vehicles lined up in staging areas, and we got a great look at three of the units parked on the property:
Hard to say for sure, but production of the $59K AWD @Cybertruck may be just getting started here on this early and soggy morning at Giga Texas … this version is much harder to visually distinguish from the premium AWD versions, so I’ll come back on Wednesday and we’ll see if… pic.twitter.com/UX7yCQpgeC
— Joe Tegtmeyer 🚀 🤠🛸😎 (@JoeTegtmeyer) May 11, 2026
Tegtmeyer notes the difficulty in visually distinguishing this base AWD model from higher-trim versions, unlike the earlier Long-Range RWD that lacked a motorized tonneau cover.
Tesla launched the $59,990 Dual Motor AWD Cybertruck in late February 2026 with a brief introductory pricing window that closed by month’s end.
Initial U.S. delivery estimates of June 2026 quickly slipped to September–October and, for newer orders, as far as April 2027.
The move underscores robust consumer interest in a more accessible all-wheel-drive Cybertruck priced under $60,000 before incentives—positioning it as a volume play for Tesla’s electric pickup lineup while premium AWD and Cyberbeast variants continue to be sold as usual.
Meanwhile, Cybercab production at the same Austin facility shows steady, if deliberate, progress. Tegtmeyer’s latest flyover documented dozens of glossy production-spec Cybercabs parked in the outbound lot—consistent with Tesla’s early statements that initial output would remain modest before scaling later in 2026.
The purpose-built robotaxi, unveiled in 2024 and lacking a steering wheel or pedals, rolled its first unit off the line in February. Volume manufacturing began in April, with early examples already undergoing autonomous testing around the factory grounds.
Elon Musk has repeatedly emphasized that Cybercab and Semi production will start slowly before ramping “exponentially” toward year-end. The presence of multiple finished units signals Tesla’s Unboxed manufacturing process is maturing, even as the company balances Cybertruck output with autonomy milestones.
Recent drone imagery also shows ongoing construction for Optimus and test-track expansions, highlighting Giga Texas’s evolving role as Tesla’s hub for next-generation vehicles.
For Cybertruck buyers, the potential ramp of the $59K AWD offers hope of shorter waits and broader market access. For autonomy enthusiasts, the growing fleet of Cybercabs hints at robotaxi service trials on the horizon.
While official confirmation from Tesla remains pending, Tegtmeyer’s footage provides the clearest public signal yet that both programs are advancing in parallel at Giga Texas.
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Tesla Full Self-Driving gains momentum in Europe with new country mulling approval
Tesla is advancing FSD’s technology across Europe with fresh talks underway in Ireland, signaling broader regulatory progress. On May 10, Ireland’s Department of Transport confirmed that Tesla is actively engaging with national authorities, including the National Standards Authority of Ireland (NSAI) to secure approval for FSD Supervised.
Tesla Full Self Driving (FSD) technology is gaining momentum in Europe, with yet another new country mulling a potential approval for operation on its roads.
Tesla is advancing FSD’s technology across Europe with fresh talks underway in Ireland, signaling broader regulatory progress. On May 10, Ireland’s Department of Transport confirmed that Tesla is actively engaging with national authorities, including the National Standards Authority of Ireland (NSAI) to secure approval for FSD Supervised.
While the department noted that full rollout in Ireland would ultimately depend on EU-level clearance, the engagement marks a notable step forward in Tesla’s European expansion strategy, Irish media outlet RTE said.
The news comes on the heels of a landmark breakthrough in the Netherlands. In April, Dutch vehicle authority RDW granted the first-ever EU type approval for FSD Supervised after 18 months of rigorous testing on public roads and tracks. The provisional approval allows the system on all Dutch roads, with Tesla already rolling it out to select owners following mandatory safety training.
The Netherlands has since notified the European Commission and is advocating for wider recognition, positioning the Dutch decision as a potential template for the bloc.
Europe has long lagged behind the United States, China, and other markets where FSD is more widely available. Strict EU regulations on automated driving systems have required extensive validation, but momentum is building.
Tesla now lists the Netherlands alongside established markets such as the U.S., Canada, Australia, and South Korea on its regional FSD page. Other countries, including Belgium, are reportedly fast-tracking their own review processes in response to the Dutch precedent.
Analysts see Ireland’s involvement as strategic. As a smaller EU member with unique road challenges—narrow rural lanes, hedgerows, and variable weather—successful validation there could demonstrate FSD’s adaptability and strengthen the case for harmonized EU approval.
Tesla has indicated it aims for broader EU deployment as early as summer 2026, though the timeline remains fluid. Discussions at the EU’s Technical Committee on Motor Vehicles continue, with a possible vote later in the year. Some member states, particularly in Scandinavia, have expressed reservations over edge cases like speeding protocols and long-term safety data.
For Tesla, European expansion is more than a software update; it unlocks significant growth. The continent’s dense population and high vehicle ownership could accelerate data collection, refine the AI models powering FSD, and pave the way for unsupervised autonomy and robotaxi services.
Owners stand to benefit from enhanced safety features and reduced driver fatigue, while regulators weigh innovation against proven risk reduction. Early Dutch results already cite safety improvements:
Tesla Full Self-Driving shows stunning maneuver in Europe to silence skeptics
But the work is far from done, and challenges are still present. FSD Supervised still requires driver attention and a readiness to intervene. EU rules emphasize that the technology is not fully autonomous, placing legal responsibility on the human operator. Tesla must also navigate varying national road conditions and public perception.
Nevertheless, the Ireland talks underscore a clear trajectory: one national approval at a time, Europe is inching closer to widespread FSD access. If the Dutch model gains traction, Summer 2026 could mark the beginning of a transformative chapter for autonomous driving on European roads.
Tesla’s persistent engagement with regulators is starting to pay off, and it suggests the company is still heavily committed to the expansion efforts across Europe, despite the red tape it has had to persist through.
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Tesla Semi gets strange-but-understandable comparison from Jay Leno
In a recent interview with MotorTrend, legendary comedian and automotive enthusiast Jay Leno shared his impressions after driving Tesla’s long-range Semi truck, offering one of the most vivid descriptions to date:
The Tesla Semi recently received a strange-but-understandable comparison from automotive enthusiast and former long-time late-night television show host Jay Leno.
In a recent interview with MotorTrend, legendary comedian and automotive enthusiast Jay Leno shared his impressions after driving Tesla’s long-range Semi truck, offering one of the most vivid descriptions to date:
“It’s like driving an office building.”
The comparison may seem quirky—office buildings evoke images of immobility rather than motion—but it aptly conveys the experience of commanding a massive 23,000-pound Class 8 electric truck that delivers sports-car acceleration.
Lenotested the production-spec Long Range model, which is rated for up to 500 miles of range. He was visibly impressed by its performance, noting how the enormous vehicle moves with surprising urgency.
“It’s as fast as a Tesla, but it’s like driving an office building,” he remarked. “It’s this huge thing that moves like right now. You go 500 miles. You get 60% charge in 30 minutes. You’re saving on fuel costs. It seems quite good.”
Jay Leno in new interview on what it’s like to drive the @Tesla Semi:
“I was quite impressed with that. It’s a fast as a Tesla, but it’s like driving an office building. It’s this huge thing that moves like right now. You go 500 miles. You get 60% charge in 30 mins. You’re… pic.twitter.com/YU7tk6a6pV
— Sawyer Merritt (@SawyerMerritt) May 8, 2026
The reaction highlights the cognitive dissonance at the core of the Tesla Semi. Traditional diesel semi-trucks are slow, noisy, and expensive to run. The Semi rewrites the rules with instant torque from its tri-motor electric powertrain, producing up to 800 kW.
Despite its size, the truck feels agile thanks to full electric steering assist, upgraded actuators borrowed from the Cybertruck, and a 48-volt electrical architecture that improves responsiveness and efficiency.
Tesla reports real-world energy consumption below 1.7 kWh per mile for the Long Range version. Megacharger stations can deliver a 60% charge in roughly 30 minutes, making the truck suitable for long-haul operations.
Additional features include an electric Power Take-Off (ePTO) capable of 25 kW for trailer refrigeration or other equipment, and a driver-focused cab with a central seating position for optimal visibility and a quiet, high-tech interior.
Fleet operators stand to benefit significantly from the economics. Diesel trucks often cost nearly one dollar per mile when including fuel, maintenance, and downtime.
Tesla projects the Semi can reduce operating costs to as low as 15 cents per mile through cheaper electricity, regenerative braking that minimizes brake wear, and reduced service requirements. While early deployments, like Pepsi’s, focused on shorter routes, the 500-mile variant targets cross-country applications.
Obstacles remain. A fully loaded tractor-trailer can reach 80,000 pounds, which reduces real-world range compared to the unloaded test conditions. Building out a nationwide Megacharger network will be essential for broader adoption. The Semi also carries a higher upfront price than conventional diesels, though total cost of ownership and available incentives frequently tip the scales in its favor over time.
Tesla Semi hauls fresh Cybercab batch as Robotaxi era takes hold
Leno’s “office building” description resonates because it captures the unexpected thrill of piloting something so large yet so capable. As the trucking industry faces pressure to cut emissions and control rising fuel expenses, the Semi offers a compelling alternative that excels in performance, comfort, and efficiency.
Coming from a man who has driven everything from vintage classics to modern hypercars, Leno’s genuine enthusiasm adds weight to the verdict.
The Tesla Semi is emerging as more than an experimental EV—it represents a practical vision for the future of heavy-duty transport where massive rigs accelerate instantly, and the numbers finally make sense. If fleet results continue to validate the claims, the era of diesel dominance could be drawing to a close.
Tesla Giga Texas buzzing as new Cybertruck appears to enter production
Tesla Full Self-Driving gains momentum in Europe with new country mulling approval
